The status of scientific research projects in the inorganic non-metallic materials discipline (E02) under the Department of Engineering and Materials Sciences of the National Natural Science Foundation of China (NSFC) in 2024 has been statistically analyzed. Taking key programs as examples, the discipline’s management of these funded projects is introduced. Representative initiatives and their implementation effects in deepening and implementing the reform tasks of scientific funding for the discipline in this year are elaborated in detail. Furthermore, the priority funding areas, key funding directions for the discipline in 2025, as well as reflections on future work are presented.

IntroductionThe remediation of tailings sand requires improving both mechanical properties and the stabilization of heavy metals. Practical engineering applications must also consider cost and feasibility. Microbially Induced Carbonate Precipitation (MICP) is an innovative technique that uses microorganisms to enhance soil properties and immobilize heavy metals. However, the traditional MICP method using Bacillus pasteurii has several limitations: reduced activity in high concentrations of heavy metals, calcium carbonate buildup on the soil surface that clogs and limits solidification depth, risks of introducing invasive species, and high costs associated with bacterial cultivation and transport. These factors make it unsuitable for large-scale applications.In situ stimulation of indigenous urease-producing microorganisms in the soil offers a solution. This approach avoids species invasion, eliminates the need for bacterial cultivation and injection, reduces costs, and minimizes clogging. Developing a cost-effective and feasible in situ stimulation strategy for tailings sand solidification is essential for applying this technology in practical engineering.MethodsThe tailings sand used in this study was sourced from the tailings reservoir of Fujian Makeng Mining Co., Ltd., moderately contaminated with cadmium and slightly with zinc. An initial stimulation solution was designed to screen and enrich urease-producing microorganisms in the tailings sand, considering the necessary carbon source, nitrogen source, urea, and other growth factors. Since urease activity is key to the effectiveness of MICP solidification, the urease activity of tailings sand suspensions after in situ stimulation was used as the evaluation metric for optimization.The optimization process involved three steps: 1) Starting with the initial stimulation solution formula, single-factor experiments were conducted to vary carbon and nitrogen sources to identify those yielding the highest urease activity. 2) Using the selected optimal carbon and nitrogen sources, along with other components and pH, a Plackett-Burman (PB) design was employed to identify key factors affecting urease activity. Single-factor tests were then conducted to determine the optimal concentration range for each key factor. 3) A Central Composite Design (CCD) response surface analysis was performed, using urease activity as the response value, to calculate the optimal concentration of each key factor. This resulted in the most effective stimulation solution for tailings sand.Different concentrations of cementation solution and numbers of solidification rounds were tested to compare the effects of indigenous urease-producing bacteria and Bacillus pasteurii on tailings sand in terms of surface strength, cementation thickness, permeability, raindrop erosion resistance, heavy metal leachate toxicity, and heavy metal morphological changes. Microbial community analysis, combined with scanning electron microscopy (SEM) and X-ray diffraction (XRD), was conducted to explore how in situ stimulation enhances mechanical properties and immobilizes heavy metals.Results and discussion1) The optimal in situ activation formula for tailings sand includes sodium acetate at 35.85 mmol/L, ammonium sulfate at 53.59 mmol/L, urea at 481.0 mmol/L, yeast extract (YE) at 0.2 g/L, nickel chloride at 0.01 mmol/L, and a pH value of 8.70, achieving a urease activity 1.944 times higher than that before optimization. 2) The best cementation solution concentration for in situ solidification of tailings sand is 1 mol/L. In situ activation demonstrated better heavy metal immobilization, deeper solidification, and more uniformity compared to Bacillus pasteurii at the same round count. Although the mechanical properties of in situ-treated sand were lower after the same number of rounds, 15 rounds of in situ treatment achieved comparable properties to 10 rounds with Bacillus pasteurii. 3) The cost per round of in situ activation is only one-fifth that of Bacillus pasteurii. Achieving similar mechanical properties, the total cost of 15 rounds of in situ treatment is only one-third of 10 rounds with Bacillus pasteurii. In situ activation eliminates the need for bacterial culture or transportation and avoids the risk of introducing non-native species, providing superior economic and environmental benefits. 4) The optimized activation solution effectively enriched previously low-abundance urease-producing bacteria, making them the dominant group (70%-90% relative abundance) by inhibiting other microorganisms. This also increased the abundance of the urease accessory protein COG0830. 5) The final product of MICP is calcite. Compared to Bacillus pasteurii, in situ activation produced smaller, fewer, and more scattered calcite crystals under the same conditions. Calcite crystal nucleation and growth were influenced by cementation solution concentration. 6) The urease-producing bacteria in tailings sand exhibited good tolerance to heavy metals and had a long survival time, continuously converting exchangeable heavy metals into stable forms. After in situ activation, the cation exchange capacity (CEC) of the tailings sand increased, effectively enhancing soil fertility for mine site revegetation after heavy metal fixation.Conclusions1) In situ activation of urease-producing microbes offers stronger heavy metal immobilization and deeper, more uniform solidification compared to traditional MICP methods. 2) After 15 rounds of treatment, tailings sand solidified using native urease-producing bacteria achieved mechanical properties comparable to those treated with Bacillus pasteurii after 10 rounds, while reducing costs by two-thirds. 3) In situ activation altered the microbial community in the tailings sand, making urease-producing bacteria dominant. These bacteria induced calcium carbonate precipitation, filling sand particle pores, and converting exchangeable heavy metals into stable forms such as metal carbonates, metal-calcium carbonate co-precipitates, or adsorbed forms on iron and aluminum oxides. This improved both mechanical properties and heavy metal immobilization. 4) By increasing the cation exchange capacity, this method enhanced soil fertility, facilitating mine site revegetation. It is an economically and environmentally viable approach for engineering applications.

IntroductionCeria (CeO2) is an important rare earth metal oxide abundant in nature. Due to the easy conversion of the oxidation valence between cerium ions, CeO2 has a high oxygen storage capacity. The band gap value of ceria is similar to that of other traditional semiconductor photocatalyst of TiO2, so it has the potential to be a suitable and efficient photocatalyst. Specifically, ion doping can introduce new energy levels into the band structure of ceria, reduce its band gap width, and enable more visible light to be absorbed, thereby ultimately improving the photocatalytic efficiency. Secondly, when other cations enter the CeO2 lattice, they form oxygen vacancies (oxygen defects) under structural deformation and charge compensation mechanisms. The oxygen vacancy formed in this process can act as an effective trapping point for photogenerated electrons, effectively reduce the recombination rate of electrons and holes, and significantly improve the photocatalytic efficiency of the material. In addition, ion doping can also change the electronic structure of cerium oxide, making it have better conductivity and charge transport performance, which is conducive to the separation and transport of photogenic carriers. Generally speaking, it is very difficult to introduce ions into the CeO2 lattice. The author focuses on designing the synthesis system of CeO2 photocatalyst doped with Sm ions and systematically studying and summarizing the reaction ratio relationship of raw materials, so as to elucidate the influence of ion doping on photocatalytic performance from the perspective of photocatalytic mechanism.MethodsFirstly, 5.88 g C6H5Na3O7·2H2O and 60 mL deionized water were stirred magnetically together at room temperature for 30 min. Then, 2.40 g urea was added and mixed for 30 min continually (solution 1). At the same time, 1.00 g Ce(NO3)3·6H2O and different molar ratios of Sm(NO3)3·6H2O were dissolved in 20 mL deionized water and stirred for 30 min, respectively (solution 2). Next, solution 2 was added into solution 1 and continue to stir for 30 min until the solution shows a light-yellow color. Then, the mixed reaction liquid was transferred to a 100 mL hydrothermal reactor, and cooled naturally after the hydrothermal reaction at 120 ℃ for 36 h. After used deionized water and ethanol to clean at least three times, and finally dried for 12 h at 70 ℃ and calcined at 500 ℃ for 4 h to obtain the target product. At the same time, CeO2 product without adding Sm(NO3)3·6H2O precursor were used as a comparison sample.Results and discussionThe influence of different doping concentrations on the photocatalytic performance of ceria was studied in detail, and the optimal doping ratio of Ce and Sm was determined to be 1.00:0.15 (0.15-SC). SEM images indicated that Sm-doped material still maintained a broom-like morphology, but the surface smoothness, average diameter and length of the nanorods showed slight changes. From XRD analysis, all the samples exhibited sharp diffraction peaks, indicating high crystallinity, and no impurity peaks are detected, meaning that the doping process does not affect the crystal purity of the final product. UV-Vis absorption spectrum shows that the bandgap value (Eg) of these Sm-doped samples is significantly reduced compared to that of pure CeO2, and the Eg of the 0.15-SC sample is the smallest at only 2.88 eV. The factors that lead to the reduction of the band gap can be attributed to two points: First, the nanoscale CeO2 composed grains can induce the quantum limiting effect, which leads to the spectral redshift; Second, the decrease of particle size will increase the Ce3+ content at the edge of CeO2. With the decrease of Ce3+ content, the UV-Vis spectra will also show a redshift phenomenon.Compared with other Sm-CeO2 samples, pure phase CeO2 showed the strongest characteristic peak strength and the lowest peak strength when the doping ratio was 1.00:0.15, indicating that Sm-CeO2 samples had the best effect on promoting the separation of photogenerated holes and electron pairs and photocatalytic performance at this ratio. The environmental pollutant bisphenol A (BPA) was used as a photocatalytic degradation model, and it was found that the efficiency of all the Sm-doped CeO2 samples was improved, and the degradation efficiency of the 0.15-SC sample was the highest, reaching 99.83%, which was 3.52-times superior than that of the pure CeO2 (28.31%). The capture experiment of the active substances can be judged that both hydroxyl radicals (，OH) and holes (h+) played very important roles in the photocatalytic degradation of BPA on the 0.15-SC sample. And after four performance cycling experiments, the degradation rate of the 0.15-SC sample was still maintained 89.53%, indicating that it has good recyclability.ConclusionsIn summary, Sm-doped ceria material exhibits high photocatalytic purification activity for environmental pollutants, fully proving that ion’s doping can act as an effective method to efficiently improve photocatalytic performance, and can further provide effective ideas for designing ion-doping systems for similar metal oxide materials in the future.

IntroductionAmid the growing emphasis on energy conservation and environmental protection, designing phosphors with multifunctional applications has become an urgent challenge. The traditional approach of combining blue light-emitting diode (LED) chips with yellow phosphors to produce white light suffers from drawbacks such as low color rendering index (CRI) and high color temperature. To address the pressing demands of lighting and display technologies, developing high-efficiency red phosphors that can be excited by near-ultraviolet (near-UV) light is crucial for applications in white LEDs and flexible display technologies.Building upon the garnet-like structure of Ca3Zn3(TeO6)2, a series of CaNaLaZn3(TeO6)2:xEu3+ (CNLZT:xEu3+) red phosphors, capable of being effectively excited by near-UV light, were designed and synthesized using a chemical unit co-substitution strategy. In this approach, the [Na+−La3+] ion pair replaces the [Ca2+−Ca2+] ions. This co-substitution significantly enhances the luminescence properties of the CNLZT:0.15Eu3+ sample. White LED devices fabricated with this material exhibit excellent luminous performance and stability. Moreover, the CNLZT:0.15Eu3+/polydimethylsiloxane (PDMS) flexible film demonstrates promising luminance, making it well-suited for applications in flexible display technologies.MethodsA series of CNLZT:xEu3+ red phosphors were synthesized using a high-temperature solid-state reaction method. Raw materials were accurately weighed according to stoichiometric ratios and thoroughly ground in an agate mortar for 25 min. The resulting mixture was loaded into alumina crucibles and sintered for 10 h in an air atmosphere at 1323 K. After cooling, the samples were reground to obtain fine powders.The prepared CNLZT:0.15Eu3+ red phosphor was then mixed with BaMgAl10O17:Eu2+ (BAM:Eu2+, blue) and (Ba,Sr)2SiO4:Eu2+ (BSS:Eu2+, green) in a specific mass ratio. This mixture, along with ZWL8820 organic silicone gel, was applied to a 395 nm near-UV chip and encapsulated to fabricate a white LED device. Additionally, a CNLZT:0.15Eu3+/PDMS flexible film was prepared by combining the CNLZT:0.15Eu3+ phosphor with PDMS in a predetermined mass ratio and cutting it to the desired size for subsequent testing.Results and discussionX-ray diffraction (XRD) analysis and Rietveld structural refinements reveal that substituting [Ca2+-Ca2+] ion pairs with [Na+-La3+] does not alter the matrix structure. The Eu3+ replace La3+ in the matrix, causing lattice contraction and a slight shift in XRD diffraction peaks toward higher angles. The main absorption peak at 394 nm aligns well with the near-UV LED chip.When x=0.15, the luminescence intensity of the optimal sample CNLZT:0.15Eu3+ reaches its maximum, 1.135 times higher than the commercial red phosphor Y2O3:Eu3+ and 1.908 times greater than the pre-substitution Ca3Zn3(TeO6)2:0.12Eu3+. The color purity is 99.78%, and the CIE color coordinates are (0.649 2, 0.350 4), close to the ideal red light point (0.670, 0.330), demonstrating excellent red luminescence. This confirms that the chemical unit co-substitution strategy effectively enhances luminescence properties.At elevated temperatures, the CNLZT:0.15Eu3+ sample exhibits good color stability. The packaged white LED device has a correlated color temperature (CCT) of 6414 K and a CRI (Ra) of 87.3. Its CIE coordinates (0.314 9, 0.325 0) lie in the white light region. Even after 100 minutes of continuous operation at 50 mA, the white LED maintains stable performance and luminescence. Furthermore, the CNLZT:0.15Eu3+/PDMS film remains intact and efficiently luminescent after bending tests, demonstrating potential for flexible display applications.ConclusionsA series of CNLZT:xEu3+ red phosphors, excitable by near-UV light, were synthesized using a high-temperature solid-state reaction method. By employing the chemical unit co-substitution strategy of [Na+−La3+] replacing [Ca2+−Ca2+], the optimized doping concentration of Eu3+ in the CNLZT matrix was effectively elevated to 15% (in mole). The luminous intensity of the CNLZT:0.15Eu3+ sample is 1.908 times that of the pre-substitution Ca3Zn3(TeO6)2:0.12Eu3+ sample and 1.135 times that of the commercial Y2O3:Eu3+.The color purity of the CNLZT:0.15Eu3+ sample is 99.78%, and its color coordinates (0.649 2, 0.350 4) are close to the ideal red point (0.670, 0.330). The chemical unit co-substitution strategy effectively regulates the luminescent properties. Temperature- dependent fluorescence spectroscopy confirms that CNLZT:0.15Eu3+ possesses excellent color stability, with a chromaticity shift of only 0.008 52 at 420 K.The packaged white LED achieves CIE coordinates of (0.314 9, 0.325 0) with a CRI (Ra) of 87.3, demonstrating precise color rendering and stable performance after 100 min of continuous operation at 50 mA. Moreover, the CNLZT:0.15Eu3+/PDMS flexible film shows promising luminance, making it suitable for applications in flexible display technologies.

IntroductionAdsorption is one of the most effective heavy metal ion treatment techniques available. Common heavy metal ion adsorbents include activated carbon, chitosan, cellulose and natural zeolite. Geopolymers, as a new type of adsorbent material, show great potential and value for application in the field of zinc-containing heavy metal wastewater treatment. Blast furnace slag is a type of bulk solid waste in the metallurgical industry, and the current high value utilisation rate is low. The use of blast furnace slag to prepare geopolymer adsorbent materials to treat heavy metal wastewater is one of the effective ways to realise the comprehensive utilisation of blast furnace slag in a high value way, which can achieve the purpose of ‘waste for waste’. At present, the related research mainly focuses on the adsorption mechanism and adsorption effect of geopolymers on heavy metal ions, while less attention has been paid to the desorption of heavy metal ions after adsorption and the recycling of geopolymers, and only a few scholars have carried out preliminary explorations by using inorganic acid, EDTA-2Na, and NaCl solution as desorbing agents. In this study, the geopolymer adsorbent material was prepared from blast furnace slag to investigate its adsorption performance and mechanism of action on zinc Zn2+, and nitric acid was used as a resolving agent to investigate the desorption effect of Zn2+ and the recycling performance of geopolymer adsorbent, which is of great guiding significance for the high value-added utilisation of metallurgical solid wastes and the treatment of zinc-containing heavy metal ion wastewater.MethodsDetermination of major oxides and their contents in blast furnace slag using XRF. Particle size distribution of finely ground blast furnace slag was analysed using a laser particle size meter. Analysis of the crystalline phase structure of blast furnace slag and geopolymers using XRD. The specific surface area of the geopolymer and its pore size were characterised using BET. The concentration of Zn2+ in solution was detected by ICP. SEM-EDS was used to analyse the crystalline structure, micro-morphology and compositional distribution of the geopolymer before and after adsorption. Kinetic analysis of geopolymers using quasi-primary and quasi-secondary kinetic models. Adsorption isotherms were simulated for geopolymers using the Langmuir adsorption isotherm model and the Freundlich adsorption isotherm model.Results and discussionThe surface and interior of geopolymers based on blast furnace slag (BFSGP) contains a large number of pore structures，which are favourable for the migration of Zn2+ in the solution, and at the same time increase the adsorption sites, thus effectively improving the adsorption capacity and adsorption efficiency of BFSGP. The N2 adsorption and desorption isothermal curves and pore size distribution curves of BFSGP indicate that BFSGP is a typical mesoporous structure. The adsorption of Zn2+ by BFSGP increased significantly with the increase in the initial ion concentration of the solution. The adsorption process of BFSGP followed the quasi-secondary kinetic model and the Langmuir model, thus indicating that the adsorption process of BFSGP was dominated by chemisorption, and its adsorption process was strongly influenced by the chemical reaction between BFSGP and Zn2+, and at the same time conformed to the characteristics of the monomolecular layer adsorption.In the desorption experiments, within the first 20 min, nitric acid rapidly enters into the pores of the adsorbent and acts to break the chemical bond between Zn2+ and BFSGP, and the desorption rate is fast. The desorption rate decreases as the readily desorbed Zn2+ decreases. Despite the loss of some active adsorption sites due to chemical bonding and Al3+ leaching during the cyclic adsorption-desorption process, BFSGP still maintains good adsorption performance for Zn2+, which provides a new idea for the recycling of BFSGP as well as for the recovery of geopolymer-loaded heavy metals by the pickling method.ConclusionsThe adsorption of Zn2+ by BFSGP increased with the initial concentration of the solution. When the initial ion concentration was 200 mg/L, the adsorption amount and adsorption rate of Zn2+ by BFSGP were 196.14 mg/g and 98.07%, respectively. The adsorption of Zn2+ by BFSGP is in accordance with the quasi-secondary kinetic model and Langmuir model and is a chemical monolayer adsorption. BFSGP showed better adsorption performance in cyclic adsorption-desorption experiments, the first desorption rate of nitric acid was 45.52%, and after two cyclic adsorption-desorption cycles, the adsorption rate of BFSGP on Zn2+ was still up to 56.83%.

IntroductionDue to the distinctive climatic characteristics of the Qinghai-Tibet Plateau, such as an extremely frigid climate and significant diurnal temperature fluctuations, concrete structures in this region necessitate substantial freeze-thaw durability. Presently, one of the most efficacious approaches to enhance the freeze-thaw durability of concrete involves incorporating tiny air bubbles into the mixture through the use of air-entraining agents (AEAs). Nevertheless, researchers have discovered that the low atmospheric pressure (LAP) prevalent on the plateau may result in inadequate air content within air-entrained concrete (AEC). Only a limited number of research findings have confirmed that LAP deteriorates the air-void structure of AEC, with relatively few studies investigating its impact on freeze-thaw durability of AEC. Furthermore, there is limited research on the impact of LAP on the distribution of air-void diameters in AEC. Therefore, the air content, air-void structure parameters and freeze-thaw durability of the AEC prepared under normal atmospheric pressure (NAP) and LAP were examined in this study. The primary focus is to investigate the impact of LAP on the distribution of air-voids with varying diameters, thus to further explore how these influences degrade both the air-voids structure parameters and freeze-thaw resistance durability of AEC.MethodsOrdinary Portland cement was used in the experiment. The coarse aggregate was crushed stone and the fine aggregate was river sand. In the experiment, two types of AEAs and a high-efficiency superplasticizer were used to produce the AEC. The experiments were conducted in laboratories located in Lhasa, China (atmospheric pressure values of 64 kPa) and Beijing, China (101 kPa). Three air content design levels (D) were used in this study, namely, 3%, 5%, and 7%. Air content tests, air-void analyzing tests and freeze-thaw durability tests were conducted.Results and discussionCompared to the AEC-N (AEC prepared under NAP), the LAP resulted in a significant increase in the loss of air content of fresh concrete (Af), with a greater magnitude observed as D increased. The average and maximum losses in air content of hardened concrete (Ah) for AEC-L (AEC prepared under LAP) were approximately 0.5% and 0.7% higher than those for AEC-N, respectively. Furthermore, due to decreased atmospheric pressure, microvoids within AEC experienced a more substantial decrease with increasing D. Notably, air-voids ranging from 0-100 m exhibited the most pronounced influence. However, increasing D still effectively enhanced the proportion of microvoids within AEC. The proportion of A1000 (the air content in voids with diameters no greater than 1000 m, the same below ) in Ah showed an overall increasing trend followed by a subsequent decreasing trend as Ah increased, both under LAP and NAP conditions. However, when comparing AEC-N to AEC-L with similar D, the former demonstrated significantly higher proportions of A1000. With similar Ah , the reduction in atmospheric pressure led to a significant decrease in the proportion of microvoids (especially A(0,100]), a pronounced increase in the proportion of trapped air-voids proportion (A(1000,4000]), and small changes in the proportion of mesovoids (A(300,500]) and macrovoids (A(300,500]) within the AEC. The variation in the proportion of microvoids and trapped air-voids significantly influenced the spacing factor (Lˉ). Specifically, an increase in the air content of microvoids (particularly A(0,100]), leads to a decreased in the Lˉ of concrete. Conversely, an increase in the air contentof trapped air-voids resulted in an increase in the Lˉ. However, the proportion of air content in the mesovoids and macrovoids was most weakly correlated with the Lˉ.Concrete subjected to a plateau environment may experience more severe freeze-thaw conditions. when the water-cement ratio was 0.44, the required A1000 under LAP and NAP was about 3.90% and 2.92%, respectively, for achieving a frost resistance durability factor (FD) of 100%.The analysis presented in this study demonstrates that the maximum allowable FD in concrete under LAP is around 3.93%, whereas under NAP it is 4.73%. Clearly, despite the deterioration of air void structures caused by LAP, as long as the air content introduced by AEAs in AEC reaches a certain threshold level, the frost resistance durability requirements can still be met. It is suggested that while meeting the mechanical performance requirements of AEC design, there should be an increase in the maximum air content level of fresh concrete by approximately 2.0% compared to plain areas. This adjustment aims to ensure that the frost resistance performance of concrete meets the design requirements.ConclusionsThe LAP caused a more pronounced loss in the air content of hardened AEC-L, and the loss increased as the D increased. The average and maximum loss was about 0.5% and 0.7% higher than those under AEC-N, respectively. Compared to the AEC-N with the same D, a decrease in atmospheric pressure resulted in a reduction in the air content of the microvoids within the AEC-L. This effect was particularly pronounced for air-voids with diameters not exceeding 100 m, and consequently leading to the deterioration of the air-void structures and a reduction in frost resistance performance of the AEC-L. The variation in the proportion of air content in microvoids and trapped air-voids has a significant impact on the Lˉ of the AEC. The Lˉ decreases with an increase in the proportion of air content of microvoids, particularly A(0,100] and A(100,200], while it increased with an increase in the proportion of air content of trapped air-voids. The increase in the D of the concrete effectively enhanced the air content proportion of microvoids, thereby enhancing the frost resistance durability of concrete. It is recommended that when designing AEC for plateau areas with severe freeze-thaw environments, the D of fresh concrete should be increased by a maximum of approximately 2.0% compared to plain areas.

IntroductionUltra-high performance concrete is an advanced cement-based material with high strength and high durability. Due to the low water-binder ratio and high binder consumption of UHPC, the early shrinkage of UHPC during the setting and hardening process is larger than that of conventional concrete and high-strength concrete, which easily leads to the cracking of engineering structures and affects the performance of structures. Therefore, it is of great significance to study the early shrinkage characteristics of UHPC for the optimization of the material and the prediction of early cracking. In this paper, the effects of binder-sand ratio, water-binder ratio, different fiber types and contents and curing environment on the early shrinkage performance of UHPC were investigated, and the early shrinkage model of UHPC was established by combining BPNN and WOA-BPNN neural network.MethodsIn this study, a total of seven groups of specimens were set up, considering four control factors, i.e., the cement-sand ratio, water-binder ratio, curing environment and polypropylene fiber volume content. Each group consisted of four specimens with size of 25 mm×25 mm ×280 mm (including three specimens for drying-shrinkage tests and one specimen for autogenous-shrinkage tests). The specimens were cured in a curing box with a temperature of (25±2) ℃ and a relative humidity of (98% ±2%). At the same time, a control group was set up, which was cured in a natural environment with a temperature of (28±5) ℃ and a relative humidity of (60%±15%). The shrinkage deformation of the specimens was measured by a specific length meter at 0, 1, 2, 3, 4, 6, 8, 10, 12 h and 1.0, 1.5, 2.0, 2.5, 3.0, 4.0, 5.0, 6.0, 7.0, 9.0, 11.0, 14.0, 18.0, 21.0, 25.0, 28.0 d. Combined with BPNN and WOA-BPNN machine learning models, the measured data were trained with small samples, and finally a neural network model that can be used to predict the early drying and autogenous shrinkage performance of UHPC was obtained.Results and discussionThe early drying-shrinkage and autogenous-shrinkage of UHPC increased with an increase of the cement-sand ratio, and the MIC values of drying shrinkage and cement-sand ratio also increased. The early drying-shrinkage and autogenous-shrinkage of specimen with a cement-sand ratio of 1.2 increased by 108% and 60%, respectively, compared with specimen with a cement-sand ratio of 0.8. The early drying-shrinkage and autogenous-shrinkage of UHPC increased with a decrease of the water-binder ratio. The appropriate amount of polypropylene fiber and steel fiber mixture would limit the early shrinkage of UHPC. With an increase of polypropylene fiber content, the inhibitory effect on both the early drying-shrinkage and autogenous-shrinkage grew firstly and then weakened. The specimens with fiber content of 0.10 % exhibit the best inhibitory effect. The drying-shrinkage expressed a great correlation with the curing method, and the MIC value was 0.56. The correlation between the autogenous-shrinkage and curing method is small, and the MIC value is 0.27. The drying-shrinkage rate and self-shrinkage rate under dry curing conditions were 2.5 times and 1.2 times that under standard curing conditions, respectively.The two machine learning (ML) algorithms were used in the shrinkage prediction and exhibit good accuracy. The WOA-BPNN algorithm expressed delightful predicted accuracy, whose R2, RMSE and MAE for drying-shrinkage model are 0.959, 0.050 and 0.040, respectively, and R2, RMSE and MAE for autogenous-shrinkage model are 0.896, 0.076 and 0.053, respectively. The predicted results indicated that the whale optimization algorithm could improve the ML model effectively.ConclusionsThe main conclusions of this paper are given as follows: 1) The fine aggregate has an inhibitory effect on the early drying-shrinkage and autogenous-shrinkage of UHPC. When the cement-sand ratio decreases from 1.2 to 0.8, the early drying-shrinkage and autogenous-shrinkage increase by 108% and 60%, respectively. 2) The early drying-shrinkage and autogenous-shrinkage of UHPC increase with a decrease of water-binder ratio, and the decrease of water-binder ratio leads to the advance of UHPC self-drying phenomenon. 3) The research found that the polypropylene fiber volume content of 0.10% exhibit the best inhibitory effect on the UHPC shrinkage. 4) The curing method had a great influence on its early drying-shrinkage and autogenous-shrinkage. The drying- shrinkage rate of specimens under dry curing condition is 2.5 times that under standard curing condition, and the autogenous-shrinkage rate of specimens under dry curing condition is 1.2 times that under standard curing condition. The early drying-shrinkage and autogenous-shrinkage predicted results of UHPC based on the WOA-BPNN neural network show nice accuracy and robustness compared to that of BPNN.

The capillary water absorption behavior of cement-based materials deviates progressively from the classical unsaturated flow theories due to specific interactions between water and cement hydrates. Although the impact of supplementary cementitious materials on the initial capillary sorptivity has been widely investigated, their influence on anomalous capillary absorption behavior need further exploration. By taking the technical advantage of low-field nuclear magnetic resonance (LF-NMR), this study investigates the long-term capillary absorption of water and isopropanol (IPA) into white cement mortars with high content of fly ash, slag, and silica fume.IntroductionThe durability of cement-based materials is significantly influenced by the transport processes of water, gases such as CO2, and ions like Cl-. Water transport, particularly capillary water absorption, is crucial for durability performance. In most engineering practices, cement-based materials are non-saturated, making capillary water absorption the primary mode of water transport. This process is driven by capillary pressure arising from the meniscus within pores and is governed by the extended Darcy's law or the Richard's equation. In one-dimensional capillary absorption scenarios, theoretically there exists a linear relationship between the cumulative absorbed volume per unit area and the square root of absorption time, which is known as the square root of time linear law. The slope obtained from linear fitting is defined as the capillary sorptivity, which serves as a quantitative indicator of durability. However, long-term capillary water absorption often deviates from this linear law due to specific physicochemical interactions between water and cement hydrates, especially calcium silicate hydrate (C-S-H) gel. The widespread use of supplementary cementitious materials such as fly ash, slag, and silica fume alters the composition and micro-structure of C-S-H gel through secondary hydration reactions, significantly impacting the properties of cement-based materials. Although the capillary sorptivity has been well recognized as a durability indicator, the anomalous phenomena observed during long-term capillary water absorption are frequently overlooked, leading to incomplete research and inconclusive findings. This study focuses on the long-term capillary absorption processes of water and IPA into cement mortars with representative supplementary cementitious materials, including fly ash, slag, and silica fume. The aim is to elucidate the influence mechanisms of supplementary cementitious materials on the capillary absorption properties of cement mortars.MethodsThe experimental section focused on investigating the impact of supplementary cementitious materials on the capillary absorption behavior of cement mortars. Samples were prepared with sands, white cement and high contents of fly ash, slag, and silica fume. These specimens were subjected to both standard curing at 20 ℃ and accelerated curing at 60 ℃ to assess the influence of curing temperature. Testing methods encompassed capillary absorption tests using IPA and water, along with low-field magnetic resonance relaxation technique to analyze pore structure evolution. The capillary sorptivity were determined by fitting the experimental data to a square root of time linear law, and deviations from this law were analyzed to characterize water sensitivity. Data analysis involved examining changes in capillary sorptivity, deviation times, and pore structure characteristics to elucidate the mechanisms by which supplementary cementitious materials affect the capillary absorption properties of cement mortar.Results and discussionThe incorporation of fly ash, slag, and silica fume significantly alters the capillary sorptivity of both IPA and water into cement mortar. Specifically, all three supplementary cementitious materials reduce the capillary sorptivity of IPA, with fly ash exhibiting the most pronounced effect. During the initial stage of capillary absorption of water, slag increases the sorptivity, while silica fume and fly ash decrease it. In the later stage, high silica fume content notably enhances the sorptivity, whereas high slag and fly ash contents decrease it. The water sensitivity of cement-based materials is also affected. High slag and fly ash increases the water sensitivity of cement mortars, leading to earlier deviation from the initial linear law and higher degrees of deviation in later stages. These findings indicate that supplementary cementitious materials modify the composition and microstructure of C-S-H gel, thereby affecting the water sensitivity and durability of cement-based materials.ConclusionsThe addition of three supplementary cementitious materials will reduce the capillary sorptivity of isopropanol, and the reduction effect of fly ash is most significant. In the initial stage of capillary absorption of water, slag significantly increases the initial sorptivity of mortar, while silica fume and fly ash show inhibiting effects. In the later stage, silica fume significantly increases the secondary sorpvitity of water into mortar, while slag and fly ash both decrease their secondary sorptivity. The addition of slag and fly ash will significantly increase the difference between the initial and secondary capillary sorptivity. High content of silica fume can reduce the water sensitivity of cement-based materials, while high content of slag and fly ash can improve the water sensitivity, so as to advance the deviation of capillary absorption of water from the square root of time linear law and to increase the degree of deviation. The improvement of water sensitivity is the most significant for the mortar with high slag substitution. Curing at high temperature slightly reduces the water sensitivity of mortar with high slag content, but almost has no effect on the water sensitivity of mortars with high silica fume and fly ash contents.

IntroductionThe use of steel slag as a cementitious material is the most likely field to achieve large-scale engineering utilization. However, the inherent defects of low activity and poor grindability caused by the high iron oxide content of steel slag limit its dosage in cement. One important direction to improve the activity and grindability of steel slag is to obtain a product similar to granulated blast furnace slag (GBFS), mainly composed of glass, by melting and reducing iron oxides in steel slag. This GBFS-like residue exhibits lower early activity due to its lower alkalinity coefficient (K=n(CaO)+ n(MgO)/n(SiO2)+ n(Al2O3)). In order to improve the early activity of the residue, this paper focuses on the effect of CaO content on the formation of clinker minerals. Coal gangue is used as a reducing agent to reduce iron oxides in steel slag for making full use of industrial solid waste.MethodsBased on the principle of complete reduction of iron oxides in steel slag and coal gangue, the appropriate ratio of coal gangue and steel slag is calculated according to the chemical composition of steel slag and the fixed carbon content of coal gangue. CaO was obtained by calcining and analytical reagent CaCO3 at 1500 ℃. Different amounts of resultant CaO (10, 20, 30, 40 g) were incorporated into 100 g mixture of steel slag and coal gangue, respectively. The reference sample without CaO and the above four samples are named as C0, C10, C20, C30 and C40, and the K of samples are 1.05, 1.33, 1.61, 1.89, 2.17, respectively. After thoroughly mixing each sample, 200 g mixture containing CaO was placed into a corundum crucible and calcined at 1500 ℃ for 30 min. After calcination, the crucible was take out from the high temperature furnace for water quenching. Iron alloy particles are obtained by crushing, peeling, and magnetic separation from water quenched slag. The remaining water quenched residue (WQR) is used for mineral phase analysis, cement mortar strength, soundness, and other tests.Results and discussionIron alloy particles in C0, C10, C20, C30 sample can be easily peeled off. But it is difficult for C40 sample and some small metal particles can be observed at the crucible bottom. This is because the increase of K leads to an increase in the viscosity of the melt, making it difficult for iron particles to sedimentation and aggregation.The analysis of the chemical composition of the WQR after stripping iron particles shows that the reduction rate and recovery rate of the reference sample C0 are about 92%. For C10 (K=1.33), the and of Fe reach maximum values. As the CaO content continues to increase, the and gradually decrease. But, these two parameters of C20 still exceed that of C0. The f-CaO content and soundness of the WQR meet the requirements of relevant national standards, although these two values will slightly increase with the increase of dosage of CaO.The results of XRD Rietveld refinement for quantification indicate that C0 and C10 samples are mainly consist of glass and contain a small amounts of Gehlenite, spinel et al. With the increase of CaO content, the diffraction peak of the crystalline phase gradually increases, while the amorphous envelope peak gradually weakens. For C20, the main crystalline phases are C2S and bredigite, and diffraction peaks of periclase can be observed. In the C30 sample, the main mineral phases are C2S, C3A, iron, and periclase. Meanwhile, C3S diffraction peak is relatively low. The C3S diffraction peak in the C40 sample is significantly enhanced, with a content of 50%. FTIR shows that as the CaO content increases from 20 g to 40 g, the absorption band of -C2S decreases, while the absorption band of M3 C3S gradually increases.BSE image show that the C10 sample is mainly composed of glass matrix, with a small amount of C2S grain, serrated-like fine stuff formed at the edge of C2S grains, snowflake like or dendritic substance surrounding the C2S, and iron particles. EDS results show that the order of Al content in several phases is C2S < fine stuff < dendritic substance < matrix. The order of Ca and Si content is C2S >fine stuff > dendritic substance > matrix.In the C30 sample, sharp edged plate-like particles with a Ca/Si of about 3 formed, indicating that C2S has begun to transform into C3S. The formation of C3S and C2S not only significantly reduces the Si content in the matrix, but also leads to an increase in the relative content of Al in the intermediate matrix. When the dosage reaches 40%, C3S has already formed in large quantities. The Ca/Al ratio of the intermediate phase is about 1.53, indicating the formation of C3A.ConclusionsThe main conclusions of this paper are summarized as following. When K value of WQR is less than 1.6, increasing the CaO content appropriately can improve the reduction rate and recovery rate of iron. The C10 sample is mainly composed of glass. When K is 1.3, a small amount of -C2S is formed in the WQR, which gradually grows by absorbing CaO and SiO2 from the glass matrix. With the increase of K, Periclase begins to form in the zone where silicate minerals are more abundant. When the CaO dosage reaches 40 g, the amount of C3S continues to increase to 50%, and C3A form simultaneously. Although high alkalinity leads to the formation of C3S and C2S minerals in the system, it also results in the formation of periclase. To avoid the potential long-term unsoundness, it is more appropriate to control K value at around 1.3.

IntroductionLow-vacuum tunnels are the core infrastructure of ultra-high-speed low-vacuum magnetic levitation transportation systems. The internal environment of these tunnels is characterized by extremely low pressure, alternating airflows, and very low humidity. Based on a comprehensive review of existing research, concrete is considered a highly competitive material for low-vacuum tunnels due to its cost-effectiveness and technological maturity. However, studies have shown that under conditions of extremely low pressure and fluctuating atmospheric pressure, concrete experiences rapid moisture loss, resulting in significant changes to its pore structure and leading to the deterioration of its mechanical properties and long-term performance. Additionally, the high-velocity airflow caused by alternating pressure in low-vacuum tunnels can induce aerodynamic fatigue damage to the internal and external surfaces of the concrete, generating severe dust that poses a significant threat to the safe operation of high-speed trains. To address these challenges and ensure the reliable performance of concrete in low-vacuum environments, protective measures or the use of high air-tightness concrete is necessary. Coating materials have been identified as an effective solution to enhance the service safety of concrete in vacuum tunnels.MethodsThe cement used was P·I 42.5 Portland cement produced by Fushun Cement Co., Ltd. Fine aggregates consisted of natural river sand with a fineness modulus of 2.8. Coarse aggregates were crushed limestone with continuous gradation, sized between 5 mm and 20 mm, with a mud content of 0.4%. Water used was municipal tap water. The water-reducing agent was a non-air-entraining polycarboxylate- based superplasticizer. The coating system was a two-component fluorocarbon material jointly developed by Beijing Jiaotong University, consisting of a solvent-free epoxy penetrating primer and a fluorocarbon resin topcoat. The primary film-forming material was fluorocarbon resin, with hexamethylene diisocyanate as the hardener, and the pigment-to-binder ratio of the coating was 0.4.To better understand the effect of coating materials on concrete performance, the coating was applied during the early hydration stage of concrete. After casting, the specimens were stored at (20 ± 2) ℃ for one day before demolding, after which the primer coat was applied. Following two days of air drying, the topcoat was applied, and the specimens were further air-dried for two days. The compressive and flexural strengths of the concrete were tested using specimens sized 300 mm × 100 mm × 100 mm and 400 mm × 100 mm × 100 mm, respectively. To evaluate the impact of surface coating on concrete mass loss, specimens of 40 mm × 40 mm × 40 mm were prepared. Adhesion strength tests were conducted to examine the effects of low-vacuum environments on the coating's adhesion. Hardened cement paste samples with the same water-to-cement ratio as C50 concrete (0.37) were also prepared, cured to the specified age, cut into cylinders with heights of 20 mm and 10 mm, and embedded in epoxy resin for analysis. Hydration was terminated by immersing these samples in isopropanol.The surface coating's effects on C50 concrete were further analyzed using scanning electron microscopy (SEM) and backscattered electron (BSE) analysis. Atmospheric curing was conducted in a standard curing chamber at (20 ± 2) ℃ and ≥95% relative humidity. A U-shaped vacuum chamber with a pressure range of 1000-2000 Pa and a temperature consistent with the local outdoor environment (-5 ℃ to 20 ℃) provided the low-vacuum exposure environment.Results and discussionThe application of surface coatings significantly reduced the mass loss of concrete under low-vacuum conditions. Compared to uncoated concrete, coated specimens exhibited a noticeably lower mass loss rate, demonstrating that the surface coating effectively suppressed the loss of free water within the concrete.The surface coating markedly improved the flexural strength of concrete under both atmospheric and low-vacuum conditions. Under atmospheric curing, the flexural strength of coated specimens at 14, 28 d, and 60 d increased by 28.2%, 23.9%, and 36.2%, respectively, compared to uncoated specimens. For coated specimens exposed to a low-vacuum environment after six days of atmospheric curing, flexural strength at 14, 28 d, and 60 d increased by 33.3%, 25.0%, and 15.4%, respectively, compared to uncoated specimens under the same conditions. Furthermore, coated specimens exposed to low vacuum after 28 d of atmospheric curing showed a 47.5% increase in flexural strength compared to uncoated specimens.In contrast, the compressive strength of coated specimens was generally lower than that of uncoated specimens under both atmospheric and low-vacuum exposure. This reduction is attributed to the adverse effects of low vacuum on the compressive strength of coated specimens. Additionally, the application of surface coatings reduces friction between the concrete specimens and the testing machine, diminishing end effects, which may also contribute to the lower compressive strength observed.Microstructural analysis using SEM revealed similar hydration products in both coated and uncoated specimens, including ettringite and C-S-H. However, uncoated specimens exhibited more needle-like ettringite and network-like C-S-H, whereas coated specimens showed fewer needle-like structures and more plate-like C-S-H. BSE analysis indicated an 18.1% reduction in porosity for coated specimens under low-vacuum conditions compared to uncoated ones, reflecting improved internal density. Nevertheless, the unhydrated cement content in coated specimens was 7.5% higher than in uncoated specimens, suggesting partial hydration inhibition by the coating.The adhesion strength of the coating increased with time under both atmospheric and vacuum conditions. Vacuum exposure slightly enhanced the coating's adhesion strength, indicating that low-vacuum environments promote better bonding between the coating layer and the concrete surface over time.ConclusionsThe surface coating effectively mitigated free water loss in low-vacuum environments, resulting in significantly reduced mass loss rates for coated concrete compared to uncoated specimens. Coated specimens demonstrated notable improvements in flexural strength under both atmospheric and low-vacuum conditions, although compressive strength was slightly reduced. Early-age exposure to low vacuum negatively impacted both compressive and flexural strength, regardless of coating protection. Microstructural analysis showed that the coating reduced porosity and enhanced internal density, mitigating the detrimental effects of low-vacuum environments on concrete's internal structure. Over time, the adhesion strength of the coating increased under both atmospheric and vacuum conditions, with slight improvements observed following vacuum exposure.

IntroductionCement-based materials are widely used because of their relatively low cost and strong mechanical properties. However, during hydration hardening and service, such materials are often subjected to multiple effects such as plastic shrinkage, self-shrinkage, drying shrinkage, freezing and thawing cycles, and external loading, which in turn induces the formation of internal microcracks. The emergence and development of internal microcracks in cement-based materials can easily become a penetration channel for erosion media such as sulfate and chloride salts, which adversely affects the stability, durability and safety of the structure. Therefore, the characterization and evaluation of internal cracks in cement-based materials have received extensive attention from scholars at home and abroad. Traditional methods still face certain challenges in measuring the width of internal microcracks in samples quickly and accurately. This paper proposes a micro-crack testing method based on the directional transport of the inert gas argon, which can rapidly and accurately determine the micro-crack width by analyzing the diffusion behavior of the gas in the cracks and the cement matrix through the comprehensive consideration of the sample size and the pressure gradient at both ends.MethodsThe cement paste cracking samples with specific crack widths were preset by the insert method, and the preset crack widths were 0.03, 0.05, 0.10, 0.15 mm and 0.20 mm. A cylinder mold with a diameter of 50 mm×100 mm was adopted. Through the insert method, steel sheets with different thicknesses were placed in the center of the mold in advance to control the formation of penetrating cracks with different standard widths.The gas transport system was mainly composed of sample chamber, gas transport control system and computer data acquisition system. During the test, the sample needed to be placed on a closed sample table and connected to the upper and lower outlets through a thermoplastic tube. The sample room maintained an oil bath environment to ensure sealing. The gas mass flowmeter was adjusted to the required flow rate, so that the gas passed through the device and recorded the pressure gradient changes at different gas flow. The crack width was calculated by Darcy’s law.Results and discussionWhen the crack width is in the range of 0.03-0.15 mm, the gas transport method can measure the width value more smoothly. When the crack width is 0.1 mm, the gas transport test results are closest to the actual crack width, and the error is less than 5%. When the crack width reaches 0.15 mm, the gas transport test can still maintain a high measurement accuracy, and the error is less than 10%. When the crack width reaches 0.2 mm, the error is more than 110% because the pressure gradient at both ends is not obvious. When the gas flow is 10-50 mL/min, with the increase of crack size, the increase of gas flow helps to reduce the error. Combined with the crack width and gas flow, it can be concluded that when the crack width is about 0.03 mm, the gas flow of 50 mL/min should be adopted; when the crack width is about 0.05 mm, the gas flow of 30 mL/min should be adopted. When the crack width is 0.10-0.15 mm, the gas flow of 20 mL/min should be adopted. In addition, there is a certain complementarity between the gas transport method and the optical microscope test in measuring the crack width. The optical microscope is suitable for the measurement of the width value of the larger crack surface, and the gas transport test can obtain the statistical average value of the penetrating crack inside the sample.In the self-healing test, with the increase of gas flow (≥20 mL/min), the equivalent crack width obtained by the test is basically in a stable state. This is because the high gas flow is more conducive to the passage of argon through the gap between SAP hydrogel particles and the formation of channels, thereby further increasing the gas fluidity in the sample and improving the gas transport effect. By comparing the crack width before and after self-healing, it can be found that the healing effect of SAP hydrogel significantly reduces the crack equivalent width, and the healing rate calculated according to the crack equivalent width.ConclusionsAt the gas flow of 20-50 mL/min, the error is less than 10%, and the test error gradually decreases with the increase of crack width. The gas transport test can accurately measure the crack volume equivalent width of the crack in a short time (400 s), and has good rapidity and reliability. When the crack width reaches 0.2 mm, the detection accuracy is significantly reduced because the pressure difference gradient at both ends is not obvious, and the error is more than 110%. When the crack width is 0.03-0.15 mm, the fluctuation range of the test results increases with the increase of the crack size, and the appropriate increase of the gas flow is helpful to reduce the test error. Therefore, the gas transport method can better quantify the microcracks within 0.15 mm. The suitable gas flow range for crack self-healing in gas transport test is recommended to be 20-50 mL/min, and the average self-healing rate of 24 h is 39.1%, indicating that SAP hydrogel can effectively seal the microcracks inside cement-based materials in a short time, reduce the equivalent crack width, and play a good self-healing sealing effect.

IntroductionIn application, different types of concrete admixtures are usually mixed to solve different problems. The varying adsorption capacities of organic molecules or polymer additives on particle surface of different mineral phase result in “competitive” or “preferential” behaviors, leading to intricate interference or synergistic effects among the additives. Competitive adsorption occurs among retarders, viscosity modifying admixtures (VMA), and superplasticizers, especially when the surface coverage is relatively high. The investigation of competitive adsorption relies on the quantification of each type of admixture based on the special characteristic signal of each admixture (e.g. signal by light scattering or gel permeation chromatography due to the clear difference of solution size between VMA, polycarboxylate superplasticizer (PCE), and retarder molecules; signal of phosphorus in some P-containing retarders). Labeling of PCE molecule by chromophores is an effective strategy. However, the low signal intensity of the labeled PCE in the few former reports limited the universality. Herein the paper reported the synthesis of a labeled PCE by the grafting of naphthylamine onto backbone as chromophore. The mixture of naphthalene-ring-labeled PCE and conventional PCE could be quantified based on UV absorption spectra and total organic carbon (TOC) method. The effect of adding two PCEs with different side chain lengths on the fluidity of cement paste was studied.MethodsJiangsu Helin P·II 52.5 Portland cement with density of 3.06 g/cm3 and BET specific surface area of 0.83 m2/g was used. The labeled PCE (PCE-A) was prepared by the simultaneously grafting naphthylamine (99%, Aladdin reagent) and polyetheramine (monofunctional, primary amine, with a terminal methyl group, from Zhejiang Lukean Chemical Co., Ltd) to polyacrylic acid (weight-averaged molecular weight Mw 2000) in the presence of 1% (in mass) H2SO4 under vacuum at 130 ℃. The molar ratio of chain unit as confirmed by 1HNMR spectra was acrylic acid/naphthylamine/polyetheramine = 4.73/0.70/1.00. PCE-B (poly(methacrylic acid) grafted with poly(ethylene glycol) monomethyl ether (MPEG, Mw 1000), molar ratio of methacrylic acid to MPEG was 3/1) was supplied by Jiangsu Sobute New Materials Co., Ltd.The UV absorption spectra was recorded between 200-400 nm. All the cement pastes were prepared with water to cement ratio of 0.18. The flow spread of cement paste (GB/T 8077—2012) with the addition of only PCE-A, only PCE-B, and both PCEs was measured, respectively. The total adsorption amount of PCE was measured by TOC method. The adsorption amount of PCE-B when both PCEs were added, was calculated based on UV absorption spectra. The standard curve (UV absorbance at 305 nm against TOC concentration) was obtained by the supernatant of cement paste when only PCE-B was added. The amount of ettringite (AFt) was calculated based on total heat absorbed between (40-105 ℃) in differential scanning calorimetry (DSC) as compared with synthetic AFt. The morphology of AFt was investigated by scanning electron microscope (SEM).Results and discussionThe main UV absorption band of PCE-A (naphthene ring) located between 250 nm and 320 nm, which enabled the differentiation with the background from the pore solution. The quantification by the UV method was confirmed by the supernatant of cement paste with only PCE-B. An excellent linear relationship (correlation coefficient of over 0.99) was found between absorbance at 295, 305 nm and TOC concentration.When only one type of PCE was added, the flow spread of cement paste achieved a maximum value at ~6 mg/g, then slight decrease could be observed at higher dosage. The maximum flow spread of cement paste with PCE-A (lower adsorption affinity, but higher saturated adsorption amount) is much larger than PCE-B, indicated a stronger steric hindrance, due to the longer side chain. When both PCE-A and PCE-B were added, at PCE-A of 2 mg/g and 4 mg/g, the flow spread of cement paste underwent a gradual increase and then decrease (especially after PCE-B of 4 mg/g) with the increase of dosage of PCE-B. At PCE-A of 6 mg/g, lower flow spread would be found at higher dosage of PCE-B. Regardless of PCE-A dosage, the adsorption amount of PCE-A would be lower at higher PCE-B dosage. The total adsorption amount always became lower at higher dosage of PCE-B, except for the condition of PCE-A 2 mg/g and PCE-B lower than 4 mg/g. The behind reason was, PCE-B could occupy the adsorption site for PCE-A. At fixed PCE-A dosage, the total surface coverage always increased with the addition of PCE-B. However, at high PCE-A dosage, the replacement of surface-adsorbed PCE-A would reduce the steric hindrance.The increase of PCE dosage induced lower amount of AFt with finer morphology. The size of AFt particle with PCE-B is smaller than PCE-A, due to the even higher adsorption affinity for the inhibition of particle growth. When both PCEs were added, high amount of PCE-B would promote the transformation of AFt particles from rod-like to fine needle-like. The aspect ratio of AFt increased from ~10.6 (PCE-B 2 mg/g) to ~14.1 (PCE-B 6 mg/g). The increase of aspect ratio would result in worse particle packing and therefore lower flow spread.ConclusionsA PCE labeled with naphthalene ring (UV chromophore) was prepared based on the grafting reaction of naphthylamine, which enabled the quantification of solution concentration in cement paste by absorbance at ~300 nm and therefore the investigation of competitive adsorption with another PCE. At extremely low water to cement ratio (0.18), as the dosage of short side chain PCE increases, the adsorption amount gradually increases, while the adsorption amount of long side chain PCE gradually decreases. At high dosage of PCE with long side chain, with the increase of dosage of short side chain PCE, part of the sites that could have been occupied by long side chain PCE are occupied by short side chain PCE. In addition, the morphology of ettringite (AFt) changes from rod-like to finer needle-shaped, showing a larger aspect ratio, which will deteriorate the packing behavior. The fluidity of the cement paste is therefore reduced.

IntroductionUltra-high performance concrete (UHPC) has garnered widespread attention in the field of civil engineering due to its exceptional mechanical properties, durability, and workability. These superior properties are primarily attributed to its dense microstructure and unique material composition, which typically includes cement, silica fume, quartz powder, and superplasticizers, along with reinforcing materials like steel fibers. The remarkable performance of UHPC not only meets the demands for high-performance materials in modern engineering but also contributes to reducing the life-cycle costs of structures by minimizing section sizes and extending service life.However, the development and application of UHPC face several challenges. The complexity of the preparation process, stringent requirements for raw materials, and the high sensitivity of UHPC properties to mix design variations increase both production costs and technical difficulties. Traditional experimental design methods struggle to efficiently optimize UHPC mixtures, and issues such as shrinkage and autogenous cracking require precise design solutions. These challenges make the composition design and performance prediction of UHPC a focal point in the field. With advancements in computer technology and data science, machine learning (ML) offers new tools and approaches for UHPC research and development. Therefore, this study aims to promote the application of ML technology in the UHPC field, thereby advancing the intelligent development of advanced construction materials.MethodsThe study introduced a comprehensive ML-based framework for UHPC performance prediction and precise design. The framework began with data cleaning, where the multiple imputation by chained equation (MICE) method with a predictive mean matching (PMM) kernel was employed to impute missing data in the UHPC database. Subsequently, the isolation forest algorithm was applied to identify and eliminate outlier data, thereby improving the quality of the dataset. The cleaned and optimized dataset was then used to train an XGBoost model, optimized via Bayesian hyperparameter tuning, to accurately predict various UHPC properties. Two AI-driven approaches for UHPC mix design were also proposed: one that combined the MAA model with ML predictions for multi-performance optimization, and another that integrated the ML model with genetic algorithm (GA) for multi-objective optimization.Results and discussionThe application of MICE combined with PMM resulted in a substantial improvement in the accuracy of the imputed data, as evidenced by the reduced average deviation between imputed and original data values. This enhanced imputation process allowed for a more reliable dataset, which directly contributed to the performance of the XGBoost prediction models. Outlier detection via the isolation forest algorithm effectively removed data points that exhibited significant deviation from the norm, particularly in compressive strength and density measurements. The refined dataset led to more accurate and consistent predictions across all performance metrics. After hyperparameter optimization, the XGBoost model demonstrated exceptional predictive capabilities, with notable improvements in performance metrics. The predictive accuracy of the model was further validated against experimental data, confirming its effectiveness in real-world applications. These results highlight the potential of ML techniques in advancing the field of UHPC research. The integration of MICE and PMM into the data preprocessing pipeline ensured more accurate and reliable datasets, which were crucial for developing robust predictive models. The success of the XGBoost model, particularly after Bayesian optimization, underscores the importance of hyperparameter tuning in enhancing model performance.Furthermore, the study proposes two ML-assisted design strategies for UHPC: 1) a combined physical packing theory and ML prediction model for initial mixture design, and 2) a multi-objective optimization approach using a metaheuristic algorithm for fine-tuning UHPC compositions. These strategies provide a framework for the intelligent and efficient design of UHPC materials, aligning with the growing demand for high-performance, sustainable construction materials.ConclusionsThis research demonstrates the significant potential of ML in predicting and optimizing the performance of UHPC. By addressing data challenges and enhancing prediction models, the study provides valuable insights into the application of ML in UHPC design. The proposed ML-assisted design strategies offer a practical approach to developing UHPC with tailored properties, paving the way for more sustainable and efficient construction practices.

IntroductionThe South China Sea islands and reefs have emerged as key regions with far-reaching implications in multiple domains, including national defense, maritime trade, resource exploration, and ecological conservation. The rapid expansion of infrastructure in this area has made concrete structures the predominant choice due to their versatility and strength. However, the local environment presents an array of formidable challenges. The durability of these structures is thus under constant threat, with potential consequences for the integrity and functionality of the entire infrastructure network. Understanding and enhancing the durability of concrete structures in such a harsh environment is not only essential for the immediate success of ongoing projects but also for the long-term sustainable development and strategic positioning of the South China Sea islands and reefs.MethodsTo comprehensively study the durability and service life of reinforced concrete structures in the South China Sea islands and reefs environment, a long-term exposure test station was established in this area. This test station was designed to closely simulate the actual environmental conditions of the South China Sea islands and reefs, providing reliable test conditions for studying the durability of concrete structures.In the experiment, different types of concrete specimens and components were prepared. These included specimens with different corrosion inhibitors and different concrete strength grades. Electrochemical tests were carried out to monitor the corrosion status of reinforcing bars. The natural corrosion potential and polarization resistance of the reinforcing bars were measured using advanced electrochemical testing equipment. Mechanical property tests were also performed to evaluate the mechanical performance of the concrete structures. Compressive strength, flexural strength, and tensile strength tests were conducted on the concrete specimens and components. Chloride ion content analysis was carried out to understand the penetration and distribution of chloride ions in the concrete. The ChaDuraLife model was used for service life prediction. This model takes into account various factors such as chloride ion diffusion, concrete strength, and environmental conditions to predict the service life of the concrete structures.Results and discussionThe experimental results showed that different corrosion inhibitors had different effects on the corrosion of reinforcing bars in concrete. The SBT-KLJ(IV) hydrophobic pore-filling agent (HPA) exhibited excellent anti-corrosion performance. After 1227 d of corrosion, the natural corrosion potential of the steel bars in the concrete specimens with HPA shifted positively, and the polarization resistance continuously increased during the erosion period from 365 d to 730 d. In the chloride ion erosion environment of the islands and reefs, adding HPA reduced the chloride ion content on the concrete surface by approximately 59.9% compared to concrete without the corrosion inhibitor.The mechanical property tests of the concrete components after on-site exposure experiments indicated that the durability of concrete structures with different strength grades varied significantly. C80 concrete showed better resistance to seawater erosion and mechanical properties than C50 concrete. The service life prediction results based on the ChaDuraLife model demonstrated that adding a rust inhibitor or increasing the concrete strength grade could effectively extend the service life of the reinforced concrete structure in the splash zone environment of the South China Sea islands and reefs. The HPA rust inhibitor was particularly effective, and under certain conditions, it could extend the service life of the concrete structure to over 50 years.ConclusionsIn conclusion, the research findings have several important implications. The HPA corrosion inhibitor has demonstrated excellent long-term stability and anti-corrosion performance in the South China Sea islands and reefs environment. Its ability to enhance the electrochemical stability of reinforcing bars and reduce chloride ion permeability makes it a preferred choice for marine engineering applications. The significant improvement in the durability of concrete structures with HPA inhibitor has been clearly established through experimental and modeling results. The differences in durability among different strength grades of concrete highlight the importance of appropriate material selection for the specific demands of the South China Sea islands and reefs infrastructure. C80 concrete's superior performance in terms of chloride ion resistance and mechanical properties indicates its suitability for critical structures where enhanced durability is required. The comparison with the national standard emphasizes the need for further research and innovation to develop more effective strategies for improving the durability of reinforced concrete in this harsh environment. This could involve exploring new admixtures, optimizing concrete mix designs, or enhancing construction and maintenance practices. The data and insights obtained from this study provide a solid foundation for future research and engineering applications, guiding the design and construction of more durable concrete structures in the South China Sea islands and reefs. Ultimately, these efforts will contribute to the long-term safety and functionality of the infrastructure in this strategically important region.

IntroductionLarge amounts of CO2 emissions have caused escalating challenges of global warming risk. The construction industry significantly contributes to global CO2 emissions, prompting the need for sustainable building materials. Carbon capture, utilization, and storage (CCUS) technologies provide a promising solution by reducing emissions and integrating carbon storage capabilities into materials. To this end, foam concrete, a lightweight porous material (normally 500-1600 kg/m3), has gained increasing attention for its significant advantages in energy-efficient and low emission buildings. Traditional foam concrete is lightweight with good insulation properties but has low strength and limited environmental benefits. In contrast, CO2 foam concrete offers the potential of reducing emissions during production and CO2 sequestration, making it a more environmentally friendly alternative.The objective of this research was to develop a high-strength CO2 foam concrete (HSCFC) that incorporates carbon capture and storage (CCS). By enhancing foam stability and optimizing the concrete mixture, this study firstly developed a new HSCFC product with assessing the CO2 sequestration efficiency and micro/macro performance of the devloped material, thereby verifying its potential as both a sustainable building material and a solution for carbon reduction.MethodsThe design concept of HSCFC was based on integration of a CO2 foam precursor into a high-strength cement-based paste, utilizing particle packing theory to optimize strength and density. The CO2 foam was produced using a amphiphilic nano-silica modified sodium dodecyl sulfate foaming agent, enhancing the stability of the foam and preventing collapse of foam concrete. The HSCFC was prepared by mixing the CO2 foam with a high-strength cement slurry, followed by curing and a series of micro and macro testing to evaluate HSCFC performance, including compressive strength, concrete density, pore structure and microstructures.Results and discussion1) The CO2 foam exhibited a well-distributed pore size of 50-100 m, which grew over time due to natural drainage and coalescence processes. The stability of the foam was attributed to the surfactant and nanoparticle interactions, which prevent CO2 diffusion and enhance liquid film strength. The overal performance of CO2 foam met the requirments of the Chinese standard for the concrete foam, which thus could be used to fabricate the foam concrete products. 2) The rheological behavior of HSCFC followed the Bingham model, with an increase in yield stress as CO2 foam volume increases, up to 110% compared to the control group. However, excessive foam content led to a reduction in yield stress due to the weakening of the matrix from enlarged pores. The plastic viscosity was inversely proportional to foam content, enhancing workability by reducing internal friction. 3) The increase in CO2 foam content led to the decrease in compressive strength of HSCFC. The compressive strength of HSCFC was found to be significantly higher than conventional foamed concretes, which is more than double that of typical foam concretes of similar density. Microhardness tests revealed values above 90 HV, close to ultra-high-performance concrete, despite the presence of foam. 4) X-ray computed tomography (XCT) analyses indicated that the pore structure of HSCFC became more complex as foam content increased, with the peak value of the pore size enlarging from 162.8 m to over 1100 m. This indicated the importance of balancing the compressive strength and density for the HSCFC. Additionally, using CO2 foam improved the cement hydration degree and led to the in-situ growth of calcium carbonate (CaCO3) on pore walls, enhancing pore wall strength. However, excessive foam amounts resulted in non-uniform pore distribution, leading to reduced material strength. 5) The thermal conductivity of HSCFC was lower than conventional concretes due to its porous structures. This property made the material suitable for energy-efficient buildings, where insulation is critical for reducing energy consumption. Therefore, the use of CO2 foam could realize the synergy of active and passive carbon reductions by carbon mineralization and decreasing engergy uses respectively.ConclusionThis research demonstrated the successful design and development of a high-strength CO2 foam concrete system with superior mechanical properties, enhanced carbonation, and thermal insulation capabilities. The use of CO2 foam not only provided an effective CCUS solution but also significantly improved the performance. The synergistic effects of foam stability, internal carbonation, and matrix densification showed a promising pathway for the sustainable development of carbon-neutral building materials. Future research could focus on improving the overall performance of HSCFC and investigating its long-term service values. This material presents a novel approach for CO2 capture and utilization, alongside advancements in foam concrete technology. The developed materials can be further optimized to improve carbon sequestration efficiency, facilitating their use in innovative structures like energy-efficient and floating buildings.

IntroductionMagnesium potassium phosphate (MKP) cements are normally composed of dead-burnt magnesia and monopotassium phosphate (KH2PO4), which react in water and yield the main hydrate of K-struvite (MgKPO4·6H2O). MKP cements have been frequently used as rapid repair materials in the field of civil engineering and as solidification/stabilization agents in the field of waste managements, due to the unique properties, such as fast setting, high early strength, low drying shrinkage, strong bonding to old Portland cement concrete substrates, low pH value, and so on. Boron compounds are the de facto standard retarders of MKP cements. Normally the increase of boron compound dosage could prolong MKP cement setting, but result in slower strength development, especially at early ages. Therefore, in order to obtain sufficient setting time and early strength at the same time, research attempts on seeking new retarders have been carrying out in recent years. Aluminum salts, Al(NO3)3 and Al2(SO4)3, were among those reported chemicals, showing promising retardation effect, especially at low M/P molar ratios. However, influence of aluminum salts on properties and hydration of MKP cements are yet to be explored, as several important aspects remain unclear, such as their impact differences on MKP cement early and late strengths, roles of Al3+ and of different anions on governing the hydration. Therefore, in this work influence of three common aluminum salts, AlCl3, Al(NO3)3 and Al2(SO4)3, on properties and hydration of MKP cements at magnesium-to-phosphate (M/P) molar ratio of 4 and water-to-cement (w/c) ratios of 0.27 and 5.00 was studied.MethodsThe raw materials for the preparation of MKP cements were industrial-grade dead-burnt magnesia and KH2PO4. The chemicals in analytical grade were borax (Na2B4O7·10H2O), Al2(SO4)3·16H2O, Al(NO3)3·9H2O, and AlCl3·6H2O. The MKP cement pastes and suspensions were prepared at same M/P molar ratio of 4, and at w/c ratios of 0.27 and 5.00. The aluminum salts were dissolved in the portioned mixing water before use, and the Al concentrations for the pastes and the suspensions were 600 mmol/L and 32.4 mmol/L, respectively. For comparison purpose, borax was used as reference, of which the dosages were 5.15% and 6.08%, by weight of cement, equal to the dosages of Al2(SO4)3·16H2O and Al(NO3)3·9H2O, respectively. Vicat needle test was used to determine the paste final setting time. Flexural and compressive strengths of the pastes with the dimensions of 25 mm × 25 mm × 125 mm were measured after 1, 3 h, 1, 7, 28, 90 d and 400 d. Additional strength measurements were carried out after 6 h and 12 h for the paste with Al(NO3)3, due to the low strengths within the first 3 h. Hydration heat of the pastes up to 24 h was measured using an isothermal calorimeter (TAM) at 20 ℃, using internal mixing method. Moreover, hydrate assemblages of the pastes after 28 d and 400 d were analyzed using XRD, TGA and FTIR methods. To track the aqueous evolution, pH and electrical conductivity of the MKP cement suspensions were continuously monitored up to 24 h at 25 ℃. Also the aqueous compositions were determined using ion chromatography and inductively coupled plasma after 15, 33 min, 3 h, 1 d and 7 d.Results and discussionCompared to the reference paste, the additions of Al2(SO4)3, Al(NO3)3 and AlCl3 could extend the setting time by around 2.5, 3.1 times and 5.1 times, respectively, corresponding to around 25%, 45% and 80% increases as compared to borax at 6.08%. It indicates better retardation effect of the aluminum salts and the anions taking effect in the order of Cl-, NO3-, and SO42-. In contrast to Al(NO3)3 and Al2(SO4)3, AlCl3 leads to clear sample expansion and cracks, suggesting its unsuitable use in MKP cement-based materials. Moreover, compared to the reference paste, both Al(NO3)3 and Al2(SO4)3 lower the early strengths. The strength weakening effect of Al2(SO4)3 mainly occur within the first 3 h, and of Al(NO3)3 is more pronounced and lasts longer up to around 12 h. However, thereafter, the strengths of the pastes with Al(NO3)3 and Al2(SO4)3 gain fast, leading consequently to similar or even slightly higher strengths at late ages compared to the reference paste.Al(NO3)3 shows better effects on slowing down hydration heat release and on decreasing cumulative heat up to 24 h, compared to Al2(SO4)3, in agreement with the setting time results. Both Al(NO3)3 and Al2(SO4)3 do not change the main hydrate, which remains K-struvite, but slightly decrease the formation contents. Compared to Al2(SO4)3, Al(NO3)3 lowers more the system pH value and extends hydration stages to later reaction times, consistent with the results of setting time and calorimetry, revealing stronger effect of NO3- than SO42- under same Al3+ concentration. The aqueous composition results suggest well that Al3+ is precipitated rapidly at the beginning of reaction, leading to certain amorphous Al-containing phases. At low w/c of 0.27 the anions of NO3- and SO42- are precipitated as crystalline KNO3 and K2SO4, filling micro-pores in hardened paste matrices, which indicates attention required on matrix volume stability as high dosages of these aluminum salts are used.ConclusionsThe main findings of this work are concluded as follows. All the investigated aluminum salts (AlCl3, Al(NO3)3 and Al2(SO4)3) could retard MKP cement setting. Furthermore, they show better retardation effect than borax at the same dosage. In contrast to Al(NO3)3 and Al2(SO4)3, AlCl3 could lead to sample expansion and cracks, indicating its unsuitable use in MKP cement-based materials. Moreover, both Al2(SO4)3 and Al(NO3)3 could lower the cement early strengths, which occurs within the first 3 h and 12 h, respectively, consistent with their retardation effects. But they show no adverse impacts on the paste strengths at late ages, compared to the reference paste. Compared to Al2(SO4)3, Al(NO3)3 is more effective on reducing system pH, extending hydration stage, slowing down hydration heat release, and on inhibiting slightly K-struvite precipitation, which contribute to better retardation effect. In addition to K-struvite, small contents of amorphous Al-containing hydrates and of crystalline KNO3 and K2SO4 are precipitated in the hydrated matrices, affecting the paste properties.

IntroductionFreeze-thaw damage is a significant factor affecting the durability of concrete in cold regions. The research on the mechanisms of freeze-thaw damage in concrete remains inconclusive. Currently, the primary methods for investigating freeze-thaw issues in concrete include experimental research and numerical simulation studies. The research focus can be categorized into two areas: macro structural performance degradation and micro pore structure analysis. However, most current value methods are limited to the micro level when simulating the freeze-thaw behavior of concrete, and there is a lack of research on the macroscopic mechanical properties of concrete following freeze-thaw cycles. At the same time, grid dependence arises when addressing crack problems. Consequently, this work proposes a mesoscopic-scale peridynamic freeze-thaw model. The relationship between pore frost heaving force and frost heaving force state is established. The pore frost heaving force is incorporated into the peridynamic motion equation as a force state, enabling the simulation of cracks and the prediction of residual bearing capacity in freeze-thaw damaged concrete.MethodsThe commercial concrete purchased by Qingdao Yehua Jianzhong Construction Engineering Co., Ltd.is used. The concrete size is 100 mm × 100 mm × 100 mm, the concrete strength is C40, and the water-cement ratio (W/Cs) is 0.51. The freeze-thaw cycle test was carried out by TDR-15D concrete rapid freeze-thaw test machine. The number of freeze-thaw cycles was set to 0, 30, 60, 90 times and 120 times, and the temperature range was (-18±2)-(18±2) ℃. Three concretes were set up for repeated tests under each cycle. Before the start of the test, the concrete was first immersed in water for 4 d to ensure that the water fully penetrated the concrete. Then the freeze-thaw test machine was started, and the freeze-thaw cycle test was carried out according to the preset cycle times and temperature. After the test, the concrete test block was taken out to dry the surface scum and water, numbered and weighed, and the dynamic elastic modulus was detected. The uniaxial compression test was carried out on the MTS Exceed E64.305 electro-hydraulic servo universal testing machine.The open porosity measured by the test is 1.68%, and the pore frost heaving force calculated by the finite element method is 58.3 MPa. After obtaining the relevant parameters, the freeze-thaw simulation is realized by matlab programming based on the peridynamics theory.Results and discussionThe results of the freeze-thaw tests and uniaxial compression tests were compared with the simulation outcomes. The diagram illustrating simulated freeze-thaw damage depicts the phenomenon of surface spalling and internal crack propagation, which aligns with the test results. The uniaxial compression stress-strain curves exhibit a similar trend, with a maximum difference in peak stress of 4.7%. After undergoing freeze-thaw cycles, the elastic modulus of the test group was initially low but subsequently increased. This is due to the cracks being filled with ice and broken concrete chips, resulting in a loose state of the concrete, which leads to a low elastic modulus during the initial stages of loading. As the load increases, the stiffness of the concrete also increases once the crack has closed.The open porosity and pore frost heaving forces of concrete are critical factors influencing its freeze-thaw performance. The freeze-thaw damage and residual bearing capacity of concrete with open porosities of 1.0%, 3.0%, 5.0%, 7.0% and 9.0%, as well as pore frost heaving forces of 40, 50, 60, 70 MPa and 80 MPa, are discussed in detail. The influence of open porosity and pore frost heaving forces on the freeze-thaw performance of concrete follows a similar pattern. When the two values are low, there are no freeze-thaw cracks or minor freeze-thaw cracks in the concrete. When the two values are large, the freeze-thaw cracks cover the whole concrete. The rate of decrease in the residual bearing capacity of concrete initially increases and then subsequently decreases. This is because when the freeze-thaw damage is small, each new damage may become the starting point of the freeze-thaw crack, so the damage will promote the new damage. The damage caused by freezing and thawing in the later stages reaches saturation, resulting in a limited number of cracks and overall damage in the concrete. The concrete has been damaged and should be regarded as having completely lost its load-bearing capacity.ConclusionsThe main conclusions of this paper are summarized as following. The peridynamic freeze-thaw model closely resembles the test used to simulate surface spalling and crack propagation in concrete subjected to freeze-thaw cycles. The simulation results of uniaxial compression for freeze-thaw concrete align closely with the experimental findings. The maximum difference in stress values is 4.7%, while the maximum difference in residual bearing capacity is 3.7%. The rate of freeze-thaw damage in concrete increases gradually during the early stages and then slows down in the later stages. The freeze-thaw damage of concrete is characterized by surface damage spalling and internal crack staggered expansion. Through regression analysis, the linear relationship between freeze-thaw damage and residual bearing capacity is established, with a coefficient of determination reaching 0.966. Compared to the mechanical model calculations, the regression curve is utilized to predict the residual bearing capacity based on freeze-thaw damage, resulting in an efficiency increase of approximately 360 times.

IntroductionCarbon emissions in the construction industry are increasing now. Against the backdrop of environmental factors and low-carbon economy, the research on reducing carbon emission in cement industry has garnered widespread attention. During the cement production procedure, the decomposition of carbonates during the calcination of raw materials is the main source of CO2 emissions. Therefore, reducing the calcium content in cement clinker is expexted to significantly reduce the carbon emissions, thereby achieving energy conservation and emission reduction in the industry. Unlike the C3S mineral in ordinary Portland cement clinker, CS, C3S2, and -C2S are three types of low calcium silicate minerals, but they are all non hydraulic minerals that cannot obtain a certain mechanical strength through traditional cement hydration. Former research revealed that the carbonation activity is higher than the hydration activity of above three low calcium minerals, and cement products can be prepared through carbonation curing.MethodsTo solve the problems of high energy consumption and high CO2 emissions in the production of ordinary Portland cement, low calcium silicate minerals (CS, C2S, and C3S2) with carbonation activity are used to replace C3S minerals. The strategy could not only reduce carbon emissions in cement production, but also enhance utilization of carbon. Research has found that incorporating -C2S into the low calcium system of -C2S can significantly enhance the mechanical properties of the system. In most reported research work, the single minerals are often blended after firing, and then the carbonization properties of the mixed minerals are studied. How to burn the C2S minerals with the optimal crystal ratio in one step and to achieve the symbiosis of -C2S and -C2S in the system remains a challenge. This work focuses on C2S minerals. By changing the calcination temperature, C2S minerals with different crystal ratios are treated in one step, and the relative content of -C2S and -C2S in low calcium cement clinker is regulated. The symbiotic mechanism of the two and the influence of different mineral contents of -C2S and -C2S on the carbonization performance of the material are studied. The carbonization products and mechanisms are explored, providing a theoretical basis for the application of low calcium fixed carbon cement in carbonization and new ideas for the carbonization research of C2S minerals. which has certain guiding significance for energy conservation and emission reduction in the cement industry.Results and discussionThis work used limestone and sandstone to obtain low calcium cement clinker with different proportions of -C2S and -C2S by adjusting the calcination temperature. The carbonization and hardening mechanism of low calcium cement clinker was analyzed using thermogravimetric analysis, X-ray diffraction, pH value, conductivity and other testing methods. The results showed that the molar ratio of -C2S/-C2S was between 0.19 and 2.63. As the ratio of -C2S/-C2S decreased, the compressive strength of low calcium cement clinker after 24 hours of carbonization gradually increased. When the calcination temperature was 1340 ℃ and the ratio of -C2S/-C2S was 0.19, the compressive strength of the system reached 163.32 MPa. The change in CO2 absorption of the sample is related to the carbonation activity of calcium silicate. The early carbonization reaction of the experimental group, mainly composed of -C2S minerals, is severe. There is a phenomenon of incomplete reaction in the test block. The experimental group mainly composed of -C2S minerals has a longer duration of exothermic reaction, which is more conducive to the progress of carbonization reaction. Among them, the heat released by -C2S during the carbonization process promotes the easier dissolution of Ca2+ from -C2S, facilitating the carbonization reaction of -C2S. The addition of a small amount of -C2S (i.e. 8.13%) has a positive effect on the carbonization degree and strength of -C2S. In addition, the dissolution of -C2S leads to a gradual increase in the pH value of the suspension, changing the liquid phase environment and accelerating the dissolution rate of -C2S in water under alkaline conditions. The excellent compressive strength of the sample is attributed to its high degree of carbonization and dense microstructure. The higher the content of -C2S minerals (-C2S/-C2S ratio=0.19), the better crystallized calcite type calcium carbonate can be observed after carbonization, presenting a stacked and dense morphology. The samples mainly composed of -C2S minerals have weak particle bonding and loose structure after carbonization, showing amorphous calcium carbonate with many pores.ConclusionsTherefore, it can be concluded that the synergistic carbonization of -C2S and -C2S mainly exists in two processes: the dissolution process before CO2 is introduced, and the carbonization reaction process after CO2 is introduced. Due to the action of water, -C2S preferentially dissolves Ca2+, changing the liquid-phase environment around -C2S particles and promoting Ca2+ dissolution. After the introduction of CO2, the carbonization reaction of -C2S becomes more intense, releasing a large amount of heat that accelerates the dissolution of -C2S minerals and promotes their carbonization reaction. The final carbonized product is mainly composed of stacked calcite, with a small amount of high polymer silica gel interspersed to bond the calcite. Therefore, the high content of -C2S carbonized product shows a more tightly aggregation of particles and thus better performance.

IntroductionUltra-High Performance Concrete (UHPC) is widely recognized for its exceptional mechanical properties and durability, making it a cornerstone material in modern infrastructure projects. However, the long-term service performance of UHPC structures with initial cracks under freeze-thaw (F-T) cycling remains a safety concern, particularly in harsh environments such as cold regions and coastal zones. While extensive research has focused on the properties of uncracked UHPC, the study on degradation of cracked UHPC under coupled F-T cycling and self-healing conditions is limited. Existing studies highlight UHPC’s intrinsic self-healing potential through secondary hydration and carbonation reactions, yet the interplay between these healing mechanisms and cyclic F-T-induced deterioration remains unclear. To address this, the present study investigates the tensile performance evolution of pre-cracked UHPC under F-T cycling and water-curing conditions. By integrating macroscopic mechanical tests with microscopic analyses, this work aims to unravel the dual effects of self-healing and F-T-induced damage on UHPC’s structural integrity.MethodsUHPC specimens were prepared using white cement, silica fume, quartz powder/sand, steel fibers (2% by volume), and a polycarboxylate superplasticizer. The mix design followed a water-to-binder ratio of 0.22. After casting and demolding, specimens underwent 48 h hot-water curing at 90 ℃. Dog-bone-shaped specimens (30 mm×13 mm×80 mm) were pre-notched and subjected to pre-tensioning to introduce controlled initial cracks (100 m width) via displacement-controlled loading. Pre-cracked specimens were divided into two groups, including 1) F-T cycling groups: Exposed to 100, 200, or 300 F-T cycles (&#x2212;17 ℃ to 8 ℃ per cycle); 2) water-curing groups: immersed in 20 ℃ water for 14, 30 d, or 60 d. Secondary tensile tests were conducted to evaluate residual strength and crack recovery. Single-fiber pull-out tests assessed interfacial bond performance, while scanning electron microscopy (SEM) and thermogravimetric analysis (TGA) characterized microstructural evolution and hydration products.Results and discussionWater-cured specimens exhibited remarkable mechanical recovery. After 60 d, tensile strength exceeded the undamaged control group by 32%, attributed to C-S-H gel and Ca(OH)2filling microcracks. SEM revealed dense microstructures with nearly closed cracks, confirming the role of secondary hydration in enhancing matrix integrity. Single-fiber pull-out tests showed interfacial bond strength fully recovered within 30 d, though prolonged immersion led to steel fiber corrosion, reducing post-peak ductility. F-T cycling initially promoted low-temperature self-healing. After 200 cycles, tensile strength increased by 14% due to partial crack closure via hydration. However, beyond 300 cycles, cumulative damage dominated: surface spalling, fiber corrosion, and interfacial debonding caused a 7.1% decline in tensile strength. TGA confirmed reduced Ca(OH)2 and CaCO3 content under F-T conditions, indicating suppressed hydration and carbonation compared to water curing. Progressive densification of the matrix with crystalline hydration products sealing cracks. Initial healing at 100-200 F-T cycles was counteracted by interfacial microcrack propagation and fiber-matrix debonding at 300 cycles. EDS analysis highlighted localized CaCO3 precipitation at crack surfaces, insufficient to offset F-T-induced damage. The study revealed a critical threshold (200 F-T cycles) where self-healing and deterioration mechanisms compete. While water ingress facilitates secondary hydration, prolonged F-T exposure disrupts the healing process through ice crystallization pressure and moisture redistribution, exacerbating matrix degradation.ConclusionsWater curing significantly enhances UHPC’s self-healing capacity, with complete tensile strength recovery, which was driven by continuous secondary hydration and carbonation, forming dense, crack-resistant matrices. Freeze-thaw cycling exhibited a dual role: healing occurred at early stages (≤200 cycles), but 300 cycles led to irreversible strength loss. Microstructural analysis underscored the importance of hydration products (C-S-H, CaCO3) in healing cracks, while F-T cycling disrupts interfacial bonding and accelerates matrix spalling. For UHPC structures in cold climates, proactive crack sealing and controlled curing are essential to maximize self-healing benefits before F-T damage accumulates. Future work should explore hybrid curing regimes and corrosion-resistant fibers to extend service life.

IntroductionAbnormal strain and structural cracks are common precursors to engineering accidents in concrete structures. However, traditional strain and crack detection methods exhibit a lag, and discovering structural abnormalities in a timely manner incurs high labor costs. Consequently, strain self-sensing cement-based materials have garnered widespread attention from researchers due to their intelligent and automated characteristics. Nevertheless, current cement-based strain self-sensing materials lack exploration in conduction mechanisms, often failing to establish a good correlation between changes in electrical resistance and system strain. Therefore, in this paper, nickel powder, which exhibits excellent durability and conductivity, is selected as the conductive component for the preparation of cement-based strain self-sensing materials. The study explores its conduction mechanism and various electromechanical constitutive models under different states, providing an important reference for correlating the electromechanical relationship of strain self-sensing materials.MethodsThe cement used is Swan Brand P&#xFF0C;O 42.5 ordinary Portland cement, and the water reducer is polycarboxylate superplasticizer with a water reduction rate of 18%-29%. The nickel powder adopts micrometer-grade high-purity ultrafine conductive nickel powder, with a Ni purity of 99.999% and a loose bulk density of 1.40-1.68 g/cm3. The execution standard is GB/T 7160—2008.Mix cement, nickel powder, water, and admixtures, then stir and disperse them before pouring the mixture into molds. Place the molds into a magnetic field coil and let them sit for a day before demolding and curing. During preparation, mix rapidly for 5 min to form Mixture 1. Then add nickel powder (with volume fractions of 0%, 5%, 10%, 15%, 17%, 20%, and 23%) to the cement and mix rapidly until the color of the mixture is uniform and no longer changes. This indicates that the nickel powder is fully dispersed and evenly distributed, forming Mixture 2. Pour Mixture 1 into Mixture 2 and mix rapidly for another 5 min. In this step, the water reducer increases fluidity while allowing re-dispersion of agglomerated cement and nickel powder particles, forming a nickel powder cement slurry called Mixture 3. Place Mixture 3 in a vacuum drying oven, adjust the temperature to 20 degrees Celsius, and vacuum for 15 min to eliminate bubbles and fully compact the mixture. Pour the defoamed Mixture 3 into molds with dimensions of 20 mm×20 mm×40 mm and 20 mm×20 mm×80 mm, and seal with plastic wrap to reduce water loss. Prepare two sets of test pieces for each volume fraction, allowing them to form under magnetic field strengths of 0 Gs (blank control) and 200 Gs for about 24 h. Then let them sit at room temperature for 2 d before demolding. Cure them in a 60 ℃ steaming box for 3 d, then cure under standard conditions for 4 d. Finally, dry them in a vacuum drying oven at 60 ℃ for about 24 h until the weight no longer decreases.Result and discussionWith the increase of the volume fraction of nickel powder, the resistivity changes can be roughly divided into three stages, namely, the stage of slow resistivity decrease, the stage of rapid resistivity decrease, and the stage of resistivity decrease again but at a slow rate. The rapid resistivity decrease stage of nickel powder cement-based materials conforms to the percolation theory, and the percolation threshold is between 15% and 17%. In this paper, the percolation threshold is taken as 15%. Near the percolation threshold, the conduction mechanism accords with the tunneling effect theory. For specimens formed under the action of a 200 Gs magnetic field, their resistivity in the direction along the magnetic field will decrease, while their resistivity in the direction against the magnetic field will increase. The measured maximum ratio between resistivity in the direction against the magnetic field and resistivity in the direction along the magnetic field is close to 4. Based on the tunneling effect and percolation theory, this paper derives an equation representing the change of resistance with strain, namely, the electromechanical constitutive model, and expresses this relationship as a polynomial function of strain. The parameters of the polynomial are determined using piezoresistive experiments. A four-point bending test is used to obtain piezoresistive curves of specimens with a 15% doping level formed under no magnetic field and under a 200 Gs magnetic field when subjected to pure bending loads. Based on the bending resistance variation of specimens with and without a magnetic field, this paper proposes an electromechanical constitutive equation representing the bending resistance variation rate and strain value. Subsequently, a supplementary equation for resistance variation after cracking of pure bending specimens is proposed, forming the basic theory for monitoring strain and cracks in bending members.ConclusionsThe specific conclusions are as follows: The optimal mixing ratio for nickel powder cement is approximately 15%. Around this ratio, the conductive behavior of the material conforms to the tunneling effect theory. Through magnetic field treatment, the resistivity of the material decreases in the direction of the magnetic field and increases in the perpendicular direction. When this material is compressed, its resistance first decreases and then increases. During the elastic stage, the relationship between resistance and strain is nearly linear, with a maximum decrease rate exceeding 60%. The material treated with a magnetic field exhibits a smoother performance under compression. When the material is bent, its resistance also decreases initially and then increases, but the decrease rate is very small, only about 1%. The material treated with a magnetic field demonstrates a more stable resistance change when bent. Based on these experimental results, we have derived the electromechanical constitutive relationship of the material under uniaxial compression and pure bending loads.

Carbon dioxide emissions from cement kiln flue gas constitute a significant contributor to global climate change and environmental pollution. As global emission reduction targets progress, research and application of carbon capture, utilization, and storage (CCUS) technologies have increasingly become critical strategies for mitigating CO&#x2082; emissions. Among these technologies, the calcium cycle method demonstrates substantial potential due to its low cost, high efficiency in CO&#x2082; trapping, and broad applicability, particularly in the context of cement kiln flue gas. However, traditional calcium-based materials, such as limestone, face challenges including high precalcination temperatures and resource wastage, highlighting the need for more efficient and sustainable alternatives.Calcium carbide slag, an industrial by-product, has shown significant promise as a material for the calcium cycle method. It contains a high proportion of reactive CaO, along with inert components such as alumina and magnesium oxide. These inert components enhance resistance to sintering after preburning. However, repeated use of calcium carbide slag leads to pore structure collapse, particle agglomeration, and sintering, severely diminishing its adsorption performance and posing a significant barrier to practical application.To address these challenges, various modification techniques have been explored to improve the absorption efficiency and sintering properties of calcium carbide slag, as well as to mitigate the impact of SO&#x2082; and NOx in flue gas on CO&#x2082; absorption.Organic acid modification has been identified as an effective strategy to enhance the adsorption performance of calcium carbide slag. Through reactions with calcium hydroxide to form organic calcium salts, pyrolysis at high temperatures releases small molecules that disrupt the original structure of the slag. This process increases porosity, specific surface area, and CO&#x2082; adsorption capacity. Different organic acids, due to their distinct molecular structures, yield variations in the molecular weight of organic calcium salts and the types and quantities of small molecules released during pyrolysis. Consequently, modifying calcium carbide slag with specific organic acids allows tailoring of its pore structure to enhance CO&#x2082; adsorption performance.Doping modification technology is another effective approach. By incorporating various substances into the slag, the properties of calcium carbide slag can be optimized through different chemical reaction mechanisms. Inert materials serve as structural frameworks, inhibiting CaO grain migration and growth to improve anti-sintering performance. Doping with oxygen-deficient materials facilitates CO&#x2082; diffusion and O2&#x207B; migration, while potassium and sodium salts increase defect concentrations in the CaCO&#x2083; product layer, enabling more efficient Ca2&#x207A; migration and enhanced CO&#x2082; absorption.Hydration processes also play a critical role in influencing sintering. While CaCO&#x2083; typically decomposes at high temperatures, introducing water vapor during calcination reduces the partial pressure of CO&#x2082;, promoting its conversion to CaO. Water vapor also shortens decomposition residence time and slows sintering, delaying sintering deactivation and improving stability. By optimizing calcination temperatures and water vapor concentrations, the CO&#x2082; adsorption performance and stability of calcium carbide slag can be enhanced over multiple cycles.In the context of cement kiln flue gas treatment, SO&#x2082; and NOx pose additional challenges to the CO&#x2082; trapping performance of calcium carbide slag. SO&#x2082;, being strongly acidic, preferentially reacts with CaO to form dense CaSO&#xFF0C; layers, which accumulate over cycles, diminishing adsorbent activity. Research suggests that specific modification methods or adjustments in the absorption sequence (e.g., absorbing CO&#x2082; before SO&#x2082;) can mitigate these effects. Regarding NOx, calcium carbide slag inherently lacks reductive properties and cannot remove NOx through traditional calcium cycle methods. Doping with reducing substances, such as copper, iron, and other metal oxides, can enable NOx reduction by promoting reactions that convert NOx into harmless nitrogen and oxygen.Summary and prospectsThe future of calcium carbide slag modification technology is expected to move towards systematic and refined strategies. These strategies can leverage the synergistic effects of multiple modification techniques to optimize performance across different reaction stages. As research progresses, the multifaceted applications of calcium carbide slag will gain increasing recognition. Beyond its role in CO&#x2082; capture, it holds significant potential for processes such as desulfurization and nitrogen removal.From an environmental perspective, utilizing calcium carbide slag addresses resource wastage while aiding the cement industry in achieving a green transformation by reducing greenhouse gases and pollutants such as CO&#x2082;, SO&#x2082;, and NOx. Continuous innovation in modification technology will ensure that calcium carbide slag not only plays a pivotal role in CO&#x2082; capture but also in mitigating pollutants, contributing to the attainment of global emission reduction goals. The enhanced versatility and cyclic stability of modified calcium carbide slag will further support the green transition of the cement industry and other high-emission sectors, contributing to efforts toward a sustainable future.

The utilization of compacted bentonite as the preferred buffer and backfill material in deep geological repositories for high-level radioactive waste disposal is well established due to its excellent engineering properties. The effectiveness of bentonite in such applications is largely influenced by its mineral composition, particularly the content and type of montmorillonite, a key clay mineral. Montmorillonite's ability to swell and its expansive nature make it highly effective in minimizing the migration of radionuclides and providing stability to the repository structure. In near-field environments, which are the zones closest to the waste container, changes in the physical and chemical properties of montmorillonite, especially its water retention and mechanical strength, have a direct impact on the long-term safety and performance of the repository. The accurate understanding of these properties under various environmental conditions is critical to ensuring that the bentonite buffer effectively isolates the waste over extended time periods.Traditionally, experimental methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), and various mechanical tests have been used to study the behavior of bentonite. While these techniques provide valuable macroscopic data, they fall short in addressing the molecular and atomic-scale interactions that govern the material's behavior. The hydro-mechanical properties of montmorillonite, which are essential for its performance as a buffer material, depend on the interactions between water molecules and the mineral's surface and interlayer spaces. These interactions occur on the molecular scale, and understanding them requires a more detailed, atomistic approach. This is where molecular dynamics (MD) simulations come into play.This paper reviews the applications of molecular dynamics in clay mineral research, particularly focusing on montmorillonite. It provides an in-depth look at how MD simulations can elucidate the mechanisms of interlayer molecular behavior that govern the hydro-mechanical properties of montmorillonite. The behavior of water in montmorillonite, such as its adsorption, diffusion, and swelling, is highly dependent on the interlayer spacing and the electrostatic interactions between the mineral surfaces and water molecules. These interactions are crucial for understanding the swelling pressure, permeability, and mechanical strength of the material, all of which are key factors in its performance as a buffer material. The paper also discusses how mesoscopic modeling, based on molecular dynamics simulations, can bridge the gap between the molecular scale and the macroscopic properties of bentonite. Mesoscopic models are useful for simulating larger systems, such as the behavior of bentonite under stress or hydration, while still retaining the molecular-level interactions. These models help to scale up the insights gained from molecular dynamics simulations, enabling researchers to predict the material's mesoscopic behavior under field conditions. In addition, the paper highlights key future research directions. Continued advancements in molecular dynamics, such as improved computational power and simulation accuracy, will enable more detailed studies of montmorillonite's interactions with other repository components, including radionuclides. Additionally, combining molecular dynamics with other methods like finite element modeling could provide a more comprehensive understanding of bentonite behavior. Future research should focus on refining mesoscopic models, improving long-term prediction accuracy, and validating simulations with real-world data.Ultimately, the goal of this research is to improve the understanding of the complex molecular mechanisms that govern the behavior of compacted bentonite in near-field environments. By using molecular dynamics simulations to explore these mechanisms, researchers can develop more accurate models of the material's performance, leading to better-designed, more effective buffers for high-level waste disposal. This, in turn, will contribute to the safety and sustainability of deep geological disposal systems for nuclear waste, ensuring that they meet the stringent requirements for long-term isolation and containment of hazardous materials.Summary and prospectsRecent advances in molecular dynamics (MD) have significantly expanded the study of bentonite buffering performance in deep geological repositories, extending the research scale from the micrometer to the nanometer level. This has provided crucial data and theoretical insights into material behavior, cross-scale modeling, and optimization. The accuracy of MD simulations largely depends on the appropriate selection of force fields and initial structures, with the development of clay-specific force fields (e.g., ClayFF) and databases providing a solid foundation. However, parameter adjustments for specific clay types are necessary to ensure computational precision. MD simulations have uncovered the molecular mechanisms behind montmorillonite expansion under various environmental conditions, challenging traditional models that simplified montmorillonite as a “parallel capacitor” and offering potential for refining theoretical models. These studies also link interlayer configurations to overall mechanical properties, supporting more accurate predictions of radionuclide migration and informing buffer material development. Additionally, the introduction of granular and discrete element methods has overcome the scale limitations of traditional MD, enabling more effective mesoscopic modeling of bentonite. Such models offer significant advantages in simulating aggregate expansion, permeability, and deformation, improving the accuracy of particle interaction and soil-water behavior. However, a unified modeling framework is still a key area of focus in current research.Looking ahead, future research should prioritize the development of new force fields that can simulate chemical processes, the creation of microstructural models to describe complex hydro-mechanical behaviors, and the integration of MD with multi-scale numerical platforms to predict long-term buffer performance. This integrated approach will provide important scientific support and technical guidance for the construction of geological repositories.

Photothermal catalysis is an innovative approach that combines typical photocatalysis and traditional thermocatalysis, which possesses all the merits of both processes, such as the efficient catalytic rate of thermocatalysis, the low energy consumption, low pollution and high selectivity of photocatalysis. Meanwhile, photothermal catalysis avoids the problems of single approach like the high temperature of thermocatalytic reaction, a series of side reactions, and deactivation of catalysts. Furthermore, the efficient solar energy utilization rate of photothermal catalysis holds the promise of elevating reaction rates to industrial levels. Due to its exceptional solar energy utilization efficiency, high catalytic reaction rates, mild reaction conditions, and low pollution, photothermal catalysis has been proposed as a promising alternative to traditional photocatalysis and thermal catalysis in the fields of energy conversion and environmental remediation.This review first introduces the mechanism of photothermal catalysis, with a focus on the plasma conversion and non-plasma conversion processes. On the basis of synergistic modes between photocatalysis and thermocatalysis, we categorize photothermal catalysis into three types: photo-assisted thermocatalysis, heat-assisted photocatalysis and photothermal co-catalysis. Subsequently, various types of photothermal materials, including metals, semiconductors, carbon-based materials and metal-organic frameworks are summarized. Thereafter we comprehensively discuss the current effective strategies to improve the photothermal performance, such as improving solar energy absorption through band engineering and morphological manipulation, increasing carrier separation efficiency via heterojunction construction, and enhancing thermal management through heat insulation, suppression of infrared radiation, and thermal energy storage. Lastly, the future research directions and challenges in photothermal catalysis is also discussed.Summary and prospectsPhotothermal catalysis, based on the photothermal conversion to drive the reaction, shows large potentials in various applications like CO2 reduction, organic pollutant degradation, organic synthesis, and hydrogen production via water splitting is the synergy of photochemical and thermochemical effects. This review summarizes the mechanisms of photothermal catalysis, including the direct process by infrared radiation absorption and the indirect process via non-radiative carrier relaxation. Moreover, the indirect way could be further divided into plasma conversion and non-plasma conversion. Based on the contributions of photocatalysis and thermocatalysis, photothermal catalysis is classified into three modes: Photo-assisted thermal catalysis, thermal-assisted photocatalysis, and photothermal co-catalysis. Metals, semiconductors, carbon-based materials and metal-organic frameworks are common photothermal materials. Various modification strategies are developed to promote the catalytic reactivity of photothermal materials, including improving solar energy utilization, accelerating the separation rate of high-energy charge carriers, and strengthening the thermal management. Though photothermal catalysis shows great advantages in comparison with the traditional thermocatalysis and common photocatalysis, it still faces a series of challenges especially in large-scale applications. Several research directions could be considered to the development and application of photothermal catalysis in the future.The development of efficient, cost-effective and robust photothermal materials is the central theme in photothermal catalysis. At present, common photothermal materials focus on metals with LSPR effect, semiconductors and carbon-based materials. Emerging two-dimensional materials such as phosphorene, borene, MXene are capable of harnessing both visible and infrared light and also exhibit high photothermal conversion efficiency. These materials hold great potential as light absorbers in photothermal catalytic systems. Additionally, covalent organic framework materials with large conjugated systems also provide a new avenue for the development of high-efficiency photothermal catalysts.The mechanism of photothermal catalysis need to be further clarified. The understanding of the insight of reaction could guide the construction of photothermal catalytic system. At present, the key research focuses on the synergestic effect between high-energy carriers and photo-derived thermal energy. More details about the exact energy conversions like light to charge carriers or non-radiative relaxation could be figure out. Furthermore, it is pivotal to distinguish the contribution of photocatalysis and thermocatalysis in photothermal catalytic reaction. The rational design of experiments, specific characterizations like in-situ techniques-including in-situ Raman, XPS, AFM, etc. and first principle calculations might provide the possible solutions to discern the catalytic mechanism.To address the limitations of photothermal catalysts, it is highly desirable to explore simple and effective modification strategies to enhance the absorption and conversion of full-spectrum solar energy. Rational structural modulation of photothermal catalysts is essential to ensure efficient separation of the generated high-energy carriers and then apply to the subsequent reaction. Additionally, reducing the heat loss during photothermal catalytic processes is also a critical research priority. This requires balancing the energy utilization and heat dissipation while optimizing reaction pathways to achieve energy-efficient and sustainable catalytic systems.The application of photothermal catalysis still requires further investigation, particularly in CO2 reduction and C-C coupling to generate high-value C2+ products with high selectivity, which are the critical approaches to achieve the carbon neutrality.

As an energy-intensive industry, cement manufacturing is a significant contributor to CO2 emissions. Simultaneously, the increasing volume of construction waste has also exerted significant pressure on the environment. Recycling demolished concrete has been proposed as a strategy to address the depletion of aggregate resources. In addition, it facilitates the disposal of construction waste and reduce carbon emissions. A particularly promising approach is the recycling of waste concrete powders (WCP) as a supplementary cementitious material (SCM), which has garnered significant attention. However, the high absorption and low reactivity of WCP pose a challenge to its direct use as SCM. Accelerated carbonation of WCP produces calcium carbonate (CaCO&#x2083;) and amorphous silica gel. These products enhance the reactivity of WCP and facilitate the effective sequestration of CO&#x2082;. This process not only promotes the high-quality utilization of WCP but also helps to mitigate the environmental and energy burdens associated with cement production.This study reviews the properties of carbonated waste concrete powder (cWCP) and provides an in-depth analysis of the carbonation process of WCP. It covers various carbonation methods, the regulation of carbonation degree and the prperties of carbonation products. Furthermore, the review evaluates the influence of cWCP on the performances of cement-based materials, including rheology, hydration behavior, mechanical properties, and impermeability.The carbonation products of cWCP are influenced by the carbonation conditions. In turn, cWCP influences the properties of cement-based materials through the properties of these carbonation products. The primary products of cWCP are CaCO&#x2083; and amorphous silica gel. Their composition, morphological characteristics, chemical properties, and relative distribution depend significantly on the carbonation method and conditions used. The reaction environments and carbonation kinetics of dry and wet carbonation processes differ significantly, resulting in variations in both the degree of carbonation and the polymorphs of products. By optimizing these carbonation conditions, it is possible to improve the degree of carbonation of cWCP while also controlling the polymorphs of CaCO&#x2083; and polymerization degree of silica gel. Furthermore, the influence exerted by these carbonation products on cement-based materials primarily stems from their surface characteristics combined with various effects. Surface properties include both geometrical and surface electrochemical characteristics of CaCO&#x2083; in diverse polymorphs, as well as the hydrophilicity of the silica gel. The effects of carbonation products include the filler effect, nucleation effect, chemical reaction with C3A, and the pozzolanic effect attributed to silica gel. Notably, improvements in rheological properties are not significantly influenced by either the filler effect or surface electrochemical characteristics of CaCO&#x2083;. Instead, more pronounced negative influences arise from the hydrophilicity of silica gel and the fibrous geometry of aragonite. These factors contribute to a significant deterioration in rheological properties, with hydrophilicity being the primary mechanism behind this deterioration. When the degree of carbonation is sufficiently high, the combined positive effects of the filler effect, nucleation effect, chemical reaction, and pozzolanic effect can surpass the negative influence of dilution effect. As a result, the incorporation of cWCP accelerates the hydration, improves the microstructure, and enhances the compressive strength and impermeability.Summary and ProspectsExisting studies have shown that the incorporation of cWCP accelerates cement hydration, improves microstructure, enhances compressive strength, and strengthens mortar impermeability. However, it may also result in a degradation in rheology.Base on these findings, further advancements are essential to fully understand the properties of cWCP-based cementitious materials and to support their widespread application. Key areas for development include: 1) establishing a model that correlates carbonation conditions with carbonation products to precisely control their performance, 2) addressing the contradiction between compressive strength and rheological properties, 3) deepening our understanding of the durability of cement-based materials containing cWCP, particularly concerning corrosion of steel reinforcement, and 4) overcoming challenges related to improving the degree of carbonation in cWCP due to an accumulation of carbonation products. These efforts will lay the groundwork for the industrial adoption of cWCP and drive the concrete industry toward more sustainable and environmentally friendly practices.

In light of the policy of ‘carbon peaking and carbon neutrality’ and the advent of artificial intelligence, there is an urgent need for research and development in the field of cementitious materials to advance low-carbon alternatives. Given the lengthy research periods associated with traditional experimental methods, digital research and development has recently emerged as a dominant trend in the field. Currently, digital models are being developed for purposes such as performance prediction, composition optimization, and low-carbon innovation, with a primary focus on algorithm optimization. However, the success of these models relies heavily on the availability of accurate, high-quality databases, which serve as the foundation for model implementation. Utilizing such databases can significantly simplify model construction and reduce the need for extensive optimization procedures. Consequently, building comprehensive databases for cementitious materials research and development has become a key objective in this field.This paper reviews the current status of databases for cementitious materials, including those related to clinker, cement, concrete, mineral admixtures, and construction mortar. The types of data, application methods, and scope of application encompassed by these databases are summarized. Databases for clinker were among the earliest to be developed, primarily cataloging diverse mineral properties, including hydration products. They include crystallographic data, thermodynamic data, and force field data, with some databases integrating models for analyzing cement hydration. Cement databases, while recording thermodynamic properties, cement types, and characteristics, have largely been focused on production control in cement plants. Moreover, the construction of databases for concrete and related materials has often been driven by specific research objectives, such as studying chemical composition, strength, and durability. Some researchers have also conducted property predictions based on their collected datasets.Despite the existence of numerous databases on cementitious materials, a significant volume of relevant data within scientific literature remains underutilized. The advancement of artificial intelligence in natural language processing has enabled the adaptation of data extraction algorithms across various domains, including metals, medicine, and biology. Named entity recognition and textual relationship extraction—two critical components of literature data mining—can be implemented through AI algorithms such as ChemDataExtractor and BERT. ChemDataExtractor and related algorithms have demonstrated accurate chemical data extraction from compounds and semi-supervised relationship extraction. Similarly, BERT, like ChatGPT, is a state-of-the-art language model developed using the Transformer architecture and has been successfully applied in automated text data extraction. However, the complex mineralogical and chemical composition, multi-scale particle characteristics, and hydration processes of cementitious materials pose challenges to the direct application of these algorithms.Summary and prospectsThe construction of comprehensive databases represents the cornerstone of the digital transformation of low-carbon cementitious material research and development. Although existing databases contain extensive datasets on cementitious materials, several challenges persist, such as non-standardized database structures, insufficiently considered data categories, and incomplete material coverage. To address these issues, future database development should prioritize unifying data formats and linking upstream and downstream processes to create a cohesive and interconnected database. Such a unified database would enable the establishment of a fully connected data chain for cementitious materials, enhancing the accuracy of predictions, supporting reverse design processes, and saving time on data cleaning.Particular emphasis should also be placed on refining databases for related materials, such as mineral admixtures. These refined databases would provide critical data for improving the durability of cementitious materials and reducing their carbon emissions. Furthermore, combining artificial intelligence algorithms, such as ChemDataExtractor and BERT, with domain expert knowledge holds significant potential for advancing literature mining techniques tailored to cementitious materials. This process could begin by focusing on individual performance attributes and gradually expand to encompass the comprehensive extraction of data for all cementitious materials.The future of cementitious materials database development is promising, with the potential to drive innovations in low-carbon materials research and development, ultimately contributing to achieving global carbon neutrality goals.

There are many methods to test the water content, pore water distribution and pore structure characteristics of cement-based materials, and they are different in the measurement principle, accuracy, ease of use and reliability. As a non-destructive testing method, low-field nuclear magnetic resonance (LF-NMR) relaxation technology uses hydrogen and 1H nuclei in water as a probe. By testing the relaxation signal of 1H nuclei, it can accurately detect the content of hydrogen protons and the interaction with the pore wall, thereby indirectly obtaining features such as water content, water distribution in pores of different sizes and pore size distribution. They can be tracked and monitored over time and through other physical and chemical processes. Compared to traditional methods such as weighing method for water content and mercury intrusion porosimetry or nitrogen adsorption for porous structure measurement, LF-NMR relaxation technology can perform non-destructive testing without drying. It avoids the destruction of the abundant nanopore structure caused by drying pretreatment, and the pore measurement range covers the nanometer and micron scale pores. These significant technical advantages are very key to the study of the properties of cement-based materials. Because of the undisturbed, non-destructive and accurate characteristics of LF-NMR relaxation technology, it is precise, and thus more and more widely used in the field of cement-based materials, especially the hydration of cement, volume stability, actions of drying-wetting and freezing-thawing cycles, and durability performance. Since almost all these studies are closely related to water content and pore structure, LF-NMR plays an increasingly key role.Based on the relaxation mechanism of 1H nuclei and the commonly used relaxation measurement methods, this paper systematically describes the transverse relaxation mechanism of pore fluid and the inversion algorithm of transverse relaxation data. The determination methods of surface relaxivity and quantitative calibration of transverse relaxation signal and continuous/discrete relaxation time spectrum into water content and continuous/discrete pore size distribution are described in detail. In addition, the application status of LF-NMR is summarized and prospected from 5 different perspectives: quantitative characterization of cement hydration process, pore structure at saturation, pore-scale water distribution at unsaturated state, imaging of water spatial distribution, and freezing-thawing damage process analysis.First of all, by testing relaxation magnetization and transverse relaxation time spectrum, LF-NMR resonance technology can non-destructively monitor the moisture content and its physical constraint state in the hydration process of cement at real time, so as to analyze the time-varying process of pores, especially nanopores, and apprehend the development history of microstructure, so as to realize the undisturbed characterization and analysis of cement hydration process. Secondly, the porosity and pore size distribution of hardened cement-based materials can be obtained according to the relaxation magnetization and relaxation time spectrum, allowing for qualitative and quantitative investigation of the relationship between pore structure and macroscopic properties. Thirdly, the pore classification method based on discrete or distinct peak T2 spectrum can monitor the distribution of water in pores of different sizes at real time and continuously under unsaturated conditions, which can be used to study the macroscopic properties of cement-based materials such as moisture shrinkage. Fourthly, the water content and relaxation time spectra of different locations can be obtained by one-dimensional imaging, which can directly characterize the internal water migration process of cement-based materials. Finally, since the LF-NMR relaxation technique can only monitor the 1H nuclear signal in evaporable water other than in solid phase such as ice and calcium hydroxide, it can be used to detect the phase transition of liquid water into ice.Summary and prospectsIt is found after literature reviewing that the LF-NMR relaxation technique using 1H nuclei in pore fluid as a probe is especially suitable for characterizing cement hydration, pore structure evolution and pore-scale water allocation and spatial distribution of cement-based materials. On the basis of reasonable selection of hardware platform, test method, test parameters, inversion algorithm and accurate calibration of relaxation magnetization and transverse relaxation time, LF-NMR technology can help accurately measure important information closely related to pore structure and pore-scale water allocation of cement-based materials, such as hydration degree, pore size distribution and unsaturated pore water distribution non-destructively.Due to the influence of ferromagnetic substances, current LF-NMR analysis is mainly recommended to use white cement as the principal cementitious material. In future, it is necessary to fully consider the influence of ferromagnetic materials on transverse and longitudinal relaxation, to establish LF-NMR relaxation test method suitable for ordinary Portland cement, and to improve the signal-to-noise ratio of relaxation signals, to reduce the dead time of the probe, and to develop an inversion algorithm with good accuracy and precision. The probe diameter (sample chamber size) should be increased to support the test analysis of concrete specimen.LF-NMR relaxation technology is the promising characterization method that can detect the multi-scale pore structure and unsaturated pore water allocation and other key information of cement-based materials without any pretreatment. Since most of the key properties of cement-based materials, such as volume stability and durability, are closely related to pore structure and pore-scale water allocation, LF-NMR relaxation technology is expected to be able to drive breakthroughs and promote the development of modern concrete science and technology, similar to the encouraging role of magnetic resonance imaging in clinical diagnosis.

Abrasion-resistant concrete is crucial for the durability and safety of hydraulic engineering structures, bridge piers, coastal embankments, and other specialized infrastructure. These structures are exposed to harsh conditions such as high-velocity water flow, sand erosion, and debris impacts. This review examines recent advancements in abrasion-resistant concrete materials, focusing on material composition, characterization methods, and abrasion damage mechanisms. It aims to provide theoretical insights and practical guidance for developing durable concrete in demanding environments.Abrasion resistance is enhanced by optimizing material composition, including supplementary cementitious materials (SCMs), fiber reinforcement, wear-resistant aggregates, rubber particles, and ultra-high-performance concrete (UHPC). SCMs such as silica fume, fly ash, and slag powder improve hydration products and densify the microstructure, significantly enhancing abrasion resistance. However, excessive silica fume can cause shrinkage cracking. Fiber reinforcement, particularly steel fibers (0.75%-1.00% by volume), improves tensile strength and abrasion resistance, with reported increases of over 20%. Wear-resistant aggregates, including iron ore and recycled glass, play a critical role, with their mechanical properties and particle size significantly influencing performance. Rubberized concrete (5%-25% rubber content) absorbs impact energy, reducing abrasion damage, though excessive rubber content may compromise strength. UHPC, with its exceptional strength and density, offers superior abrasion resistance, and further optimization of its fiber, aggregate, and cementitious components is key to its performance in complex environments.Concrete abrasion resistance is evaluated using various characterization methods that simulate different mechanisms of wear. The underwater method (ASTM C1138, DL/T 5150—2017) measures bed load impacts in high-velocity water flow. The sandblasting test, or water-borne sand jet method, simulates suspended load erosion under varying impact angles and velocities. The ring method and high-speed ring method (SL/T 352—2020) assess abrasion in low-velocity sand-laden water flow, while the rotating jet method simulates high-speed suspended load abrasion. The water-borne sand jet method combines suspended load and cavitation effects to provide a comprehensive evaluation of abrasion resistance. Recently, 3D scanning technology has been increasingly adopted to characterize surface morphology, offering precise measurements of wear depth and volume loss for detailed analysis of abrasion damage.Abrasion damage mechanisms in concrete involve bed load impact, suspended load abrasion, and cavitation erosion. Bed load impact, caused by large particles such as rocks, results in brittle failure, surface spalling, and internal microcracking, as simulated by the underwater steel ball method. Suspended load abrasion, driven by the continuous scouring of sand particles, gradually erodes the cement paste and exposes aggregates, as modeled by the sandblasting and rotating jet methods. Cavitation erosion, caused by the collapse of bubbles in high-velocity water, forms erosion pits that expand over time, as simulated by the water-borne sand jet method. In real-world environments, concrete is often subjected to combined abrasion mechanisms alongside environmental stressors such as freeze-thaw cycles, debris flow, and seawater exposure. For example, freeze-thaw cycles weaken the concrete matrix, exacerbating erosion by suspended sediments. These combined effects significantly accelerate abrasion damage, highlighting the need for a deeper understanding of the synergistic interactions between abrasion mechanisms and environmental factors.Summary and prospectsThis review highlights recent progress in abrasion-resistant concrete materials, emphasizing material composition, characterization methods, and damage mechanisms. It offers valuable insights for enhancing durability in harsh environments. Future research should focus on optimizing UHPC composition for specific applications, exploring the combined effects of environmental stressors on abrasion resistance, and leveraging advanced techniques such as 3D scanning for precise damage assessment. By clarifying abrasion mechanisms and improving material performance, this research will drive innovation in hydraulic engineering and coastal protection, ensuring infrastructure resilience in demanding service conditions.

From the initiation of hydration when water is added to cement until the end of service life of cement-based materials, the influence of water permeates almost the entire lifecycle, comprehensively affecting both the development and degradation of their properties.Water transport is a critical fundamental factor determining the durability of cement-based materials (CBMs) and service life of structures. Since most concrete structures under service are unsaturated, capillary water absorption is the primary and efficient mechanism for water transport in concrete. An in-depth analysis of capillary water absorption process and sorptivity is of great significance for quantitatively studying and improving the durability of CBMs.This study systematically investigates the capillary water absorption process and its anomalies in CBMs. While existing theories attribute sorptivity anomalies to factors such as gravitational effects, material heterogeneity, and secondary hydration of unhydrated cement particles, certain experimental phenomena remain inadequately explained. Through macro- and micro-scale testing combined with theoretical modeling, it is hypothesized that the unique physicochemical interactions between water and C-S-H gel may underpin these critical anomalies.Although sorptivity testing is operationally simple, its results are highly sensitive to experimental conditions (e.g., temperature, humidity, and initial saturation). The moisture state of specimens plays a decisive role in sorptivity measurements, while inconsistencies in testing protocols can lead to disparate outcomes. Consequently, adopting a scientifically rigorous and practical testing methodology is imperative. This paper reviews international standards for sorptivity testing, including the widely recognized and scientifically reliable ASTM C1585—20 and ISO 15148:2002. However, these standards exhibit limitations, such as short testing durations that overlook the significance of secondary sorptivity. Given the anomalous long-term absorption behavior of CBMs, a systematic consideration of the two-stage sorptivity process is essential. Furthermore, China urgently requires the development of a national testing standard tailored to its specific material and environmental conditions.To elucidate the influencing factors of sorptivity, this study compiles and analyzes experimental data from diverse studies. The results reveal that cement content, water-to-cement ratio, and the dosage of supplementary cementitious materials profoundly alter hydration kinetics, hydration products, and pore structure, thereby significantly affecting sorptivity. Beyond material composition, variations in pretreatment methods (e.g., drying protocols) also induce substantial discrepancies in test results due to differing moisture states. Moreover, the coupling effects of these factors further complicate the interpretation of sorptivity behavior. Therefore, during the sorptivity test, it is crucial to adopt a scientific pretreatment protocol to minimize the impact of drying, equilibration, and moisture content on the test results.The study also explores correlations between sorptivity and other macroscopic performance indicators. Sorptivity demonstrates strong linkages with transport properties such as permeability and electrical flux, as these metrics are fundamentally governed by pore structure. Additionally, sorptivity exhibits predictive potential for mechanical properties and durability outcomes, including carbonation resistance, freeze-thaw durability, and sulfate attack resistance. Compared to other durability indicators, sorptivity not only boasts a relatively straightforward testing process, but its primary advantage lies in its high sensitivity to durability changes in long-age concrete. It also provides highly accurate assessments of the carbonation resistance of cement-based materials. Furthermore, it contributes effectively to evaluating frost resistance and sulfate erosion resistance. When used in conjunction with other durability indicators, sorptivity enables a comprehensive assessment of the durability performance of cement-based materials. As a durability indicator, sorptivity shows promise in forecasting the service life of cement-based materials.In conclusion, this work underscores the need for refined theoretical models, standardized testing protocols, and comprehensive investigations into the coupling mechanisms governing sorptivity. Addressing these challenges will enhance the reliability of sorptivity as a critical parameter for optimizing material design and durability assessment in cement-based systems.Summary and prospectsCement-based materials exhibit water sensitivity due to their unique physicochemical interactions with water. Current understanding and quantitative characterization of capillary water absorption (sorptivity) require further refinement through integrated theoretical and practical studies. Notably, the two-stage sorptivity mechanism, particularly the physical significance and engineering implications of the secondary sorptivity, demands deeper exploration to enhance its practical application.Critical anomalies observed in sorptivity evolution highlight the urgent need to develop more scientifically robust testing protocols. A standardized framework for evaluating concrete quality based on sorptivity should subsequently be established.The measured sorptivity is significantly influenced by material composition and mix design parameters, including cement type, supplementary cementitious materials, water-to-binder ratio, curing conditions (temperature and humidity), aging, and drying pretreatment. Systematic investigations into the correlations between sorptivity and material composition are essential to optimize mix designs for improved durability.Although sorptivity demonstrates varying degrees of correlation with mechanical properties, other transport indices (e.g., chloride diffusion), and accelerated durability test results, it exhibits unique potential as a complementary indicator for assessing concrete durability. Integrating sorptivity with conventional metrics could enhance the accuracy of service life prediction models for concrete structures. However, further theoretical, experimental, and field studies are imperative to validate its application in engineering practice.In summary, advancing research—spanning mechanistic interpretation, standardized testing, material optimization, and durability assessment—will provide critical insights into the performance and longevity of cement-based materials in real-world environments.

Concrete infrastructure in China has entered a large-scale phase of maintenance and repair, with organic adhesives being essential materials for enhancing structural durability. Enhancing the long-term effectiveness of adhesion between these adhesives and cementitious materials is crucial for extending the service life of concrete structures. This study reviews the primary types of organic adhesives used for infrastructure repair work, including epoxy resins, polyurethanes, and silicone adhesives, and discusses the performance advantages of their various applications. The adhesion mechanisms are determined in terms of mechanical interlocking, intermolecular interactions, and thermodynamic interactions, identifying the main sources and driving forces behind adhesion. The degradation mechanisms of interfacial adhesion under moisture, salt solutions, adhesive aging, and cyclic load coupling are analyzed. Finally, the study summarizes various techniques for enhancing interface adhesion, providing insights and innovative approaches for the design of organic adhesives and adhesion durability. The main conclusions are as follows:The adhesion mechanism of organic adhesives to cement-based materials is primarily considered from three perspectives: mechanical interlocking, intermolecular interactions, and thermodynamic interactions. Compared to the roughness of the interface, the penetration of organic adhesives into the cement-based material promotes mechanical interlocking more effectively. In the absence of interface modification, hydrogen bonds formed between the adhesive and the substrate dominate the intermolecular interactions. Moreover, hydrophobic interactions between the adhesive and the substrate play a significant role in driving the interface adhesion process.Moisture is the predominant factor responsible for debonding at the interface between organic adhesives and cement-based materials. Moisture molecules replace the hydrogen bonds formed during the adhesion process, while aggressive ions accelerate the degradation of adhesion. Furthermore, moisture and aging effects gradually degrade the mechanical properties of the organic adhesives, weakening the interfacial adhesion strength. Environmental temperature and vibration loads also contribute to the deterioration of adhesion performance.Techniques such as interface roughening, jet treatment, and coating with silane coupling agents can significantly enhance the adhesion strength between organic adhesives and cement-based materials. These methods primarily alter the surface roughness, surface tension, and surface-active groups of the substrate. Additionally, reducing the viscosity of the organic adhesive over time, increasing the content of polar groups in the adhesive molecular structure, and improving the wetting of both the adhesive and substrate phases can further strengthen the interface adhesion.Summary and ProspectsBoth domestic and international scholars have conducted extensive research on the adhesive performance between organic adhesives and cement-based materials from a multi-scale perspective. Significant progress has been made in understanding adhesion mechanisms and enhancement techniques. However, research on the driving forces of adhesion at the micro-nano scale remains relatively underdeveloped, especially when compared to the adhesion mechanisms observed with metal materials. Furthermore, there are still several pressing issues regarding the environmental adaptability of adhesives and cement-based materials, which demand higher standards for their long-term reliability in practical applications. Although researchers have gained a deeper understanding of the mechanism of mechanical interlocking and clarified the corresponding intermolecular interactions, there is still a need to further analyze the individual contributions of mechanical interlocking and intermolecular interactions to overall adhesion. From a thermodynamically driven molecular adhesion mechanism perspective, optimizing the molecular structure of adhesives remains an area worth exploring. Existing studies typically link macroscopic adhesion strength directly with intermolecular interactions at the nano-scale, such as hydrogen bonds, while overlooking the important role of the mesoscopic mechanical properties of the adhesive interface. Therefore, it is essential to develop a method for characterizing the mesoscopic mechanical properties of the adhesive interface, taking into account the phase composition characteristics of cement-based materials. Furthermore, a more thorough understanding of the quantitative relationship between these properties, macroscopic adhesion strength, and nano-scale chemical composition is needed. The degradation mechanisms of interfacial adhesion of organic adhesives under coupled working conditions remain unclear. How factors such as vibration loads, temperature, and moisture coupling accelerate debonding of organic adhesives from cement-based materials requires further investigation. In addition, the time-dependent damage behavior of interface adhesion under service conditions should be explored in greater detail. This research is crucial for identifying key parameters that can enhance the durability of concrete structures, thereby providing technical support for ensuring the long service life of infrastructure.