As China experiences a deceleration in infrastructure construction and the gradual aging of existing buildings, the impending demand for the repair and reinforcement of engineered structures is poised to surge, accompanied by a growing necessity for special repair materials. The cost-effectiveness and performance optimization of magnesium phosphate cement (MPC), a rapid repair and reinforcement material, are key considerations for its practical application. The incorporation of industrial solid waste is considered an effective means to regulate the cost and performance of MPC. Recent studies have demonstrated the potential for industrial solid waste, such as fly ash, to be utilized in the fabrication of MPC, with the objective of enhancing its performance and reducing its cost. Numerous reviews have been published on the subject of MPC development. However, the majority of these reviews have concentrated on the fundamental mechanisms and application domains of MPC, with comparatively fewer studies addressing the mechanisms, reactivity, physical stacking effects, and chemical bonding principles of solid wastes within MPC system. This review is innovative in that it investigates the research progress of solid waste-modified MPC from two perspectives: performance and mechanism, based on the principle of chemical bonding. It discusses the working, mechanical properties and mechanism of solid waste-modified MPC, and comprehensively evaluates the current situation. Finally, it summarizes existing research and puts forward future research directions with a view to improving the performance of MPC, reducing the cost, and promoting its wide application in practical engineering.

Phosphogypsum-based excess-sulphate slag cement (PESSC), as a non-calcined cementitious material, offers benefits such as minimal heat release, great volumetric stability, and significant resistance to sulphate erosion. Nonetheless, its application is constrained by prolonged setting periods, inadequate carbonation resistance, and poor stability of long-term performance due to the persistent release of impurity derived from phosphogypsum, as well as the sulphate-rich and low alkalinity hydration environment. Recently, effective strategies are needed to regulate the hydration environment of PESSC, enhance the formation of highly stable hydrates, optimise the microstructure of matrix, and provide systematic design theories and performance regulation methodologies. This study focuses on the impact of impurity release on gypsum crystallisation and the hydration hardening of PESSC, as well as the mechanisms and performance advancements of alkali and sulphate-activated slag, bases on the fundamental physical and chemical features of the raw components. A comprehensive discussion is presented on the feasibility of accelerating condensation through phosphogypsum pretreatment, promoting sustainable reactions by adding appropriate alkali-activators to regulate the hydration environment, enhancing the long-term performance and durability of PESSC by synergizing multiple components, and generating stable hydrates by incorporating modifiers. This work seeks to offer theoretical and technological support for the development of new theories and methodologies for PESSC design and large-scale applications.

With the advancement of the “Dual Carbon” strategy, circulating fluidized bed (CFB) ash has become an important research direction for solid waste resource utilization due to its large amount of production, complex component and urgent treatment needs. This paper reviews the composition and characteristics of CFB ash, focusing on its expansion characteristics and loose structure, and summarizes the low-carbon application status and high value-added utilization research of CFB ash in the fields of cement-based materials, geopolymers, road base materials, aerogel preparation and zeolite preparation. The research shows that CFB ash has significant advantages in improving the mechanical properties of cement-based materials, optimizing microstructure and improving durability. Although there are questions such as expansion caused by high sulfur content and high calcium content, the potential of CFB ash as geopolymer and high value-added functional material is gradually explored through physical or chemical modification technology, and the application value can be significantly improved. In the future, researchers should strengthen the research and development of modification technology and the exploration of resource recycling path, promote the application of CFB ash in low-carbon circular economy, and provide theoretical basis and technical support for the sustainable utilization of industrial solid waste.

Biochar is an ecological carbon-negative material. Adding an appropriate amount of biochar to concrete can improve the mechanical properties and durability of concrete. However, there are still controversies over whether biochar can be used as a pozzolanic material for concrete and whether biochar has pozzolanic activity. In response to this, this paper conducts a literature review and comprehensive analysis on aspects such as the pozzolanic activity of biochar, the impact of biochar on the mechanical properties of concrete, and measures to improve the pozzolanic activity of biochar. The results show that biochar has pozzolanic activity, and its pozzolanic activity is not affected by the loss on ignition, while the reactive SiO2 content is the decisive factor for the pozzolanic activity of biochar. The high pozzolanic activity of biochar can promote the pozzolanic reaction and hydration reaction, which is beneficial to the compressive strength of concrete. Controlling the pyrolysis temperature and fine grinding treatment can help to improve the pozzolanic activity of biochar, but the impact of activation treatment on the pozzolanic activity of biochar still requires in-depth research.

The recycling of discarded masks has become a key research direction to deal with environmental pollution and waste of resources. As the main component of masks, polypropylene fiber has attracted more and more attention in the application of cement-based building materials due to its renewability. This paper reviews the application status of discarded masks in cement-based building materials, and summarizes the recycling technologies of discarded masks, including cutting, hot extrusion, shredder and wall breaker. Studies have shown that the incorporation of discarded mask fibers has a significant impact on the mechanical properties, fluidity and durability of materials such as concrete, mortar and road base. In addition, the influences of different application scenarios on the performance of materials are also different, which provides a basis for further exploring the resource utilization of discarded masks and provides a theoretical basis and practical guidance for the sustainable development of cement-based building materials.

With the rapid development of wind power industry, the recycling and treatment of retired wind turbine blades (RWTB) has attracted widespread attention. Wind turbine blades are mainly composed of glass fiber reinforced composites, and the limitations of recycling technology have become an important obstacle to the sustainable development of wind energy industry. The traditional chemical, pyrolysis and landfill methods not only cause waste of resources, but also lead to serious environmental pollution. In view of this, this paper reviews the current development status of installed wind power capacity and RWTB at both domestic and international levels, analyses the potential application of recycled materials prepared by mechanical recycling technologies as supplementary cementitious materials, concrete fillers or fiber reinforced materials in construction sector, and provides an in-depth analysis of the critical issues encountered in current research. In addition, this paper highlights the importance and potential value of resource utilization of RWTB, aiming to provide a scientific basis and decision-making reference for relevant policy formulation, technological advancement, as well as the recycling and resource application of RWTB.

As a new type of bulk industrial solid waste, the harmless disposal and large-scale resource utilization of silicon-manganese slag urgently need to be addressed. In this study, silicon-manganese slag was used as precursor and water glass as alkaline activator to prepare alkali-activated silicon-manganese cementitious material. The effects of water glass content, water glass modulus, and slag modification on the macroscopic properties and microscopic properties of alkali-activated silicon-manganese slag cementitious material were investigated. The results show that, within a curing period of 90 d, the alkali activation of silicon-manganese slag cementitious material continues, with the polymerization degree and yield of gel products gradually increasing. The porosity of hardened paste decreases, and the mechanical properties are enhanced. With the devrease of water glass modulus, the early-stage alkali activation reaction is strengthened, the heat release increases, the setting time shortens, and the mechanical performance of hardened paste improves. However, excessively low water glass modulus hinders the later-stage alkali activation. The best mechanical performance of alkali-activated silicon-manganese slag cementitious material is achieved when the water glass modulus is 1.2 and the water glass content is 12% (mass fraction), with strengths of 86.0 and 100.1 MPa at 28 and 90 d, respectively. The incorporation of slag significantly improves the poor early-stage mechanical performance of alkali-activated silicon-manganese slag cementitious material, but excessive addition leads to too rapid alkali activation, causing shrinkage cracks in hardened paste. The optimal slag content is 10%.

In this paper, the effects of groundnut shell ash (GSA), plant ash (PA), Suzhou biomass ash (SZA) and corn stover ash (CSA) on the fluidity, setting time, hydration properties, shrinkage properties and compressive strength of alkali-activated slag (AAS) cementitious materials were investigated when 10% (mass fraction) blast furnace slag powder (GGBS) was replaced by four different ashes. The results show that the incorporation of biomass ash can increase the pH value of alkali-activated solution and promote the hydration process of AAS to varying degrees. After the incorporation of GSA, PA, SZA and CSA, the cumulative heat release of AAS specimens increases by 31.2%, 27.1%, 16.9% and 19.5%, respectively, compared with the blank group. The laboratory ash (GSA and PA) cumulative heat release is higher than the power plant ash (SZA and CSA). The incorporation of laboratory ash (GSA and PA) increases the autogenous shrinkage of paste specimens, which increases by 61.5% and 44.9%， respectively， compared with the blank group. The incorporation of SZA and CSA alleviates the autogenous shrinkage to a certain extent, which decreases by 15.0% and 15.7%, respectively, compared with the blank group. The compressive strength of AAS specimens is improved by adding biomass ash. The 28 d compressive strength of AAS specimens after adding GSA, PA, SZA and CSA is 20.0%, 18.3%, 15.9% and 16.9% higher than that of the blank group, respectively.

Granulated blast furnace slag with volcanic ash charateristics can be used to produce slag-based cementitious materials after grinding. Compared with traditional cement, the hydration activity of slag-based cementitious materials is low. In order to enhance the hydration activity of grind granulated blast furnace slag （GGBS） in slag-based cementitious materials， this paper innovatively proposed to use polymerized aluminum sulfate solution to infiltrate and treat GGBS, accelerated the depolymerization of GGBS glass network structure, and improved the performance of slag-based cementitious materials. The ion dissolution behavior, surface elemental composition and microstructure morphology of GGBS-infiltrate were compared to GGBS-mix. The mechanism of infiltrated process to enhance the performance of slag-based cementitious materials was also analyzed by compressive strength, exothermic hydration, phase changes, and microscopic morphology tests. The results show that the amount of silicon ions dissolved in infiltrated filtrate is significantly higher than the amount of silicon ions dissolved in the mixed filtrate, the molar ratio of n(Ca)∶((n(Si)+n(Al)) on the surface of the GGBS-infiltrate is reduced to 0.266, and the structure of GGBS-infiltrate is corroded. The setting time of the slag-based cementitious material prepared using infiltrated GGBS is reduced to 147 min, and the compressive strength of samples reaches to 3.75 MPa at 1 d. The GGBS-infiltrated process can promote the generation of ettringite and C-A-S-H gel, accelerate the hydration process of slag-based cementitious materials, and improve the performance of slag-based cementitious materials.

The low hydration reactivity of steel slag （SS） significantly limits its application as supplementary cementitious materials (SCMs). In this study, SS was converted into carbonated steel slag (CS) with high activity by carbonization, and the effect of CS on the hydration process and mechanical properties of cement composites was systematically studied. The results show that CS markedly accelertes the cement hydration reaction, enhances the setting rate, and substantially enhances the compressive strength of cement composites. When the CS content is 20% (mass fraction), the compressive strength of the cement composite increases by approximately 0.9% and 14.4% compared with the reference sample at 1 and 28 d, respectively. The enhancement in hydration process and mechanical properties of cement composites with CS is primarily attributed to the highly reactive silica gels and calcium carbonate, which accelerate the formation of hydration products. In addition, the ultrafine particles in CS play a filling effect and enhance the compactness of the microstructure, thus effectively improving the compressive strength.

The carbonation of steel slag for the production of building materials is an effective solution to the storage issues associated with steel slag. This study addressed the challenges of existing steel slag carbonation processes, such as prolonged carbonation time and low calcium conversion rate, by developing a novel suspended state steel slag powder carbonation device. The optimal process parameters for suspended state carbon fixation under low water-solid ratio were investigated. The results indicate that the optimal carbonation reaction parameters are: air velocity of 11 m/s, CO2 concentration of 90% (volume fraction), and water-solid ratio of 0.10. Under these conditions, after 240 s of carbonation of steel slag powder, the CO2 uptake reaches 4.85%, and the Ca conversion rate is 17.32%. The carbonation activity of steel slag is relatively high, with the primary carbonation product being calcite (CaCO3). An increase in carbonation time leads to a reduction in the heat release during the hydration of the carbonated steel slag. The inhibitory effect of steel slag on the early hydration of cement is significant, but carbonation can notably improve this inhibitory effect. The suspended state carbonation process offers advantages of shorter carbonation time and higher calcium conversion rate. This technology aids steelmaking enterprises in achieving resource utilization of steel slag and reducing carbon emissions, providing a reference for the optimization of steel slag carbonation processes.

In this paper, a low carbon and low cost solid waste based grouting material was developed using steel slag, slag and desulfurization gypsum. The workability, mechanical properties and impermeability of the solid waste based grouting materials were systematically studied. The hardening mechanism was analyzed by XRD, SEM and MIP, and compared with cement based grouting materials. The results show that compared with cement, the solid waste based cementitious materials can improve the workability and stone rate of the grouting material, reduce the bleeding rate significantly in water-rich environment, but the setting time is greatly extended. The early strength of solid waste based grouting materials is low, and the late strength is greatly increased, which exceeds the requirement of 2.5 MPa for 28 d strength of grouting materials used for water plugging. More hydration products ettringite (AFt) and hydrated calcium silicate (C-S-H) gels are generated from the hydration of solid waste based grouting materials, which interpenetrate and overlap with each other, fill the internal pores, make the microstructure more dense, increase the content of gel pores, and decrease the porosity, thus greatly improving the impermeability and mechanical properties

Ground granulated blast furnace slag (GGBFS) and sulfate were used to reinforce and modify circulating fluidized bed fly ash (CFBFA)-based cementitious materials. The cement content in cementitious material was 30% (mass fraction, the same below), the total content of CFBFA and GGBFS was 70%, and the addition of desulfurization gypsum and sodium sulfate was 0%~4% and 0%~1.5%, respectively. The effects of the mass ratio of CFBFA and GGBFS and the content of desulfurization gypsum and sodium sulfate on the setting time and mortar compressive strength of the composite cementitious materials were studied. Then the composite reinforcement mechanism of GGBFS and sulfate on CFBFA-based cementitious materials was investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that CFBFA-based cementitious materials have long setting time and low compressive strength. The composite of CFBFA and GGBFS can significantly improve the 3 and 7 d compressive strength of cementitious materials, but the reinforcement strength of 28 d is limited. The introduction of sulfate in CFBFA-GGBFS system can significantly improve the compressive strength. Desulfurization gypsum whose suitable content is 2% is more effective in improving the strength of low content CFBFA system, and sodium sulfate whose suitable content is 0.5% have a better effect on the strength reinforcement of high content CFBFA system, but sodium sulfate has a negative effect on the 28 d compressive strength. The composite of CFBFA and GGBFS increases the amount of gel generation in the early hydration stage of cementitious materials. Desulfurization gypsum can accelerate the formation rate of ettringite (AFt) and stabilize its growth. Sodium sulfate reacts with Ca(OH)2 to form strong alkaline NaOH and highly active CaSO4, which further increases the formation rate of gel and AFt.

In this paper, through the life cycle assessment method, combined with the experimental mix proportion, the actual measured consumption and emission data of the cement plant and the data of the China life cycle database, the incinerated sewage sludge ash (ISSA) is used to replace part of the raw material for clinker production and as a mixture for cement production. The assessment of integrated environmental load indicator and the coupling evaluation of environmental impact and compressive strength were carried out. The results show that as the dosage of ISSA replacing raw materials increases, the global warming potential (GWP) of clinker gradually decreases, and the consumption of abiotic depletion potential gradually increases. At the ISSA dosage of 3.6% (mass fraction, the same below), the integrated environmental load indicator of clinker decreases by 1.05% compared with cement plant clinker; at the ISSA dosage of 3.0%, clinker has the lowest integrated environmental load indicator of unit compressive strength. As the dosage of ISSA as a mixed material increases, the integrated environmental load indicator of cement significantly reduces, and the reduction of GWP is the highest. When the ISSA dosage reaches 30.0%, the integrated environmental load indicator of cement declines by 29.41%. When the ISSA dosage is within 20.0%, cement shows the relatively optimal integrated environmental load indicator of unit compressive strength.

Aiming at the problem of insufficient toughness of one-part geopolymer, three kinds of fibers, polyvinyl alcohol fiber, imitation steel fiber and calcium carbonate whisker, were selected to design the composition of single-doped and mixed-doped geopolymers. The effects of three kinds of fibers on the fluidity and mechanical properties of geopolymers were analyzed. Combined with scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy, the mechanisms and patterns of fibers influence on the properties of geopolymers were investigated. The results show that all kinds of fibers reduce the fluidity of geopolymer to varying degrees. When the volume content of polyvinyl alcohol fiber, imitation steel fiber and calcium carbonate whisker is 0.6%, 1.5% and 1.5%, the fluidity of three kinds of single fiber geopolymer is 54.0%, 33.4% and 19.8% lower than that of the reference group, respectively. The incorporation of polyvinyl alcohol fiber and imitation steel fiber has a negative effect on the compressive strength of geopolymer, while calcium carbonate whisker shows a reinforcing effect. When the volume content of polyvinyl alcohol fiber, imitation steel fiber and calcium carbonate whisker is 0.4%, 1.2% and 1.2%, the flexural strength of hybrid fiber geopolymer increases by 89.1%. Microscopic analysis indicates that polyvinyl alcohol fiber enhances the toughness of geopolymers via bridging effects, imitation steel fiber contributes to toughening primarily through slip mechanisms, and calcium carbonate whisker improves flexural strength by filling voids. Optimized fiber proportion results in hybrid fiber geopolymers with superior fluidity and flexural strength.

Compressive strength and uniaxial tensile tests were conducted on polyethylene fiber reinforced engineered cementitious composites (PE-ECC) with varying steel slag powder content (0%, 20%, 40% and 60%, mass fraction) to examine the influence of steel slag powder on the compressive strength of PE-ECC and the change rule of tensile stress-strain. Microstructural analysis of the interface between PE fiber and steel slag powder-incorporated engineered cementitious composites (ECC) matrix was performed using scanning electron microscopy (SEM). The results show that the incorporation of steel slag powder reduces the compressive strength, cracking stress and peak stress under tension of PE-ECC, while improving the tensile toughness. Additionally, the presence of steel slag powder enhances the bonding state between fiber and matrix. The tensile stress-strain relationship of PE-ECC can be effectively described using bilinear constitutive model. The findings of this study provide valuable insights for diversified preparation and engineering applications of ECC.

Magnesium slag is a solid waste produced in the process of magnesium smelting, which has low hydration activity and high carbonation activity. Through the optimization of mix proportion, magnesium slag slurry with high fluidity and high stability was successfully prepared in this paper, and a carbonized preplaced lightweight aggregate concrete was prepared by using magnesium slag slurry as grouting material. And the effect of carbonation curing on the mechanical properties and microstructure of lightweight aggregate concrete was systematically studied. The results show that the fluidity of magnesium slag slurry reaches 245 mm, which meets the technical requirements of precast concrete grouting. After drying pretreatment and 24 h carbonation curing, the compressive strength of sample reaches 24.5 MPa, and the carbon sequestration reaches 100 kg/m3. The CaCO3 crystal formed by the carbonation reaction is mainly vaterite, and a small amount is aragonite. The filling of matrix by carbonation product is the key mechanism for the strength improvement of carbonized preplaced lightweight aggregate concrete.

To enhance the resource utilization efficiency of electrolytic manganese residue (EMR), this study used EMR-based cementitious materials in conjunction with EMR tailings sand and EMR-based ceramsite to prepare EMR-based green lightweight aggregate concrete (EGLAC) and permeable concrete (EGPC). The study primarily investigated their strength, pore characteristics, and environmental impact effects. The results indicate that the multi-level collaborative resource utilization of EMR can successfully produce high-performance and low-carbon-emission EMR-based green concrete. Both EGPC and EGLAC show significant increases in compressive strength and dynamic elastic modulus with prolonged curing age. The 28 d compressive strengths of EGPC and EGLAC are 22.5 and 48.5 MPa, and their permeability coefficients are 1.8 and 5.2×10-9 mm/s, respectively. The permeability coefficient of EGLAC and EGPC decreases with curing age, and shows an exponential decrease in relation to strength. This is primarily attributed to the optimization of pore structure through the hydration of EMR-based cementitious materials and the improvement of the interface bonding between aggregates and the matrix. Compared with conventional C30 and C50 concrete, EGLAC’s carbon emissions are reduced by 48.1% and 60.2%, respectively. After the collaborative optimization of carbon source and energy processes, EGLAC’s carbon emissions are reduced by 92.9% and 94.6%, respectively. Compared with conventional permeable concrete, before collaborative optimization, EGPC’s carbon emissions can be reduced by 55.2%, and after collaborative optimization, EGPC’s carbon emissions can be reduced by 93.3%. This study provides significant guidance for the efficient and graded resource utilization of EMR in building materials.

This study systematically investigated the complex factors influencing the mechanical properties of alkali-activated slag-fly ash (AASF) pastes and concrete through an integrated approach combining experimental investigations and machine learning techniques. The critical parameters governing compressive strength and elastic modulus were analyzed using random forest regression (RFR) and gradient boosting regression (GBR) models. The results show that the machine learning predictions demonstrate high accuracy, with deviations of compressive strength and elastic modulus predictions maintained within ±15% of the experimental values. Quantitative predictive formulas are established to enhance the efficiency and effectiveness of mechanical performance optimization. A dual-objective analysis framework reveals synergistic relationships between compressive strength and elastic modulus in both paste and concrete systems, providing effective pathways for mix proportion optimization. The results demonstrate a threshold effect in fly ash content: positive correlation with compressive strength at content below 25% (mass fraction), transitioning to negative correlation when ranging between 50% and 75% (mass fraction). This research presents an efficient intelligent solution for performance optimization of AASF materials while establishing a practical foundation for low-carbon material development in civil engineering applications.

In order to explore the effects of lithium slag substitution rate, basalt fiber length， basalt fiber dosage and their interaction on the mechanical properties of lithium slag-coal gangue solid waste concrete and realize the optimization of multiple indicators, a single-factor test was conducted to determine the optimal baseline level of each factor in the response surface methodology (RSM).Quadratic polynomial regression models were established for the 28 d uniaxial compressive strength and splitting tensile strength of concrete to determine the optimal material parameters. The results show that the optimal substitution rate of lithium slag, the length and dosage of basalt fiber in the single-factor test are 25% (mass fraction), 18 mm, and 0.16% (volume fraction), respectively. The interaction between lithium slag substitution rate and basalt fiber dosage, and the interaction between basalt fiber length and dosage, in the response surface experiments are the key factors affecting compressive strength and tensile strength, respectively. The optimal parameters obtained by regression simulation as 22.875% (mass fraction) lithium slag substitution rate, 0.184% (volume fraction) fiber dosage, and 18 mm fiber length, and shows a high degree of fit with the results of parallel tests, indicating that the regression model can provide an effective reference for the multi-objective optimization of the mechanical properties of basalt fiber-lithium slag-coal gangue concrete.

The preparation of phosphogypsum-based fine lightweight aggregate (PG-LWA) by using activator, slag powder and phosphogypsum (PG) is one of the effective ways to recycle PG. In this paper, the preparation method of PG-LWA was introduced, and the quality of PG-LWA was evaluated from the aspects of physical properties, strength and microstructure. PG-LWA was used to prepare cement mortar, and the expansion, setting time and mechanical properties of mortar samples were tested. The results show that during the preparation of PG-LWA, the raw materials undergo alkali activation reaction to form hydrated calcium silicate (C-S-H) and ettringite (AFt). When the mass fraction of PG is 70%, the fineness modulus of the prepared PG-LWA is 4.4, the cylinder compressive strength at over dry is 4.65 MPa, and the porosity is 37.29%. When the water-binder ratio is 0.5 and the mass fraction of PG is 70%, the expansion degree of cement mortar prepared by replacing sand with PG-LWA is 213 mm, the final setting time is 300 min, and the 28 d compressive strength is 22.1 MPa.

This study developed a kind of non-sintered core-shell type ceramsite using expandable polystyrene (EPS) particles as the core, and the mixture of waste soil residual clay-geopolymer as the shell. The influences of the mix proportion of shell, the interfacial treatment agent type of EPS, core particle size, and shell thickness on the properties of the ceramsite were investigated. Subsequently, two types of ceramsites with distinct density grades were used to replace all natural coarse aggregates in the production of concrete, examining their effects on the physical and mechanical properties of the resulting concrete. The test results show that the strength of shell, core particle size, and shell thickness significantly impact the bulk crushing strength, bulk density, and water absorption of the ceramsite. In addition, the interfacial treatment agent of EPS also has great influence on the bulk crushing strength of the ceramsite. The performance of the optimal non-sintered ceramsite reaches the performance level of 900 grade sintered high-strength ceramsite. The employment of EPS particles as the core material effectively reduces the density of the non-sintered ceramsite, but the decrease in the bulk crushing strength of the ceramsite is more pronounced, thus it is not economical for preparing lightweight ceramsite below 800 grade. Furthermore, the incorporation of EPS and residual clay into the concrete reduces its thermal conductivity, enabling the ceramsite concrete to simultaneously satisfy the requirements of lightweight, load-bearing, and thermal insulation, while providing a new path for the environmentally friendly disposal of residual clay separated from engineering waste soil.

In order to further explore the effects of particle size and substitution rate of waste rubber particles on the mechanical properties of cement mortar under static loading, three kinds of rubber particle sizes (0.100, 0.425 and 2.000 mm) were selected to replace natural sand with volume fraction of 0%, 5%, 10%, 15% and 20%, respectively. The compressive, flexural and splitting tensile strength tests were carried out, and the influence mechanism of rubber particle on the mechanical properties of cement mortar were studied by mercury intrusion porosimetry test, scanning electron microscopy analysis and energy dispersive spectroscopy analysis. The results show that the compressive, flexural and splitting tensile strength of rubber cement mortar decrease with the increase of rubber substitution rate, and the effect of particle size on the strength of mortar is not obvious. When the rubber substitution rate increases from 5% to 20%, the 28 d compressive strength of rubber cement mortar decreases by 27.2%~61.0%, the flexural strength decreases by 22.5%~31.7%, and the splitting tensile strength decreases by 30.0%~38.9%, respectively. The ratio of bending-compression ratio increases with the increase of substitution rate and particle size. The total porosity and average pore size of rubber mortar specimens are negatively correlated with compressive, flexural and splitting tensile strength.

In order to study the effect of freeze-thaw cycle on the fatigue resistance of rubber concrete, rubber particles with a particle size of 30 mesh (0.55 mm) were selected to replace sand in equal volume to prepare rubber concrete. After different freeze-thaw cycles of ordinary concrete specimens and rubber concrete specimens, a constant amplitude uniaxial compression fatigue test was carried out to analyze the fatigue deformation characteristics of specimens, and the fatigue life equation and fatigue damage model considering failure probability were established. The results show that the maximum strain of rubber concrete is about 500 με higher than that of ordinary concrete under non-freeze-thaw state. With the increase of freeze-thaw cycles, the ductility characteristics are weakened. Adding rubber particles can improve the ductility of concrete fatigue failure. The fatigue life of rubber concrete under freeze-thaw cycle action obeys lognormal distribution. The ultimate fatigue strength of rubber concrete is about 9.8% higher than that of ordinary concrete, and the critical damage of rubber concrete is about 37% lower than that of ordinary concrete. Under the action of freeze-thaw cycle, the incorporation of rubber particles greatly improves the fatigue resistance of concrete.

In order to improve the working properties of recycled aggregate concrete (RAC), the effects of the amounts of homemade mineral viscosity reducer (VR) (8%, 10% and 12% of cement replaced by equal mass) on the rheological properties, strength, durability and shrinkage properties of RAC were investigated. The microstructure of RAC was also analyzed using scanning electron microscopy. The results show that the rheological properties of RAC improve with the increase of VR amount, the plastic viscosity of the paste decreases by 32.8% at 12% of VR amount, the yield stress and plastic viscosity of the mortar decrease by 42.0% and 17.9%, the slump and slump flow increase by 50， 40 mm, and the emptying time of inverted slump cylinder is shortened by 65.7%. At the same time, the VR incorporation makes the microstructure of the paste and interface transition zone of RAC become dense, which has a good improvement effect on the strength and durability of RAC. The best improvement is achieved when the VR is incorporated at a amount of 10%, with the 28 d compressive strength and splitting tensile strength of RAC increasing by 7.6% and 17.2%, the water absorption decreasing by 22.6%, and the electric flux and carbonation coefficient decreasing by 47.9% and 29.9%， respectively. In addition, the VR slightly reduces the drying shrinkage of RAC, but increases its early autogenous shrinkage to some extent.

In order to improve the mechanical properties of recycled concrete prepared from recycled aggregate from construction waste, recycled mortar and concrete were prepared by carbonized recycled fine aggregate instead of original recycled fine aggregate, and the effect of carbonized recycled fine aggregate on the mechanical properties of recycled mortar and concrete was studied. At the same time, X-ray diffraction (XRD) and mercury injection (MIP) were used to characterize the phase composition and pore structure of the recycled fine aggregate and recycled mortar after carbonization. The results show that the compressive strength and flexural strength of the recycled mortar prepared from recycled fine aggregate with carbonization treatment (7, 14, 28 d) are significantly increased, and the strength is positively correlated with the carbonization treatment time of recycled fine aggregate, and the strength increases the most in 28 d (compressive strength increases by 40.5% and flexural strength increases by 27.1%). The compressive strength of recycled concrete prepared from recycled fine aggregate with carbonization treatment (28 d) is improved (about 15.4%). XRD and MIP results show that Ca(OH)2 and other substances in the carbonized recycled fine aggregate are converted into CaCO3 after carbonization treatment, which reduces the porosity of the matrix by filling pores and microcracks, improves the shape and surface structure of aggregate particles, enhances its combination with the cement matrix, and optimizes the performance of recycled mortar and concrete.

Waste concrete and waste bricks are the important components of construction waste, and the resource utilization of recycled powder from construction waste is one of the important ways to achieve carbon reduction in the construction industry. Therefore, in this paper, recycled concrete powder (RCP) and recycled brick powder (RBP) were used to replace part of cement to prepare self leveling mortar (SLM). The effects of RCP content and RBP content on the fluidity and compressive strength of SLM were studied, and the microscopic mechanism was revealed by scanning electron microscope, X-ray diffraction and nitrogen adsorption method. The results show that the addition of RCP and RBP reduces the fluidity of SLM, but when the content of RBP and RCP is 10% (mass fraction) respectively, it has little effect on the fluidity of SLM. When the RBP content is 10% (mass fraction), the strength of SLM is the highest and the internal structure is the densest. The addition of RCP can have an adverse effect on the properties of SLM. The use of recycled powder to replace part of the cement is beneficial for reducing carbon emissions during the SLM preparation and promoting green and sustainable development in the construction industry.

Reasonable determination of construction water content is of great significance to ensure the best comprehensive performance of subgrade filling. In order to investigate the influence of water content on the strength deformation characteristics of fly ash subgrade and determine the water content suitable for the construction of fly ash subgrade, the fly ash in Ningxia area was used as the test material. Combined with the results of compaction test, consolidation compression and shear were carried out to analyze the mechanical properties of fly ash under different water content, and the best water content under each single factor was determined. Based on the gray relational analysis, the construction water content of fly ash subgrade can be proposed to ensure the best comprehensive performance. The results show that with the increase of water content, the coefficient of compression decreases first and then increases, the modulus of compression increases first and then decreases, the final vertical strain fluctuates within a certain range, and the compressibility of fly ash is the smallest when the water content is 31%. At high normal stress and high water content, the shear stress-shear displacement curve of fly ash shows strong strain softening type. With the increase of water content, the residual internal friction angle decreases, the residual cohesion increases and then decreases and tends to stabilize, and the residual shear strength of fly ash is the largest when the water content is 23%. When the water content in the range of 31%~35% of the mechanical index correlation degree value maintained in a high and relatively stable interval, which can be used as a guide to the construction of the comprehensive water content.

In order to explore the evolution characteristics of the meso-structure of slag solidified soil under load, this paper carried out in-situ computed tomography (CT) scanning test during uniaxial compression. The quantitative information of fractures in 2D and 3D form was extracted by combining image processing and 3D reconstruction techniques. With the volume parameters of fractures, the structural damage variables of slag solidified soil were calculated accordingly. Subsequently, a microscopic damage model was established to quantitatively describe the stress-strain relationship of the samples. The results show that the stress-strain curves of slag solidified soil under uniaxial compression loading obviously presents characteristics strain-softening, with a peak stress of 1.85 MPa. With the increase of axial strain, the 2D porosity and the dispersion of fracture distribution increase continuously. The 3D reconstruction model dynamically reveals the cracking process and the evolution of the main fracture surface, and the 3D porosity increases from an initial 3.39% to 9.78% at failure. Both the 3D porosity and fracture connectivity exhibit an logarithmic function relationship with axial strain. The failure of the sample involves three distinct stages: fracture initiation (ε=0%~0.2%), rapid propagation (ε=0.2%~1.5%) and stabilization (ε=1.5%~2.0%). The mesoscopic damage model based on damage variables, which were deprived from fracture volumes, is simple in form, easy to determine parameters, and can accurately predict the stress-strain curves of slag solidified soil. This study provides a novel perspective for the multi-scale analysis of failure mechanism of slag solidified soil.

In order to improve the utilization rate of soola residue and reduce the harm to the environment caused by soda residue storage, this paper proposed to use soda residue and fly ash stabilized clay, and add cement and lime to prepare soda residue-fly ash stabilized soil. Taking the maximum dry density, optimal water content, unconfined compressive strength (UCS) and shear strength parameters as the indexes, the orthogonal matrix analysis method was used to analyze the influence of soda residue, fly ash, cement and lime on the mechanical properties of soda residue-fly ash stabilized soil according to the influence weight. The results show that the fly ash content has the greatest influence on the maximum dry density. The soda residue content has the greatest influence on the optimum water content, 7 d UCS and the internal friction angle of 7 d shear strength. The lime content has the greatest influence on the cohesion of 7 d shear strength. The soda residue-fly ash stabilized soil has good strength performance. Based on the gradation mechanism of soda residue-fly ash stabilized soil and the cementation mechanism of cementitious materials, the orthogonal matrix analysis method is used to recommend the scope of application of the mix ratio, so that the soda residue-fly ash can better serve the actual project.

The engineering properties of yellow floodplain silt are poor, and it needs to be solidified before it can be used as a roadbed fill material. However, traditional solidification solutions require large amounts of cement, and the cement production process consumes large amounts of energy. To solve this problem, silica fume (SF) and ground granulated blast furnace slag (GGBS) were used as precursors, and carbide slag (CS) was used as an exciter, based on the Box-Behnken design (BBD) test in the response surface methodology, to compare and analyse the effects of different mix ratios of silica fume-ground granulated blast furnace slag-carbide slag (SGC) cementitious materials and cement on the mechanical properties and water stability of loess in yellow floodplain, and the microscopic solidified mechanism of the cured soil was explored by using X-ray diffraction (XRD) test and scanning electron microscope (SEM) test. The results show that the optimal mass mix ratio of silica fume, slag and calcium carbide slag is 5.94%∶21.87%∶4.31%. The 7、 28 d unconfined compressive strength of solidified soil under this ratio is 6 531.58 and 9 269.26 kPa, respectively, which increase the 7, 28 d unconfined compressive strength by 28.3% and 21.4%, respectively, compared with that of the cement solidified soil. SEM and XRD test results show that the main hydration products of SGC solidified soil are cementitious materials such as calcium silicate hydrate (C-S-H) and calcium aluminates hydrate (C-A-H), and the micro-morphology of SGC solidified soil at the age of 28 d is more compact than that of cement solidified soil. The effect of SGC stabilizer on the improvement of loess in yellow floodplain is significant, and it has good engineering application value.

Steel slag powder and fly ash solid waste materials were used to replace part of cement, and lime and NaOH were used as activators to form a new composite curing agent to modify mucky soil. The mass change rate, moisture content and unconfined compressive strength of solidified soil samples modified by composite curing agent under seawater erosion were studied. SEM was used to analyze the microstructure changes of soil particles, the distribution of cements and their interaction with soil particles in solidified soil under seawater erosion. The results show that the mass change rate of 28 d solidified soil is generally lower than 7 d solidified soil, which indicates that the longer the curing age of solidified soil is, the more stable the internal structure is. The moisture content of each sample decreases with the increase of seawater erosion concentration. When the content of composite curing agent is 20% (SLFA-CS-20%), the moisture content of solidified soil sample is the lowest. With the increase of the concentration of erosion ions in seawater, the strength of solidified soil gradually increases with the increase of erosion time. Mucky soil can produce a large number of cementitious materials and calcium vanadium stone under the action of composite curing agent, so as to improve the unconfined compressive strength of composite solidified soil.

The response surface method was used to optimize the mix ratio of industrial waste slag curing sand washing sludge, cement was added to improve the curing effect, and the composite curing agent of industrial waste slag was obtained. Through unconfined compressive strength test, water stability test and dry-wet cycle test, the effects of initial moisture content, curing age and curing agent content on the strength and durability of curing soil were studied, and the mechanism was analyzed by XRD and SEM. The results show that the optimal mix ratio (mass ratio) of slag, fly ash, calcium carbide residue and cement is 5.4∶1.7∶4.5∶2.0, and the curing effect is better than that of the same amount of cement. The synergistic effect of industrial waste slag and cement promotes the pozzolanic reaction. The strength and water stability of curing soil increase with the increase of age and content, but the strength decreases when the industrial waste slag composite curing agent content reaches 21.7% (mass fraction). The hydration reaction of CaO in calcium carbide residue improves the alkalinity of soil. The active aluminosilicate in slag and fly ash reacts in an alkaline environment, and the generated calcium silicate hydrate and calcium aluminosilicate hydrate fill pores and agglomerates soil particles. The dry-wet cycle provides high temperature conditions and moisture for specimen, and the strength of solidified soil is improved within a certain range.

Ceramsite filter material has been widely used in water treatment fields such as biological filter, aerated filter and constructed wetland due to its advantages of light weight, many pores and large specific surface area. In order to solve the large-scale storage of mine stripping materials, this paper used the solid waste of sand and gravel aggregate mine stripping materials as main raw material, and added bauxite and limestone to prepare ceramsite filter materials by sintering method. The effects of batch ratio, water consumption, firing conditions and other factors on the performance of ceramsite filter materials were studied, and the sintering mechanism was clarified. The results show that the minerals inside raw materials form strong mineral phases such as anorthite, diopside and corundum. When the mass ratio of stripping material, bauxite and limestone is 7∶4∶1, the sintering temperature is 1 120 ℃ and the holding time is 45 min, the ceramsite filter material with a bulk density of 765.90 kg/m3, a crushing rate of 3.24%, and a porosity of 54.45% is prepared, which provides a new way for high value utilization of mine stripping materials.

Shield muck (SM) is characterized by low activation and challenging disposal. The conventional ‘pre-firing-sintering’ process for preparing ceramsites is complex, the temperature changes frequently, and the production is low. In this paper, the combined process of thermal activation and NaOH-waterglass activation was used to prepare ceramsites from burning shield muck (BSM) and ground granulated blast furnace slag (GGBFS). The effects of thermal activated temperatures, material ratios, thermal activated time, and curing time on the physical properties of ceramsites were investigated in detail. The results show that when the thermal activation temperature is 1 000 ℃, m(SM/BSM)∶m(GGBFS) is 6∶4, the thermal activation time is 0.5 h, and the curing time is 28 d, the performance of the prepared ceramsite is excellent. The 28 d compressive strength of ceramsite is 10.38 MPa, the particle density is 1.90 g·cm-3, the bulk density is 895 kg·m-3, and the water absorption is 5.69%. The results of micromorphology analysis show that the hydration reaction inside the ceramsites produced calcium silicate hydrate (C-S-H) and sodium (calcium) silicaluminate hydrate (N(C)-A-S-H) composite gel, which closed most of the pores and made the grains closely bonded, thus improving the compressive strength of the ceramsites. This study can optimize the preparation technology of shield muck-based ceramsites, improving the efficiency of industrial production.

Zinc secondary slag is a type of low-carbon solid waste rich in heavy metals, and its conversion into ceramics can achieve resource utilization. This study employed X-ray diffraction （XRD） analysis and heavy metal leaching experiments to investigate the effects of preheating temperature on the physical properties and heavy metal solidification efficacy of ceramics derived from low-carbon slag solid waste. The ceramic samples produced after preheating at 500 ℃ exhibit optimal performance. The preheating process effectively removes carbon and sulfur components from the ceramic green body and facilitates the early volatilization of volatile substances, thereby reducing internal micropores during subsequent sintering and enhancing densification. This ultimately leads to a significant improvement in the bending strength of the ceramic samples. During the sintering process following preheating, Fe2+ is oxidized to free Fe3+, promoting the transformation of clinopyroxene to pyroxene. The pyroxene structure possesses excellent heavy metal solidification capabilities, with some Zn2+ and Mn4+ being fixed in this structure. Additionally, the presence of sulfates within the ceramics promoted its silicoaluminization. Heavy metal leaching experiments reveal that the release rates of various heavy metals are less than 0.3%, with their leaching concentrations being 1~2 order of magnitude lower than national standard limits. Ceramics prepared from preheated low-carbon slag solid waste not only exhibit excellent mechanical properties, but also demonstrate good heavy metal solidification effects, making them suitable for the resource utilization of heavy metal-containing solid waste.

Under the dual carbon goals, coordinated governance of air pollution is the key to promoting the comprehensive green transformation of industry. Papermaking sludge undergoes complex physical and chemical transformations during the coordinated disposal of industrial kilns, producing NOx and other pollution. Exploring the generation mechanism of NOx in the process of coordinated disposal of papermaking sludge by industrial kilns and analyzing the form and migration characteristics of its nitrogen-containing functional groups can provide new ideas for controlling NOx pollution emissions. In this paper, the transformation and migration of nitrogen-containing functional groups in papermaking sludge and pyrolysis at different temperatures were analyzed by means of nuclear magnetic resonance (NMR) analysis and gradient temperature inversion method. The results show that the release of nitrogen-containing functional groups is mainly concentrated in the temperature range of 250 ℃ to 300 ℃. From 200 ℃ to 250 ℃, imine and R3C—N, RCH2—N are released; from 250 ℃ to 300 ℃, thiourea, R2CH—N, RCH2—N, R3C—N are released; from 300 ℃ to 350 ℃, CH3—N, carbodiimide and cyanate are released; from 350 ℃ to 400 ℃, thiocyanate, isocyanate and CH3—N are released. TGA/DSC curve analysis further confirm the release of these functional groups, providing a reference for further environmental governance and process optimization.