With the continuous promotion of Chinese “double carbon” strategy, the application of green, low-carbon and environmental-friendly natural fiber in cement-based materials has become a research hotspot in the construction industry and received extensive attention. However, due to the poor mechanical properties, aging and weak adhesion of plant fiber, it is difficult to apply them directly to concrete matrix. This paper summarized the microstructure and properties of plant fiber, the influence of plant fiber on the macro properties of concrete, such as mechanical properties, durability and thermophysical properties, and the micro evolution mechanism of setting time, interface bonding and internal curing of plant fiber reinforced concrete. The methods of matrix modification and fiber modification in plant fiber reinforced concrete were discussed, and the mechanism of different methods was deeply understood, so as to seek more effective ways to improve the performance. Sisal fiber and bamboo fiber improve the performance of concrete and are most widely used. The sustainable development direction of plant fiber was prospected and some suggestions were put forward for further research on plant fiber reinforced concrete.

Sulphoaluminate cement has excellent performances, such as low sintering temperature, low CO2 emission, fast hardening and early strength, frost resistance and impermeability. It has broad application prospects in the field of building materials and solid waste, and derived a series of sulphoaluminate cements such as belite-calcium sulphoaluminate cement and belite-barium calcium sulphoaluminate cement, and etc. However, belite (β-C2S), one of the main mineral components of above sulphoaluminate cement, has low hydration activity and slow hydration speed, easily resulting in slow growth of cement strength in the later stage. Ternesite (C5S2) was once considered to be an “inert” mineral, but it can show stronger hydration activity than β-C2S in sulphoaluminate system, so the research on ternesite-sulphoaluminate cement (TSAC) is of great significance. Firstly, this paper summarizes the research status of C5S2 and TSAC from aspects such as the formation and hydration of C5S2, and the preparation and performance of TSAC. Secondly, this paper puts forward the problems that TSAC needs to further study and solve, such as the exploration of solid waste materials, the performance regulation of TSAC and the optimization of mineral composition of TSAC clinker. Overall, it is expected to provide positive and favorable reference and support for the research and application of new low-carbon cement.

The dispersibility of photocatalysts in cement-based materials has always been one of the important factors restricting the performance of photocatalytic cement-based materials. In this paper, photocatalytic cement-based materials were in-situ synthetized by adding bismuth-based photocatalytic precursor solutions in the molding process of cement-based materials. The dispersion of photocatalysts in cement matrix was improved. The photocatalytic properties to cement-based materials were imparted and the compressive strength of cement matrix was improved. The microstructure and composition of photocatalytic cement-based materials were characterized by scanning electron microscopy and EDS energy spectroscopy. The results show that the rhodamine B degradation efficiency of photocatalytic cement-based materials reaches up to 91.64%. The degradation efficiency of nitrogen oxides reaches up to 15.03%, and the early mechanical strength increases by about 10%. The photocatalyst is more uniformly dispersed in the cement matrix, and the density of cement matrix is improved. In this paper, the photocatalytic performance and mechanical performance improvement mechanism of in-situ photocatalytic cement-based materials are revealed, which provides a theoretical basis for the preparation of other functional cement-based materials.

In this paper, compressive and flexural strength tests of seawater sea sand mortar (SSM) with different curing ages and water-cement ratios were carried out. The influences of water-cement ratio, curing age and water temperature on capillary water absorption properties of SSM were studied by weighing method. The relationship between mechanical properties or capillary water absorption properties and corresponding microstructure of SSM was studied based on low field nuclear magnetic resonance technology. Finally, the representative capillary diameter calculated based on the water absorption model of porous media capillary was compared with the pore diameter estimated based on the transverse relaxation time of low field nuclear magnetic resonance technology. The results show that the strength of SSM developed rapidly in the first 3 days, and the compressive and flexural strength of SSM specimens with water-cement ratio of 0.4 curing for 3 d are 56.2% and 70.3% of those of SSM specimens curing for 28 d. When the water temperature rises from 20 ℃ to 40 ℃, the capillary water absorption coefficient of SSM specimen with water-cement ratio of 0.4 curing for 28 d increases 1.2 times. In the long-term one-dimensional water absorption process, the cumulative capillary water absorption volume per unit area of specimen is linearly related to the 0.25 power of the water absorption time. The porosity of SSM specimens decreases with the increase of curing age. The typical capillary diameter based on capillary water absorption model is close to the mortar pore diameter estimated based on transverse relaxation time of low field nuclear magnetic resonance.

The effects of single adding and mixing polyoxymethylene (POM) fibers with different lengths on fluidity, flexural strength, compressive strength, flexural toughness and drying shrinkage of mortar were studied in this paper, and the microstructure of mortar was observed by scanning electron microscope. The results show that mortar fluidity decreases with the increase of POM fiber length and content, and the influence of mixed fiber with different lengths on the fluidity of mortar is less than that of single fiber. POM fiber effectively enhances the flexural strength of mortar, but the strengthening effect is weakened when the content is more than 0.6% (volume fraction, the same below). Compared with the sample without fiber, the 6 mm fiber with 0.6% content has the highest increase of 28 d flexural strength, which is 14.67%. The compressive strength decreases with the increase of fiber content. The flexural toughness of 12 mm fiber is improved more significantly than that of 6 mm fiber and mixed fiber, which increases of 49.43% at most compared with the sample without fiber. The addition of fiber greatly reduces the drying shrinkage of the sample, the 90 d drying shrinkage of the sample decreases first and then increases with the increase of fiber content. Compared with the sample without fiber, the 90 d drying shrinkage rate of 6 mm fiber sample with 0.6% content decreases the most, which is 27.39%. The hybrid POM fiber still significantly improves the flexural strength and reduces the drying shrinkage when the content is more than 0.6%.

Polymer modified cement-based toughness thin spray material is the development direction of coal mine roadway surface sealing material. Redispersible emulsion powder has the characteristics of increasing cement-based material adhesion and improving toughness, but at present, there is less research on redispersible emulsion powder modified cement-based thin spray material. In this paper, thin spray material was prepared by using silicate and sulphate aluminium composite cement modified by redispersible emulsion powder, and the effect of redispersible emulsion powder on slurry viscosity, setting time, and flexural and compressive strength, uniaxial compressive stress-strain and uniaxial tensile load-displacement of the stone body was studied. The results show that with the increase of the content of redispersible emulsion powder, onset time for rapid increase of slurry viscosity is extended, setting time increases, the flexural and compressive strength of the stone body increase first and then decrease, and reach the maximum value at the content of 2.25% (mass fraction), and the compression and tensile deformation rates increase and the toughness is improved. The mechanism of the effect of redispersible emulsion powder on the macroscopic properties of cement-based materials was explained by microscopic analysis.

In order to study the damage evolution characteristics of cement mortar subjected to repeated high temperature and local water cooling, the central part of the cement mortar specimen was drilled. After heating the specimens to 400 ℃, water was poured into the hole for cooling, and then the operation was repeated continuously. Low field nuclear magnetic resonance technology, digital acoustic instrument and digital microscope were used to study the damage behavior of cement mortar specimens under repeated 400 ℃ and local water cooling. The results show that with the increase of high temperature treatment and local cooling times, the pore size and content of the small hole of the specimen increase continuously, while the pore size of the large hole decreases. After the first treatment, the performance degradation of the specimen is the most obvious, and the damage around the hole is greater than other parts due to local water injection cooling. Meanwhile, with the increase of high temperature treatment and local cooling times, the gray value corresponding to the peak probability density increases and moves to the right. In addition, the heat treatment weakens the cementing ability of cement mortar and sand particles. Repeated high temperature treatment further weakens the cementing ability of cement mortar and sand particles, and the wave velocity of specimen is reduced. However, the temperature stress generated by water injection cooling in the hole causes a sharp decline in the cementing ability. The effect of temperature stress caused by sudden drop of temperature on cementing ability of cement mortar and sand is much greater than that of repeated high treatment.

In order to mitigate the drying shrinkage of foamed concrete, lightweight aggregates (shale ceramsite and fly ash ceramsite) were used to prepare foamed concrete. Effects of lightweight aggregates on the compressive strength, drying shrinkage, internal humidity and pore structure of foamed concrete were studied, and the internal curing mechanism of lightweight aggregates was analyzed. Experimental results reveal that lightweight aggregates can adjust the internal humidity of foamed concrete, restrict the deformation of the matrix, and decrease the drying shrinkage of foamed concrete. However, lightweight aggregates can also introduce defects in foamed concrete, resulting in the decrease of compressive strength. The ink-bottle pores larger than 100 nm in lightweight aggregates are the control factor of efficient internal curing. The lightweight aggregates with more ink-bottle pores larger than 100 nm tend to possess stronger water release capacity and better effect of internal curing, thus resulting in lower drying shrinkage of foamed concrete.

To identify the influence of MgO expensive agent (MEA) on the shrinkage performance and compressive strength of ultra-high performance concrete (UHPC), this paper aims to evaluate the effect of MEA with different activity and dosages on the compressive strength and autogenous shrinkage of UHPC and analyze the mechanism. The results show that MEA with different activities effectively inhibits the shrinkage of UHPC. The high activity MEA has a relatively high hydration rate and shows a significant inhibition effect on the early autogenous shrinkage for UHPC. However, the compressive strength of UHPC containing high activity MEA is about 6% lower than that of UHPC with low activity MEA due to the existence of the water contention effect between MEA and cement. The content of MEA is an important factor affecting the shrinkage reduction effect. When the content of MEA exceeds 6% (mass fraction), the expansion performance of UHPC cannot be fully stimulated due to the limitation of the free water content in the UHPC matrix, and it is difficult to further improve the expansion performance of MEA considering the influence of MEA on the shrinkage performance and mechanical properties of UHPC, a low-activity MEA with a reactivity value of 220 s and a dosage of 6% is suggested in this study.

In order to study the effect of limestone powder on the shrinkage performance of self-compacting concrete, tests with different water to binder ratios and mass fractions of limestone powder were designed, and the change rules of autogenous shrinkage and drying shrinkage of self-compacting concrete at the age of 28 d with water to binder ratio of 0.30, 0.34, 0.37 and mass fraction of limestone powder of 0%, 10%, 20% were obtained. The results show that the autogenous shrinkage increases with the decrease of water to binder ratio, and increases with the increase of mass fraction of limestone powder. When water to binder ratio ranges from 0.30 to 0.37, its effect on drying shrinkage is not significant. The moderate amount of limestone powder almost has no effect on drying shrinkage, and when the mass fraction of limestone powder reaches 20%, the drying shrinkage increases significantly. The forecast models of autogenous shrinkage and drying shrinkage of self-compacting concrete considering the effect of water to binder ratio and limestone powder mass fraction were proposed on the basis of tests.

In this paper, the effects of different pretreatment methods and high performance coating cementitious materials on physical properties, chloride ion dissolution behavior and mechanical properties of reef aggregate were studied. The reef aggregate pretreated by coating was used to prepare reef concrete, and the effects of pretreatment method and aggregate replacement level on the mechanical properties, chloride ion permeability and volume stability of reef concrete were discussed. The results show that the pretreatment method of standby after evenly coated the aggregate with slurry and then drying in oven exhibits the best aggregate modification results than other pretreatment methods, and the technical properties of reef aggregate such as void fraction, water absorption, crushing value and chloride ion dissolution characteristics are optimized. When the reef aggregate is added into concrete with the volume replacement of 20%, 40% and 60%, comparing with uncoated reef concrete, the compressive strength of coated reef concrete increases by 6.67%, 15.40% and 20.05% at 28 d, the diffusion coefficient of chloride ion decreases by 6.25%, 17.31% and 38.10%, and the drying shrinkage reduces by 5.81%, 17.05% and 24.43%, respectively. After coating, the interface transition zone between reef aggregate and cement mortar is modified, and the mechanical properties, chloride ion permeability and volume stability of reef concrete are improved.

To study the failure characteristics of recycled coarse aggregate concrete under uniaxial compression, the strain change law of concrete cube in the failure process was recorded by digital image correlation technology, and the width and porosity of interfacial transition zones were characterized by microhardness test and backscattered electron imaging. The experimental results show that the compressive strength of recycled concrete increases by 17.86% and 35.55% compared with untreated samples after aggregate reinforcement and mortar reinforcement, respectively. It indicates that mortar reinforcement is more helpful for improving the compressive strength of recycled concrete. The microhardness of the old mortar increases, and the porosity of the interface transition zone between old aggregate and old mortar is reduced by aggregate reinforcement. The microhardness of new mortar increases, and the porosity of the interface transition zone between old aggregate and new mortar and between old mortar and new mortar is reduced by mortar reinforcement. The probability of passing penetrating cracks decreases for reinforcement interfaces.

The 48 concrete specimens were prepared with fiber content as variable. Piezoelectric ceramic sensors as signal exciter and signal receiver were placed on the surface of concrete specimen. The damage of basalt-polypropylene fiber reinforced high performance concrete (BPHPC) was monitored in real time based on piezoelectric effect. The damage index (DI) based on wavelet packet analysis method was obtained by analyzing the piezoelectric stress wave signals of concrete specimens with single and hybrid fiber, and the function relationship of fiber content-load-DI was fitted. The results show that the health state of specimens can be evaluated qualitatively by observing the damage state of appearance and the variety of piezoelectric stress wave signals. The addition of fiber can reduce appearance damage of concrete. The amplitude of stress wave signals of concrete specimens with single fiber is larger than that of concrete specimens with hybrid fiber. When the volume content of basalt fiber and polypropylene fiber is 0.15% and 0.10%, respectively, DI value is the smallest. When DI exceeds 0.8, the specimen is considered to be completely destroyed. The test data is in good agreement with the test phenomena, which indicates that it is feasible to monitor the damage of BPHPC in real time through piezoelectric ceramics.

In order to study the effect of the initial notch-to-depth ratio on the fracture properties of steel fiber reinforced concrete, the fracture toughness tests for steel fiber reinforced concrete with different initial notch-to-depth ratios (0.1, 0.2, 0.3) were carried out and the fracture parameters were calculated. By combining acoustic emission (AE) and digital image correlation (DIC) techniques, the variation law of AE energy and full-field strain during fracture development was analyzed. The results show that the fracture toughness of steel fiber reinforced concrete decreases with the increase of the initial notch-to-depth ratio. When the initial notch-to-depth ratio of steel fiber reinforced concrete reaches 0.3, the fracture properties begin to decrease rapidly. The fracture process of steel fiber reinforced concrete is divided into elastic-plastic stage, stable crack propagation stage and fracture stage according to AE energy. With the increase of the initial notch-to-depth ratio, the duration of elastic-plastic stage decreases. The analysis results of DIC show that the prefabricated crack tip produces a large stress concentration and the transverse strain of the crack is large during the whole loading process. The research results reveal the crack development mechanism of steel fiber reinforced concrete, which provides theoretical support for its engineering application.

Nine push-out test specimens were made and experimented to study the bond-slip behavior between steel section and geopolymer concrete. The influences of four factors such as compressive strength of geopolymer concrete, concrete cover thickness, embedded length of steel section and stirrup ratio on the load-slip curves, failure modes and bond-slip properties of the steel reinforced geopolymer concrete specimens were studied. The results show that the load-slip curves of different specimens have the same development tendency and can be divided into four stages: no slipping stage, load increasing stage, load declining stage and horizontal residual stage. The failure modes of specimens are bond splitting failure, cracks originate from the flange of the steel section at loading end and develop to the free end. As the compressive strength of geopolymer concrete, concrete cover thickness and stirrup ratio increase, the values of characteristic bond strength of specimens present a tendency towards growth. Unlike the steel reinforced concrete with ordinary cement, the values of characteristic bond strength of the specimens increase with the increase of embedded length of steel section. According to the test results, the calculation formulas of the characteristic bond strength are established, and the constitutive model of the steel reinforced geopolymer concrete is proposed. The bond-slip curves calculated by the model agree well with the experimental curves of steel reinforced geopolymer concrete specimens.

In order to investigate the effects of different ester monomers on the dispersion performance and dispersion retention performance of slow-release polycarboxylate superplasticizer and their action mechanism, different slow-release polycarboxylate superplasticizers were prepared with different molecular structure ester monomers as modified raw materials. The macroscopic dispersion performance and dispersion retention performance, and the microscopic structural change and action mechanism were analyzed by the tests of fluidity of cement paste with time, Zeta potential, total organic carbon, electrical conductivity, Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. The results show that the dispersion retention performance of slow-release polycarboxylate superplasticizer modified with monoester monomer (hydroxyethyl acrylate, hydroxypropyl acrylate and methyl acrylate) and diester monomer (dimethyl maleate) as functional monomers are superior while the fluidity at 4 h is still improved comparing to the initial fluidity. At the same time, compared with the unmodified control group, the later dispersion performance is better, while the fluidity at 4 h is significantly improved. The main mechanism is as follows: the ester group is slowly hydrolyzed in the alkaline environment of cement paste and produces the anchoring group carboxyl group to achieve the effect of dispersion. The steric hindrance effect and the electronegativity of the contained groups with different molecular structures lead to different hydrolysis rates and degrees of hydrolysis, resulting in different dispersion performance and dispersion retention performance of various slow-release polycarboxylate superplasticizer.

In order to study the fatigue performance of cement stabilized crushed stone mixed with polyvinyl alcohol (PVA) fiber, firstly, according to the influence law of polyvinyl alcohol fiber on the mechanical properties of cement stabilized crushed stone, the optimal fiber content and length were determined. Based on the indirect tensile fatigue test and Weibull distribution, the fatigue life test results were analyzed and the fatigue equation was established. The results show that the optimum content and length of PVA fiber are 0.06% (mass fraction) and 24 mm. Under the optimum content and length, the unconfined compressive strength of PVA fiber cement stabilized crushed stone increases by about 24%, and the cracking strength increases by about 26%, compared with the cement stabilized crushed stone material without fiber addition, basides its fatigue life also presents a significant advantage. When the cement mass dosage is 4%, the ratio of slope b of polyvinyl alcohol fiber-doped and non-fiber-doped cement stabilized crushed stone is 0.94~0.99, and the ratio of intercept a is 1.06~1.23.

As a new aluminosilicate green material, geopolymers have the advantages of excellent mechanical properties, high durability, wide source of raw materials, low energy consumption and simple production process, etc. Geopolymers are widely used in the fields of construction materials, refractory materials and immobilization of heavy metal ions, etc. The mechanisms of immobilization of heavy metal ions are divided into physical mechanism （physical encapsulation and ion exchange） and chemical mechanism （chemical bonding, compound formation and reducing agent coupling）. The recent research progress of geopolymers in the field of immobilization of heavy metal ions was reviewed, the preparation process of geopolymers and the process of geopolymerization reaction were briefly introduced, and the mechanism of immobilization of heavy metal ions by geopolymers was highlighted. In addition, the effects of additive types and content, alkali exciter types and content, silicon to aluminum ratio, curing temperature and heavy metal ions on immobilization effect were presented. Finally, the study and application progress on heavy metal ions immobilized by geopolymers in recent years were summarized, the problems were analyzed, and the future research directions were prospected.

The copper tailings discharge and reserve are huge in China, resulting in environmental pollution and resource waste. The complex mineral composition and fine particle size of copper tailings limit the efficient and high value-added utilization of copper tailings. This paper summarized the mineral properties, physical and chemical properties of copper tailings, and the technical and control requirements in the industrial application of building materials. The main application modes, action characteristics and the influencing rules of main components of copper tailings were summarized from the application ways of copper tailings in autoclaved aerated concrete, cement-based material, cement clinker, brick, glass-ceramics, porous material and filling material. It provides reference for copper tailings and other solid waste production enterprises to cooperate with building materials industry to systematically solve the problem of tailings recycling. In coordination with the development direction and product requirements of building materials industry, the key problems of building materials disposal of tailings resources in the future are put forward, which provides support for the real realization of resource utilization of tailings products.

In order to solve the problem of pulp viscosity in the modification process of sodium bentonite, the effects of sodium carbonate dosage, pulp concentration and dispersant on the effect of sodium modification and pulp viscosity were systematically studied, and the mechanism of reducing pulp concentration and adding dispersant were discussed. It is found that by reducing the pulp concentration, the “house-of-cards” structure by edge-to-edge and edge-to-face contact is obviously reduced, and the problem of pulp viscosity is improved, but the pulp quantity and the treatment difficulty increase at the same time. By adding dispersant sodium pyrophosphate, phosphate ions are adsorbed on the positive edge of montmorillonite, which increases the repulsive force between montmorillonites and reduces the viscosity of pulp, and improves the sodium effect. Through systematic experiments, high quality sodium bentonite is prepared with 0.5% （mass fraction） sodium pyrophosphate, 5% （mass fraction） pulp concentration and 5% （mass fraction） sodium carbonate. In this condition, the swelling index and colloidal value of bentonite have been greatly improved, the colloid value of sodium bentonite increases from 95 mL/15 g to 975 mL/15 g, and the swelling index increases from 8 mL/2 g to 25 mL/2 g after 1.5 h sodium modification.

Manganese slag and recycled brick aggregates both belong to bulk solid waste. Improving the utilization rate of bulk solid waste has important environmental and economic benefits. In this paper, non-fired bricks were prepared using manganese slag and recycled brick aggregates, the effect of manganese slag content on various properties of non-fired bricks were investigated, and the microstructure and harmful substance leaching behavior were analyzed. The results show that the non-fired bricks have good appearance quality, uniform color and standard size. Combining strength requirements and frost resistance requirements, MU20 non-fired bricks with excellent strength, water resistance and durability are prepared when manganese slag content is less than 10% (mass fraction). MU15 non-fired bricks with excellent properties are prepared when manganese slag content is less than 15%. More ettringite hydrate phase is formed in the non-fired bricks, which is beneficial to strength development. The non-fired bricks made from manganese slag and recycled brick aggregates have good application effect in sidewalks and other municipal projects. The research results provide technical support for the low carbon resource utilization of manganese slag and production and application of ecological brick products.

Mixing blast furnace slag (BFS) in coal gasification coarse slag (CGCS) based geopolymer improves its early mechanical properties. In this paper, CGCS and BFS were used as raw materials to prepare geopolymer, and the effect of different BFS content on the early mechanical properties and microstructure of geopolymer was studied. The microstructure of activated CGCS-BFS based geopolymer was characterized by X-ray diffraction, mercury intrusion porosimeter, scanning electron microscope and Fourier transformed infrared spectroscopy. The results show that the compressive strength of geopolymer increases gradually when the BFS content increases. When the BFS content reaches 40% (mass fraction), the 28 d compressive strength of sample is as high as 531 MPa. According to the microscopic analysis, a large amount of calcium/sodium silicate aluminate hydrate (C(N)-A-S-H) gel is formed on the surface of the geopolymer, which makes the microstructure of geopolymer more denser, and thus improves the mechanical properties of geopolymer.

Fluid solidified soil is a new material developed in recent years to improve backfill quality of narrow space in municipal and construction engineering. In this paper, steel slag powder, CFB desulfurization ash, rice husk ash and other low-quality solid wastes were used as clinker-free cementitious materials to prepare fluid solidified soil, and the unconfined compressive strength, drying shrinkage property, heavy metal leaching property and microstructure of fluid solidified soil were tested. The research shows that the flow expansion degree and unconfined compressive strength of fluid solidified soil prepared by cementitious materials without clinker meet the requirements of general filling engineering, the drying shrinkage value of hardened body is significantly lower than that of cement solidified soil with the same content, and there is no risk of excessive leaching toxicity of heavy metals. Under the synergistic effect of various solid wastes, the soil particles aggregate into clusters, and the pores are significantly reduced. The flocculent gel and acicular ettringite crystal are intertwined, adhere to the surface of soil particles and connect to soil particles, which enhance the strength of solidified soil.

The CaO-Na2CO3 activated slag (CNS) mortar and the ordinary Portland cement (OPC) mortar were immersed in sodium sulfate and magnesium sulfate solution respectively, and the flexural strength, compressive strength and SO2-4 concentration in different depths of CNS and OPC mortars were studied before and after sulfate corrosion. Meanwhile, the corrosion products and pore structure of CNS and OPC mortars were analyzed by XRD, SEM and MIP. Then the corrosion mechanism of sodium sulfate and magnesium sulfate on CNS and OPC mortars was compared and discussed. The results show that the hydration products of CNS mortar are mainly calcium aluminium silicate hydrate (C-A-S-H) with low Ca/Si ratio, and there is no calcium hydroxide. The pore structure of CNS mortar is better than OPC mortar due to the filling effect of calcium carbonate, and the sulfate resistance of CNS mortar is greater than that of OPC under the same corrosion environment. The corrosion products of CNS mortar under magnesium sulfate are mainly brucite (the mortar on the specimen surface will be peeled off together in the later stage of corrosion) and non-adhesive magnesium aluminium silicate hydrate (M-A-S-H). Compared with sodium sulfate, magnesium sulfate is more corrosive to CNS mortar.

The geopolymer-based lightweight porous material was prepared using slag micronized powder as main raw material, mix solution of sodium silicate and sodium hydroxide as alkaline activator, and aluminum powder as foaming agent. The effects of foaming agent, water-cement ratio and naphthalene water reducer on the pore structure and physical properties of material were systematically investigated. The results show that Al powder reacts rapidly with alkaline activator to generate H2, which promotes the foaming of geopolymer slurry to form porous material, and the dry density and compressive strength of material decrease rapidly with the increase of the Al powder content. However, if Al powder content exceeds 0.40% (mass fraction, the same below), the cell increases sharply, resulting in cell aggregation and a significant reduction in strength. Raising the water-cement ratio can reduce cell growth resistance and promote a rapid reduction in density. Nonetheless, when the water-cement ratio＞0.40, the slurry viscosity and activator concentration significantly decrease, setting time prolongs, pore size increases and structure deteriorates. Thus, the optimal water-cement ratio is 0.35. In addition, naphthalene water reducer is effective in regulating the pore structure of porous geopolymer. Adding only 0.4% of naphthalene water reducer could promote uniform pore size distribution, enhance pore wall integrity, and improve the compressive strength of specimens.

Study on the mechanical properties of alkali-activated materials is able to promote its practical application in engineering. In this paper, the effects of slag content and fine aggregate content on the compressive strength, elastic modulus and stress-strain curves of alkali-activated paste/mortar were investigated. The results show that the addition of slag significantly improves the compressive strength and elastic modulus of alkali-activated paste/mortar. The addition of fine aggregate reduces the compressive strength while improves the elastic modulus. The elastic modulus of alkali-activated slag/fly ash paste ranges from 12.83 GPa to 19.53 GPa at 28 d. The elastic modulus of alkali-activated slag/fly ash mortar ranges from 18.72 GPa to 23.10 GPa at 28 d. When the amount of fine aggregate is 40% (mass fraction), the peak stress and peak strain decrease obviously while elastic modulus increases. The piecewise equation is used to fit the stress-strain curves of alkali-activated slag/fly ash paste/mortar. The fitting curves are in good agreement with the measured curves. The fitting results indicate that the stress-strain curves of alkali-activated slag/fly ash paste/mortar become steeper with the increase of slag content and the curing age, reflecting the brittleness of materials, which is consistent with the rising curves.

In order to better promote the engineering application of magnesium oxychloride cement (MOC), the effects of raw material ratio, single mixing of different phosphate modifiers, combined mixing of phosphoric acid and mineral admixture modifiers on the water resistance of MOC were studied. The improvement effect of modifier on the water resistance of MOC was comprehensively evaluated by using flexural strength, compressive strength (mechanical properties), variation coefficient (strength stability with modifier dosage) and water resistance coefficient (water resistance), and the improvement mechanism of water resistance was analyzed by scanning electron microscope. The results show that when the molar ratio of raw materials is n(MgO)∶n(MgCl2)∶n(H2O)=7∶1∶15, and 1.0% phosphoric acid and 60% silica fume (mass fraction of MgO), the water resistance of MOC is the best, and the water resistance coefficient of modified MOC is above 1.1. Microaggregate filling effect, pozzolanic effect and enhancement effect of strength phase (P5) stability together improve the water resistance of MOC.

Phosphogypsum (PG) is an industrial solid waste produced in the wet process of phosphoric acid, which piles up in large quantities and pollutes the environment. However, anhydrous phosphogypsum (APG) obtained by PG after ball milling and calcination can be used as filler for polymer materials after hydrophobic modification on the surface, to improve the comprehensive mechanical properties of the materials by toughening and strengthening the materials, and it is an effective way for the resource utilization of PG. In this study, taking APG as the main raw material and the activation index as the response value, the process conditions of hydrophobic modification of APG were optimized by single factor test and the response surface methodology. The results show that the mathematical model established by the response surface has a high fitting degree. NaOH concentration, KH570 dosage and reaction time have significant effects on the activation index, and the dosage of KH570 is the main factor affecting the modification. The optimal hydrophobic modification conditions of APG are as follows: NaOH concentration is 2.6 mol/L, KH570 dosage is 3.10 g, and the reaction time is 149 min. Under the optimal conditions, the activation index and contact angle of the modified APG are 0.968 9 and 84.51°, respectively.

The collaborative and efficient disposal of construction solid waste and industrial solid waste is of great significance to the comprehensive utilization of solid waste. In this paper, CT scanning technology and digital volume correlation method were used to analyze the damage evolution characteristics of geopolymer recycled concrete under uniaxial compression, so as to establish the damage constitutive model of geopolymer recycled concrete under uniaxial compression. The results show that the main reason for the failure of geopolymer recycled concrete is the generation of non-uniform strain field. The damage parameter and strain present a quintic function relationship considering the numerical and spatial characteristics. The damage constitutive model based on the strain equivalence principle can better characterize the stress-strain relationship under load. This research can provide theoretical basis and technical support for the application of geopolymer recycled concrete in engineering, and provide a new method for the study of mechanical damage of recycled concrete.

The performance of concrete is greatly affected by recycled coarse aggregate (RCA). Understanding how they affect performance of concrete is crucial to maximizing RCA utilization, reducing carbon emissions in the construction industry, and contributing to achieving national carbon peaking and carbon neutrality targets. Four groups images of aggregate characteristic of lithium slag recycled aggregate concrete with different RCA replacement rates were acquired by using CT scanning. The shape factor (SF), angularity (AN), angularity and surface texture (AT index), and three-dimensional sphericity (SP) were calculated by using digital image processing techniques. Based on the analysis of their distribution rules and characteristics, a gray correlation analysis method was used to determine the relationship between different aggregate characteristics parameters and compressive strength. The results show that the RCA has a higher irregularity, and its surface is rough and angular due to the different amounts of paste remaining in the aggregate. There is a high gray correlation degree among the four aggregate characteristic parameters, among them, the SP correlation degree reaches the maximum, 0.942. Samples meet the strength requirements of C30 concrete in aggregate mixing ratio appropriately and gain the best mechanical properties with RCA replacement of 30% (mass fraction).

Silica aerogel is a kind of nanoporous material with many excellent properties such as high porosity, high specific surface area and low thermal conductivity. It has a wide application prospect in aerospace, chemical, construction and many other fields. However, its intrinsic ceramic brittle structure greatly limits its practical application. For the perspective of strengthening the neck zone of silica aerogel nanoparticles, this review focuses on the research progress of nanoscale network reinforcement methods of silica aerogels by categorizing them as liquid phase and gas phase reinforcement, and explains the enhancement mechanism in these two methods. Finally, the future development direction of nanoscale network reinforcement technology of silica aerogel is prospected.

Ceramic membranes have been used in many fields because of their high mechanical strength, high temperature resistance, good chemical stability, controllable pore size distribution, good regeneration performance and environmental friendliness. However, their high production cost result in a low market. In addition, ceramic membranes also suffer contradiction between high permeability and high selectivity, which limits their large-scale application. Researches on reducing production cost and improving the performance of asymmetric ceramic membranes by using cheap raw materials, adding sintering additives and optimizing preparation process were summarized. Meanwhile, the advantages and disadvantages of relevant methods on ceramic membranes were analyzed. Moreover, the future development and application prospect of ceramic membranes were given as well.

The Pb0.962 5La0.025(Mg1/3Nb2/3)1-zTizO3 (z=028, 029, 030, 031) piezoelectric ceramics were synthesized by two-step pre-sintering process. The morphotropic phase boundary (MPB) of ceramics was found at 0.29 mol and 0.30 mol of PbTiO3. Selecting the chemical composition on both sides of morphotropic phase boundary, and the tetragonal phase Pb(Mg1/3Nb2/3)0.66Ti0.34O3 powder and rhombohedral phase Pb1-1.5xLax(Mg1/3Nb2/3)1-yTiyO3 (x=0.083 3~0.041 7, y=0.206 7~0.273 3) powder rhombohedral phase were prepared, respectively. Two crystal phase powders (rhombohedral phase mole fraction w=0.3, 0.4, 0.5, 0.6) were mixed and pressed into disks. The ceramics with the same chemical composition and different crystal phase proportion of Pb0.962 5La0.025(Mg1/3Nb2/3)0.70Ti0.30O3 were sintered. The effect of crystal phase ratio on the piezoelectric, dielectric, and ferroelectric properties of ceramics were investigated. The results show that the rhombohedral and tetragonal phase ratios of ceramics are pasically the same as the proportion of ingredients. For the sample with w=0.5, the rhombohedral and tetragonal phase ratios of ceramics sintered at 1 250 ℃ is about 0.47, 0.53, respectly. The average grain size is (5.24±0.23) μm. The relative density of ceramics is 96.76%. The piezoelectric constant d33, planner electromechanical coefficient kp, thickness electromechanical coefficient kt, relative permittivity εr, remnant polarization Pr, and field-induced strain S (1 Hz, 3.5 kV/mm) of ceramics are 1 014 pC/N, 0.67, 0.64, 10 955, 24 μC/cm2, and 0.21%, respectively. For the chemical composition near MPB, the rhombohedral and tetragonal phase ratios of ceramics could be tuned artificially via this method.

Porous silicon carbon (SiC) ceramics with coherent laminated structure were prepared by freeze-drying process with micron SiC powder as raw material. With porous SiC ceramics as matrix and paraffin as phase change material, the porous SiC ceramics/paraffin composite phase change materials were synthesized via vacuum impregnation method. Infiltration behavior of paraffin in laminated porous SiC ceramics and the heat storage performance and stability of composite phase change materials were investigated. The results show that the microstructure of laminated porous SiC ceramics has a significant effect on the infiltration process and heat storage properties of paraffin. When the paraffin load is 21.7% （mass fraction）, the melting point and freezing point of composite phase change materials are 59.6 ℃ and 53.9 ℃, respectively, the latent heat of melting is 28.4 J/g, and the thermal conductivity at room temperature reaches 2.4 W·(m·K)-1. The intensity of endothermic and exothermic peaks of phase change materials decreases with decrease of paraffin load. When the temperature is 200 ℃, the weight loss of porous SiC ceramics/paraffin composite phase change materials is 5% (mass fraction), indicating that the material has good thermal stability. The composite phase change materials maintain its shape without any leakage after being treated in 100 ℃ for 30 min. The composite phase change materials aslo have stable latent heat and good shape stability after 100 thermal cycles.

Five different concentrations of sodium silicate solutions were prepared from fly ash. The sodium silicate solutions were treated by sol-gel method, and hydrophobic SiO2 aerogel was obtained via ambient pressure drying. The influence of sodium silicate modulus on the structure of aerogels was investigated through measurements of density, specific surface area and contact angle. The chemical reaction mechanism of nucleophilic substitution SN1 for hydrophobic modification of aerogel surface was proposed. The results show that the hydrophobic performance of aerogel is directly related to the number of -Si-(CH3)3 attached to the surface. When sodium silicate modulus is equal to 2.50, the best hydrophobic performance of aerogel is achieved. The density and specific surface area of aerogel increase with the increase of sodium silicate modulus. When the sodium silicate modulus is equal to 0.75, the lowest density and specific surface area of aerogel are recorded, which are 0.073 9 g/cm3 and 588.5 m2/g, respectively.

In order to improve the performance of ceramic bonded diamond grinding wheels, microwave sintering technology was used, and the effects of microwave sintering temperature, ceramic bond content and diamond abrasive size on the performance of ceramic bonded diamond grinding wheels were analyzed through a series of experiments. The results show that microwave sintering temperature is the most important factor affecting the performance of ceramic bonded diamond grinding wheels, far exceeding the remaining two. The Rockwell hardness and bending strength of ceramic bonded diamond grinding wheel specimen reach great value at 740 ℃ and the porosity is small. The Rockwell hardness is 66 HRB, the bending strength is 76.5 MPa and the porosity is 17.8%. It is observed from the microstructure that the ceramic bonded diamond grinding wheels achieve the uniform encapsulation of diamond abrasive by ceramic bond at 740 ℃, and there are few pores.

The basalt fiber was surface modified by high energy laser beam, and basalt fiber/epoxy resin composite was prepared. The microstructure, mechanical properties and phase structure of basalt fiber were characterized by scanning electron microscope, atomic force microscope and X-ray diffraction. The influence of laser on the microstructure and properties of basalt fiber was systematically studied. And mechanical properties of basalt fiber/epoxy resin composites were tested. The results show that the depth and area of surface defects of basalt fiber increase with the increase of laser modification power. When the modification power increases from 0 W to 120 W, the maximum depth of surface defects increases from 9 nm to 180 nm, the distribution range of surface defects increases from 3.5~6.5 nm to 90~120 nm, the surface roughness increases from 141 nm to 2470 nm. After laser modification, the tensile property of basalt fiber decreases. The relationship between the depth of surface defect and tensile strength of basalt fiber does not follow the classical theory because of the radiation effect of laser on the fiber. XRD peaks of basalt fibers are basically the same before and after laser modification, and the types of elements on the surface of basalt fiber do not change. Laser modification can improve the mechanical properties of basalt fiber/epoxy resin composite. With the increase of laser power, the tensile strength and impact of composites increase first and then decrease.

The stress state on the surface of material plays an important role on the erosion wear behavior of material. In this paper, the effects of erosion angle, erosion velocity and abrasive particle size on the erosion stress of glass-ceramic coating were discussed by finite element method. The volume wear rate of glass-ceramic coating under different erosion angle was measured by erosion tester at room temperature. The results show that the erosion stress of glass-ceramic coating increases with the increase of erosion angle, erosion velocity and abrasive particle size. Under the same erosion angle and erosion velocity, the effect of abrasive particle size on the improvement of coating erosion stress is significant. The erosion wear rate of glass-ceramic coating increases with the increase of erosion angle, and its change trend is basically consistent with the change trend of erosion stress, which verifies the reliability of finite element stress simulation.

90SrF2 and waste with high content of Na2O, Fe2O3, P2O5 are two kinds of waste generated from nuclear power plants. Glass wasteforms composed mainly of SrF2, Na2O, Fe2O3 and P2O5 can be prepared when the two kinds of wastes are combined to solidify. Glass forming ability, actual composition, structure and thermal stability of samples in SrF2-Na2O-Fe2O3-P2O5 system were investigated by X-ray fluorescence spectrometer, X-ray diffractive spectrometer, infrared spectrometer, thermal expansion instrument and differential thermal analyzer. The water resistance was studied by dissolution rate method and product consistency test method. The results show that the mass loss of Sr is little but the mass loss of F is as high as 30%~34% in glass after melting at 1 000 ℃ for 0.5 h. With the decrease of P2O5/SrF2 molar ratio, the thermal stability of glass decreases sharply, but the water resistance improves obviously. Samples with pyrophosphate glass structure have good stability, and the glass with 30% (mole fraction) SrF2 has both high water resistance and high thermal stability.

The thermal insulation material prepared by sodium silicate has many advantages such as incombustibility, light weight and low thermal conductivity, but the poor water resistance restricts its application. Therefore, sodium tetraborate was chosen as the modifying agent and added into sodium silicate solution to prepare thermal insulation material by low temperature sintering. The chemical structure and physical properties of the material were characterized and ion leaching experiments were carried out to investigate the effects of sodium tetraborate. The results show that sodium tetraborate can effectively reduce the number of -OH groups in the material, and make Si-O structure more complex, which can improve the water resistance of the material. When the content of sodium tetraborate is 1% (mass fraction, the same bellow), it has the most significant inhibitory effect on the leaching of sodium ion and silicate ion in the material, and the ion concentrations of the two are reduced by 65.33% and 45.02%, respectively. When the sodium tetraborate content is 3%, the softening coefficient of the material is increased by 84.6%, and its compressive strength, thermal conductivity and apparent density are 0.46 MPa, 0.046 W/(m·K) and 123.1 kg/m3, respectively.