IntroductionModerate heat Portland cement (MHC) enhances early concrete strength, reduces hydration heat, and increases crack resistance, making it widely used for dam construction. Most dams located underwater therefore having to face to leaching issues. Prolonged concrete exposure to water leads to the dissolution of Ca(OH)2 from hydration products, thus decreasing internal alkalinity so as to cause the breakdown of ettringite, C-(A)-S-H, and clinker. The phenomena result in deterioration of mechanical properties and impermeability. Current research on the leaching of cementitious material mainly focuses on ordinary Portland cement (OPC) and its blends with mineral admixtures, while little attention is paid to MHC and moderate heat Portland cement-fly ash (MHC-FA) systems. The latter two MHCs are commonly employed in dam construction. In this work, leaching tests were conducted on MHC pastes and MHC-FA pastes. Comparison with OPC pastes system was further carried out, focusing on the evolution of leaching depth, deterioration of compressive strength, and the impact on phase composition and C-(A)-S-H structure.MethodsSpecimens with a water-to-cement ratio of 0.5 were prepared from MHC pastes (M0), MHC with 30% FA pastes (M30), and OPC pastes (P0). The size of the formed specimens was 40 mm× 40 mm×40 mm. After curing in a standard concrete curing room for two years, five surfaces of the specimens were sealed with epoxy resin, leaving one surface exposed for accelerated leaching in a 5 mol/L NH4Cl solution. The specimens were taken out from the solution after 7, 14, 28 d, and 56 d, following a test on compressive strength and leaching depth. The leaching depth is determined by spraying a 1% phenolphthalein solution in alcohol on the cut-open specimens. Samples were taken from areas 0–3 mm and 3–6 mm from the leaching exposure surface and pristine surface at 56 d. The thickness of 0–3 mm is labeled as the external layer of the leaching zone, and the thickness of 3–6 mm is labeled as the internal layer of the leaching zone. Characterization techniques included X-ray diffraction (XRD), Thermogravimetric Analysis (TGA), and Solid-State 29Si Nuclear Magnetic Resonance (29Si NMR) spectroscopy. In addition, the porosity of samples was evaluated using the hydrostatic weighing method.Results and discussionThe Leaching depth of M0 develops slower than OPC, while the M30 is the fastest. Initially, the compressive strength of M0 is higher than P0, but adding 30% fly ash to M0 lowers its compressive strength. Before leaching, the compressive strength of M0 is higher than that of P0, and the M30 has the lowest compressive strength. The compressive strength of the specimens decreases as the leaching time increases. Among them, the compressive strength of M0 is always the highest, and M30 is always the lowest. Compared with OPC, MHC has higher initial compressive strength and a lower strength decline rate, benefiting its long-term corrosion resistance. Although M30 has the lowest initial intensity, its intensity decreases more slowly. Additionally, before leaching, M30 has the highest porosity, P0 is in the middle, and M0 the lowest. Leaching increases the porosity of all samples evenly. Despite M30 has the highest initial porosity, the increasing rate of porosity is the lowest. Similar phenomena are observed for M0 and P0, while P0 shows the highest increasing rate of porosity. There is no significant difference in hydration products among the P0, M0 and M30 in the unleaching regions. The prominent XRD diffraction peaks of the sample before dissolution include Ca(OH)2, sjoegrenite, ettringite, CaCO3 and gypsum, and C3S, C2S and C4AF. M30 also contains quartz peaks. The long-time curing leads to carbonation in the external layers. Thus, after leaching, a significant CaCO3 peak appears. For the leached external layers of P0 and M0, the main phases include CaCO3, sjoegrenite, ettringite and gypsum, as well as C3S, C2S and C4AF. All ettringite dissolves in the leached external layers of M30, showing weakened peaks of C3S and C2S, yet ettringite remains in the internal layer. TGA reveals the Ca(OH)2 contents of 26.0% for P0, 22.1% for M0, and 5.3% for M30, showing that P0 has the strongest leaching buffering effect. Based on the former result that M0 has the best leaching resistance, the experiments reveales no guaranteed relationship between strong buffering and optimal leaching resistance. This can be understood as that Ca(OH)2 is the most soluble, and is therefore easier to create more pathways for leaching, leading to significant microstructural damage. The 29Si NMR results reveal that a significant increase in MCL is observed in all the samples due to the decalcification of C-(A)-S-H. Both the internal and external layers of M30 exhibit the highest growth proportions, accompanied by the formation of Si-Al gel. Although the MCL of M0 exceedes that of P0 in both the internal and external layers after leaching, the growth of silicate chain is still lower than that of P0. However, M30 experiences the lowest compressive strength reduction rate, suggesting that microstructural changes from soluble substance leaching may show greater impact on declining mechanical properties than silica gel formation due to C-(A)-S-H decalcification. During the leaching, the stability of AlVI is greater than AlIV.ConclusionsThe main conclusions are summarized as follows: Compared to OPC pastes, MHC pastes experience a slower leaching depth development, leading to enhanced residual compressive strength, decreased pore degradation, mitigated declines in compressive strength and changes in C-(A)-S-H gel structure. Before leaching, OPC pastes has the highest Ca(OH)2 content, MHC pastes the middle and MHC-FA pastes the lowest. Leaching leads to a significant increase in the MCL of C-(A)-S-H in the paste. After leaching, both the internal and external layers MHC-FA pastes exhibit the largest increase in MCL, accompanied by the production of silica-alumina gel. The average increase of silicate chain length is observed greater in C-(A)-S-H of OPC pastes than that of MHC pastes. During leaching, the stability of AlVI exceeds that of AlIV.

IntroductionDe-icing salt has been a common way to melt snow accumulated on concrete structures. But this often leads to the deterioration of concrete structures. Therefore, frost resistance durability of concrete subjected to de-icing salt is crucial. Conventionally, concrete is allowed to freely deform during single-side freezing and thawing (SSFT) tests. However, a concrete specimen is only equivalent to a unit of the concrete component in actual, and its deformation subjected to SSFT is restrained by the surrounding concrete, leading to alterations in salt frost damage. The differences in the evolution of concrete’s frost damage between the laboratory and actual engineering are highlighted. The different internal damage of concrete subjected to freezing and thawing with pure water and de-icing salt is usually related to the water migration and phase transformation inside the concrete. However, the only difference between restrained concrete and unrestrained concrete is the restraint effect. The significant difference in internal damage of the two concretes subjected to SSFT cannot be explained by classical theory. Additionally, the influence of restraint effect on water migration in concrete also needs to be clarified. Thus, it is crucial to study the effect of restraint on the internal damage of concrete subjected to SSFT, which will provide guidance for the mix design of high frost resistant concrete in cold regions. In this paper, restraint ring and anchors were designed to confine the deformation of concrete to simulate the serving condition during SSFT tests. The relative dynamic elastic modulus and water absorption in volume of restrained and unrestrained concrete with a water cement ratio of 0.60 were tested after every 4 SSFT cycles. The temperature and humidity sensors were used to monitor the evolution of the relative humidity (UIRH) inside the concrete during the SSFT test. The influence and mechanism of restraint effect on the internal damage of concrete subjected to SSFT were clarified from the perspective of moisture migration.MethodsP·I 42.5 cement complying GB 8076—2024, natural river sand with a fineness modulus of 2.68, and graded stone by uniformly mixing the crushed stone with 5–10 mm and 10–20 mm in a mass ratio of 4:6 were used to prepare fresh concrete with water to cement ratios of 0.60. The slump and air content of fresh concrete are 120 mm and 1.4%, respectively, tested according to GB/T 50080—2016. The 28 d cube compressive strength of the concrete specimen is 28.3 MPa, tested according to GB/T 50081—2019.Two groups of moulds were used to cast concrete specimens. For unrestrained specimens, cylindrical plastic moulds with a diameter of 100 mm and a height of 70 mm were used. For restraint specimen, a restraint device was designed, which is used as the mould to cast a restrained concrete specimen meanwhile used as the restraining device to limit concrete deformation in SSFT tests. The device consists of a restraint ring, 24 restraint anchors, a counter-force ring, and a flange. All parts of the device are made of 304 stainless steel.The curing and pre saturation of concrete specimens were carried out according to the salt freezing method in CIF test and GB/T 50082—2009. The CDF/CIF TESTER produced by Schleibinger Gerte was used to provide SSFT cycles. After every 4 SSFT cycles, the relative dynamic elastic modulus (rn) and water absorption in volume (Vn) of the concrete specimens were tested. The evolution of internal relative humidity (UIRH) of 28 SSFT cycles was monitored, and the pore size ratios of restrained and unrestrained concrete during the first cooling cycle were calculated.Results and discussionThe results show that after every one freeze-thaw cycle, the UIRH of both restrained and unrestrained concrete increased, resulting in hysteresis of the UIRH-temperature curves, which reflects the process of water migration inside concrete subjected to SSFT cycles. The hysteresis of the UIRH-temperature curves of unrestrained concrete is more significant than that of restrained concrete. After 28 SSFT cycles, the UIRH increment, rn loss and Vn of restrained concrete are 30%, 32% and 28% less than those of unrestrained concrete, respectively.The calculated results based on the UIRH-temperature curves show that the radius of pores (rpr) in restrained and unrestrained concrete increases with SSFT cycles. After 28 SSFT cycles, the rpr of restrained concrete is 58% less than that of unrestrained concrete. A model for the internal water migration of concrete subjected to SSFT is established to analyze the influence of restraint on the water migration. The ratio of pore radius of the restrained and unrestrained concrete before freezing point during the cooling process in first SSFT cycle was calculated. The results indicate that under the influence of restraint, the water migration inside the concrete driven by SSFT is effectively weakened.ConclusionsThe main conclusions of this paper are summarized as following. The conventional SSFT test of unrestrained concrete overestimates the internal damage. The restraint effect weakens the water migration before the freezing point of concrete during the cooling process, which is the basis for reducing internal damage induced by SSFT cycles. Moreover, the restraint effect also reduces the pore size expansion of concrete subjected to SSFT cycles, which is manifested macroscopically as less loss of relative dynamic elastic modulus and less increase of water absorption in volume.

IntroductionIn cold regions, concrete is widely used as a material in hydraulic structures. Its durability is crucial for ensuring the stability of concrete structures over service life. As a porous medium, concrete undergoes freeze–thaw cycles where the water in the pores freezes and expands, causing water migration and pore pressure. This phenomenon results in internal structural damage and thus degradation of concrete performance. Therefore, it is important to analyze the relationship between temperature, humidity, and pore pressure of concrete during the freeze–thaw cycles. Scholars have proposed various mechanism theories, and a general knowledge is given that the thermo–hydro coupled behavior of concrete imposes the major machinal loads inducing the freeze–thaw damage. But the dominant mechanism is still not clear. The hydrostatic pressure theory and the crystallization pressure theory explain the freeze–thaw damage of concrete from the perspective of the effective stress principle of fluids. The theory of poroelasticity explains the freeze–thaw damage of concrete from the perspective of internal pressure and deformation generated by the pores inside the concrete during the formation and thawing of ice crystals. Hence, it is believed that an additional attention should be paid to the combined mechanical effect of solid phase expansion and the load contribution of the fluid phase. By conducting a detailed analysis of pore pressure and ice expansion deformation during the freeze–thaw process, the dominant mechanism of freeze–thaw damage can be further analyzed.MethodsThe spatial discretization method of flow lattice network (FLN) considering the concrete mesoscopic heterogeneity is adopted to describe the heat transfer and mass transport behavior. Within the framework of FLN, a thermo–hydro coupled model for concrete during the freeze–thaw cycles is proposed and its mechanical mechanism are discussed based on the poroelasticity and effective stress principle. The proposed model implemented into UEL subroutine and solved by standard/implicit solver in ABAQUS. The proposed model is used to simulate the freeze–thaw process of concrete under uniform and non-uniform temperature change.Results and discussionFirstly, the numerical simulations of concrete under freeze–thaw conditions are conducted based on existing concrete ice content and the corresponding deformation experiments. As the temperature decreases, the relative ice content predicted by the model begins to increase at 0 ℃, and the ice crystallization first increases and then decreases. At –55 ℃, the relative ice content reaches 0.42. Subsequently, due to the consideration of freeze–thaw hysteresis, the relative ice content does not decrease with the increase in temperature, but starts to gradually decrease only when the temperature rises to the melting temperature (–15 ℃). The ice completely thawed at 0 ℃, which is in good agreement with the experimental results. In the simulation with constant and temperature-dependent thermal expansion coefficient, the total deformation and deformation trend calculated by the freezing stage model are in good agreement with the freeze–thaw deformation test data. However, during the thawing stage, due to the damage (cracking strain) in the experimental, the model calculation results do not match the experimental results. The strain of m and show expansion, and th shows contraction deformation. dominates the over deformation. Additionally, through the calculation of relative errors in deformation, it can be observed that the calculation results with constant al and ac keep relatively consistent with the experimental results. During the cycling process, the peak pore pressure of 5 MPa during the freezing stage of concrete appears at 4.4 hours, and the peak pore suction pressure of 9 MPa during the thawing stage appears at 21.5 h. In the evolution of frost heave strain, the peak strain appears at 13 h.In the simulation of non-uniform temperature distribution, the variation depth of relative ice content gradually expands towards the temperature invariant region as the number of freeze–thaw cycles increases. The peak value also increases with the pore pressure expands towards the rear side. In addition, the peak deformation occurs alternately with the peak pore pressure. During the process of water freezing and thawing, the mechanical loads of the ice-water mixture in pores on the solid skeleton presents two stages. The first stage is dominated by fluid pressure and is computed by the principle of generalized effective stress. The second stage is ice crystallization induced expansion computed by the poroelasticity.ConclusionsA thermo–hydro coupled model for concrete during the freeze–thaw cycles is proposed within the framework of FLN. The numerical results of relative ice content and the corresponding deformation are in good agreement with the experimental results, which verifies the accuracy of the proposed model. The consideration of the temperature-dependent mathematical pore distribution in the calculation of ice content can simulate the hysteresis of ice content during freezing and thawing. It is numerically found that the pore pressure and frost heave strain play the rotatory dominant role during the freeze–thaw cycle. One stage is dominated by fluid pressure and another stage is dominated by ice crystallization induced expansion computed. The effective stress caused by the pore fluid and the calculation of frost heave strain are comprehensively considered.

IntroductionThe wide range and strip-like distribution of high-speed rail crossings, as well as the exposed service characteristics, result in ballastless track concrete not only directly bearing train loads, but also facing freeze–thaw damage in severely cold or cold areas such as high-latitude cold regions and high-altitude mountainous areas. In the service process, the coupling beween environmental effects and train loads has significantly affected the ballastless track concrete at the micro- and macro-levels. However, current standards do not consider the effects of high-speed train fatigue loads and freeze-thaw cycles on the service performance of concrete. During the operation of high-speed trains, the flexural fatigue load frequency that causes damage to the concrete exceeds 20 Hz, which is a significant difference from the test system commonly used in current fatigue tests.To reflect the actual service conditions of ballastless track more realistically in cold regions, a coupled test system of ‘freeze-thaw cycles and 20 Hz fatigue loads’ was designed. The effects of freeze–thaw cycles on the performance of concrete were analyzed from the perspectives of mechanical properties, fatigue life, and stiffness. The freeze–thaw cycles were divided into freezing and thawing stages, and their damage characteristics and energy transfer laws were analyzed. A life prediction model considering the coupling of freeze-thaw and fatigue was established from a probabilistic perspective to predict the service life of ballastless track manufactured sand concrete in cold regions.MethodsThe study used C60 manufactured sand concrete as the research object, with specimen dimensions of 100 mm (width) × 100 mm (height) × 400 mm (length). A SUNS-890 electro-hydraulic servo static and dynamic universal testing machine was used for fatigue tests. The stress level (maximum stress fmax/flexural strength ff) was fixed at 0.6, stress ratio (minimum stress fmin/peak stress fmax) was 0.1, loading frequency was 20 Hz, and displacement data was simultaneously recorded during loading. After being saturated, the concrete underwent a series of freeze–thaw cycles, including 0, 150, 300, 450 cycles, and 600 cycles, before undergoing fatigue testing. To analyze the evolutionary of concrete performance during different stages, the freeze-thaw cycles were divided into two stages: freezing (–20 ℃) and thawing (0 ℃ and 20 ℃). After saturation, the specimens were placed at –20, 0 ℃, and 20 ℃ to conduct bending fatigue tests. Simultaneously, in order to analyze the temperature rise caused by fatigue loads at a constant temperature, a temperature measurement point was taken every 25 mm along the side of the concrete during the loading process, and a thermometer was used to measure its temperature.Results and discussionAfter 300 freeze–thaw cycles, the ballastless track concrete exhibits accelerated brittle failure characteristics. Both flexural strength and fatigue performance show a trend of accelerated decline with freeze–thaw cycles exceeding 300 times, resulting in a 46.3% decrease in fatigue life and a 12.9% increase in stiffness degradation after 600 freeze–thaw cycles. The internal and surface defects caused by freeze–thaw cycles serve as initiation points for fatigue damage propagation, with the increased actual stress level making the concrete more prone to fatigue fracture. Defect connectivity induced by the cycles becomes the main factor contributing to the deterioration of concrete performance. From an energy perspective, the loading process involves both potential and internal energy, with concrete dissipating energy mainly through deformation energy generated by deformation. The decrease in maximum strain and increase in residual strain caused by freeze–thaw cycles result in reduced deformability of the concrete, thereby negatively affecting its fatigue performance. Ice within the concrete pores during the freezing stage has a reinforcing effect, leading to an improvement in fatigue performance. Additionally, ice helps alleviate internal friction and accelerates internal energy dissipation, thereby mitigating fatigue damage during the freezing stage. By introducing a fatigue damage factor, a life analysis model for concrete under freeze–thaw + fatigue service conditions are established. Predictions of concrete life under different environments are made based on freeze–thaw environmental criteria, revealing that C60 manufactured sand concrete can meet the freeze-thaw design requirements of cold region at level D1 and level D2, but considerations must be made for the intensified damage from fatigue loads.ConclusionsA test regime of ‘freeze–thaw cycle + high-frequency fatigue’ was established to investigate the damage mechanism of concrete under the coupled action of freeze–thaw and fatigue from the perspectives of damage progression and energy transfer. It was found that high-speed train fatigue loads exacerbated the freeze–thaw damage of ballast-free track concrete, with defect connectivity caused by freeze–thaw cycles being the main reason for the decline in concrete fatigue performance. Freeze–thaw cycles lead to a decrease in maximum strain and an increase in residual strain, resulting in reduced deformability of the concrete. Compared to fatigue performance at room temperature, ice within the concrete pores during the freezing stage has a reinforcing effect, and ice in the frozen state can accelerate internal energy dissipation, thereby alleviating fatigue damage. A life analysis model for concrete under ‘freeze-thaw + fatigue’ service conditions, considering a fatigue damage factor, was successfully established to predict the service life of ballast-free track C60 manufactured sand concrete.

IntroductionThe climatic features of plateau regions include low atmospheric pressure, large temperature variation, and intense radiation, presenting numerous challenges for concrete structures in these areas during the service life. The substantial diurnal temperature fluctuations expose concrete structures to the risk of cracking over prolonged temperature cycles, particularly notable in complex facade structures like bridge piers, where cracks often intersect and spread across the surface. In the plateau with significant temperature variations, the surface cracks that occur in bridge pier concrete do not directly impact the structural load-bearing capacity. However, if surface damage is allowed to progress, this deterioration accelerates the penetration of moisture and CO2, among other corrosive agents, into the interior of the concrete, thereby causing the durability of the concrete structure to fail.This study focuses on typical bridge pier concrete in plateau regions with significant temperature variations, employing finite element analysis and secondary development techniques to establish a temperature fatigue damage model for bridge pier concrete under such conditions. By incorporating cohesive elements to simulate the cracking behavior of bridge pier concrete under long-term temperature cycling, this research elucidates features such as the initial crack time and temperature gradient distribution in plateau regions with significant temperature variations. Furthermore, through an analysis of the fatigue stress evolution patterns and energy accumulation processes of bridge pier concrete under temperature cycling, this study aims to uncover its cracking mechanisms.MethodsBased on the cracking mechanism of bridge piers in the high plateau environment with significant temperature variations, this study establishes a finite element model for a dual-lane circular bridge pier. The model dimensions are 7.4 m (length) × 3.0 m (width) × 9.0 m (height). The mesh consists of hexahedral elements, with element types C3D8R and cohesive elements embedded along the mesh boundaries. The concrete material properties for the bridge pier include an elastic modulus of 42 GPa, tensile strength of 2.5 MPa, poisson's ratio of 0.2, linear expansion coefficient of 1.5×10–5, density of 2 420 kg/m3, and specific heat capacity of 1 100 J/(kg·℃). Diurnal temperature variations are set at 20–40, 20–60 ℃, and 20–80 ℃, respectively. Additionally, considering the difference between the sunny and shaded sides of the bridge pier concrete, a temperature variation of 10 ℃ is defined for the shaded side. The bottom of the bridge pier concrete is fully constrained, while the top is subjected to an upper load of 9 000 kN. Importantly, a threshold value is introduced to determine whether fatigue effects on concrete need to be considered during alternating diurnal temperature cycles.Results and discussionIntense solar radiation and longer hours of sunshine in plateau regions lead to the appearance of randomly distributed cracks with widths less than 0.5 mm in bridge piers after 1–2 years of normal usage. The cracking mechanism of bridge pier concrete in plateau environments is as follows: the bridge pier concrete surface heats up to 50 ℃ due to thermal radiation and air convection. Heat is then transferred internally through a heat transfer process consistent with Fourier's law. The temperature gradients generated inside the bridge pier concrete, due to its low thermal conductivity, create temperature fatigue stresses, ultimately resulting in surface cracking under the influence of temperature fatigue stress.Based on finite element analysis, this study demonstrates that in plateau environments with significant temperature variations, bridge pier concrete tends to initiate cracking from the bottom and gradually extend upwards. Additionally, it is shown that the alternation between day and night results in a more complex internal temperature field within the bridge pier concrete. It is noteworthy that as the diurnal temperature variation increases, the rate of damage accumulation on the surface of the bridge pier concrete gradually increases. Furthermore, the plastic dissipation energy generated in the bridge pier concrete over the same period also increases with the rise in diurnal temperature variation, thereby revealing the cracking mechanism of the bridge pier concrete.ConclusionsThis paper takes typical bridge piers in high plateau regions as an example and, through theoretical analysis, reveals the complete process of "thermal response-stress generation-fatigue damage accumulation" cracking mechanism of bridge piers in environments with significant temperature variations. Based on the cracking principles of bridge piers in such environments, a fatigue damage model under temperature fatigue is established using finite element simulation and secondary development techniques. Concurrently, cohesive elements are utilized to simulate the cracking behavior of bridge piers under prolonged temperature cycling. Subsequently, it is demonstrated that in environments with significant temperature variations, cracks in bridge piers extend upwards from the bottom according to a certain development pattern. Moreover, with the increase in temperature variation on the bridge pier surface, both the initial crack time and damage accumulation rate gradually accelerate.

IntroductionReinforced concrete structures are currently the most widely used structural form. However, a large number of concrete structures deteriorate with premature failure under the action of environmental factors. Numerous studies and engineering investigations have reported that cracking and expansion of microcracks in concrete structures under various conditions provide a channel for the diffusion of erosive media, which is the most important factor leading to the deterioration of concrete and thus reducing the durability of the structure. Shrinkage of concrete is an important causative factor for its cracking, and the rational use of mineral admixtures can effectively reduce the shrinkage, which is an important way to improve the crack resistance of concrete. Moreover, concrete is subjected to continuous tensile stress caused by contraction and temperature difference during the setting process. It has been proved that improving the early tensile creep of concrete can relax the tensile stress, and thus effectively inhibit the cracking of concrete. In this study, a design method of low shrinkage high creep cementitious materials was realized by adjusting the mineral admixture amount, mineral admixture fineness and water-cement ratio. The enhancement of cracking resistance was finnally obtained as expected.MethodsP·II 42.5 cement, Class II fly ash, S95 slag, ultrafine fly ash and S115 slag were selected for this test. The mineral admixtures were used in a double mixing mode combining coarse and fine particles, i.e., double mixing of S95 slag with ultrafine fly ash, and double mixing of S115 slag with Class II fly ash, with the range of mineral admixtures to the total cementitious materials from 50% to 80%. The substitution rate of each component changed with a increment of 10%.Three series of tests were included in this work: a full-age shrinkage test, an ultra-early tensile creep test, and a cracking test. The full-age shrinkage test apparatus was used to test the autogenous shrinkage from casting to 3 d and the drying shrinkage from 3 d to 28 d of cementitious materials. The ultra-early tensile device was used to test the tensile strain of cementitious materials from initial to final setting. This device used a polyurethane mold to hold the specimen and transfer the tensile load. The creep displacement was monitored by a laser displacement sensor. A low-elasticity circular restrained cracking mold was used to monitor the restraining stresses due to autogenous shrinkage from casting to demolding, as well as the restraining stresses caused by drying shrinkage after demolding. The mold was made of polyvinyl chloride resin plastic material. A pair of vertically placed strain gauges were pasted on the inner surface of the inner ring to detect the stresses.Results and discussionShrinkage test results show that at constant total replacement rate of mineral admixtures, the mixing group of ultrafine fly ash and S95 slag is smaller than the mixing group of Class II fly ash and S115 slag. The reason is that the activity of the slag is higher than that of the fly ash. Using of smaller fineness slag and larger fineness fly ash in combination is beneficial to decrease the difference in the reaction rate of these two materials, leading to a reduction in the porosity. When the total replacement rate of mineral admixture is 60%, the effect of improving the particle grade matching to reduce the shrinkage of the cement stone reaches maximum. In addition, the shrinkage of the cement stone increased with increasing water-cement ratio for all different mineral admixture substitution rates. Ultra-early tensile creep test results show that under relatively high total substitution rate (60%–80%), the ultra-early creep of cementite with different particle gradation shows obvious differences. Compared with the mixing group of Class II fly ash and S115 slag, the mixing group of ultra-fine fly ash and S95 slag exhibits larger ultra-early creep and later cracking. Contrary to the shrinkage law, under relatively high total substitution rate (60%–80%), increasing the substitution rate of ultrafine fly ash while simultaneously decreasing the substitution rate of S95 slag, the ultra-early creep is shown to increase first and then decrease. Increasing the water-cement ratio slightly increases the ultra-early specific creep and delays the cracking time. The use of low shrinkage high creep cement stone can effectively reduce the internal stress growth rate, resulting in shrinkage stress relax and cracking time delay.ConclusionsExperimental studies are carried out on the early age shrinkage, creep and cracking properties of cementitious materials. The following conclusions are drawn. The cement stone using S95 slag with coarse particles and ultrafine fly ash with fine particles in combination exhibits characteristics of low shrinkage and high creep. When the total replacement rate of mineral admixture is in the range of 60%–80%, increasing the admixture of ultrafine fly ash while simultaneously decreasing the admixture of S95 slag, the shrinkage of specimens is observed to decrease first and then increase. While the ultra-early creep is characterized by increasing first and then decreasing. The use of low shrinkage high creep cement stone can effectively reduce the growth rate of the internal stress and delay the cracking time.

IntroductionThe interfacial bonding properties between steel fibers and cementitious matrix under harsh marine environment are crucial for the mechanical properties and durability of UHPC. However, studies on the deterioration mechanism of the steel fiber-cementitious matrix interface in marine environments are insufficient. There is a lack of effective approaches to improve the interfacial bonding properties. This study provides novel approach to strengthen the interfacial transition zone and enhance the interfacial bonding properties using silane coupling agent (SCA). Based on molecular dynamics simulation and steel fiber pull-out test, the variation rules of bonding performance and debonding strength of steel fiber-matrix interface in UHPC under harsh marine environment were clarified. The microstructural variation, bonding network evolution and bonding trend of interfacial chemical bonds for the pristine and SCA-modified interfaces in the harsh marine environment were investigated. Based on this, the interfacial bonding degradation mechanism of the pristine and modified interfaces under marine chloride environment was revealed. This study is expected to provide theoretical basis and methodological support for optimizing and regulating the durability of UHPC in harsh marine environment.MethodsBased on molecular dynamics simulation, the variation of interfacial interaction energy and initial contact area before and after SCA modification in the harsh marine environment was calculated and the images of interfacial configurations in the marine environment were captured. Using interface debonding simulation and steel fiber pull-out experiments, the load-displacement curves and interfacial fracture energy pristine and SCA-modified interfaces were investigated during the debonding process in the marine environment. Microscopic morphology of interfacial transition zones in the marine environment was observed by scanning electron microscopy (SEM) and backscattered electron imaging (BSE). Moreover, molecular dynamics simulation was used to statistically characterize the evolution of the hydrogen bonding network in the interfacial region and to calculate the formation probability of chemical bonds during the interfacial debonding process.Results and discussionThe bonding property of the steel fiber-matrix interface under marine environment was severely damaged, where the initial contact area of the interface was significantly deteriorated. Compared to the dry environment, the initial contact areas of pristine and modified interfaces under the NaCl environment were reduced by 51.6% and 39.2%, respectively. Moreover, the interfacial transition zone around the SCA-modified steel fiber was dense. The interfacial bond strength and pull-out energy of the SCA-modified sample after seawater erosion were 23.6% and 21.3% higher than those of pristine sample, respectively. The SCA modification can effectively enhance the adsorption effect between interfacial molecules and improve the denseness of the interfacial transition zone, thus improving the interfacial debonding strength.The hydrogen bonding network within the pristine interface consists only of OCuO—HCSH hydrogen bonds, while that within the SCA-modified interface consists of OAPS—HCSH, OCSH—HAPS and NAPS—HCSH hydrogen bonds. The number of hydrogen bonds in the modified interface is over 2 times higher than that in the pristine interface. The high atomic compatibility between the cross-linked APS molecules and the C-S-H matrix leads to the formation of a variety of stable hydrogen-bonded connections in the interfacial region, which enhances interfacial bonding.Under the marine environment, the bonding probability between the C-S-H matrix and water molecules in the pristine interface is higher than that between matrix and steel fibers. The bonding probability between the Cl– and C-S-H matrix is much higher than that between the matrix and pristine steel fiber atoms in the dry environment. It is indicated that in marine environment, water molecules and aggressive ions are prone to intrude into the pristine interface, forming strong interactions with the interfacial materials and destroying the interfacial bonding between the steel fiber and matrix. Conversely, in the marine environment, the bonding probability between the modified steel fiber and the matrix is higher than that between the interfacial material and the water molecules. Specifically, in the NaCl environment, the bonding probability of silicon-oxygen covalent bonds between the cross-linked APS and the C-S-H matrix remains high. It is demonstrated that SCA modification facilitates the formation of a stable interfacial bonding network, enhancing the interfacial bonding properties and elevating the interfacial corrosion resistance to water molecules and aggressive ions.ConclusionsThe main conclusions of this paper are summarized as follows. 1) The marine chloride environment can seriously damage the integrity of the steel fiber-matrix interface and weaken the interaction energy between the steel fibers and matrix. The SCA modification can effectively enhance the adsorption effect for the interfacial molecules and improve the denseness of the interfacial transition zone, thus improving the interfacial debonding strength. 2) Strong interfacial bonding between the steel fiber and the matrix is achieved through the formation of hydrogen bonds. Water molecules in the erosive environment seize the initial hydrogen bonding bonding sites, generating Owater—HCSH, OCSH—Hwater hydrogen bonds, breaking the bonding network connection between the steel fiber and the matrix. Moreover, Na+ and Cl– are easy to accumulate on the surface of C-S-H matrix, cutting the covalent bond connection between steel fiber and matrix, expanding the invasion channel of water molecules, and eventually exacerbating the interfacial deterioration. 3) Due to the rich type of hydrogen bonding and large number of hydrogen bonds between SCA-modified steel fibers and the matrix, a strong hydrogen bonding network connection is formed within the interface, which improves its resistance to water molecules and aggressive ions. Furthermore, in the SCA-modified interface, the cross-linked APS molecules can develop stable silicon-oxygen covalent bonds with the matrix, and its good compatibility with the matrix promotes the crosslinking of silicate chains in the interfacial zone. This leads to enhanced interfacial bonding properties and ultimately improved interfacial corrosion resistance to the harsh marine environment.

IntroductionOn the Loess Plateau in western China, there exists a large number of saline soils, most of which contain salts, typically of sulfate and chloride salts. Since the sulfates in saline soils are sensitive to temperature changes, they are susceptible to salt crystallization expansion and frost heave at low temperatures, which can lead to destruction of concrete structures. Salty soils and freeze–thaw environments cause concrete to be subjected to the coupled effects of simultaneous sulfate attack and freezing and expansion, which further increases the deterioration degree of concrete and seriously threatens the durability of concrete in this area. Adding fibers to concrete can effectively inhibit the plastic shrinkage cracking and improve the durability of concrete such as wear resistance, impermeability and frost resistance. Basalt fiber (BF) has excellent properties such as high strength, light weight, high temperature resistance, high elastic modulus, fracture resistance and corrosion resistance, and it is easy to disperse in concrete and has excellent cooperative work performance with concrete. Therefore, in this paper, the durability of concrete is improved by incorporating an appropriate amount of BF into the concrete to reduce the initial defects and slow down the rate of corrosive ions into the interior of the concrete. Furthermore, the effect of different BF admixtures on the relative dynamic modulus of elasticity, mass loss, compressive strength, and splitting tensile strength of concrete during salt freezing were investigated. The effect of the included BF is also clarified.MethodsThe concrete was prepared by P·O 42.5 ordinary Portland cement, II grade fly ash, 5–20 mm continuous graded gravel and natural river sand fineness modulus of 2.83. The volume content of basalt fiber was 0%, 0.1%, 0.2% and 0.3%. The test was carried out with reference to the quick-freezing method in GB/T 50082—2009 ‘Test method for long-term performance and durability of ordinary concrete’, using HC-HDK9/Y type fast freeze–thaw cycle tester. According to the content of corrosive ions in saline soil in western China, Na2SO4 salt solution with a concentration of 23 g/L was selected for freeze–thaw cycle test. The loss rates of mass, relative dynamic elastic modulus, the compressive strength and splitting tensile strength during the test were tested. At the same time, Numerical simulation tests were carried out using finite element software ABAQUS to analyze the changes of internal stress and strain fields of basalt fiber reinforced concrete (BFRC) during the tests.Results and discussionThe mass and relative dynamic elastic modulus of BFRC under the action of Na2SO4 solution-freeze–thaw cycle raised first and then decrease with growth of the number of freeze–thaw cycles. The compressive strength and split tensile strength decrease with the increase of the number of freeze–thaw cycles. The addition of BF slows down the formation of corrosion products and expansion products. Under the same number of freeze–thaw cycles, the addition of BF reduces the generation of microcracks in concrete and prevents crack propagation. The addition of BF improves the freeze–thaw resistance of concrete in Na2SO4 solution. And the freeze–thaw resistance performance gradually improves with the increase of the BF volumetric doping within the range of 0.1% to 0.3%. Moreover, the best performance of freeze resistance in Na2SO4 solution is achieved when BF doping is 0.3%.The internal stress and strain fields of BFRC with different BF dosage during Na2SO4 solution-freeze–thaw cycle test decrease with increasing the BF dosage. At the same BF dosage, the stress and strain increase with increasing the number of freeze–thaw cycles, and the dynamic numerical simulation was in good agreement with the experimental results. Using the ‘equivalent temperature load’ method, the salt solution-freeze–thaw cycles test process can be effectively simulated by ABAQUS finite element software. The numerical simulation results also show that the stress field of concrete and BF as well as the strain field of BFRC have changed, and that BF plays the role of transferring and dispersing the stresses during the freeze–thaw cycling process, which leads to the phenomenon of stress redistribution inside the concrete, and improves the salt-freezing resistance of concrete.ConclusionsIn this work, the macroscopic properties and microscopic changes of BFRC with different amounts of BF were studied under the combined effect of Na2SO4 erosion and freeze–thaw. The main conclusions are that the addition of BF significantly reduces the loss rate of concrete mass, relative dynamic elastic modulus, compressive strength and splitting tensile strength during the freeze–thaw cycle of Na2SO4 solution. BF can transfer and disperse the stress, so that the stresses are redistributed inside the concrete during the freeze–thaw process, thus improving the salt-freeze resistance of concrete. In addition, when the BF content is 0.3%, BFRC has the best resistance to Na2SO4 salt erosion-freezing performance. Meanwhile, BF shows an important effect in the evolution of freeze-thaw damage evolution of concrete, which can be visualized effectively by finite element model.

IntroductionWith the implementation of national policies like the ‘Belt and Road Initiative’, major infrastructure projects are rapidly advancing into the western plateau regions. These regions, nestled deep inland, exhibit typical plateau environmental characteristics, including frequent temperature fluctuations, low precipitation, strong winds with high velocities, low atmospheric pressure, limited oxygen levels, and widespread saline soil/salt lakes, which pose serious challenges to the long-term serviceability of major infrastructure. Determining the service environment is a prerequisite for conducting durability analysis and design of concrete structures. However, compared to the increasingly mature research on extreme loads such as earthquakes and typhoons, research on the long-term environmental actions suffered by concrete is still in its infancy. Most existing studies analyzed environmental factors from the ‘environmental’ rather than the ‘engineering’ perspective, lacking suitable environmental analysis tools for actual engineering applications. Furthermore, although extensive experimental research has been conducted on concrete durability, the inconsistency between the actual service environment and laboratory accelerated tests can lead to significant discrepancies in concrete deterioration rates and damage mechanisms. Using performance indicators obtained under laboratory accelerated conditions to design the expected service life of concrete in actual engineering projects will result in significant errors. The absence of a long-term environmental action model for concrete is a key challenge to the quantitative design of concrete durability.MethodsBased on 21 years of meteorological data from 687 weather stations and chemical composition data from 396 salt lakes, using ordinary kriging (OK) interpolation method, with the geographic coordinate system as World Geodetic System 1984 and the projected coordinate system as Albers, regional distribution maps of key environmental parameters were created. Python's distfit library was used to fit the best probability density function (PDF) of environmental data. The Kolmogorov–Smirnov (K–S) test, a non-parametric statistical method, was employed to determine if the sample data sets conformed to the theoretical PDF. Environmental data were categorized using the unsupervised learning method K-means clustering. An intelligent and efficient WeChat mini program was developed to provide technical support for durability analysis and longevity design of engineering structures under special environmental action in the Chinese plateau regions.Results and discussionThe action levels of temperature differences in China were divided into six zones, closely related to the terrain. The temperature differences in the western plateau regions were significantly greater than that in the eastern plain regions. In cities such as Xizang, Xinjiang, Sichuan, Qinghai, and Heilongjiang, the maximum cumulative monthly average temperature difference reached 23 ℃. The cumulative monthly average relative humidity gradually decreased from the southeast coast to the northwest inland, with most Chinese plateau regions having an average relative humidity of less than 40%. The frequency of freeze-thaw cycles differed significantly between the Chinese plateau and plain regions, with Xizang experiencing the highest annual average of up to 188 times. Taking freeze–thaw(F–T) temperature amplitude, the lowest freezing temperature and the annual freeze-thaw cycles as indicators, the F–T action levels in China were divided into six zones, nonfrozen zone, slight F–T zone, light F–T zone, moderate F–T zone, severe F–T zone, and extreme F–T zone, each showing significant differences in annual average freeze-thaw cycles. The variability of annual average atmospheric pressure was relatively small across regions, exhibiting a step-like pattern similar to China's terrain.For regions with large temperature differences and strong aridity, the month with the most severe environmental action was considered the primary month, and representative values such as frequent occurrence, moderate occurrence, and rare occurrence were provided. For high-frequency freeze–thaw cycles, basic environmental parameters and key design parameters for different regions were provided. Given the relatively small variability of annual average atmospheric pressure across different regions, the mean value of each region was recommended. For hypersaline attack, representative values such as the 95th percentile, third quartile, median, and mean were provided, and it was suggested to set concentration gradients according to representative values.ConclusionsThe main conclusions of this paper are summarized as follows. Special service environments affecting concrete durability, such as large temperature fluctuation, strong dryness, high-frequency freeze–thaw cycles, and low atmospheric pressure, have the most severe impact in the Qinghai-Xizang Plateau. There are significant differences in environmental actions across different regions of China, and even within the same province, it is not appropriate to summarize different cities in one group. Indicators characterizing the action level of freeze–thaw cycles include freeze–thaw temperature amplitude, lowest freezing temperature, and annual freeze–thaw cycles. There are distinct differences in freeze–thaw action levels in different regions of China, especially evident in the clear gradient differences in annual average freeze–thaw cycles. The formation and distribution of saline-alkali soils and salt lakes are closely related. A comprehensive analysis of aggressive ion concentrations in different salt lakes reveals strong variability, suggesting the setting of concentration gradients based on statistical results. A rapid query mini program for special environments has been developed on the WeChat platform, integrating meteorological data query, freeze–thaw action analysis, and environmental parameter zonation, offering technical support for improving the efficiency of obtaining real-time information on the special environment near the project location.

IntroductionThe bonding properties of Fiber Reinforced Plastics (FRP) -concrete composites is directly related to the load carrying capacity and durability of FRP reinforced concrete structures. In addition, the study of bond properties can help us better understand how FRP bars behave in concrete and how they react under specific environmental conditions (e.g., high temperature, humidity, corrosion, etc.). This is valuable for predicting and improving the long-term performance of concrete structures. However, in offshore engineering, structures are exposed to strong corrosive environments all year round. Under the erosion of internal FRP bars by corrosive ions and the highly alkaline environment of the concrete pore solution, the matrix on the surface of FRP bars firstly suffers from deterioration phenomena such as dissolution, plasticization, and microcrack formation. Consequently, the bonding properties of the FRP-concrete interface are seriously affected, leading to the deterioration or failure of the concrete structure. Therefore, improving the corrosion resistance of FRP reinforcement is an important measure to ensure the long-term service of FRP-reinforced concrete structures. In this paper, the resin matrix modification of GFRP bars was realized by self-synthesized organosilicones and surface hydrophobic modification of nanofillers to obtain highly corrosion-resistant GFRP bars. To investigate the degradation of the interfacial adhesion between highly corrosion-resistant GFRP reinforcement and seawater-seasand concrete (SSC) in simulated pore solution of SSC at 60 ℃, and to reveal the mechanism of GFRP reinforcement-concrete adhesion enhancement through interfacial microstructure analysis.MethodsOrganosilicon synthesis: Hydrogen-containing silicone oil (PMHS) was mixed with -(2,3-epoxypropyloxy) propyltrimethoxysilane (KH560) in a mass ratio of 1:1, with ethanol as the solvent, and reacted under the catalytic effect of NaOH for 8 h at ambient temperature using a magnetic stirrer (200 r/min), and then kept for spare.CNT surface modification: 0.03% (mass fraction) of CNTs was stirred and dispersed into an ethanol and KOH organic solvent, and the CNT modifier was subsequently obtained by adding hydrogen-containing silicone oil (PMHS) and ethyl silicate (TEOS) after ultrasonic dispersion.Surface modification of EG: EG was dripped onto the surface of expanded graphite in the mass ratio of TEOS:PMHS=3:1 in a vacuum environment; subsequently, the samples were placed in a microwave oven at 800 W for a rapid expansion for 10 s. The modified expanded graphite was placed in the organic solvents of KOH and anhydrous ethanol with heating and stirring until the mixture was homogeneous.Preparation of modified epoxy resin hybrids: A bisphenol A-type epoxy resin (EGEBA), methyl tetrahydrophthalic anhydride curing agent (MeTHPA), and an accelerator (DMP-30) were mixed in a mass ratio of 100:85:5. Subsequently, 5% of the self-synthesized organosilicon was mixed with CNT and EG surface-modified nanofillers with a total solid content of 0.03% into the epoxy emulsion, and the mixed solution was stirred homogeneously using ultrasonication combined with triple-roller shear dispersion to obtain the modified epoxy resin mixture.Preparation and testing of pull-out specimens: modified GFRP bars were embedded in the upper surface of concrete to a depth of 5 mm, and the size of the concrete was set to 100 mm × 100 mm × 300 mm. Hydraulic jacks were used to carry out single-end pull-out tests on the bonded specimens, and a digital CCD camera was used to capture the displacement and deformation of the interface throughout the entire process of de-bonding.Microstructural characterization: the scaled-down specimens were prepared, and the microstructural changes at the FRP-concrete interface of the scaled-down specimens after corrosion were observed using scanning electron microscopy and X-ray computed tomography.Results and discussionFrom the pull-out damage pattern of the GFRP-concrete interface, it can be seen that after 120 d of corrosion, large areas of resin degradation on the surface of the N-GFRP reinforcement resulted in fiber exposure and carbon fiber rib detachment. Compared with N-GFRP, the corrosion degree of M-GFRP bar is less severe, and its surface only has speckled local yellowing and surface roughness phenomenon. Compared with the unmodified bars, the initial interfacial adhesion between corrosion-resistant GFRP bars and concrete was improved by 7.87%, and the interfacial adhesion was improved by about 15% in the 120 d-corrosion experiment. In addition, the maximum strain values at the interfaces of N-GFRP and M-GFRP with concrete decreased to 22.8×10–3、28.7×10–3, respectively in the 120 d-corrosion experiment. After the modification of the resin matrix of the FRP bars, the corrosion resistance of the bars is improved, which can better absorb and disperse the stress brought by the external load, making the stress distribution at the FRP-concrete interface more uniform and the deformation increased, thus slowing down the rate of loss of adhesive force.Corrosion to 120 d, the interfacial spacing between N/M-GFRP and concrete reached 158.11 m and 67.91 m, respectively, which increased by about 100% and 60% compared to the uncorroded condition. The Vr value at the M-GFRP-concrete bonded interface (23.35%) was higher than that of N-GFRP (18.52%). The surface substrates at the N-GFRP reinforcement-concrete interface all were detached and a new layer was exposed. In contrast, the localized matrix spalling at the M-GFRP-concrete interface was less corrosive than that of the N-GFRP bars. Therefore, the debonding of GFRP-concrete mainly depends on the degradation degree of the matrix at the interface. The affinity between the resin matrix and the concrete was improved by matrix modification, and the introduction of hydrophobic network led to the improvement of the waterproofing performance of the bars, which effectively mitigated the degradation of the resin matrix of the bars, and then improved their bonding performance.ConclusionsThe main conclusions of this paper are summarized as following. Compared with the unmodified bars, the initial interfacial adhesion between corrosion-resistant GFRP bars and concrete was improved by 7.87%, and the interfacial adhesion was improved by about 15% in the 120 d-corrosion experiment. In addition, the maximum strain values at the interfaces of N-GFRP and M-GFRP with concrete decreased to 22.8×10–3、28.7×10–3, respectively in the 120 d-corrosion experiment. Compared with the two, the maximum strain at the interface increased by about 25.87% after modification. The damage modes of the debonding process were dominated by concrete cracking and GFRP bar pullout. The degradation rate of the interfacial matrix was mitigated by resin matrix modification, which improved the adhesive properties of the GFRP-concrete interface.

As a fundamental construction material in modern engineering, concrete is extensively utilized in structural buildings across various industries due to its exceptional workability, mechanical properties, durability, constructability, and safety. In recent years, the pursuit of increasingly innovative structural designs and the escalating demands and complexities of construction technologies, coupled with the rapid advancements in materials science, have led to the emergence of Ultra-high Performance Concrete (UHPC), whose preparation and production techniques have undergone significant enhancements. Consequently, catering to the diverse requirements of construction materials in different service environments, multiple novel UHPC materials have been developed and gradually introduced into pivotal construction projects, encompassing high-rise or super high-rise buildings, long-span bridges, underground structures, nuclear power projects, and massive dams. Nevertheless, fire remains one of the primary risks confronting modern engineering safety, posing a severe threat to the structural stability and service life of UHPC components. Under elevated temperatures, UHPC experiences a sudden imbalance between internal and external temperatures, triggering a series of physicochemical degradations such as dehydration, decomposition, embrittlement, and thermal deformation incompatibility of hydration products. Notably, these detrimental effects are more pronounced in UHPC with higher strength grades. Therefore, conducting systematic research on the elevated performance of UHPC and proposing feasible enhancement measures are of paramount importance for enhancing the fire resistance of structural engineering.The elevated stability of UHPC is paramount to ensuring the long-term safe service of building structures in fire environments. Therefore, there is an urgent practical need to develop novel construction materials with exceptional elevated performance through a systematic overview of mechanical properties and degradation mechanisms of UHPC at elevated temperatures. In this paper, the macro-mechanical properties of UHPC at elevated temperatures, encompassing compressive strength, tensile strength, flexural strength, bond strength and elastic modulus, were comprehensively reviewed. The thermal decomposition of hydration products, pore structure and pore water, C-S-H gel, and the interfacial transition zone characteristics of UHPC at elevated temperatures were further summarized. Additionally, the degradation mechanisms of concrete properties at elevated temperatures and their applicability in UHPC were discussed, and the critical issues pertaining to UHPC’s elevated performance in existing research were elucidated. Lastly, some insights into future research directions and prospects were proposed. Based on the conclusions summarized in this paper, valuable references can be provided for the design of UHPC materials with enhanced elevated resistance, as well as for the inspection, evaluation, and repair of structures after fire events.Summary and prospectsAs one of the most prevalent safety risks faced by modern building structures, fire can lead to elevated spalling failure of UHPC, resulting in rapid loss of load-bearing capacity, posing significant challenges to the serviceability, lifespan, structural stability, and safety of structural engineering. Conducting relevant research holds practical application value in pushing the limits of UHPC materials and structures in terms of elevated resistance and fire prevention capabilities. The main conclusions of this paper are as follows: 1) At elevated temperatures, the strength of UHPC is primarily influenced by factors such as its strength grade, temperature, cooling method, raw material composition, moisture content, reinforcement or fiber type, and specimen dimensions. As the temperature increases, the compressive strength, flexural strength, tensile strength, and bond strength of UHPC decrease, with the loss of strength exhibiting distinct trends within different temperature ranges. 2) At elevated temperatures, UHPC undergoes phenomena such as evaporation and diffusion of pore water, deterioration of pore structure, decomposition of C-S-H gel, and failure of the interfacial transition zone, which initiate the formation of microcracks and accelerate their propagation. 3) Regarding the spalling behavior of concrete at elevated temperatures, scholars have proposed theories including the vapor pressure theory, thermal stress theory, and thermal cracking theory. While these theories can, to some extent, explain the degradation mechanisms of ordinary concrete in extreme temperature environments, they remain controversial, particularly when applied to UHPC.Despite the extensive research conducted by scholars worldwide on UHPC in the context of building fires and elevated environments, as well as the significant achievements made in experimental and theoretical analyses of fire resistance for concrete materials or structures, the current literature reveals a lack of effective technical measures to enhance the elevated resistance of UHPC, necessitating further in-depth investigation. This field is plagued by numerous critical issues that urgently require research and resolution: 1) The elevated environment inevitably exerts negative effects on the performance of UHPC, and the enhancements achieved through existing research on improving the thermal resistance remain insufficient. It is thus imperative to develop novel intelligent elevated-resistant concrete that can efficiently prevent, resist, and insulate heat, while also integrating rapid fire warning response capabilities, through advancements in concrete material composition design, mix proportion optimization, and structural directional control. 2) At elevated temperatures, UHPC undergoes simultaneous processes of secondary hydration enhancement from unhydrated cement particles and elevated degradation of hydrated product phases. The key to deeply analyzing and comprehensively understanding the degradation mechanisms of UHPC at elevated temperatures lies in achieving in-situ microscopic characterization of hydrated product phases and accurately quantifying the contribution ratios and development patterns of these two processes to the strength of UHPC. 3) The spalling behavior of UHPC at elevated temperatures is complex and multidisciplinary. The current theories on elevated failure can only partially explain the elevated degradation of UHPC, making it difficult to predict the randomness and uncertainty of UHPC's elevated peeling and establish a correlation mechanism. It is crucial to comprehensively explore the elevated failure mechanisms of UHPC by integrating multiple disciplines such as material mechanics, thermodynamics, fracture mechanics, and blast dynamics.

IntroductionWhite light emitting diode (LED) is widely used as a high-quality lighting source, and its performance depends critically on the selected light-emitting materials. Early white LEDs were mainly composed of a combination of blue light chips and yellow light emitting phosphors, but suffered from low color rendering index, high color temperature, and blue light hazards. To solve these problems, researchers have turned to improving the color rendering performance of white LEDs by using red phosphors that can be excited by blue light.Professor Zhiguo Xia's group at the State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, has proposed a new material design principle for Eu2+-activated oxide phosphors that are difficult to obtain red light emission: Eu2+ occupying a low coordination number of polyhedra can cause a large crystal field cleavage, which can in turn realize red light or even near-infrared emission. A novel Sr3Ga4O9 phosphor matrix with multiple low-coordination cation lattice sites was designed and synthesized, and broadband red light emission under 450 nm blue light excitation was successfully achieved by doping Eu2+, with the emission peak located at 618 nm.MethodsSr3Ga4O9:Eu2+ and Sr3Ga4O9:Eu2+, 0.05Zn2+ phosphors were prepared by high-temperature solid-phase method. According to the proportional content of the different raw materials in the chemical formula, SrCO3 (A.R.: 99.5% analytically pure), Ga2O3 (A.R.), H3BO3 (A.R.) and Eu2O3 (99.99%) were weighed and ground in an agate mortar for half an hour. The mixture was transferred to an alumina crucible and fired at 900 ℃ in an air atmosphere for 6 h, then cooled naturally to room temperature. The mixture was ground again to powder form and refilled into the crucible, which was placed in a tube furnace with a continuous flow of reducing gas ([V(N2):V(H2)] = 80%:20%). The samples were burned at 1 200 ℃ for 10 h, cooled to room temperature naturally, and then ground carefully to obtain the desired phosphor samples.A white light illumination device was fabricated using a blue LED chip stacked with green and red phosphors. The green light was partly provided by Lu3Al5O12:Ce3+ (LuAG:Ce3+) commercial green phosphor, while the red light was contributed by the experimentally prepared Sr3Ga4O9:Eu2+,0.05Zn2+ phosphor.Results and discussionThe Sr3Ga4O9 cell structure belongs to the P-1 space group of the triclinic crystal system. The results of XRD characterization tests indicate that the prepared samples are in pure phase. A heterovalent substitution strategy was used to introduce Zn2+ into Sr3Ga4O9, and the XRD results showed that this co-doping did not change the structure of the matrix material. Further analysis revealed that Zn2+ ions replaced Ga3+ sites, while Eu2+ may occupy two 6-coordinated Sr2+ lattice sites.Under the excitation of 450 nm, the Sr3Ga4O9:xEu2+ phosphor emits red light at 618 nm, and the emission intensity reaches the maximum at x = 0.04. The low-temperature emission spectra at 78 K can be decomposed into two Gaussian peaks, which indicates that the Eu2+ occupy two different luminescent centers and emit the red light, respectively. The fluorescence lifetime decay curves of the Sr3Ga4O9:0.04Eu2+ sample at low temperature (78 K) can be well fitted by the double-exponential function, which again demonstrates that the Eu2+ ions occupy two different lattice sites.After Zn doping, the luminescence intensity of Sr3Ga4O9:Eu2+,0.05Zn2+ phosphor was enhanced and the thermal stability was also improved significantly. The enhancement of thermal stability is from the presence of defects in the crystal, which compensates for the heat loss. The average decay lifetime of the co-doped Zn2+ is significantly higher than that of the sample without Zn2+, and a clear bulge of new pyroelectric peaks at 210 ℃ and 325 ℃ is clearly seen. Thus the addition of Zn2+ can increase the concentration of traps and contribute to the formation of deeper defect energy levels.For Sr3Ga4O9:0.04Eu2+, the thermal stability is poor due to its shallow trap depth, which causes the electrons to escape from the shallow traps immediately at room temperature. Whereas, Sr3Ga4O9:Eu2+,0.05Zn2+ has deeper trap 2 and trap 3 in it, and thus maintains a good thermal stability even at high ambient temperatures.The white LED device was fabricated to cover the entire visible region of the emission spectrum with a color rendering index of Ra = 87, a color temperature of CCT = 3 500 K, and CIE color coordinates of (0.410, 0.380).ConclusionsNovel Sr3Ga4O9:Eu2+ red phosphors that can be excited by blue light were designed and prepared, and their crystal structures and spectral properties were investigated. It is found that the Sr3Ga4O9:Eu2+ red light emission comes from two low-coordination polyhedra Sr1O6 and Sr3O6 occupied by Eu2+ with 5d-4f leaps. Zn2+/Ga3+ heterovalent substitution occurs by the introduction of Zn2+ into Sr3Ga4O9, which is proved to introduce a defective energy level through the fluorescence decay lifetime and thermoluminescence to improve the thermal stability of the phosphor. A white LED device prepared using a commercial blue LED chip, Sr3Ga4O9:Eu2+,0.05Zn2+ red phosphor, and a commercial green phosphor, LuAG:Ce3+, has a high color-rendering index, Ra = 87, and a low correlated color temperature, CCT = 3 500 K, which suggests that it is suitable for warm-white-light lighting.

IntroductionThe easy dissolution of Fe under acidic conditions results in the decreased activity of traditional Fenton-like catalysts. It was reported that the encapsulated or framework stabilized Fe-based materials showed excellent stability. Zeolite is a crystalline silicate/aluminosilicate with a stable framework structure, high specific surface area, uniform microporous and mesoporous structure, good acid-base resistance property. These characteristics make it a promising carrier or main material for Fenton-like catalysts. Therefore, a Fe-doped nanosheet MFI (MFI-Fe) zeolite was synthesized in this study. The Fe sites was embedded in the framework of MFI-Fe zeolite to inhibit the dissolution of Fe under acidic conditions, which could improve the performance of MFI-Fe zeolite for activating H2O2 towards acidic red G (ARG) degradation in water.MethodsWith the assistance of diquaternary ammonium-type structural directing agents, the solid products were obtained through hydrothermal reactions (160 ℃, 5 d) using tetraethyl orthosilicate and ferric chloride as the main raw materials. Then, MFI-Fe zeolite was obtained by calcining the solid products in air at 550 ℃ for 3 h. X-ray diffraction spectroscopy (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR), N2 adsorption-desorption and X-ray photoelectron spectroscopy (XPS) were applied to determine the physicochemical properties of MFI-Fe zeolite. The prepared MFI-Fe zeolite was applied to active H2O2 for ARG degradation. The effects of catalyst dosage, H2O2 dosage, solution pH value, reaction temperature, ARG concentration and coexisting ions on the degradation of ARG were studied. The concentration of ARG in the water was determined by an ultraviolet and visible (UV–Vis) spectrophotometer.Results and discussionAccording to the XRD and FTIR results, the prepared MFI-Fe zeolite exhibited the characteristic peaks of MFI zeolite, and there were not impurity peaks of silicon oxide or iron oxide, indicating that both silicon and iron entered into the framework of MFI zeolite. The XPS spectra of MFI-Fe zeolite exhibited peaks of Fe 2p3/2 and Fe 2p1/2 at 711.8 eV and 725 eV, respectively. They were very close to the binding energies of the 2p3/2 and 2p1/2 peaks of Fe2O3. Moreover, there was no Fe2+ peak (approximately 708 eV) in MFI-Fe zeolite. These results indicated that Fe in MFI-Fe zeolite existed in the form of +3 valence and was directly connected to O. The SEM images showed that MFI-Fe zeolite was composed of many nanosheets. Si and Fe were uniformly distributed in the crystals. According to the N2 adsorption and desorption results, the specific surface area and external surface area of MFI-Fe zeolite reached to 343.71 m2·g–1 and 176.78 m2·g–1, respectively. The average pore size of MFI-Fe zeolite reached 4.19 nm. These structural characteristics endowed MFI-Fe zeolite with excellent catalytic activity. The catalytic experiment results showed that ARG could only be rapidly removed when both H2O2 and MFI-Fe zeolite existed. The reaction mechanism results indicated that HO• was generated by the activating of H2O2 with MFI-Fe zeolite, leading to the degradation of ARG. In solution having pH values of 3–9, the removal rates of ARG gradually decreased with the increase of pH values. It can be explained that a lower pH value conduced to the activation of H2O2, thereby accelerating the degradation of ARG. Under the optimum conditions (initial pH=3, 25 ℃, MFI-Fe 0.40 g/L, H2O2 20 mmol/L), the removal rate of ARG (20 mg/L) reached to 98.40% within 180 min. The coexistence of NO3–, Cl–, and SO42– in the solution had not effect on the removal of ARG. The degradation of ARG was slightly inhibited by humic acid (HA). The removal rate of ARG was significantly slowed down with the coexistence of HCO3–. It can be explained that the pH value of the solution would increase and partial HO• would be consumed when HCO3– is added into the reaction system. After reuse for 5 times, the concentrations of leached Fe were less than 0.42 mg/L, and the removal rates of ARG exceeded 87.64%.ConclusionsA nanosheet MFI-Fe zeolite was synthesized and applied to active H2O2 for ARG degradation. When the pH value of the solution was between 3 and 9, the removal rates of ARG gradually decreased with the increase of the solution pH values. The reaction rate reached to the maximum (0.023 min–1) at a pH value of 3. Under the optimal conditions (pH=3, 25 ℃, 0.40 g/L MFI-Fe and 20 mmol/L H2O2), the removal rate of ARG (20 mg/L) reached approximately 98.40% within 180 min. The coexistence of NO3–, Cl–, and SO42– ions in the solution had not effect on the removal of ARG, while the degradation of ARG was slightly inhibited by humic acid (HA). The removal rate of ARG decreased significantly with the coexistence of HCO3–. After reuse for 5 times, the concentrations of leached Fe were less than 0.42 mg/L, and the removal rates of ARG exceeded 87.64%.

IntroductionAccompanied by industrial production, the issue of hexavalent Cr6+ contamination in water environments is becoming increasingly severe. The adsorption method for removing Cr6+ from water has attracted attention due to its operational simplicity and low cost. MOF as adsorbents possess structural advantages such as large surface area and high porosity. Hybridization of MOF can increase the adsorption sites, enhance reaction activity, and further improve the adsorption performance of MOF. Research on synthesizing MOFs using KHP as an organic ligand is scarce. In this study, KHP was utilized as the organic ligand to synthesize urea-doped N/MOF(Fe) via a solvothermal method. The optimal urea doping concentration of N/MOF(Fe) was characterized using SEM, TEM, BET, XRD, XPS, and other techniques. The effects of factors such as the initial concentration of Cr6+, the dosage of N/MOF(Fe), the initial pH of the solution, the presence of coexisting ions on the adsorption reaction, and the corresponding mechannisms, were analyzed. The adsorption kinetic equation was established, the adsorption isotherm model, and adsorption thermodynamic parameters, were calculated.MethodsAfter determining the optimal preparation conditions for MOF(Fe) through orthogonal experiments, a solution was prepared by adding 0.306 g of KHP 1.212 g of Fe(NO3)3·9H2O, 0.6 mL of acetic acid, and 0.028 mmol/L of urea into 24 mL of DMF. The solution was stirred until completely dissolved and then transferred to a reaction vessel lined with PTFE. The reaction was carried out at 180 ℃ for 20 h. Afterward, a reddish-brown precipitate was obtained by centrifugation. The precipitate was washed several times with deionized water and ethanol, followed by drying overnight at 80 ℃. The resulting material was named as N/MOF(Fe). A certain amount of the adsorbent was added to a 140 mL solution of Cr6+. At specific intervals, aliquots of the solution were taken out and the absorbance was measured to study the N/MOF(Fe) adsorption behavior.Results and discussionOrthogonal experiments indicate that controlling the pH value is crucial for the adsorption of Cr6+ by MOF(Fe). The optimal preparation conditions for MOF(Fe) are a reaction temperature of 180 ℃, a reaction time of 20 hours, a metal-to-ligand molar ratio of 1.0:0.7, and a pH value of 2.3. After urea doping, the material's adsorption capacity and adsorption rate were significantly enhanced. When the urea doping concentration was 0.028 mol/L, the adsorption rate of N/MOF(Fe) reached its maximum. N/MOF(Fe) exhibited a spherical structure with a lattice spacing of 0.12 nm. The diffraction peaks were broad, indicating low crystallinity and diffraction intensity. BET analysis showed that the adsorption of N/MOF(Fe) followed a type II isotherm with a hysteresis loop, indicating primarily mesoporous characteristics with pore size distribution mainly around 5 nm. With the increase in urea doping concentration, the pore volume and pore size of N/MOF(Fe) first increased and then decreased. The adsorption effect followed the same trend. Characterization by XRD and XPS revealed that the Fe3+ present in N/MOF(Fe) did not undergo a change in oxidation state during the adsorption process. There was a certain amount of Cr3+ in the solution.The optimal experimental conditions were found to be an initial Cr6+ concentration of 5 mg/L, an adsorbent dosage of 0.8 g/L, and no adjustment of the initial pH of the solution. Electrostatic interactions enabled N/MOF(Fe) to exhibit superior adsorption performance in acidic environments. The SO42– being divalent, exerted stronger electrostatic attraction compared to chromate ions in the solution, leading to a more significant competitive adsorption effect. Apart from SO42–, other coexisting ions have little effect on the adsorption of N/MOF(Fe). BET analysis indicated that the material regenerated twice exhibited similar N2 adsorption-desorption isotherms to the original material. The regeneration process had a slight effect on the pore size, pore volume, and specific surface area of N/MOF(Fe), but it did not significantly affect its adsorption performance. N/MOF(Fe) demonstrated good repeatability in reuse tests, with the adsorption rate remaining at around 70% even after multiple regenerations. The n in the Freundlich model is 8.13, indicating that the adsorption process is the main chemical adsorption and is easy to occur. In the intra-particle diffusion model, the intercepts of all three stages were non-zero, reflecting that surface diffusion is not the only limiting step. The a in the fitting result of Temkin model is 0.671, which proves that the adsorption of Cr6+ by N/MOF (Fe) is an exothermic process. By BQ, the mechanism of Cr6+ adsorption by N/MOF(Fe) was investigated, revealing the involvement of ·O2– in the reduction of Cr6+ during the adsorption process.ConclusionsUrea was employed as a structure-directing agent to modify MOF(Fe), resulting in the preparation of N/MOF(Fe) via a solvothermal method. The adsorption reaction followed a second-order kinetic equation, and the adsorption model conformed to the Langmuir model. The adsorption process was characterized as a spontaneous exothermic reaction. N/MOF(Fe) demonstrated excellent regeneration performance, with the adsorption process involving physicochemical reactions. This process facilitated the in-situ adsorption and reduction of Cr6+ by N/MOF(Fe), rendering it more environmentally friendly compared to traditional adsorbents.

IntroductionCo-disposal in cement kilns is a disposal method to achieve harmless and resourceful reuse of solid waste. However, cement kiln co-disposal technology is constrained by some specific components in solid waste. For solid wastes with a high content of heavy metals, such as waste battery slag, fly ash and electroplating sludge, heavy metals are involved in the clinker firing process through solid-phase and liquid-phase reactions during co-disposal in cement kilns, which may ultimately increase the content of heavy metals in the cement clinker, which can be re-released in the course of use, posing a threat to the environment and human safety. Also the presence of heavy metal ions can have a hindering effect on cement hydration.In recent years, fiber adsorbent materials have been widely used to treat heavy metal ions in wastewater, and researchers have prepared related materials with excellent performance. Chitosan is one of them, which is a natural biopolymer similar in structure to cellulose fibers commonly used in construction projects. Chitosan has its unique advantages: renewable resource, wide range resource, relatively low cost, having functional groups such as hydroxyl and amino, which, makes it an excellent adsorbent for metal ions. This work prepared modified chitosan material and its application on heavy metal-containing cement was investigated.MthodsChitosan, disodium EDTA, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, N-hydroxysuccinimide, formaldehyde, aminothiourea, copper nitrate, lead nitrate, zinc nitrate, anhydrous ethanol and other compounds at analytically pure grade were supplied by Beijing Jiashiteng Trade Limited Liability Company. The cement P·I 42.5 and standard sand used in this study were produced from Fushun Ausair Technology Limited Liability Company.In this study, an aminothiourea combined with ethylenediaminetetraacetic acid modified chitosan material (TS-EDTA-C) was prepared to increase its adsorption and stability of heavy metal ions by modification. TS-EDTA-C was added to the cement containing heavy metal ions to test the leaching concentration of heavy metal ions in the cement specimens at 7, 14 d and 28 d as well as the compressive and flexural strengths of the cement specimens at 3, 7, 14 d and 28 d. In addition, the heat of hydration of the cement specimens at 7 d was tested. Cement specimens at various ages were tested by XRD. The presence of heavy metals in the cementitious materials was tested by Tessier's five-step sequential extraction method.Results and discussionThe adsorption of modified chitosan (TS-EDTA-C) for Zn2+, Cu2+ and Pb2+ in solution was greatly improved and far exceeded that of unmodified chitosan (CS). The higher adsorption is mainly due to the introduction of a large number of groups such as —OH, —COOH, —NH2 and S on chitosan that can react with metal ions, while the modified chitosan surface is rougher, providing a larger adsorption surface. By comparing the cement specimens, it was found that the strength of the cement specimens containing heavy metals with the addition of TS-EDTA-C was higher than that of the specimens containing heavy metals without the addition of TS-EDTA-C at all ages, and the strength of the cement specimens without the addition of heavy metal ions was the highest. Because the hydration of cement occurs in an alkaline environment, heavy metal ions preferentially calcium ions react with OH– to generate some insoluble products, and the precipitation adsorbed on the surface of the cement particles impedes the further dissolution of cement mineral ions, leading to a decrease in the hydration products contributing to the cementitious properties and causing a significant decrease in the early strength of the cement mortar. The additional TS-EDTA-C will react with the heavy metal ions in the cement and adsorb them on the modified chitosan material, reducing the presence of free heavy metal ions and insoluble hydroxyl compounds, weakening their influence on the hydration reaction of the cement as well as lowering the leaching concentration of heavy metal ions.From the heat of hydration and XRD plots of the cement specimens at 7 d, it can be seen that Zn2+, Cu2+ and Pb2+ played an obvious inhibitory effect on the early hydration of cement and prolonged the hydration induction period of cement. The addition of TS-EDTA-C attenuated the effect of heavy metal ions on the early hydration of cement. Because when TS-EDTA-C was added to the heavy metal-containing cement, TS-EDTA-C adsorbed the heavy metal ions in the cement, which led to an increase in the heavy metal ions in the Q4 form and a decrease in the heavy metal ions in the Q1+Q2+Q3 form, reduced the presence of free unstable heavy metal ions, and lowered the unfavorable effects of the heavy metal ions. To a certain extent, it enabled Ca2+ to react with OH-, which promoted the hydration reaction. Meanwhile, the adsorbed heavy metal ions existed in a more stable form, reducing the leaching toxicity of heavy metal ions in cement.ConclusionsIn this paper, modified chitosan TS-EDTA-C (aminothiourea combined with ethylenediaminetetraacetic acid modified chitosan), which can effectively adsorb heavy metal ions, was prepared, and TS-EDTA-C had a good adsorption effect on Zn2+, Cu2+ and Pb2+, with the maximal adsorption amounts of 21.92, 68.08 mg/g, and 36.27 mg/g, respectively. TS-EDTA-C can effectively mitigate the adverse effects of heavy metals on cement properties. The 3, 7, 14 d, and 28 d compressive strengths of cement specimens with TS-EDTA-C were increased by 41.6%, 7.87%, 14.46%, and 2.51%, respectively, compared with those of heavy metal-containing cement specimens without modified chitosan. The heat of hydration and XRD tests proved that the addition of TS-EDTA-C attenuated the adverse effects of heavy metals on cement hydration. Modified chitosan is beneficial for cement stabilization and curing of heavy metals. The leaching concentrations of heavy metal ions were lower than those of the heavy metal-containing cement specimens without the addition of TS-EDTA-C. This is understood like that the addition of TS-EDTA-C stables the organic bound state (Q4) of heavy metals in cement, leading to a more stable form of heavy metal inos in cement.

IntroductionConcrete structures serving in cold regions are often affected by freeze－thaw damage, which is the main reason for the loss of durability in cold region concrete. Additionally, cold region concrete is also subject to salt erosion due to factors such as soil salinity and winter salt application. The coupled action of freeze－thaw and salt attack causes more severe damage to the internal structure of concrete materials, greatly impacting their service life. The deterioration of concrete durability under the coupled action of freeze–thaw and salt attack is primarily manifested as degradation of macroscopic properties such as mass, dynamic elastic modulus, and strength, accompanied by changes in the microstructure. The deterioration process is a complex physical-chemical process involving multiple scales. Merely focusing on the evolution of macroscopic properties often hinders a deep understanding of the degradation mechanisms. Therefore, it is of great significance to clarify the evolution process of microscopic features of concrete under the coupled action of freeze–thaw and salt attack, quantitatively characterize the damage evolution laws from the perspective of pore structure, spalling depth, and compactness, in order to gain a profound understanding of the coupling mechanism and degradation mechanisms of both phenomena.MethodsConcrete specimens were prepared using volume-stable P·O 42.5 ordinary Portland cement, river sand with a fineness modulus of 2.5, and coarse aggregates ranging from 5 mm to 10 mm. The dimensions of the concrete specimens were 100 mm× 100 mm × 100 mm. NaCl solutions with four different concentrations, namely 0%, 3.5%, 5.0%, and 8.0%, were used as the corrosive medium in the freeze–thaw process. A freeze–thaw cycling tests according to the fast freezing method specified in GB/T50082—2009.Concrete specimens were scanned using a LightSpeed 64-layer helical CT scanner with a resolution of 512×512 pixels and an X-ray tube voltage of 120 kV. To prevent water evaporation and loss of moisture during CT scanning, the specimens were wrapped in plastic film. After obtaining the CT data, three-dimensional reconstruction analysis was performed to investigate microstructural parameters such as delamination depth, volumetric loss rate, pore structure, and CT value.Results and discussionThe depth and volume of concrete spalling under the coupling effect of freeze–thaw and salt erosion gradually increase with the increase of freeze–thaw cycles, and the damage is mainly manifested as surface spalling. The degree of spalling in specimens with different concentrations of chloride salt solution is significantly different, increasing first and then decreasing with the increase of chloride salt concentration, and the spalling depth is the largest when the chloride salt concentration is 3.5%. The volume loss rate of concrete gradually increases with the increase of freeze–thaw cycles, and first increases and then decreases with the increase of chloride salt concentration. Among the four concentrations used in this experiment, the volume loss rate is the highest at a chloride salt concentration of 3.5%, followed by 5%, 8%, and 0%. The ultrasonic wave amplitude of concrete gradually decreases with the increase of freeze–thaw cycles, and there is a good exponential relationship between the two. The mass loss rate of concrete gradually increases with the increase of freeze–thaw cycles, and first increases and then decreases with the increase of concentration.The coupling effect of freeze–thaw and salt erosion leads to dynamic changes in the pore structure of concrete, mainly occurring on the outer side of the specimens. With the increase of freeze–thaw cycles, the overall porosity shows a fluctuating increasing trend. With the aggravation of freeze–thaw damage, some closed pores gradually transform into open pores and then disappear with the peeling off of mortar. The damage evolution model based on the relative CT value definition has a good linear relationship with the damage characterization of amplitude and mass, and has a higher agreement with the mass loss rate. The damage degree of concrete gradually increases with the increase of freeze–thaw cycles, and first increases and then decreases with the increase of chloride salt concentration. A certain range of chloride salt concentration can accelerate the freeze–thaw damage of concrete, but when it exceeds this range, the development of damage is slowed down, and the concrete freeze–thaw damage degree reaches the maximum value at a chloride salt concentration of 3.5%.ConclusionsChloride salt has two effects on the freeze–thaw damage of concrete. On one hand, chloride salt increases the concentration difference between the inside and outside of the concrete pores during the freeze–thaw process, increases the liquid absorption rate of the specimen, and generates more pore ice during freezing, which accelerates the damage of concrete within a certain concentration range. On the other hand, the freezing point of chloride salt solution is lower than that of pure water. High concentration chloride salt solution has a slower freezing rate during the cooling process and a faster melting rate during the warming process. Compared with low concentration solution, the specimen has a shorter freezing time, which reduces the extent of concrete damage. Based on the analysis of indicators such as peeling depth, volume loss rate, amplitude, and mass loss rate in this study, it's found that a certain range of chloride salt concentration can accelerate the freeze–thaw damage of concrete, but the development rate of damage slows down when the range is exceeded. Among the four chloride salt concentrations used in this experiment, the concrete damage reaches the maximum value when the concentration is 3.5%.

IntroductionAs a heterogeneous multiphase material, cement-based material has a significant correlation between its macroscopic properties and microstructure, and exhibits significant scale dependent characteristics. Representative element is defined as the smallest element that can represent the macroscopic property of multi-scale material. It is usually very difficult to study materials at the full scale. Selecting representative element of appropriate size can to some extent represent the overall characteristics, providing possibilities for microscopic calculations. Therefore, the appropriate selection of representative elementary size (RES) is of great significance for further elaborating the structure-performance relationship in micro computational research. For cement mortar, there has been considerable research on the RES of mortar’s microstructure of, but there is a lack of research on the RES of mortar’s mesostructure. Only scholar such as Winslow reported a value of 10–30 mm in early research with relatively single dependent indicator. In view of this, combined with digital image processing and analysis techniques, the statistical characteristics of the spatial distribution of aggregates were calculated from two-dimensional and three-dimensional perspectives by using the average proportion function, two-point correlation function and radial distribution function in this paper. Finally, the representative elementary size of the mortar’s mesostructure was explored.MethodsThree types of cement mortars blended with cement, fly ash (FA), silica fume (SF) and sand were prepared in this research. The cement used was P·II52.5 in accordance with the relevant Chinese standard. The density of cement and FA are 3.11 g/cm3 and 2.27 g/cm3, respectively. The specific surface area of FA and SF are 420 m2/kg and 22 000 m2/kg, respectively. The fineness modulus of natural sands and manufactured sands are 1.66 and 2.25, respectively. Besides, one kind of polycarboxylic-type high performance water reducer was adopted as the superplasticizer and the water reducing ratio was not less than 40%.The raw materials (cement, fly ash, silica fume, and sand) were mixed uniformly and then the mixed water and additives were added and stirred for 2－3 min until the mixture enters the viscous flow state. Then the uniform mixed slurry was poured at molds and vibrated to enhance compactness. The specimens were demolded after 1 d and then cured in the standard curing room ((20±2) ℃, room humidity >95%). After 28 d of standard curing, the specimens with size of 15 mm×15 mm×15 mm were cut and dried in vacuum at 60 ℃ for 3 d. Afterwards, computed micro-tomography (CT) testing was conducted and 1 000 CT slice images for each specimen were obtained with a resolution ratio of 10 m.Results and discussionAfter image processing, the influence of noise has been removed and the distribution information of aggregates has been obtained. It can be found that the presentation of natural sand (NS) in CT image is relatively clear and the particle size is relatively uniform, while the shape of manufactured sand (MS) is irregular and the particle size is uneven. Comparing the calculation results of the average volume fraction with the design volume fraction, it can be seen that the former is significantly lower than the latter. The reason is that the composition of the MS is uneven and uneven grayscale values inside may happen due to the crushing process. Therefore, some aggregate information will be lost during the image processing, resulting in a significant deviation between the final result and the design volume fraction. Although the grayscale range of the NS group is very close to that of the cement matrix, its composition is uniform and its shape is regular. After image processing, its distribution information can be retained to a high extent, so the deviation between its calculated volume fraction and the designed volume fraction is very small.As the aggregate fraction increases, there is a significant fluctuation in the RES obtained by calculating the average area fraction on a single CT image, while the average volume fraction obtained by stacking multiple CT images on a three-dimensional structure is equivalent to the average value on a larger area, and the RES results tend to be consistent. The RES is not related to the volume fraction of sand, but is significantly affected by its type. For mortar with natural sand, RES is 2.75–2.90 mm, which is about 9 times of its average particle size. For mortar with manufactured sand, RES is 3.1–3.2 mm, which is about 7 times of its average particle size. Compared with the result mentioned by Winslow that the RES of mortar or concrete is within the range of 10–30 mm, the accuracy of the conclusion in this paper has been improved by one order of magnitude.ConclusionsThe RES of mortar prepared in this paper is not related to the volume fraction of sand, but is significantly affected by its type. For mortar with natural sand, the RES obtained through the average volume proportion function is 2.75 mm, and the RES is 3.1 mm for mortar with manufactured sand. For mortar with natural sand, the RES obtained through two-point probability function and radially distribution function are both 2.9 mm. For mortar with manufactured sand, the RES obtained through two-point probability function and radially distribution function are 3.2 mm and 3.1 mm, respectively.

IntroductionThe volumetric deformation of cement-based materials continues over setting, hardening and service periods, as a result of both cement hydration and changes in temperature and humidity. Under restricted conditions, excessive volume shrinkage may lead to cracking in cement-based materials, seriously threatening the long-term performance and durability of structure. As an important admixture to compensate for shrinkage and to control cracking, expansive agents are widely used in engineering construction. The influence of expansive agents on the compensatory effect for drying shrinkage of cement-based materials is closely linked to the evolution of chemically bound water and physically adsorbed water. Since most mesoscopic and microcosmic testing techniques require drying preparations for specimens, it is challenging to analyze the development process of shrinkage-compensating. Low-field nuclear magnetic resonance (LF-NMR) technique has a unique technological advantage for investigating cement-based materials. Taking hydrogen nuclei in water as a probe, LF-NMR technique can non-destructively, rapidly and accurately characterize the pore water content and water distribution in specimens in situ, which promotes to accurately analyze the connection between micro change of pore water and macro volumetric deformation. Therefore the cement paste samples mixed with expansive agents are monitored by non-destructive LF-NMR technique in this work, the weight and length are also measured. From the perspective of water content and its state, the quantitative analysis on evolution of chemically bound water and physically adsorbed water is conducted. Furthermore, the shrinkage-compensating deformation of cement paste is thoroughly analyzed.MethodsWhite cement, calcium sulfoaluminate and MgO expansive agents (CSA and MEA) are used to prepare cement paste specimens. Water to cement ratio (W/C) is 0.40, and the weight ratio of expansive agent to cement is 5%. The expansion agents are produced by Wuhan Sanyuan Special Building Materials Co. The sizes of cement paste specimens are 20 mm×20 mm×280 mm (size A) and 20 mm×20 mm×50 mm (size B).Starting from the 3rd day of water-curing, the weight and length of 3 specimens of each sample are measured at regular time intervals, as well as the low-field magnetic resonance tests. In addition, at 56th day of water-curing, another 3 specimens of each mixture proportion and each size are transferred into a high humidity environment (20℃, 98% relative humidity (RH)) for air-curing, and measurements of weight and length, and low-field magnetic resonance tests are conducted periodically. The length test is carried out using a length gauge with an accuracy of 0.001 mm. An electronic balance with an accuracy of 0.001 g is used in the weight test. The low-field magnetic resonance test is performed by a low-field magnetic resonance instrument with a magnetic field strength of 0.047 T and a main frequency of 2 MHz. And the transverse relaxation signal of pore water in specimen is characterized with a CPMG pulse sequence.Results and discussionAfter curing in water for 3 d, the weight, expansion deformation and evaporable water content of paste continuously increased during curing process, while the rate of increase gradually decreased. CSA and MEA can significantly increase the increment of chemically bound water and the expansion deformation caused by each unit increment. However, their influences on the evolution of physically adsorbed water and the expansion deformation are both insignificant. During the process of air curing in high humidity (98% RH), starting from the day 0 of air curing (i.e., water curing 56 d), the weight of paste decreases initially and then increases. Similarly, the paste initially shrinks and then expands. Additionally, the evaporable water content decreases rapidly in the first 28 days and then stabilizes. Both CSA and MEA can increase the loss of evaporable water content of paste in the early stage and also enhance the expansion deformation in the later stage to compensate for shrinkage. Considering the complicated expansive process of cement-based materials mixed with expansive agents, the utilization of low-field nuclear magnetic resonance relaxation technique and other testing methods can accurately analyze the expansion deformation, which can improve the expansion mechanism and assist the selection of expansive agents.ConclusionsThe main conclusions of this paper are summarized as following. During the period of 6-month water-curing, all the tested indicators, including weight, expansion deformation, and evaporable water content of paste, continuously increase, while the increasing rate keeps declining. Both CSA and MEA continue to hydrate, resulting in the larger content of chemically bound water. In the meanwhile, they increase the expansion deformation caused by unit increment of chemically bound water. The evolution of chemically bound water significantly influences the effect of expansive agents on compensating for shrinkage. Nevertheless, the evolution of physically adsorbed water and its effect on volumetric deformation is independent of the addition of any expansive agent.After air-curing at a high humidity (98% RH), the reduction rate of evaporable water content of cement paste with CSA and MEA increases significantly in the early stage, but the difference in its shrinkage deformation is relatively small. And the compensatory effect of expansive agents on shrinkage is still effective in the later stage.

Introduction:Thermogravimetry (TG) is widely used to evaluate the hydration process and the degree of reaction of cementitious materials. However, it is still challenging to accurately quantify the overlaps of hydration products using TG alone because cement hydration produce complex and multiphase composites. Mass spectrometry (MS) with its high specificity, sensitivity and fast testing speed, can promote TG quantification by eliminating overlapping decomposition peaks, further achieving the accurate quantification of cementitious hydration products. Therefore, this study designed the exposure conditions with different temperatures (5, 20, and 40 ℃) and humidity levels (RH ≈ 33%, RH ≈ 59%, and RH ≈ 95%) to study a dissolution process of the hydrated granulated blast furnace slag (GGBS). Hydration products at 6 different periods of dissolution (5, 10, 20, 30, 60 min, and 120 min) were analyzed to assess the applicability and feasibility of the TG–MS coupling technique for quantifying the early reaction products of GGBS.Methods:Granulated blast furnace slag (GGBS) was used in dissolution-carbonation experiments, using deionized water and the 4 mol/L NaOH solution as solvents. The liquid-solid ratio was 50:1, and the dissolution temperatures were set at 5, 20 ℃, and 40 ℃. Three ambient relative humidity (RH) (33%, 59% and 95%) were controlled using saturated MgCl2, NaBr, and KNO3 solutions. Mechanical stirring was performed at 750 r/min, and the vessel was covered with parafilm throughout the dissolution process. The samples were taken at 5, 10, 20, 30, 60 min, and 120 min. The precipitated products were hydration-stopped using the solvent-exchange method, followed by carbonation in a CO2 concentration of 600 × 10–6 for 28 d. Water and carbon dioxide were detected using a TG–MS system.Results and discussion:The C-(A)-S-H thermal decomposition mass loss in TG correlated well with the H2O signal in the MS system under tested conditions, whereas the relation depends on degree of hydration. This phenomenon may be attributable to the following factors: on the one hand, it is due to the overlapping peaks observed in the thermogravimetric loss curve affected by water vapor mass loss released by C-(A)-S-H decomposition and heat absorption peaks of the dehydration of loss-combined water in the hydrotalcite-like phases (Mg-Al-LDH). On the other hand, it is related to the partial-pressure system in the MS system that was constantly changing during the gas release. In the quantitative analysis of CaCO3, the samples with different degrees of hydration exhibited disparate degrees of carbonation, indicating that the degree of hydration influenced the degree of carbonation. Notably, CaCO3 quantification (expressed as the amount of CO2 detected) presents different correlations, and there is also a correlation in the quantitative analysis of C-(A)-S-H gel. With the increased hydration (temperature and time), the amount of C-(A)-S-H gel increased, resulting in more CaCO3 generated by carbonation. Since the decomposition of the C-(A)-S-H gel occurred throughout the entire heating process, an overlap between the decomposition curves of C-(A)-S-H and CaCO3 should be taken into account. However, the current study did not fully account for gas partial pressures, which led to multiple linear relationships in the correlations within the TG–MS system. This phenomenon can be quantified and calibrated using equivalent characteristic spectrum analysis (ECSA).Conclusions:TG–MS was used to analyze the dissolution-precipitation-natural carbonation products of GGBS under several storage humidity and temperature conditions. This method enabled the quantitative description of the amorphous hydration product C-(A)-S-H gel and the crystalline product CaCO3. The degree of GGBS hydration and natural carbonation varies depending on the dissolution environment (storage humidity, dissociation temperature, and dissolution time), and these processes exhibit a positive correlation between mass loss and MS quantification. Using MS helps to separate overlapping peaks in the TG quantitative process, serving as a complementary and validation method for thermogravimetric analysis. However, when using the TG–MS system for correlation analysis, experimental errors may occasionally arise due to the inherent inaccuracies of TG, the amount of gas within the TG–MS system, and the presence of multiple gases.

IntroductionUltra-high performance concrete (UHPC), as an advanced cementitious fiber-reinforced composite material, is often widely used as a load-bearing member in the critical parts of various types of large-span and high-rise structures. However, the increasingly frequent fire disasters have posed a great challenge to the safe serviceability of UHPC. Steel fiber, as an important factor for UHPC to achieve ultra-high toughness, the cracking mechanism of steel fibers exposed to high-temperature will directly affect the high-temperature residual properties of UHPC. Although some scholars have carried out studies on the residual properties of UHPC after high temperature, there are less systematic studies on the influence of steel fibers on the mechanical and thermal properties of UHPC, especially on the deterioration mechanism of steel fibers exposed to high temperature. In view of this, this work systematically investigates the influence of steel fiber on the mechanical and thermal properties of UHPC exposed to high temperature. The mathematical model between steel fiber dosage-temperature-mechanical properties/thermal properties was established. In addition, the changes in the pull-out behavior of steel fibers from the UHPC matrix at different temperatures were investigated for the first time, and the deterioration mechanism of steel fibers exposed to high temperature was elucidated based on SEM tests.MethodsThe Onoda P.II 52.5 cement and the blending material produced by Jiangsu Sobute New Material Co. were used, respectively. At the same time, an appropriate amount of polypropylene fiber was mixed to reduce the risk of explosive spalling of UHPC. UHPC with 0%, 1.0%, 2.0% and 2.5% steel fiber volume mixing were prepared. The concrete molding size was 100 mm×100 mm×100 mm, and 28 d standard curing was carried out after the casting was completed. Then the mechanical and thermal properties were tested after high temperature. The changes in the pull-out mechanism of steel fibers after high temperature were also investigated.Results and discussionThe compressive strength of UHPC after high temperature with different steel fiber dosage increases and then decreases with temperature. The addition of steel fibers can improve its overall compressive strength to different degrees. The tensile strength of UHPC shows almost monotonically decreasing with the increase of temperature, and the degree of loss rate is greater. Among them, the enhancement of steel fiber addition can obviously improve the tensile strength of UHPC at room temperature as well as at 200 ℃, but the degree of its enhancement with the increase in temperature gradually weakened. The elasticity modulus of UHPC with the increase in temperature first increased and then decreased, and the overall rule of change is similar to the compressive strength. The thermal conductivity of UHPC shows a monotonically decreasing law with temperature, which is mainly because the high temperature makes the organic fiber in UHPC melt, free water continues to evaporate, and the hydration products continue to decompose and so on to reduce the apparent density of the system. The addition of the steel fibers effectively improves the thermal conductivity of UHPC. The specific heat capacity showed the opposite law to the thermal conductivity. In addition, the maximum pull-out load, pull-out work and bond strength of steel fibers at 200 ℃ increased to varying degrees, compared to room temperature. At 400 ℃, relevant parameters began to have a substantial decline. When the temperature reached 600 ℃, the failure mode of steel fibers changed from pull-out to pull-off mode.ConclusionsThe compressive strength of UHPC increases at the beginning and then decreases with the increase of temperature, and reaches the peak value at 200 ℃. The addition of steel fiber does not affect the trend of UHPC residual compressive strength exposed to high temperature, but improve absolute value of its residual strength. Temperature changes pull-out mode of steel fiber. At 25–200 ℃, the surface of the steel fibers was smooth when they were pulled out, and the tensile strength of UHPC did not change much. At 400 ℃, steel fibers were attached to part of the matrix when they were pulled-out, UHPC tensile strength began to drop significantly. At 600 ℃, the failure mode of steel fibers changed from pull-out to pull-off mode. The tensile strength of UHPC with different steel fibers continues to decline, and the difference gradually narrowed. The elasticity modulus of UHPC reached its peak at 200 ℃ and began to decline rapidly, and its sensitivity to high temperature is much greater than the compressive and tensile strength changes, the value of the proposal can be used as an important indicator for the assessment of the safety of the relevant building after the fire, and the incorporation of steel fibers does not affect the overall development of its law. Steel fiber can significantly increase the thermal conductivity of UHPC, but will not change the overall trend of thermal conductivity with the increase in temperature. The thermal conductivity of UHPC decrease with the increase of temperature and the gradual decrease in the overall trend of change; specific heat capacity shows the opposite development law with the thermal conductivity. Copper-plated steel fiber as UHPC commonly used metal fiber, can maintain good mechanical properties and play a toughening crack resistance before 400 ℃. When the temperature reached at 600 ℃ and later, the degree of deterioration of copper-plated steel fiber itself is greater than the fiber-matrix interface transition zone, which leads to UHPC tensile and compressive drop in coordination, it is recommended that the steel fiber's own high-temperature performance enhancement should be focused on under this condition.

IntroductionAccurately and effectively predicting ionic diffusion coefficient of cement-based materials is one of the crucial issues in the study of concrete durability. Recently, many novel prediction methods based on General Effective Media (GEM) equation have been proposed and their applicability has been verified. As a significant parameter in diffusivity models based on GEM equation, percolation exponent n characterizes the diffusion properties of micro-pore structures in cement paste. The value of percolation exponent n is affected by the shape and direction of the medium, namely the morphological characteristics of micro-pore structures in cement paste. With the hydration process, the material composition and pore structure of cement change greatly, as well as the value of percolation exponent n. The value-taking of percolation exponent n has a great influence on the accuracy of the diffusion prediction model. However, a systematic study to reveal its physical meaning and determine its value is deficient. In this paper, the strong correlation between percolation exponent n and the morphological characteristic of cement paste was verified, and quantitative expressions of percolation exponent n was given by fitting experimental data.MethodsReference cement complying GB8076—2008 was used to prepare 25 groups of cylindrical cement paste specimens (=100 mm, h=200 mm) with water-cement ratios (w/c ratio) of 0.30/0.35/0.40/0.45/0.50 and curing periods of 28/60/90/120/180 d, respectively. There were 3 specimens in each group, 2 of which were cut in the center of specimen height (50–150 mm) to obtain 4 standard test specimens (=100 mm, h=50 mm) for NEL test, and 1 of which was drilled at the center of height and section of specimen to obtain a cylinder (=32 mm, h=50 mm) for low-field NMR (Nuclear Magnetic Resonance) test. Saturated saline water was saturated into specimens for NEL test using the NELD-CCM vacuum water saturation instrument at vacuum degree of 87%. The NELD-CCM540 cement chloride ion effective diffusion coefficient tester was used in NEL test, 4 specimens in a group were tested and the test data was averaged as the representative effective diffusion coefficient. To determine the pore characteristics of specimens in each group, NMR test was conducted for corresponding specimen twice. For the first time, deionized water was saturated into specimens for NMR test using NELD-CCM vacuum water saturation instrument at vacuum degree of 98%, and NMR test was performed for saturated specimen to obtain total transverse relaxation time spectra of water in pore and chemically combined water. The specimen was then dried in an oven at 110 ℃ for 12 h and placed for 3 h to reduce the sample temperature to room temperature. NMR test was performed again for dry specimen to get transverse relaxation time spectra of chemically combined water. Combined with total spectra, pore size distribution of tested specimen was available. Moreover, the porosity of specimen was obtained by establishing the quantitative relation between water volume porosity and nuclear magnetic signal.Results and discussionFor all groups of specimens, the effective diffusion coefficient increases firstly and then decreases with hydration process. Considering the change of gel pores and capillary pores quantity and effective diffusion coefficient data simultaneously, it can be known that the auxiliary effect of gel pores on diffusion cannot be ignored. Capillary porosity of all specimens is keeps decreasing, while the 2.5–10.0 nm gel porosity increases greatly in the first 60 d of curing and decreases at a relatively smaller rate after 60 d of curing. With the increase of w/c ratio of cement paste, the proportion of diffusion effect of capillary pores to that of gel pores increase. As the hydration process carries on, the pore characteristics of the specimens shows the following rules: the continuous pore size sc of the pore structure system decreases for specimens with w/c ratio of 0.30/0.35/0.40/0.45, and the continuous pore size sc of the pore structure system keeps relatively stable for specimens with w/c ratio of 0.50; the tortuosity factor of pore structure system decreases at first and then increases, which is influenced by coupling effect of hydration products formation and morphological difference between two kinds of pores.The sample correlation matrix between percolation exponent n, continuous pore size sc, and tortuosity factor reflects the strong correlation between these three parameters. Percolation exponent n is negatively correlated with continuous pore size sc, and positively correlated with the tortuosity factor . The results prove the morphological meaning at physical level of percolation exponent n. With the increased hydration degree, the percolation exponent n of cement paste with different w/c ratio shows different variation: the percolation exponent n of cement paste with w/c ratio of 0.30 and 0.35 increases, the percolation exponent n of cement paste with w/c ratio of 0.40 and 0.45 decreases at the beginning and then increases, and the percolation exponent n of cement paste with w/c ratio of 0.50 decreases. The different phenomena is primarily from different diffusion effect ratios between capillary pores and gel pores.ConclusionsBased on the theory of micropore structure analysis, the relationship between percolation exponent n and diffusion property of cement paste is explained from the aspect of mechanism. For cement paste with different w/c decreases at the beginning and then increases, the difference in ratio between capillary porosity and gel porosity leads to the difference in change law of pore characteristic parameters and percolation exponent n. With the experimental results, the relational expression of function between percolation exponent n and hydration degree was obtained.

IntroductionThe corrosion of steel bar in tunnel lining concrete under high geothermal environment is the result of the combined effect of temperature, pH value of pore solution, and erosion ions. In this paper, the critical ion concentration and corrosion behavior of steel bar under the combined action of ambient temperature (20 ℃ and 60 ℃), pH value of pore solution (12.55, 12.15, and 11.75) and erosion ions (Cl–, SO42–, and Cl–, SO42– composite) were studied by simulating concrete pore solution. The results show that the critical chloride concentration of steel corrosion is 0.04–0.06 mol/L in the saturated concrete simulated solution with temperature of 60 ℃ and pH of 12.55 during chloride corrosion. The stability of the passivation film decreased when the pH value decreased (12.15 and 11.75), and the corresponding critical chloride ion concentration also decreased (0.03–0.05 mol/L and 0.02–0.04 mol/L, respectively). The corrosion induction period of steel bar becomes longer when the steel bar is eroded by single sulfate. The threshold value of sulfate ion concentration is between 0.06–0.08 mol/L when the temperature is 60 ℃ and the pH value is 12.55 and 12.15, and it becomes 0.05–0.08 mol/L when the pH value decreases to 11.75. There is no significant difference in the sulfate concentration threshold of steel corrosion, because the gypsum covers the steel surface and delays the steel corrosion which formed by the reaction of sulfate with Ca(OH)2 in the simulated pore solution. Therefore, temperature and pH value have not significant effect on the corrosion concentration threshold caused by SO42–. Under the combined action of Cl– and SO42–, SO42– will repel the Cl–, and it reacts with Ca2+ to form CaSO4, which covers the surface of steel bar, densifies the passive film, and slows down the corrosion rate of steel bar. When the pH value is 12.55 and 12.15, SO42– reaches 0.03 mol/L and 0.04 mol/L respectively, which can inhibit the corrosion of steel bar caused by Cl–. However, when the pH value is 11.75, SO42– has not inhibition effect on the corrosion of steel bar caused by Cl–.MethodsThe electrochemical experimental instrument was Wuhan Koster electrochemical workstation, model CS1350, with a current range of 2 A–20 A and a constant potential control range of ±10 V. A three-electrode system includes working electrode, counter electrode, and reference electrode, was chosen for electrochemical testing, that is, the steel bar sheet (10 mm in diameter and 0.785 cm2 of exposed area) as the working electrode, a platinum sheet electrode (20.0 mm×20.0 mm×0.1 mm) as the counter electrode, and a saturated copper sulfate electrode (CSE) as the reference one. The corrosion potential (Ecorr) of the steel bars was tested by the Open Circuit Potential Method (OCP). During the test, the working electrode was immersed in the simulation solution, and the test began after the corrosion potential of the steel bar was stable. Then the polarization curve of the steel bar was tested by linear polarization method (LPR), the changes of corrosion current density (Icorr) and polarization resistance (Rp) of the steel bar were analyzed. The corrosion products of steel bars under different erosion ions were studied by X-ray diffractometer.Results and discussionIn this paper, rapid corrosion tests of steel bars in concrete simulated pore solutions under the combined effect of different temperatures, erosion ions types and concentrations and pH values were carried out. The critical chloride ion concentration and sulfate concentration thresholds for the steel to start rusting in different temperatures and pH values were clarified. Moreover, the corrosion products generated by steel corrosion under different erosion ions were investigated by XRD.ConclusionsThe results showed that the critical chloride ion concentration of steel corrosion was 0.04–0.06 mol/L in the saturated concrete simulated solution with pH value of 12.55 at 60 ℃. When the pH value reduced to 12.15 and 11.75, the stability of the passivation film decreased at the same time. The critical concentration of chloride ion also reduced to 0.03–0.05 mol/L and 0.02–0.04 mol/L. The corrosion induction period of steel bar becomes longer when the steel bar is eroded by single sulfate. The threshold value of sulfate ion concentration is between 0.06–0.08 mol/L when the temperature is 60 ℃ and the pH value is 12.55 and 12.15, and it becomes 0.05–0.08 mol/L when the pH value decreases to 11.75. There is no significant difference in the sulfate concentration threshold of steel corrosion, because the gypsum covers the steel surface and delays the steel corrosion which formed by the reaction of sulfate with Ca(OH)2 in the simulated pore solution. Therefore, temperature and pH value have not significant effect on the corrosion concentration threshold caused by SO42–. Under the combined action of Cl– and SO42–, SO42– can inhibit the corrosion of steel bar caused by Cl– when the pH value is 12.55 and 12.15, and the corresponding concentration of SO42– is 0.03 mol/L and 0.04 mol/L. However, when pH decreased to 11.75, SO42– had not inhibition effect on steel bar corrosion caused by Cl–.

IntroductionGranulated blast furnace slag (GBFS) has been widely applied in Marine cement, low-carbon cement, alkali-activated cementitious materials, and geopolymer cementitious materials due to its excellent potential hydration activity and hydration product optimization ability. The glass phase (SGP) is the predominant active mineral in GBFS, and its ionic dissolution ability in an alkaline environment directly influences the hydration activity of GBFS. Therefore, establishing the correlation between the structural characteristic and their hydration properties is imperative for optimizing the utilization of GBFS. Accurately describing the structural characteristics of SGP remains a pivotal challenge that has yet to be resolved. The hydration activity of GBFS can be partially elucidated by investigating the structural characteristics of alkali earth metal aluminosilicate glass using molecular dynamics (MD) simulation. Given the influence of potential functions on the accuracy of MD simulation results, it is imperative to undertake a comparative investigation into SGP structure simulation employing different potential functions. This paper compared the locally ordered structure, oxygen atom type, polymerization behavior, and clustering behavior using four different potentials: Buckingham potential, Broyden-Mor-Hnon (BMH) potential, Miyake potential, and SHIK potential. The accuracy and reference ability of the simulation is achieved by comparing the matched degree between the simulation results and experimental data, thereby providing a valuable reference for investigating the nanostructure and hydration characteristics of SGP in GBFS using MD simulations.MethodsThe SGP structure was simulated using molecular dynamics with the Buckingham potential, BMH potential (optimized based on mineral crystal structure), Miyake potential (combining multiple potential functions), and SHIK potential (optimized through first-principles molecular dynamics). The initial random configuration of the SGP structure, consisting of 3 000 Ca, Si, Al, Mg, and O ions, was generated using the Amorphous Cell module in Materials Studio software. The proportions of different ion types in the SGP structure were determined based on the chemical composition of industrial GBFS and encompassed variations within a specific range for the mass ratio of SiO2/Al2O3 and quaternary alkalinity. A Large-scale Atomic/Molecular Massively Parallel Simulator was employed to calculate the MD process with periodic boundaries in real units using an integral step size of 0.8 fs. The simulation process involved six stages of relaxation to simulate the quench granulation process observed in industrial GBFS.The laboratory synthesis of SGP utilizes chemically pure SiO2, Al2O3, CaO, and MgO powders with a chemical composition matching referenced in the MD simulation. The homogenized oxide powder is melted in a Muffle furnace using a graphite crucible. The melting process occurs at 1 500 ℃ for 2 h, followed by quench cooling using an ice water mixture at 0 ℃. After crushing and grinding the cooled SGP block with an agate grinder, the resulting fine powder (200-mesh) is selected for X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and 29Si solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) experiments. These experimental results are used to evaluate the accuracy of the MD simulation findings.Results and discussionThe MD simulation results of SGP structures under all potential functions are consistent with the glass random network model. The optimization of Buckingham potential, BMH potential, and Miyake potential parameters pertains to specific crystal structures, offering advantages over SHIK potential in simulating local ordered structure characteristics. Furthermore, a comparison between the MD simulation results and XPS experimental data reveals that Buckingham potential, BMH potential, and Miyake potential exhibit contrasting or localized fluctuation patterns in bridging oxygen, non-bridging oxygen, and free oxygen contents compared to the experimental findings. Notably, an increase in alkalinity leads to a decrease in non-bridging oxygen content, according to some simulation results; however, this contradicts the charge balance principle of glass structure. In comparison, the variation trend of non-bridging oxygen and bridging oxygen under SHIK potential aligns with the outcomes observed in XPS experiments.The experimental results from 29Si MAS NMR indicate that SGP primarily consists of Q0 and Q1 types [SiO4]. However, the simulation results using all potential functions exhibit a significantly higher degree of polymerization for [SiO4], with a large number of Q3 and Q4 types present. This discrepancy can be attributed to the short time scale of the simulation process, leading to an abundance of free oxygen. These findings highlight inherent technical limitations in MD simulations for accurately predicting the quantitative distribution of Qn. Notably, only the SHIK potential simulations demonstrate consistent trends with experimental observations, whereas Buckingham potential, BMH potential, and Miyake potential fail to capture the decreasing trend in polymerization degree as the SiO2/Al2O3 mass ratio decreases and alkalinity increases. Combined with the quantitative XRD data, the clustering behavior of Ca remained largely unaltered in the Miyake potential as the local enrichment of Ca increased; however, a transition from isolated Ca to clustered Ca was observed in both BMH and SHIK potentials.ConclusionsThe main conclusions of this paper are summarized as follows. Buckingham, BMH and Miyake potential exhibit suitability for simulating local ordered structure. Moreover, SHIK potential has higher stability in simulating the effect of chemical composition on the content variation trend of different types of oxygen and the Qn distribution. Lastly, SHIK potential and BMH potential, which define the interaction forces between metal ions, are more suitable for the clustering behavior as network modifiers. This study demonstrates that for the optimization of MD simulation of SGP in GBFS, it is a reasonable approach to add the potential parameters governing ion interactions and optimize the existing potential based on Ab initio molecular dynamics simulations of target structure characteristics.

IntroductionFiber-Reinforced Cement-based Materials (FRCM) have excellent toughness and impermeability, and have a broad application in the repair of deteriorated concrete structures and the reinforcement of fractured rock mass. The bonding performance between the cement-based material and the substrate is affected by many factors, including the mix ratio of cement-based materials, the saturation of substrates, and the surface roughness of substrates. The initial water content of substrates affects the water exchange between substrates and fresh cement-based repair materials, further affects the water-binder ratio of repair materials, the hydration of cementitious materials and the shrinkage deformation of materials, etc., and ultimately affects the mechanical properties of the interface. Further research is needed on the effect of water saturation of different types of substrates on the interfacial bonding properties between them and FRCM with different mixing ratios. Appropriately increasing the surface roughness of old cement-based materials and rock substrates is an effective method to improve the bonding performance between them and cement-based materials. Compared with ordinary mortar, the content of fly ash and other auxiliary cementitious materials in FRCM is higher, and the toughening effect of fiber is remarkable. The bonding performance between FRCM and mortar substrates with different surface roughness is worthy of further study. Cement-based repair materials are generally poured on the surface of existing substrates, and the impermeability is crucial to the long-term effectiveness of repair and reinforcement. The water transport properties of FRCM bonded with different types of substrates with various initial water content are worthy of further study. In this work, the effects of fiber type, fly ash content, initial water saturation of substrates, and grooving form of the substrate surface on the interfacial shear strength between FRCM and ordinary cement mortar, concrete, granite, and sandstone were systematically studied through mechanical performance tests. The capillary water absorption properties of FRCM bonded to different types of substrates with different initial water saturations were studied by weighing method.MethodsThe dynamic quality monitoring method was used to control the saturation of the substrate to 0%, 50% and 100%, and an angle grinder was used to cut different forms of grooves on the surface of mortar substrates. FRCM was prepared with cement, fly ash, quartz sand, water, superplasticizer and fibers. The fiber types included PVA fiber and basalt fiber, and the fly ash content was 1.2 times and 1.8 times of the cement mass, respectively. After reaching the curing age of 28 d, three specimens were selected for interfacial shear strength test. Three 28 d old bonding composites in each group were subjected to capillary water absorption test.Results and discussionThe increase in the saturation of the mortar substrate was not conducive to its adhesion to basalt or PVA FRCM. It’s speculated that the above phenomenon was related to the water exchange between repair materials and substrates. When the substrate was dry, the water in the fresh repair material can carry cement particles to the substrate under the action of capillary suction. The water exchange across the interface was beneficial to the adhesion of repair materials to substrates, and at the same time the decrease of water-binder ratio of the repair material at the interface improved the interfacial shear strength. The increase of fly ash content enhanced the interfacial shear strength between PVA FRCM and substrates, but lead to the decrease of interfacial shear strength between basalt FRCM and substrates. Due to the pozzolanic effect and filling effect of fly ash, the increase of fly ash content in FRCM was conducive to the formation of denser microstructure, which was beneficial to its bonding with substrates. However, the improvement of fly ash on the toughness of cement-based materials can be affected by its synergistic effect with fibers. When the mechanical properties and content of fibers were low, excessive fly ash can lead to the reduction of material toughness. In the case of dry substrates, the increase of the number of grooves on the substrate surface has a more significant effect on the interfacial shear strength between PVA FRCM than that of basalt FRCM, which may be related to the excellent mechanical properties of PVA FRCM.The increase of fly ash content can significantly improve the capillary water absorption properties of basalt or PVA FRCM bonded to mortar substrates, while the change of substrate saturation has insignificant effect on the capillary water absorption properties of basalt FRCM bonded to mortar substrates. When the mass ratio of fly ash to cement in the repair material was 1.2 and the substrate saturation was 0%, 50% and 100%, the capillary water absorption coefficient of basalt FRCM was significantly lower than that of PVA FRCM, which may be related to the higher porosity of PVA fiber.ConclusionsThe interfacial shear strength between PVA and mortar substrates, or basalt FRCM and mortar substrates decreased with the increase of substrates saturation. When the saturation of mortar substrates was constant, the increase of fly ash content enhanced the interfacial shear strength between PVA FRCM and substrates, but reduced the interfacial shear strength between basalt FRCM and substrates. The more the number of grooves on the substrate surface, the higher the interfacial shear strength between it and PVA or basalt FRCM. This phenomenon was more obvious for PVA FRCM. The effect of the grooves on the surface of dry substrates on the improvement of the interfacial shear strength between dry substrates and the basalt or PVA FRCM was more obvious than that of saturated substrate. The interfacial shear strength between PVA FRCM and concrete and sandstone substrates decreased with the increase of substrates saturation. When the substrates were dry, the interfacial shear strength between PVA FRCM and concrete was higher than that of mortar, sandstone and granite. When the substrates were partially saturated, the interfacial shear strength between PVA FRCM and concrete and mortar was equivalent or higher than that of sandstone. When the substrates were saturated, the interfacial shear strength between PVA FRCM and mortar was higher than that of concrete and sandstone. The capillary water absorption coefficient of FRCM bonded to dry mortar, concrete and sandstone substrates was generally lower than that of the same type of FRCM bonded to pre-wetted substrates. There was no significant difference in the capillary water absorption coefficient between PVA FRCM with the same mix ratio bonded to different types of substrates. The increase of fly ash content can significantly increase the capillary water absorption coefficient of FRCM bonded to substrates. When the content of fly ash was low, the capillary water absorption coefficient of PVA FRCM was significantly higher than that of basalt FRCM bonded to mortar substrate with same saturation.

The integration of Machine Learning (ML) in material science, particularly in cement-based materials, is revolutionizing the field. This approach addresses challenges like high non-linearity and significant time-lags in data, which are prevalent in the complex interplay of composition, process, structure, and performance in these materials. ML’s effectiveness in this context is not just in predictive accuracy, but also in its potential to significantly advance research and development.ML operates at the intersection of computer science and statistics, functioning as a ‘black-box’ that links data without requiring an understanding of the underlying mechanisms. This enables a comprehensive cycle from data collection to performance prediction and experimental validation. By transitioning from a traditional ‘experience plus trial-and-error’ method to a data-driven approach, ML facilitates a deeper understanding of the cause-effect relationships aiming at material properties. This is particularly transformative in cement-based materials research, where ML’s ability to predict various properties opens up new possibilities for enhancing the efficiency of their development and application.This comprehensive article delves into the intricate characteristics and varied application processes of ML in the realm of material science, with a specific focus on cement-based materials. It provides a thorough review of the recent progress, showcasing how ML techniques have become instrumental in predicting key aspects such as microstructure, components, mechanical properties, and durability of these materials. The article not only illustrates the predictive power of ML, but also sheds light on its role in enhancing the understanding of complex material behaviors and properties. Additionally, the article examines the unique characteristics and structural intricacies of various ML models used in this context. It meticulously discusses and compares different model algorithms, dissecting their methodologies and computational approaches. By doing so, it offers a clear picture of the strengths and limitations of each algorithm, providing valuable insights into their practical applicability in predicting and understanding the behavior of cement-based materials. Moreover, the article reviews the evaluation metrics used to assess the performance of these ML models, emphasizing the importance of accuracy, reliability, and efficiency in material science research. This evaluation not only highlights the current state of ML applications in this field, but also suggests areas for future improvements and developments.Despite the notable advancements in using ML for predicting the structure and performance of cement-based materials, significant challenges remain. Firstly, there is an issue of data quality and quantity imbalance due to the multi-temporal relationship between the cement process and the development of its properties, which necessitates the creation of a comprehensive database including diverse factors such as material components, structures, performance metrics, environmental influences, and chemical reaction parameters. Secondly, the highly complex and nonlinear nature of most predictive models for cement-based materials leads to insufficient model interpretability, that is, understanding of these models' decision-making processes is quite complicated. Enhancing interpretability is essential for a deeper comprehension of material performance under various conditions, which can be achieved through advanced post-processing tools and integrating ML with precise physical models. Lastly, the limited generalizability of ML models, due to the inherent complexity of cement-based materials, poses a challenge. Training data may not cover all categories, leading to diminished performance upon treating new data sets. To address this problem, it requires exploring meta-learning methods that can quickly adapt to new material combinations and combining these methods with other advanced ML techniques to improve the predictive power and adaptability of models.The evolution of Artificial Intelligence and increased computational power, as exemplified by advanced generative AI models like ChatGPT, offer boundless potential in enhancing the efficiency of material research and development. Their multi-dimensional data processing capability allows for comprehensive consideration of various factors affecting target performance, predicting cement properties under different conditions. As these models evolve in self-learning and optimization, integrating molecular dynamics simulations of cement-based materials, three-dimensional simulations of hardened paste structures, and reaction kinetics and thermodynamics data becomes feasible. This integration could lead to precise predictions of composition, structure, and performance, and even the reverse engineering of cement-based materials, significantly accelerating the development of new cement-based materials.Summary and prospectsThe integration with ML is a major advancement in the field of cement-based materials. ML is able to process and to learn from huge datasets to predict a range of material properties. This approach not only solves the complex problem of nonlinear regression of materials, but also marks a new era in materials research. However, to realize the full potential of machine learning in this area, challenges such as imbalances in data quality and quantity, insufficient model interpretability and limited model commonality need to be addressed. The research prospect of cement-based materials by integrating with artificial intelligence is promising. And, with the continuous improvement of AI capability and computational power, we can foresee that more complex models combined with more advanced algorithms will be able to predict and design cement-based materials more accurately. This progress will likely lead to the development of new materials with enhanced properties, contributing significantly to the field of construction and material science. This research area remains a hotspot, promisingly exciting developments and breakthroughs in the near future.

The development of advanced technology has escalated electromagnetic space warfare in major power confrontations, and the resulting electromagnetic radiation poses a serious threat to military security, human health and information security. Traditional cementitious composites have poor electromagnetic protection capabilities due to the characteristics of low-loss dielectrics. The development of building systems with electromagnetic protection capabilities is of great significance for resisting radar surveillance and reducing electromagnetic pollution. This review aimed to reveal the influence of filler components and structural design on the electromagnetic protection performance of cementitious composites from two aspects: Electromagnetic wave absorption and electromagnetic wave shielding.Electromagnetic wave absorbing cementitious composites include both filler-based and structural-based types. The filler-based electromagnetic wave absorbing cementitious composites were mainly summarized from three types of fillers: carbon-based, magnetic, and composite system. Carbon materials such as carbon black and carbon fibers are utilized to enhance the internal dielectric loss mechanism of cementitious composites through their high conductivity, thus improving the electromagnetic wave absorption capability. In addition to high conductivity, carbon nanotubes and graphene also exhibit polarization relaxation effects by virtue of their unique structural properties to enhance electromagnetic wave attenuation within the cement. Carbon fillers can achieve excellent electromagnetic wave absorption performance even at low concentrations, thus making them popular fillers for cementitious composites. The high dosages of magnetic materials limits their practical applications in cementitious materials, which are gradually developing towards nanomagnetic fluids. However, single absorbing fillers hardly achieve a balance between excellent impedance matching and strong attenuation capability, leading to narrow bandwidth and weak absorption. Therefore, the inclusion of multiple absorptive fillers to harness multiple loss mechanisms and optimize impedance matching, is considered as an important measure to gain outstanding microwave absorption performance.The structure-based electromagnetic wave absorbing cementitious composites were elaborated on from the aspects of porous structure, layered structure, and metastructure. Porous aggregates as ‘pores’ are introduced into the cement to enhance connectivity with the outside air, optimizing the impedance matching of cementitious composites. This approach also extends the propagation path of electromagnetic waves, promoting multiple reflections and scattering. The layered structure is designed to improve the electromagnetic wave absorption capability of cementitious composites through the use of impedance gradient systems. However, the porous structure suffers from a high porosity, and the layered structure exhibits interface connection defects and excessive thickness as drawbacks, which is not conducive to structural mechanical properties. By adjusting the geometric dimensions of the resonant layers, the metastructure can obtain ultra-wideband characteristics at lower thickness, freeing microwave absorbing of cementitious composites from limitations imposed by the content of absorptive fillers and structural thickness. Nevertheless, the widespread application of metastructure in cementitious composites is still limited from the view of economic costs and operational processes.Electromagnetic wave shielding cementitious composites serve as another important form of achieving electromagnetic protection requirements, primarily involving three types of filler components: Carbon materials, metal materials, and composites. Carbon materials or metal materials are mainly used to enhance the reflection loss on the surface of materials through their high conductivity and high permeability, aiming to improve the electromagnetic wave shielding effectiveness of cementitious composites. However, reflection loss can easily lead to secondary electromagnetic pollution and is constrained by the conductivity or permeability of the fillers themselves. Recently, composite filler-based electromagnetic wave shielding cementitious composites have raised more attention owing to boosting internal absorption loss, which is gradually converging towards the field of electromagnetic wave absorption.Summary and prospectsElectromagnetic protection cementitious composites are widely applied in various civil-military building sectors, such as military command centers and research institutes and so on. The effects of filler components and structural design on the electromagnetic protection capability of cementitious composites were briefly summarized, providing a reference for the future development direction of functional cementitious composites. In order to minimize trial error costs, electromagnetic simulation analysis needs to be conducted to assess the contribution of various filler components in cementitious composites to electromagnetic protection effectiveness. The coupling effects among multiple factors should also be taken into account in this analysis. To elevate the feasibility of practical applications of metastructure in cementitious composites, the accuracy of the design of conductive resonance layers and long-term durability needs to be emphasized. Additionally, further research is required to study the impact of metastructure on the mechanical properties of cementitious composites. Furthermore, to support the carbon neutrality strategy, the development of electromagnetic protection cementitious composites based on waste materials including straw and iron tailings is a potential direction for reducing economic costs and addressing electromagnetic pollution issues.

Renewable energy is now facing a challenge that the demand and supply of energy is not stable, which should be balanced by energy storage. The energy can be stored chemically, physically, or in a hybrid. However, most energy storage suffers from one or more of the following: pollution caused by the leakage of the electrolyte in batteries and supercapacitors; limitation to the location of pumped storage; high cost of flywheel battery, etc. Energy storage by a cement-based structure is attractive and promising due to advantages such as low cost, no pollution to the environment, high durability, large energy storage volume, and multi-functional properties.The energy can be stored in a cement-based battery or a cement-based supercapacitor. The mechanism behind them is different. The cement-based battery pertains to the traveling of charges (produced by redox reaction) among the anode, electrolyte, and cathode. The cement-based supercapacitor relies on the interaction of charges and electrodes, providing double-layer capacitance and/or pseudo capacitance. The design of both cement-based energy storage devices involves the design of the structure and composition of electrodes, particularly the active components, the type and concentration of ions in electrolytes, separators, and current collectors. To evaluate the performance of cement-based batteries and supercapacitors, energy-related parameters, such as electrical resistivity, relative permittivity, specific capacitance, power density, energy density, and capacitance retention, are used. In the design of a cement-based battery or supercapacitor, the electronic resistivity of electrodes should be low enough to increase the current density and energy density; the ionic conductivity of electrolytes should be high to facilitate ion movement between two electrodes; the separator should be porous and insulating to allow ions to go through and hinder electrons; the electrical resistivity of the contact materials between electrodes and current collectors should be low to decrease the contact resistance; the porosity of conductive components in cement-based electrodes should be high to increase the specific capacitance, etc.Factors affecting the energy storage performance of cement-based batteries and supercapacitors involve the type of cement-based materials (paste, mortar, and concrete), water-to-cement ratio, electrode materials, and composition of cement-based electrolytes. The performance decays in this order: Cement paste, mortar, and concrete because the electrical resistivity increases in this order. The presence of aggregates weakens the conductive network in cement-based electrodes. The water-to-cement ratio does not affect the open-circuit voltage much, but it affects the current density. Carbon materials (graphene, biochar, etc.) are widely used in the preparation of electrode materials due to their low density, low electrical resistivity, and relatively high porosity. However, the dispersion of conductive materials in cement-based electrodes should be well-designed because poor dispersion weakens both mechanical and conduction behavior. Conductive polymers and ionic liquids are used to increase the ionic conductivity of pore solution in cement-based electrolytes.The cement-based battery and supercapacitor can be in the form of part of structures, such as beams, columns, walls, railings, and bricks. The overall principle is to improve the energy performance of these structures without sacrificing their structural properties. To satisfy this requirement, the structural batteries and supercapacitors should entirely be made of cement-based materials, i.e., cement-based electrodes, cement-based electrolytes, and cement-based separators.Summary and prospectsThough the cement-based batteries and supercapacitors provide a new way to store the electricity, the related research and techniques are still at the infancy, and more issues need to be addressed in the future: 1) Effects of environment factors on the energy storage performance; 2) Balance between the cost and performance in terms of active components in cement-based electrodes and electrolytes; 3) Prediction of the lifespan of cement-based batteries and supercapacitors; 4) Recycle of some active components in cement-based electrodes, etc. The enhancements observed in the energy storage performance through the utilization of cement-based materials underscore the significance of incorporating conductive additives as a pivotal strategy for increasing energy density, power density, and current density. Nevertheless, several policy implications must be addressed to ensure the successful integration of active components in the development of intelligent, dependable, and sustainable cement-based batteries and supercapacitors. These include fostering effective collaborative partnerships among universities, research institutes, private enterprises, and state-owned entities; implementing monetary incentives such as government subsidies, tax exemptions, and specialized loans to incentivize the recycling of conductive waste in cement-based batteries and supercapacitors; facilitating the exchange of knowledge between scientists and industry stakeholders; integrating sustainable electro-tribological technologies into eco-labeling initiatives and the development of green conductive additives; and providing essential financial backing, technical support, and consultancy services to promote the practical application of cement-based batteries and supercapacitors across the energy sector.