Engineered cementitious composites (ECC) designed based on micromechanics theory have strain-hardening behavior and multiple cracking characteristics. The ultimate tensile strain of ECC is 500 times that of fiber-reinforced concrete. ECC have excellent crack control ability, and can significantly improve the mechanical properties and durability of concrete structures. However, the limited raw material origin and high production cost limit the broad application of ECC. Based on this, this paper reviews the relevant literature on ECC, discusses the feasibility of using local raw materials or even recycled waste to prepare ECC that meets the performance requirements, and discusses the influences of cementitious materials, aggregates and fiber materials on the mechanical properties of ECC and the relative mechanism. In addition, the research direction of ECC is discussed to provide a reference for future research.

Polycarboxylate superplasticizer (PCE) provides a new approach to improve the dispersity and workability of alkali-activated slag (AAS) cementitious materials. In this paper, the effects of PCE molecular structure and solubility on the dispersity, workability of AAS slurry, as well as the mechanism of PCE on AAS are reviewed. α-allyl-ω-hydroxy poly (ethylene glycol) ether (APEG)-based PCE (APEG PCE) synthesized by maleic anhydride has strong calcium ion binding ability and superior dispersity. The acid ether ratio of polyethylene glycol methallyl ether (HPEG)-based PCE (HPEG PCE) is 7, the side chain length is 7 epoxy ethane (EO), and the structural sequence with more AAA (A= acid monomer) and AAE (A= acid monomer, E= HPEG) is beneficial for improving the flowability and workability of AAS slurry. There is no correlation between the solubility and dispersity of PCE in AAS slurry. And the current research problems and future research directions of PCE in AAS cementitious materials to promote the green and low-carbon development of the construction industry are proposed.

The problems of strength and durability of concrete materials for infrastructure structures in plateau climate are becoming more and more prominent. It is of great significance to study the influence of plateau climate environment on concrete properties. The low pressure test chamber was used to simulate the air pressure environment of 95.0, 70.7, 57.6, 47.0 and 38.7 kPa, and the performance indicators such as compressive strength, pore structure and phase composition of cement paste under different curing air pressures were tested. The results show that at the same age, with the decrease of curing air pressure, the compressive strength of cement paste decreases and the porosity increases, the most probable pore diameter of the sample increases, the proportion of transition pore decreases, the proportion of capillary pore and macropore increases, and the Ca(OH)2 in the hydration products of cement paste decreases. In addition, the correlation between the compressive strength of cement paste and pore structure was analyzed, based on the pore structure parameters of cement paste, and the prediction model of compressive strength of cement paste was established.

To investigate the impact of different lithology stone powder as supplementary cementitious material on hydration and microstructure of cement paste, the fluidity ratio and activity index of stone powder were used to study the activity of three stone powder with different lithology, namely basalt, granite and limestone and their influence on adsorptivity of water reducer. Besides, the hydration heat, hydration products and microstructure of the cement pastes mixed with different lithology stone powder were tested by hydration calorimetry, X-ray diffraction, comprehensive thermal analysis and scanning electron microscope, respectively. The results show that the order of adsorption capacity of three stone powders to water reducer is granite powder>basalt powder>limestone powder. The 3 d activity index of limestone is the highest, the 28 d activity index of basalt is the highest, while the 3 and 28 d activity indexes of granite are the lowest. The addition of limestone can promote the early hydration of cement, and more hydration products are formed in the paste mixed with limestone in the early stage, accompanied by the formation of hemicarboaluminate. Basalt has pozzolanic reactivity, which promotes the formation of more hydration products and reduces the amount of Ca(OH)2 in the cement paste mixed with basalt in the middle and late stages. Granite has no hydration reaction activity, and the hydration reaction degree of the paste mixed with granite is the lowest.

A composite of multi-scale fiber hybrid system was prepared by mixing polyoxymethylene (POM) fiber and basalt fiber (BF). The basic mechanical properties, including flexural strength, compressive strength, bending toughness and direct tensile strength were investigated. Microscopic analysis was conducted using scanning electron microscopy and digital electron microscopy. The results of flexural and compressive strength tests show that the flexural strength and early compressive strength of the specimens mixed with two types of fibers are significantly better than those mixed with POM fiber alone, and there is a small decrease in the 28 d compressive strength. The three-point bending test shows that POM fiber alone can improve the toughness of cement-based materials and increases the equivalent flexural strength of the material. After mixing with BF, the equivalent flexural strength is further improved. Microscopic analysis shows that POM fiber and BF are tightly combined with the matrix, and the two fibers can act synergistically at the macro and micro scales, to jointly play a crack resistance effect, improving the toughness and strength of cement-based composite materials.

Taking flexural-compressive strength ratio, tensile strength and bonding strength as evaluation indexes, the optimal scheme of mixture ratio of vinyl acetate-ethylene copolymer latex powder (VAE latex powder) modified cement mortar was determined by orthogonal test. Based on the optimal scheme, the effect of VAE latex powder content on mechanical properties and frost resistance of mortar was studied. The results show that the optimum scheme of VAE latex powder modified cement mortar is that the cement-sand ratio is 0.375, the content of VAE latex powder is 10% (mass fraction), and the water-cement ratio is 0.38. VAE latex powder can significantly improve the flexural strength, tensile strength, bonding strength and toughness of mortar. With the increase of VAE latex powder content (8%~12%), the flexural strength, bonding strength and flexural-compressive strength ratio of mortar increase continuously, and the tensile strength decreases continuously, but it is still significantly greater than that of ordinary mortar. The water absorption, mass loss rate and strength loss rate of mortar decrease with the increase of VAE latex powder content. The compressive strength increases first and then decreases with the increase of VAE latex powder content. When the content of VAE latex powder is 12%, the compressive strength of mortar begins to be lower than that of ordinary mortar. Considering the strength and toughness of mortar, the optimum content of VAE latex powder is 8%~10%.

After long-term service in rich water environment, the mechanical properties of double liquid slurry are easily degraded by water corrosion. The variation law of the mechanical property attenuation of cement-sodium silicate double liquid slurry under the mixing ratio parameters and curing system was studied. Combined with various microscopic analysis methods, the mechanism of the mechanical property attenuation of cement-sodium silicate double liquid slurry under rich water environment was analyzed from the aspects of mineral composition and microstructure evolution. The results show that, curing in the low water content sand layer of 10%, 15% (mass fraction) are beneficial to the early strength development, but the strength gradually decreases in the later stage. The early strength of the test block in the 25% (mass fraction) high water content sand layer decreases by 23.5% compared to the 15% (mass fraction) water content sand layer, but the water corrosion effect is significantly weakened in the later stage, and the compressive strength at 220 d increases by 15% compared to 90 d. The standard curing conditions accelerate the deterioration of the mechanical properties of double liquid slurry, and the strength of the test block is 80.6% and 91.0% lower than that of water curing and sealed curing, respectively. The development of the mechanical properties is mainly controlled by hydration reaction and water corrosion. In the early stage, hydration reaction dominates, and in the later stage, water corrosion dominates. The development of the mechanical properties is essentially the effect of superposition of the two effects. The double liquid slurry material system is maintained in the rich water environment for a long time, and the hydration products on the outside of the matrix are constantly migrating and dissolving out. The outer layer of the test block forms a porous structure coating layer with a certain thickness, and becomes a migration channel for sodium ions, silicate ions and hydration products in the internal structure, which leads to continuous deterioration of the mechanical properties of the matrix.

In order to promote the diversified utilization of recycled brick concrete aggregate with different particle sizes, recycled brick concrete fine aggregate was used to completely replace quartz sand, and mixed with different content of polypropylene fiber to prepare recycled brick concrete engineering cementitious composites (ECC). The effects of failure characteristics, strength influence mechanism and microstructure on mechanical properties were studied. The results show that the failure mode of specimens without fiber is brittle failure, and recycled brick concrete ECC with fiber has obvious strain hardening characteristics during tensile stress. With the increase of fiber content, the flexural strength, ultimate tensile strength and ultimate tensile strain of recycled brick concrete ECC continue to increase, and the compressive strength increases first and then decreases, which shows good ductility and ductile failure characteristics. The porosity of recycled brick concrete ECC is 11.28%~13.68%. Fiber has good bonding property with recycled brick concrete ECC observed by SEM, the fiber failure modes are mainly pull-out and tensile failure, and the strain hardening tensile amplitude and tensile strength after cracking are lower than that of ordinary ECC concrete. The interface bonding property of old and new mortar is relatively weak, and micro-cracks are easy to occur and develop in the interface transition zone during failure.

Fine silica sand aggregate particle size in high-strength engineered cementitious composites (HS-ECC) is usually less than 0.30 mm, which is expensive and not conducive to shrinkage reduction of HS-ECC, while the mining and processing of fine silica sand has some negative impact on the environment. In this paper, geopolymer aggregate (GPA) in the range of particle size 0.30~＜4.75 mm was used as a replacement aggregate for fine silica sand to prepare HS-ECC. The particle size of GPA was divided into three groups, 0.30~<1.18 mm, 1.18~<2.36 mm and 2.36~<4.75 mm, to investigate the effect of each particle size interval on the compressive strength, tensile strain capacity and microstructure of HS-ECC. The results show that the ductility of HS-ECC is significantly improved when the particle size of GPA and silica sand is the same, but the effects on the compressive strength and tensile strength are smaller, the average crack width and average crack spacing are significantly reduced, and the width of GPA-cement matrix interface transition zone is larger than that of silica sand-cement matrix interface transition zone. When the particle sizes of GPA are different, the ductility, compressive strength and tensile strength of HS-ECC decrease with the increase of GPA particle size, the average crack width and average crack spacing increase with the increase of GPA particle size, and the width of GPA-cement matrix interface transition zone decreases with the increase of GPA particle size.

In this paper, the variation laws of alkalinity and mechanical properties of vegetated concrete with CO2 curing pressure were investigated, and the effect of CO2 curing pressure on the reaction rate and product generation was discussed by combining X-ray diffraction quantitative phase analysis (XRD-QPA), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The results show that increasing the CO2 curing pressure can improve the carbonation rate of tricalcium silicate (C3S), dicalcium silicate (C2S) and calcium hydroxide (CH). At the same time, the carbonized dense layer can be generated rapidly, which is conducive to delaying the generation and leaching of CH. The calcium carbonate (CaCO3) and hydrated calcium silicate (C-S-H) gel generated by the carbonation reaction increase the cement stone compactness and effectively improve the compressive strength of vegetated concrete. Compared with normal pressure CO2 curing, the 3 d compressive strength of vegetated concrete cured under CO2 curing pressure of 0.3 MPa for 1 h increases by 72.8%, the 28 d compressive strength increases by 4.8%, and the 28 d pH value decreases from 11.4 to 8.2. Moderately increasing the CO2 curing pressure is effective in reducing the alkalinity and increasing the strength of vegetated concrete.

Electric heat tracing curing is an effective method to avoid early freezing damage of concrete, improve cement hydration and concrete strength in winter construction in recent years. In order to improve the curing efficiency and effect, and optimize the electric heat tracing curing parameters under negative temperature environment, the air sandwich method and the built-in method were adopted to lay the electric heat tracing bands. The temperature change history and the cube compressive strength of C30 ordinary concrete during the heating curing process were obtained by taking the pre-curing parameters and constant temperature curing parameters as variables. The results show that the temperature distribution of specimens cured by air sandwich method is more uniform, and the compressive strength of concrete cubes increases by 7.6% compared with the built-in method. The optimal pre-curing time at 35 ℃ is 6 h, the pre-curing time increases, the cost increases, but the strength increases inconspicuously. When pre-curing at 10 ℃ for 6 h and constant temperature curing at 55 ℃ for 36 h, the strength is 81.5%fcu,k (cubic compressive strength standard value), which meets the requirements of plate mold removal strength. The purpose of this study is to provide reference for the design of concrete winter construction with electric heat tracing band, and then guide the construction method and engineering application.

The basic mechanical properties and stress-strain constitutive relationship of polypropylene foam concrete (PPFC) were studied by orthogonal test. The results show that the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens decrease with the increase of polypropylene fiber (PP) volume content (0.5%, 1.0% and 1.5%) in the range of test variables. With the increase of PP length (3, 6 and 9 mm), the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens increase first and then decrease. The cubic compressive strength of PPFC specimens increases first and then decreases with the increase of fly ash (FA) mass content (40%, 45% and 50%), and the axial compressive strength and splitting tensile strength decrease with the increase of FA content. Based on intuitive analysis method, the optimal ratio combination of orthogonal test is A1B2C2, that is, the volume content of PP is 0.5%, the length of PP is 6 mm, and the mass content of FA is 45%. The failure mode of PPFC compression specimens is compression-shear failure. The failure cracks are mainly inclined cracks, accompanied by vertical cracks, and the failure surface is generally inclined failure. The failure modes of splitting tensile specimens are splitting failure, and the failure cracks are vertical cracks along the direction of load application. Based on the single factor variable method, it can be concluded that with the increase of PP volume content (0%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5% and 0.6%), the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens increase first and then decrease. When the PP volume content is 0.2%, the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens reach the maximum value of 16.00, 14.56 and 1.96 MPa, respectively. The apparent density has a linear relationship with the cubic compressive strength, axial compressive strength and splitting tensile strength of PPFC specimens. The stress-strain constitutive model of PPFC was established by piecewise expression.

In order to study the development patterns and differences in compressive strength, splitting tensile strength, and elastic modulus of self-compacting concrete (SCC) and normal concrete (NC) specimens at different ages, eight groups of SCC and NC specimens were designed and poured at different ages (3, 7, 14, 28, 56, 120, 200, 400 d) with strength class C40, and the cube compressive strength, prism compressive strength, splitting tensile strength and elastic modulus of SCC and NC were tested at different ages. According to the test results, the development laws and differences of the two kinds of concrete mechanical parameters at different ages were compared and analysed. The results show that the compressive strength, splitting tensile strength and elastic modulus of the two types of concrete have similar development law at long ages, with rapid growth in early stage (before 28 d) and slow and stable growth in later stage (after 200 d). The compressive strength and splitting tensile strength of SCC at the same strength level are greater than NC, and the elastic modulus is smaller than NC. The compressive strength of SCC is about 25% higher than NC, the splitting tensile strength is about 9% higher than NC, and the elastic modulus is about 8% smaller than NC at long age (after 400 d). The measured elastic modulus of NC is in good agreement with the calculated elastic modulus of specification formula, and the measured elastic modulus of SCC is about 85.9% of calculated elastic modulus of specification formula. If the NC elastic modulus formula is used to predict SCC elastic modulus, the correction should be multiplied by 0.859.

In order to reasonably design and utilize recycled aggregate concrete, the larger porosity at the interface of primary aggregate, the pores and microcracks at the mortar and the aggregate interface effect were considered in the homogenization process of recycled aggregate concrete. A set of models that can predict the elastic modulus of recycled aggregate concrete with initial defects under aggregate interface effects was also developed by combining with the torsional deformation principle, Mori-Tanaka method, differential method and Christensen’s three-phase model. The calculation results show that with the increase of recycled aggregate replacement rate from 0% to 100% (mass fraction), the elastic modulus of recycled aggregate concrete decreases by 24.4%, and the decrease of elastic modulus of new mortar and primary aggregate also lead to the decrease the elastic modulus of recycled aggregate concrete by different degrees. The prediction model can better predict the elastic modulus of recycled aggregate concrete with initial defects under the interface effect, and realize parametric analysis.

In order to investigate the influence of loading rate on fracture performance of super absorbent polymer (SAP) concrete, the SAP concrete specimens with different water-cement ratios of internal curing were poured, and three-point bending test of notched beam with three loading rates was carried out. The fracture modes, crack mouth opening displacement and fracture toughness of specimens were measured and analyzed. The results reveal that SAP concrete and ordinary concrete all exhibit strain rate effect, and appropriate content of SAP and internal curing water can enhance the fracture energy of concrete. With the increase of water-cement ratio of internal curing, the peak strength ratio gradually decreases, and both the initiation toughness and unstable toughness show a decreasing trend. Conversely, as the loading rate increases, two toughness parameters exhibit an increasing trend. This study proposes a fitting model for the peak strength ratio and fracture toughness, considering the dual influence of the water-cement ratio of internal curing and the loading rate. The findings offer valuable insights for the practical application of SAP concrete in engineering project.

A two-dimensional particle flow program based on the Fish language of particle flow code (PFC) was compiled to construct a two-dimensional concrete fine-view model, and the calibrated PB model parameters were used to analyse the damage crack evolution and damage mechanism of concrete with different sizes. The results of the simulations show that the uniaxial compressive failure of concrete is caused by the expansion and evolution of cracks at the cement mortar interface and at the intersection of aggregate and cement mortar. Different sizes and random distribution of aggregates have certain influences on the peak stress and failure mode of concrete. Cracks in uniaxial compression specimens initiate at the interface between cement mortar and aggregate, and then propagate primarily along the interface between aggregate and cement mortar. As the load increases, cracks extend into the interior of the concrete. After reaching 90% of the peak compressive strength, the extension and increase speed of cracks enter a sudden increase stage. The interaction between the main crack and secondary cracks at the interface between cement mortar cause the concrete specimens to fail in a perforated manner. As the size of concrete and the quantity of aggregates increase, the number of cracks also increases. Moreover, with the decrease of concrete size, the ratio of sudden crack increase speed and crack quantity become larger.

In order to examine the effects of different reinforcement ratios on the creep properties of concrete, compression creep tests lasting 350 d were conducted on three types of specimens: plain concrete, 8 mm reinforced concrete, and 10 mm reinforced concrete. A modified Burgers model was developed by introducing a non-linear viscous element in series with the original Burgers model. The creep curves were obtained by fitting both the CEB-FIB (MC90) model and the modified Burgers model using the creep test datas of concrete with various reinforcement. The results indicate that reinforcement effectively mitigates concrete creep, and the mitigation effect becomes more pronounced with the increase of reinforcement ratios. Moreover, the modified Burgers model demonstrates superior accuracy compared to the CEB-FIP (MC90) model and provides better prediction for reinforced concrete creep.

A new silane-based nanocomposite coating is proposed. Based on molecular dynamics simulation results, it is confirmed that the introduction of dopamine can greatly reduce the transport ability of salt solution in the micro-nano channels of silane coating and the movement ability of water molecules and ions at the interface of the composite coating. For the graphene oxide-silane coating, water molecules can diffuse into the silane layer and form hydrogen bonds with the hydrophilic ends of the silane molecules. The extreme grafted graphene oxide-dopamine-silane composite coating can fully utilize the hydrophobic property of silane molecules and completely block the water molecules from entering the silane layer, reducing the water molecule transport depth by 87.5%.

Aluminosilicate phosphate geopolymers (ASP-GP) refer to the aluminosilicate inorganic polymers with three-dimensional network structure generated by the reaction of aluminosilicate and acidic solution (phosphoric acid or phosphate). They can be used as traditional building materials, heat insulation refractory and high temperature resistant materials, solid sealing materials, electronic packaging materials and so on, for their advantages of simple preparation process, high mechanical strength (the maximum compressive strength reaches to 146 MPa), good fire resistance and high temperature resistance, excellent solid sealing performance and dielectric properties. The low carbon-emission and energy-saving preparation fit the demands of friendly-environment, energy conservation and emission reduction. Thus, they are applied widely in the fields of civil engineering, mechanical engineering, aerospace, metallurgy, nuclear waste sealing and others. Based on the existing research achievements about ASP-GP at home and abroad, the development of reaction mechanism and mechanical properties are reviewed. The factors that affect the mechanical properties of ASP-GP are summarized, including aluminosilicate activity, activator, raw material ratio, curing system and so on. It is expected to guide properly the follow-up research of ASP-GP.

Geopolymers made from fly ash provide a promising alternative to ordinary Portland cement, with significant reductions in associated carbon emissions and the potential for developing high-value-added and green products from fly ash. In the past 10 years, nearly 6 000 articles have been published in the field of fly ash-based geopolymers, and it is necessary to conduct a quantitative analysis by scientometric methods to provide a reference for the research of fly ash-based geopolymers and the green integrated utilization of fly ash. This review used scientometric methods to analyze literatures from the Web of Science Core Collection and the China National Knowledge Infrastructure repository to gain insights into the research trends and hotspots of fly ash-based geopolymers. We conducted CiteSpace-based author and institution analyses and constructed a co-occurrence network to examine "fly ash" and "geopolymer" research. Our findings indicated that the number of publications on fly ash-based geopolymers increased yearly from 2013 to 2023, with sustained research interest. The core authors in Chinese and English literature publications accounted for more than 5% of respective publication frequencies. Institutions collaborated more closely in English literature than in Chinese literature. Keywords co-occurrence mapping, clustering, and emergence analyses suggested that recent research on fly ash-based geopolymers had focused on mechanical and adsorption properties, including the trapping of CO2 and the removal of nutrients, heavy metals, and organic matter from water bodies. The chemical composition of the reaction system is the main factor that distinguishes the mechanical and adsorption properties of fly ash-based geopolymers from other geopolymers. Using chemical composition to regulate the mechanical and adsorption properties synergistically is a major trend for future research.

Activated bentonite is a kind of inorganic adsorbent material, which is usually prepared by acid modification of bentonite. In this paper, natural bentonite was modified by sulfuric acid to acquire activated bentonite with high adsorption capacity. According to the results of single-factor experiment, the range of values of activation temperature A, activation time B, acid dosage C and liquid-solid ratio D were obtained. The removal rate of β-carotene in soybean oil was considered as the response value, and the Box-Behnken response surface method was used to optimize the adsorption performance of activated bentonite by analyzing the effects of four factors on the removal rate. The results show that the established response surface model is reliable enough to be used for the optimization of the adsorption capacity of activated bentonite. Besides, activation time and acid dosage have the greatest effect on the removal rate. However, liquid-solid ratio has no significant effect on the adsorption rate within the selected range. Finally, the predicted parameters of the optimal adsorption capacity are as follow: activation temperature 92.5 ℃, activation time 5.5 h, acid dosage 40% (mass fraction), liquid-solid ratio 4∶1, and the best adsorption rate of β-carotene can reach 97.71%.

Red mud is an industrial solid waste discharged during the extraction of aluminum oxide in the aluminum industry. Its high alkali content limits its utilization. Using calcium carbide slag to replace natural calcium-based materials for red mud dealkalization, the effect of four factors including dealkalization’s temperature, carbide slag’s dosage, liquid-solid ratio and reaction time on red mud dealkalization were analyzed, and the reaction mechanism of calcium carbide slag for red mud dealkalization was explored. The results show that as the temperature increases, the amount of calcium carbide slag increases, the reaction time increases and the dealkalization efficiency increases. Under the reaction condition of temperature 90 ℃, liquid-solid ratio 4∶1, reaction time 6 h and a 1∶1 mass ratio of red mud to calcium carbide slag, the dealkalization efficiency reaches 81%. After dealkalization, the Na2O content in the red mud is not more than 1% (mass fraction), which meets the standard for use as cement raw material. For red mud dealkalization reaction by calcium carbide slag conforms to the internal diffusion unreacted shrinking core model, and increasing the reaction temperature or the amount of reactants can improve the dealkalization rate.

Red mud from Bayer process contains more hematite and has lower activity, which limit its resource utilization to some extent. The Bayer red mud, blast furnace slag and fly ash were mixed at a mass ratio of 5∶3∶2, sodium silicate and sodium hydroxide were used as alkali activator, calcium stearate was used as foam stabilizer and hydrogen peroxide was used as foaming agent, then the foamed geopolymer was prepared. The influence of alkali activator modulus on the bulk density, strength and microstructure of red mud-based foamed geopolymer was investigated. The results show that, with the increase of modulus of alkali activator, the bulk density of foamed geopolymer increases first and then decreases, and the compressive strength decreases gradually. When the modulus of alkali activator is 1.4, the bulk density at 28 d of foamed geopolymer is the lowest (195.86 kg/m3), the compressive strength at 28 d is the highest (0.55 MPa), and the specific strength reaches the highest (2 821.12 N·m/kg). The results show that the foamed geopolymer has the best performance of low density and high strength when the modulus of alkali activator is 1.4.

To reduce the degree of efflorescence in the alkali activation metakaolin geopolymer, modified 5A zeolite with cation exchange property was used to reduce the content of free alkali metal cations in the pores of geopolymer. The effect of modified 5A zeolite on the microstructure and properties of geopolymer were investigated by compressive strength test, pore structure analysis (BET) and SEM-EDS. The cation content in the leachate was detected by inductively coupled plasma optical emission spectrometer (ICP-OES), and the efflorescence area of geopolymer was calculated by Image Pro Plus software in the fixed efflorescence mode to evaluate the effect of modified 5A zeolite on the efflorescence degree of the geopolymer and reveal the effect of modified 5A zeolite on the migration patterns of Na+ and Ca2+ in geopolymer. The results show that the modified 5A zeolite with 4% (mass fraction) content can optimize the pore structure, enhance the mechanical properties of geopolymer through internal curing and micro-aggregate effect, and exchange cation in pore solution to form (N,C)-A-S-H gel. Na+ leaching concentration reduces by 19.4% and the efflorescence area of geopolymer reduces by 57.3%.

Slurry widely existes in river dredging, cast-in-place piles, pipe-jacking construction and other projects, whose treatment is a long-term problem in the engineering field. In this study, solid waste geopolymer which was synthesized by coal gangue, blast furnace slag and fly ash was adopted to solidify the slurry with a moisture content of 60% (mass fraction). The mechanical properties, durability and microscopic mechanism of the solidified soil were investigated. The feasibility of the solidified soil as the backfill material was also estimated. The results show that strength of the solidified soil increases with the content of solid waste and alkaline activator. When 20% (mass fraction) solid waste is added, the cohesion c, the internal friction angle φ and strength of the solidified soil were 60 kPa, 19°, and 400 kPa after 7 d solidification. The solidified soil meets the properties requirements of the backfill soil. In addition, the geopolymer-solidified soil displayes better freeze-thaw resistance than the cement-solidified soil with the same content of cement. The gel products of geopolymer-solidified soil are mainly calcium silicate hydrate and gismondine, which can bind soil particles and fill the pore structure, then strengthenes the solidified soil performance.

In the process of coal gasification, the inorganic components of coal ash will be pyrolyzed, agglomerated or slagged in a short time, which seriously affects the safe and stable operation of gasifier. In order to explore the melting process of coal ash staying in gasifier and the transformation behavior of coal ash minerals, XRF, XRD, FTIR and other test methods and FactSage sofeware were used to analyze the chemical composition, mineral composition and melt structure of coal ash treated at different temperatures and time spans. The results show that under the conditions of 1 200, 1 300 and 1 400 ℃, when the constant temperature time gradually increases from 10 s to 30 min, the mineral type in coal ash has no obvious change, while the proportion of SiO2, CaO and SO3 in coal ash has a great change. The amorphous substance of mineral increases with the increase of temperature and the extension of constant temperature time. At the same time, the structure of ash melt is gradually depolymerized from complex frame structure to simple ring, island and other structures. The viscosity of coal ash also decreases gradually with the increase of temperature. After reaching the turning point of 1 240 ℃, temperature and constant temperature time have little influence on melting behavior of coal ash melt.

The low carbonization of cement has been a research hotspot at home and abroadand in recent years, using active mineral admixture to replace cement is an effective method to reduce CO2 emission. In order to verify the feasibility of activated coal gangue as cement mineral admixture, the effect of activated coal gangue on rheological properties, mechanical properties, hydration products and hydration degree of cement were studied, and the effects of water-binder ratio, age and activated gangue content on compressive strength and flexural strength of cement mortar specimens were revealed. XRD, SEM and TG/DTG were used to characterize the effect of activated coal gangue on hydration products and microstructure of cement. The results show that the rheological properties of activated coal gangue cement are more sensitive to the change of water-binder ratio. The incorporation of activated coal gangue into cement can effectively reduce the early hydration rate of cement. The activated coal gangue contains a lot of activated SiO2 and Al2O3, and has strong rehydration activity. The secondary hydration products calcium silicate hydrate and calcium aluminate hydrate gel can fill the pores of cement body and improve the strength of cement matrix. Compared with 30% (mass fraction) activated coal gangue sample, the 28 d flexural strength and compressive strength of 30% (mass fraction) activated coal gangue sample increases by 11.69% and 11.82%, respectively.

A sulfate dry-wet cycle test was conducted on ultra-high performance concrete (UHPC) mixed with recycled sand and ultra-fine fly ash, in order to investigate the sulfate resistance of recycled sand UHPC. The compressive strength, relative dynamic elastic modulus and mass change of specimens before and after sulfate solution corrosion were tested. The effect of compounding recycled sand and ultra-fine fly ash on sulfate ion transport was analyzed by ion titration to determine the distribution of sulfate ions at different corrosion depths. The results show that the corrosion resistance coefficient of UHPC increases first and then decreases with the increase of ultra-fine fly ash content after 90 sulfate dry-wet cycles. When the content of ultra-fine fly ash is 20% (mass fraction, the same below), the corrosion resistance coefficient and relative dynamic elastic modulus of whole corrosion process are the largest, and the sulfate ion content is low. At 50% of recycled sand, UHPC has the highest relative dynamic elastic modulus before 45 dry-wet cycles, and the lowest sulfate ion content at the same depth. The UHPC compounded with 20% ultra-fine fly ash and 50% recycled sand has the best sulfate resistance.

In order to improve coarse aggregate system and further improve the performance of recycled concrete, two series of recycled concrete were prepared with 64% and 36% replacement ratio of recycled coarse aggregate without changing natural coarse aggregate gradation. The effects of natural/recycled coarse aggregates with different particle sizes (［5,10) mm, ［10,20) mm, ［20,31.5］ mm) on workability, mechanical properties and durability of concrete in mixed coarse aggregate system were investigated. The results show that when the total replacement rate of recycled coarse aggregate is constant, with the increase of recycled coarse aggregate size, the slump/slump flow of recycled concrete increases continuously, the compressive strength, flexural strength and elastic modulus basically increase, and the electric flux and carbonation depth gradually decrease. Under the condition of high replacement ratio of recycled coarse aggregate, increasing the proportion of 20 mm to 31.5 mm recycled coarse aggregate is more conducive to improving the mechanical properties and durability of recycled concrete.

In order to evaluate the chemical stability of magnetite tailings in alkaline environment of cement, the influences of magnetite tailings on pH value of saturated Ca(OH)2 solution, expansion rate of mortar bars, and corrosion rate of reinforcement were studied. The results show that the magnetite tailings with particle sizes of 2.500 and 1.250 mm have more significant effect on the decrease of pH value of saturated Ca(OH)2 solution in early stage. With the extension of age, the effects of magnetite tailings with particle size below 1.250 mm on the decrease of pH value become more significant. When magnetite tailings with different particle sizes replace parts of natural sand, the expansion of mortar bars is different. The influences of magnetite tailings with particle sizes of 0.630 and 0.315 mm on the volume deformation of mortar bars are more significant. Moreover, the mortar bar expansion rate of magnetite tailings with particle size of 0.630 mm is the largest after a longer age. In a mixed solution of Ca(OH)2 and NaCl, the magnetite tailings react more readily than reinforcement, which can slow down the corrosion of reinforcement.

In view of the problems that CO2 is easy to corrode Portland cement stone, damage the structural integrity of cement stone and induce interlayer sealing failure, this paper uses slag to modify calcium aluminate cement, and studies the change law of compressive strength of calcium aluminate cement-slag system at 60, 80, 100, 120 ℃ and pure CO2 conditions. The effect of CO2 corrosion on hydration products and microstructure of calcium aluminate cement-slag system were investigated by X-ray diffractometer, thermogravimetric analyzer and scanning electron microscopy. The results show that compared with pure calcium aluminate cement stone, the slag transforms the hydration product of calcium aluminate cement stone into C2ASH8, which greatly improves the early compressive strength of cement stone. When the mass ratio of calcium aluminate cement to slag is 5∶5, the compressive strength of calcium aluminate cement increases by 215.4% after curing at 60 ℃ for 14 d. After CO2 corrosion, the hydration products of calcium aluminate cement-slag system change from C2ASH8 to C2AS, and CaCO3 is formed, which increases the density of corrosion layer. The compressive strength of cement stone increases with the increase of corrosion time at same temperature.

The silicate-cement clinker was prepared by sulfuric acid leaching ferronickel slag, and the effects of various temperatures and limestone saturation coefficients on the structure and microscopic morphology of the clinker were investigated. The burnability of the cement clinker was judged by the determination of f-CaO content in the clinker, and the phase structure, elemental distribution and microscopic morphology of the clinker were analyzed by XRD, EDS and SEM. The results show that the higher the calcination temperature is, the lower the f-CaO concentration is, and the better the burnability is. When the sintering temperature is 1 350 ℃, the Portland cement clinker appears pulverization and does not form C3S phase after sintering. However, when the calcination temperature is 1 400 ℃, the crystal phase dominated by C2S and C3S appears in the Portland cement clinker, and pulverization not occurs. When the sintering temperature reaches 1 450 ℃, the cement phase grain structure is fully developed. After the clinker is mixed with gypsum to make cement, the compressive strength and flexural strength of the hydration products of cement mortar after 28 d curing are 37.34 and 7.01 MPa, respectively.

In order to explore the effect of steel slag coarse aggregate on sulfate resistance of concrete, erosion tests of concrete in different concentrations (5%, 10%, 15%,mass fraction) of sodium sulfate (Na2SO4) solution were carried out under different substitution rates of steel slag coarse aggregate (0%, 30%, 60%, 90%). Based on the entropy weight method, the comprehensive durability evaluation index D of steel slag coarse aggregate concrete was established with three typical durability indexes of concrete mass, compressive strength and relative dynamic elastic modulus as parameters. The influence of substitution rate of steel slag coarse aggregate and the concentration of Na2SO4 solution on durability of concrete were reflected by D value, and the service life of steel slag coarse aggregate concrete under different erosion conditions was predicted by GM(1,1) model of grey theory. The results show that in the whole erosion process, the D value of steel slag coarse aggregate concrete with steel slag substitution rate less than 60% is higher than that of ordinary concrete, indicating that concrete prepared with steel slag instead of natural aggregate can improve the sulfate resistance of concrete. The prediction results of GM(1,1) model are basically consistent with the experimental results, and the service life of concrete with 60% steel slag coarse aggregate substitution rate is better than that of other groups.

To explore the macroscopic mechanical properties and failure evolution mechanism of desulfurization gypsum fly ash flowable lightweight soil, a numerical model of desulfurization gypsum fly ash flowable lightweight soil was constructed by PFC2D, and the microscopic parameters of the model were derived through indoor uniaxial compression tests.By extracting the types, quantities, ages and particle displacement trends of discrete crack networks in numerical models, the morphological characteristics and propagation evolution of cracks in desulfurization gypsum fly ash flowable lightweight soil were explored.And the destructive properties of desulfurization gypsum fly ash flowable lightweight soil materials were evaluated through energy indicators.The results indicate that the constructed discrete element numerical model can effectively simulate the stress-strain curves and failure characteristics of materials. Under uniaxial compression conditions, desulfurization gypsum fly ash flowable lightweight soil undergoes microcracks dominated by shear failure at the initial stage of loading. When the loading exceeds the peak stress, through cracks dominated by tensile failure occur. The solidified soil particles of desulfurization gypsum and fluidized fly ash gradually show a horizontal displacement trend from vertical displacement. The evolution of dissipated energy in desulfurization gypsum fly ash flowable lightweight soil is relatively gentle, and its corresponding macroscopic manifestation is that there is a certain degree of delayed cracking in the failure of fluidized fly ash after exceeding the peak stress point.

In order to expand the application range of flexible graphite gasket in harsh working conditions, polytetrafluoroethylene (PTFE)was selected as impregnating agent, and flexible graphite gasket was modified by liquid phase impregnation method. The optimum impregnating agent ratio and impregnation process were determined by single factor condition experiment. The results show that the best impregnation effect can be obtained under the conditions of impregnation vacuum degree of -0.095 MPa, vacuum pressure of 0.65 MPa, impregnation times of two times, impregnation time of 30 min, impregnation concentration of 60% (mass fraction) and impregnation temperature of 35 ℃, and the leakage rate of impregnated flexible graphite gasket is 2.03×10-4 cm3/s, the weight gain rate is 4.39%, the compression rate is 32.17%, and the rebound rate is 22.34%. SEM and EDS test results show that polytetrafluoethylene emulsion penetrates into the gaps between graphite lamellae through impregnation, effectively filling the gaps between lamellae and particles in flexible graphite gasket, and improving the leakage of gasket. Carbon element is mainly distributed uniformly in the form of graphite, oxygen element is distributed uniformly in graphite as impurities, and fluorine element is concentrated.

The recycling of solid waste needs to not only expand to a wider dimension but also extend to a higher value-added depth. The scientific preparation and extensive application of foam ceramics have attracted great attention from scholars at home and abroad, as they not only help to dispose of a large amount of solid waste but also fully utilize the potential value of solid waste. In this review, the component effect and foaming principle of foam ceramics were firstly introduced in detail, followed by analysis on thermal transformation process and micro-mechanism. Subsequently, the effects of different factors were summarized. Finally, the challenges of foam ceramics development and the possible direction of further research were proposed. The purpose of this study is to provide reference for the efficient utilization and in-depth study of foam ceramics.

Al2O3 ceramics is an important microwave dielectric material with excellent dielectric properties and is widely used in microwave circuits. However, its high sintering temperature leads to high energy consumption. Lowering the sintering temperature at a low cost is of great significance for the further development of Al2O3 ceramics. Low temperature sintering of Al2O3 ceramics was achieved by doping MnO2-CuO-TiO2, and its sintering behavior and microwave dielectric properties were studied. The results show that doping 0.7% (mass fraction) MnO2, 0.5% (mass fraction) CuO and 0.8% (mass fraction) TiO2 can greatly reduce the sintering temperature of Al2O3 ceramics, and the obtained ceramics have good microwave dielectric properties. When the sintering temperature is 1 250 ℃, the density of Al2O3 ceramics can reach 3.92 g/cm3, the dielectric constant εr is 10.02, and the quality factor Q×f resonant frequency value is 51 239 GHz. The lattice distorting activation of Al2O3 caused by the solid solution of Ti4+, Mn4+, Cu2+ and the formation of the low eutectic may be the reasons for promoting the low-temperature sintering of Al2O3 ceramics.

Mullite-cordierite sagger is particularly important for the preparation of high-performance lithium battery cathode materials. In this paper, mullite (1.18~0.6 mm) and cordierite (2~1 mm) were used as aggregates, and mullite (0.074 mm), calcined alumina (0.044 mm), Foshan yellow mud (0.044 mm) and coal gangue (0.044 mm) were used as matrix. Mullite-cordierite sagger for lithium battery cathode material LiNixCoyMnzO2 (LNCM) was prepared by sintering at 1 380 ℃ for 3 h. The corrosion behavior of cathode material on sagger during sintering process was investigated by burying corrosion method. The results show that the mechanical properties and thermal shock resistance of sagger sintered at 1 380 ℃ for 3 h are good. The flexural strength at room temperature is 10.02 MPa, and the residual strength retention rate is 51.52%~53.26% after three thermal shock cycles. The corrosion resistance of mullite-cordierite sagger can be effectively improved by appropriately increasing the content of coarse particles (1.18~0.6 mm) of mullite. After 25 times of erosion, the maximum reaction layer thickness on sagger surface is 447 μm, and the minimum reaction layer thickness is 211 μm.

In order to promote the application of small-size steel slag in thin-layer asphalt mixtures, the aggregate mix ratio of SMA-5 asphalt mixtures was designed using the V-S (volumetric mix) method. Adding 1.18~2.36 mm and 2.36~4.75 mm steel slag aggregates (equal volume replacement of limestone aggregates) into SMA-5 asphalt mixtures, and its effect on the percent voids in coarse mineral aggregate VCAmix in asphalt mixtures and the optimum asphalt content of asphalt mixtures was analyzed. The high temperature stability, low temperature cracking resistance and moisture stability of steel slag asphalt mixtures were evaluated using rutting test, beam bending test, freeze-thaw splitting test and water-immersion Marshall test. The results show that the inclusion of steel slag reduces the effect of skeleton structure between aggregates and increases the amount of asphalt used in asphalt mixture. The high temperature stability of asphalt mixture is reduced by adding steel slag. However, with the increase of steel slag content, the low temperature performance of asphalt mixture decreases, and the moisture stability and high temperature stability increase. It is recommended that 75% of steel slag of 2.36~4.75 mm in SMA-5 steel slag asphalt mixture is the optimal ratio.