Chloride ions induced corrosion of reinforcing steel is a major cause of concrete durability problems. The essence is that chloride ions diffuse through the porous structure of the material matrix in the cementitious material and gradually migrate to the surface of the reinforcing steel, where adverse physicochemical reactions occur. Hydrotalcite, known as layered double hydroxides (LDHs), is a new type of admixture to delay the corrosion of reinforcement. It has unique layered structure and ions exchange properties which ensures ion exchange between chloride ions and interlayer cations of LDHs and reaches the purpose of adsorption of chloride ions, thus extending the service life of concrete structures. This paper introduces the structural properties, modification method of hydrotalcite as well as its adsorption mechanisms on chloride ions, and summarizes the research results of recent years on the adsorption capacity of chloride ions through different modified hydrotalcite systems to improve the corrosion of steel reinforcement. The results indicate that the chloride ions adsorption capacity of hydrotalcite-based composite materials is mainly affected by LDHs preparation procedure, pH value of the pore solution and the chloride ions concentration. The chloride ions adsorption of calcined LDHs is more effective. When the addition of LDHs is 1%~3% (mass fraction), the resistance to chloride ions permeability of cement-based materials will be obviously improved.

The chloride binding capacity of cementitious materials is a key factor affecting the service life of marine concrete structures. Calcium nitrite was selected as additional calcium phases, and metakaolin or nano alumina was selected as additional aluminum phases. The effects of Ca-Al phases on hydration products, chloride binding capacity and macro performance of alkali activated slag cementitious materials were investigated. The results show that the addition of Ca-Al phases effectively promotes chemical reaction, and improves the chloride binding capacity of alkali activated slag cementitious materials. Compared with control group, the amount of binding chloride increases by 11.5%~34.8%. m(Ca)/m(Al) value in system has an important influence on chloride binding capacity. The decrease of m(Ca)/m(Al) value results in the increase of the content of AFm phases, C-(A)-S-H gels and other products. The content of calcium nitrite has an optimum value. Excessively high content of calcium nitrite negatively affects the strength, but nano alumina compensates for the strength loss. In general, the relative content of Ca-Al phases is important for phase composition and chloride binding capacity of alkali activated slag.

The pH value of superfine cement (SC) grouting material stone body with silica fume (SF) content of 30%~50% (mass fraction, the same below) and water-binder ratio of 14 at different ages was measured by simplified ex-situ leaching method. Meanwhile, the effects of SF content, SiO2 content and theoretical Ca/Si molar ratio of C-S-H gel on grouting material pH value were investigated. The rheological properties and mechanical properties of 60%SC+40%SF low-pH grouting material were examined. In addition, SEM, XRD and TG were used to examine the hydration products and microstructure of stone body. The results show that when SF content is more than 40%, SiO2 content is more than 50% and Ca/Si molar ratio of C-S-H gel is less than 0.8, the pH value of stone body is less than 11.00. The naphthalene superplasticizer (SP) greatly reduces the marsh funnel viscosity of slurry, and the appropriate content of SP is 1.6%. The Bingham model provides a satisfactory description of the rheological properties of slurry. The increase of water-binder ratio has adverse effect on the compressive strength of stone body, so the water-binder ratio should not exceed 1.6. Due to the pozzolanic effect and dilution effect of SF, there is no Ca(OH)2 in stone body after curing for 180 d, and its principal hydration products are C-S-H gel with a low Ca/Si molar ratio and ettringite.

In this paper, the standard consistency water consumption, setting time, stability and the change law of compressive and flexural strength of sulfoaluminate based composite cementitious materials with different boric acid amounts were studied, and the hydration mechanism of composite cementitious materials was analyzed by XRD and SEM. The results show that the incorporation of boric acid does not affect the stability of cementitious materials, its standard consistency water consumption increases, and the standard consistency water consumption is inversely proportional to the amount of boric acid. The greater the amount of boric acid is, the more obvious the prolongation of the initial and final setting time is. When the amount of boric acid is 0.20% (mass fraction), the early strength of the test group with a high proportion of sulfoaluminate cement increases, and the late strength can not be inverted shrinkage. Boric acid can make the morphology of AFt stouter. The doping of boric acid can make the dry shrinkage rate decrease and the quality change rate show a decreasing trend.

The synthesized nano-SiO2 was attached to the surface of polyvinyl alcohol (PVA) fiber and polyethylene (PE) fiber by chemical deposition method, and the distribution of SiO2 on the modified fiber surface was observed by scanning electron microscope (SEM). The strength and toughness of engineering geopolymer composites (EGC) were compared by compressive tests, flexural tests and uniaxial tensile tests before and after the surface modification of fibers. And the reason for the change of macro-mechanical properties was verified by single fiber pull-out tests from the microscopic mechanical point of view. The results show that the compressive and flexural strength of PVA fiber EGC specimen after hydrophobic modification of SiO2 decrease and those properties of PE fiber EGC specimen after hydrophilic modification of SiO2 improve. In the process of uniaxial tension, most EGC specimens show different degrees of tensile strain hardening, and it is more obvious after the fibers are modified. The results of single fiber pull-out tests show that the EGC specimens have a more obvious slip hardening stage and the interface property of fiber-matrix is improved after fiber surface modification.

In this paper, a kind of colloidal of nano-silica (CNS) was prepared, which was a comb-like structure polymer. Its main chain synthesized by acrylic acid, polyoxyethylene ether and silane coupling agent, side chain grafted with nano-silica particles. By optimizing the parameters, a reasonable synthesis process and formula were determined. The morphology and particle size distribution of the nano-silica in CNS were characterized by scanning electron microscope (SEM) and dynamic light scattering (DLS). The effects of different amounts of CNS on cement hydration heat, setting time, pore structure, hydration products, mechanical properties and impermeability of concrete were evaluated. The test results show that the addition of CNS can increase the hydration heat release rate, promote the early hydration of cement, accelerate the formation and precipitation of hydration products, increase the hydration temperature and shorten the setting time. The effect on hydration products is that CNS promotes the formation of C-S-H gel at 7 d and reduces the content of Ca(OH)2(CH) in hydration products. At 28 d, CNS accelerates the formation of hydration products and increases the content of CH in hydration products. The macroscopic performance shows that the 7 and 28 d compressive strength and impermeability of concrete are improved.

The concretes with recycled aggregate mass replacement rate of 30% were placed in 3%Na2SO4, 5%Na2SO4, 10%Na2SO4 (3%, 5%, 10%, mass fraction) solution and water for freeze-thaw cycles test by quick freezing method. The mass loss rate, relative dynamic elastic modulus change and compressive strength loss rate of recycled aggregate concrete were tested. The microstructure of the damaged layer of recycled aggregate concrete was analyzed by electron microscope, energy spectrometer and X-ray diffraction. The thickness of the damaged layer was determined by ultrasonic flat measurement method, and the erosion coefficient was introduced to optimize the damage degree with the thickness of the damaged layer as the evaluation index. The results show that: when freeze-thaw cycles is 0~200 times and the concentration of Na2SO4 solution is greater than 5%, the erosion coefficient of compressive strength is always less than 1, in other ways, Na2SO4 solution has obvious promoting effect on the macroscopic mechanical performance damage of recycled aggregate concrete, but has obvious inhibitory effect on the microstructure damage. In the early stage of freeze-thaw cycles of recycled aggregate concrete, freeze-thaw erosion is the main factor. In the later stage of freeze-thaw cycles, sulfate chemical erosion is the main factor. After chemical erosion, expansion products such as ettringite and gypsum are formed in recycled aggregate concrete, and they lead to expansion cracks. The cracks expand rapidly under the action of freeze-thaw cycles, and the thickness of the damaged layer increases. The accuracy of the damage degree based on the thickness of the damage layer as the evaluation index is improved by at least 26.33% after optimization.

In order to investigate the capillary water absorption characteristics of recycled sand concrete, the influences of these factors, such as replacement ratio of recycled sand (0%, 30%, 50%, 70%, 100%, mass fraction), fine powder content in the recycled sand (3%, 7%, 10%, mass fraction), water-binder ratio (0.37, 0.45, 0.58), type and content of mineral admixture and pre-wetting degree of recycled sand (0%, 50%, 100%) as well as silane immersion treatment, on compressive strength and capillary water absorption performance of recycled sand concrete were investigated. The relationship between pore structure and capillary water absorption coefficient of concrete with different content of recycled sand was analyzed. The results show that the capillary water absorption of recycled sand concrete in the two stages of 0~240 min and 240~1 440 min is linear with the square root of time. With the increase of replacement ratio of recycled sand and fine powder content, the capillary water absorption coefficient of concrete increases gradually. When the replacement ratio of the recycled sand exceeds 50%, the capillary water absorption and strength of concrete will be significantly affected. The capillary water absorption coefficient of recycled sand concrete decreases by reducing the water-binder ratio, increasing the pre-wetting degree of recycled sand, adding ternary composite mineral admixtures (15% fly ash+15% slag powder+8% silica fume) and impregnating the surface of concrete with silane. With the increase of replacement ratio of recycled sand, the porosity and critical pore size of concrete increase, which leads to the increase of capillary water absorption coefficient of concrete.

Considering the shortage of natural sand and the environmental crisis caused by waste concrete, recycled fine aggregate (RFA) with different replacement rates was used to prepare recycled fine aggregate concrete (RFAC), the evolution law of RFAC performance under dry-wet cycle was analyzed, and chloride ion erosion resistance of RFAC was studied. The results show that the compressive strength of concrete is reduced by the addition of RFA. The 28 d compressive strength of RFAC with RFA mass replacement rate of 100% is 77.0% of ordinary concrete. The free chloride ion content of RFAC increases first and then decreases and finally stabilizes with the increase of erosion depth under the dry-wet cycle. The convection zone and diffusion zone of chloride ion appeares obviously, and the depth of the convection zone is about 5 mm, and the depth of the convection zone also increases with the increase of the dry-wet cycles times and the RFA replacement rate. The porosity of RFAC increases exponentially with the increase of dry-wet cycles times. The porosity of concrete with high RFA replacement rate increases more obviously under dry-wet cycle, which is the reason why its chloride ion erosion resistance becomes worse.

The green foaming agent was prepared by water extraction method with natural plant tissue camellia meal as raw material, and the foam concrete was prepared by physical foaming method. The effects of mixing time, water-binder ratio and foam content on the dry density, compressive strength and pore structure of foam concrete were investigated. The results show that the green foaming agent has high foam stability and can be used to prepare low-density foam concrete, so it is a high-quality new green foaming agent. When the foam content is 750 mL, the mixing time is 180 s, and the water-binder ratio is 0.45, the water absorption of the prepared A05 density grade foam concrete is 45%, and the compressive strength is 1.52 MPa. The foam concrete prepared by green foaming agent has uniform pore size distribution, small pore size (maximum pore size dmax<0.6 mm), and complete pore morphology.

In order to study the uniaxial compression characteristics of foamed concrete under freeze-thaw environment, foamed concrete with four kinds of densities (500, 600, 800 and 1 000 kg/m3) were studied with different loading rates (10~100 N/s). Moreover, the pore structure model of foamed concrete under freeze-thaw environment were illustrated by using X-CT. The characteristics and influencing factors of load-displacement curves in the uniaxial compression process were studied, and the relational degrees among the density, freeze-thaw cycles, loading rate and compressive strength of foamed concrete were analyzed utilizing the regression analysis and grey relational theory. The results show that the tangent modulus of load-displacement curve of foamed concrete is reduced greatly and the nonlinear characteristics are enhanced in the uniaxial compression process after freeze-thaw cycles. Besides, the porosity of specimen increases after freeze-thaw cycles, and the discretization of pore size distribution increases. There remains an exponential relationship between compressive strength and density grade of foamed concrete under freeze-thaw environment, and the correlation coefficients are all above 0.9. According to the grey relational theory, the density grade of foamed concrete is more related to the compressive strength than freeze-thaw cycles and loading rate, and the grey relational degrees are all above 0.65.

In recent years, ultra-high performance concrete (UHPC) has been widely used. However, due to excessive cement consumption in the production process of UHPC, the solid durability and long life of UHPC, the level of carbon emission from UHPC is not yet well understood. Therefore, the life cycle assessment (LCA) method was used to build a quantitative UHPC emission analysis model to compare and analyze the carbon emissions in the whole life cycle between steel-UHPC bridge deck and conventional steel-concrete bridge deck structure. The results show that although the carbon emission of UHPC in the production stage is about 1 245.84 kg CO2eq/m3, which is 1.58 times that of the ordinary concrete, in terms of performance, the carbon strength of UHPC is 62.25% of the ordinary concrete, so UHPC is a greener building material. Over the entire life cycle, the average annual carbon emissions of steel-UHPC bridge decks decrease by 35.76% than conventional steel-mixed bridge deck, offering significant carbon reduction potential and contributing to the sustainability of infrastructure development. The steel-UHPC bridge deck scheme has engineering comparison advantages and excellent economy, and its carbon emission per unit output value is 0.89 t CO2eq/103 yuan, which is 86.41% of that of the conventional steel-mixed bridge deck and has a better carbon reduction effect. The reliability of the results and further emission reduction measures are discussed, and finally, the contents to be further studied are put forward.

High-strength concrete is vulnerable to impact damage during service, so it is necessary to prepare high-performance concrete with certain guarantee of strength and impact resistance. In this paper, C100 high-strength concrete was designed with normal-pressure and high-pressure curing process, and its toughness difference law and mechanism were discussed from macroscopic and microscopic levels. The test results show that the difference of compressive strength of concrete under the two curing systems is small, but the difference of splitting tensile strength and flexural strength is big within 28 d. At the same time, the toughness of high-pressure curing concrete is better than that of normal-pressure curing concrete, and its tension-compression ratio, flexural-compression ratio and initial cracking impact energy consumption are 1.37 times, 1.21 times and 1.24 times of that of normal-pressure curing concrete on average. Compared with normal-pressure curing concrete, the internal admixture reaction of high-pressure curing concrete develops more fully with age, and calcium silicate hydrate (C-S-H) is flocculent, which makes it more easily fill the internal weak areas such as pores and cracks. There is no plate-like Ca(OH)2 in the hydration products of high-pressure curing concrete, and C-S-H effectively plays a bridging role. The prepared high-pressure curing concrete has better toughness.

In order to study the influence of high temperature on the residual strength and microstructure evolution of hybrid fiber reinforced concrete (HFRC), the basic mechanical properties of HFRC at different temperatures were tested. The microstructure of the interface between fiber and cement paste was studied by scanning electron microscopy and the compressive strength of HFRC after different heat treatment temperatures was predicted by BP neural network. The results show that the synergistic effect of fiber significantly improves the high temperature resistance of concrete, and the compressive strength and splitting tensile strength of HFRC are higher than those of plain concrete after high temperature. The compressive strength and splitting tensile strength of HFRC reach the maximum value when the volume fraction of cellulose fiber and basalt fiber is 0.15%. The internal structure of HFRC is dense, and the basalt fiber is filled in the pores and has good bonding with the matrix, which effectively inhibits the crack propagation. The prediction data based on neural network matches with the experimental data, and the BP neural network well predicts the compressive strength of HFRC after high temperature.

Insulation property and frost resistance have an important impact on measuring the durability of functional integrated materials and improving green energy conservation and emission reduction. Using orthogonal test, expanded polystyrene (EPS) content, water-binder ratio, polyoxymethylene (POM) fiber content were used as the influencing factors, and the mechanical properties, insulation property and frost resistance of EPS lightweight concrete were tested. The test results were analyzed to obtain the EPS lightweight concrete foundation mix ratio with the best comprehensive performance by range analysis and AHP-CRITIC hybrid weighting analysis. The results show that EPS content has the greatest influence on the mechanical properties of EPS lightweight concrete, POM fiber can significantly increase the tensile strength of EPS lightweight concrete, and water-binder ratio has the least influence on the mechanical properties of EPS lightweight concrete. When the volume fraction of EPS is 35%, the mass fraction of POM fiber is 0.9%, and the water-binder ratio is 0.21, the mechanical properties of EPS lightweight concrete are the best. Under freeze-thaw cycles, the freeze-thaw damage of EPS lightweight concrete satisfies two-parameter Weibull distribution model, which can better reflect the change rule of freeze-thaw damage.

Serpentine aggregates were selected from Hubei Qichun, Jiangxi Yiyang and Shaanxi Hanzhong (hereinafter referred to as Hubei, Jiangxi, Shaanxi serpentine aggregate). The anti-neutron radiation preference and structural stability at high temperature of serpentine aggregate were studied by scanning electron microscope (SEM), X-ray diffractometer (XRD) and thermogravimetric analyzer (TG). The results show that the crystal water content of Hubei, Jiangxi and Shaanxi serpentine aggregate are 6.89%, 12.55% and 12.50% (mass fraction), respectively. The (10, 16］ and (16, 20］ mm particle sizes of Hubei serpentine aggregates have thermal cracking behavior at 500 ℃, and their thermogravimetric losses are 1262% and 2472%, respectively. Because of Shaanxi serpentine aggregate containing brucite, the brucite is thermally decomposed and dehydrated at 300~500 ℃, and the thermogravimetric loss of the aggregate at 500 ℃ reaches 2.75%~4.04%. At 500 ℃, the maximum thermogravimetric loss of Jiangxi serpentine aggregate is 2.26%, and it has no thermal explosion behavior and the influence of brucite content, and it has a great high-temperature structural stability, which has the best performance of serpentine aggregate from three producing areas. The test method for structural stability of serpentine aggregate with different particle sizes at high temperature is proposed, which has certain guiding significance for promoting the engineering application of domestic serpentine aggregate in anti-neutron radiation concrete such as nuclear power reactors, spallation neutron sources and maintainable test units in nuclear fusion material irradiation facilities.

The interfacial bonding performance between epoxy resin and concrete is one of the key factors affecting the effect of fiber-reinforced concrete structures, and the carbonation of concrete affects the interfacial bonding performance between epoxy resin and concrete. The effect of carbonation on the interfacial bonding performance between epoxy resin and concrete was investigated based on molecular dynamics. The research results show that the existence of carbonation can enhance the interfacial bonding performance between epoxy resin and concrete. The distribution of epoxy resin is closer to the concrete surface, and the interaction energy between epoxy resin and the substrate is higher. Static structure analysis shows that epoxy resin and concrete substrate are mainly connected by calcium oxygen bond and hydrogen bond, and the number of chemical bond connections on the calcium carbonate surface is more and the chemical bond strength is higher. Dynamic analysis shows that the surface of calcium silicate hydrate is bound by fewer ion pairs and hydrogen bonds, and epoxy resin can move freely, which is not beneficial to strong interfacial bonding performance.

The interface transition zone is the weakest area in mechanical properties of concrete structures, and its strength directly affects the mechanical properties of concrete. The strength and uniformity of aggregates are also the parameters that need to be focused for concrete structure design. Based on the discrete element method, the effect of aggregate strength, interfacial transition zone strength, aggregate homogeneity and size on concrete strength and deformation were studied. The results show that the crushing of aggregate provides a new path for propagation and merging of microcracks in sample, and the formation of a large number of network crack surfaces accelerates the destruction of sample. The peak strength and elastic modulus of sample increase linearly with the increase of interface transition zone strength, and the increase of interface transition zone strength reduces the radial deformation of sample. The post peak stage of stress-strain curve of concrete changes gradually from toughness to brittleness with the increase of interface transition zone strength. The aggregate strength has little effect on the peak strength and elastic modulus. The radial deformation of sample with good homogeneity of aggregate is smaller than that of sample with poor homogeneity. The peak strength and elastic modulus of sample increase with the increase of aggregate size, but the increase is far less than the increase of peak strength brought by interface strength.

The changes of phase and structure of low-grade clay at different calcination temperatures (650, 700, 750, 800, 850 ℃) were studied by DSC-TG, XRD, IR, Raman and NMR. The results show that the low-grade clay is mainly composed of quartz with high crystallinity, and contains a small amount of phengite, kaolinite, illite, calcite, pyrite and microcline with low crystallinity. After calcination at 650~850 ℃, kaolinite and illite decompose into amorphization SiO2 and Al2O3, and some quartz transform into amorphous SiO2. The adsorbed water and the structure water in the low-grade clay decompose, the aluminoxy octahedron gradually transforms into aluminoxy tetrahedron, and the short-range order structure of Si-O-Si in quartz is also destroyed to a certain extent.

Coal gangue is a solid waste produced by the coal industry. The continuously produced and long-term stored coal gangue has a certain impact on the environment, so it is urgent to carry out coal gangue resource utilization. The coal gangue in Qianxi city, Guizhou province was used as the research object, coarse coal gangue was used as aggregate, thermal activated fine coal gangue was used as mineral admixture, and the influence of thermal activated coal gangue powder on the properties of matrix-aggregate interface transition zone was studied by compressive and flexural strength testing machine, microhardness meter and scanning electron microscope. The results show that with the increase of thermal activated coal gangue powder amount, both the flexural strength and compressive strength of cement sand test block increase first and then decrease. The thermal activated coal gangue powder with a mass fraction of 2.5% improves the mechanical properties of cement sand test block, reduces the width of interface transition zone, promotes the microhardness of interface transition zone, and compacts the interface structure. With the amount of thermal activated coal gangue powder further increasing, the width of interface transition zone increases, and the number and size of micropore also increase. Some cementing materials are attached to the surface of coal gangue aggregate in clumpy form, which have adverse effects on the mechanical properties of cement sand.

Circulating fluidized bed fly ash (CFB fly ash) can form a high-strength solidified body by adding water to harden itself and has the potential to be used as roadbed. However, the hydration of f-CaO and II-CaSO4 in CFB fly ash to form ettringite and dihydrate gypsum causes the volume expansion of the solidified body, which may affect the volume stability of the subgrade. Therefore, the effects of standard curing time, sulfur and calcium content of CFB fly ash and compactness on California bearing ratio (CBR), water absorption and CBR expansion rate of CFB fly ash solidified body were studied in this paper. And the expansion mechanism of CFB fly ash in dry and hard system was studied. The results show that the expansion of CFB fly ash solidified body mainly comes from the water absorption expansion and hydration expansion of CFB fly ash. The longer the standard curing time is, the larger the CBR value of the consolidated body and the lower the water absorption and expansion rate are. The CBR value and water absorption rate tended to be stable and the expansion rate did not change at 7 d of standard curing. The higher the sulfur and calcium content of CFB fly ash is, the larger the CBR value of the consolidated body, the longer the expansion stability time, the higher the expansion rate after stabilization, and the lower the water absorption rate are. With the increase of compactness, the density of solidified body increases and porosity decreases. Therefore, the CBR increases gradually and the water absorption gradually decreases. Due to the increase of the constraint effect of CBR on the expansion, the expansion rate of the solidified body decreases gradually.

In order to study the resource utilization of slag, fly ash and carbide slag, the hydration product composition and strength characteristics of slag-fly ash composite cementitious materials were studied with carbide slag as alkali activator. The crystal structure, thermochemical properties and microscopic morphology of the composite cementitious materials were analyzed by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), thermogravimetric-differential scanning calorimetry (TG-DSC), scanning electronic microscopy-energy dispersive spectroscopy (SEM-EDS), and the interaction mechanism of carbide slag activating slag-fly ash composite cementitious materials was studied. The results show that carbide slag as alkali activator provides a strong alkaline environment for the initial hydration of slag-fly ash composite cementitious materials, and it can also drive the hydration reaction of slag and fly ash. With the increase of slag content, the strength of composite cementitious materials increases first and then decreases. When the mass proportion of fly ash and slag is 4∶6, and the mass addition of carbide slag is 4%, the compressive strength of composite slurry reaches 25.9 MPa under the conditions of 4 d normal temperature curing and 32 h high temperature steam curing. The hydration products of the slag-fly ash composite cementitious system are unevenly distributed, containing C-S-H, C-A-H, C-A-S-H gel and etc. Carbide slag has a good effect as alkali activator in slag-fly ash system.

Nano-silica was used to improve the anti-MgSO4 erosion performance of solidified soil with soda residue and ground granulated blast furnace slag. The unconfined compressive strength (UCS), nuclear magnetic resonance and X-ray diffraction tests were carried out on solidified soil soaked in MgSO4 solution. The influences of nano-silica content, curing time and soaking time on strength and microstructure of solidified soil were studied. The results show that the sample with 3%(mass fraction) nano-silica content shows the smallest pore volume and highest UCS, and the products such as calcium aluminate hydrate are generated under standard maintenance conditions. In MgSO4 erosion environment, the samples cured for 7 d have good erosion resistance. When the silica powder content is 3% (mass fraction), the solidified soil has the best anti-MgSO4 erosion performance, and the unconfined compressive strength increases with the increase of soaking time. For the samples cured for 28 and 60 d, the anti-MgSO4 erosion performance is weaker. The functional relationship between UCS of solidified soil and nano-silica content and soaking time is given, and the minimum UCS is predicted. Appropriate nano-silica promotes the hydration rate and degree for solidified soil and reduces the generation of ettringite and its adverse effects, which improves anti-MgSO4 erosion performance for solidified soil with soda residue.

In this paper, fly ash, slag and carbide slag were used as precursors, and sodium hydroxide and sodium silicate were used as mixed activators to prepare geopolymer. The effects of precursor ratio and activator parameters on the compressive strength of fly ash-slag-carbide slag based geopolymer were investigated, and the microstructure was observed by mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). It is found that the compressive strength of geopolymer increases first and then decreases with the increase of the carbide slag replacing fly ash content, liquid-solid ratio, and activator modulus. When the carbide slag replacing slag content decreases, or the activator concentration increases, the compressive strength increases continuously. Adding carbide slag in the precursors with appropriate amount to replace fly ash positively affects the geopolymer compressive strength. The total porosity and the large pore proportion of geopolymer are generally negatively correlated with the compressive strength. The higher the strength is, the denser the microstructure of geopolymer is. The optimum ratio of geopolymer derived from the test is 32∶15∶3 for the mass ratio of fly ash, slag and carbide slag, 0.55 for the liquid-solid ratio, 30% (mass fraction) for the activator concentration, and 1.2 for the activator modulus, which corresponds to a 28 d compressive strength of 77.83 MPa.

There is a large stock and serious pollution of electrolytic manganese residue and municipal solid waste incineration bottom ash in our country, and it is urgent to develop economically and technically feasible resource utilization technologies. Electrolytic manganese residue and municipal solid waste incineration bottom ash were used to prepare a road base material (RBM), and the chemical composition, mechanical properties, durability, leaching characteristics, hydration products, and pore structure of RBM with different Ca/Si ratios (mass ratio) were studied. The hydration products and microstructure of RBM were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TG), scanning electron microscope-energy dispersive spectrometer (SEM-EDX), and mercury intrusion porosimetry methods. The leaching characteristics of RBM were studied by leaching test. The results show that when the Ca/Si ratio is 0.8, the mechanical properties and pore structure of RBM are optimal, and the unconfined compressive strength (UCS) reaches 9.06 MPa after curing for 7 d, which meets the Class I standard of cement soil road base in China. The 28 d UCS of RBM after 9 freezing-thawing cycles and drying-wetting cycles is 11.63 and 9.90 MPa, respectively. The main hydration products in RBM are CaAl2Si2O8·4H2O, 3CaO·Al2O3(C3A), 2CaO·SiO2(C2S), and CaMnSi4O8. The strength and durability of RBM are improved by the interlacing of hydration products. The leaching concentrations of heavy metals and ammonia nitrogen in RBM meet the Chinese groundwater standard. This study can save the cost of road base materials while realizing the large-scale utilization of electrolytic manganese residue and municipal solid waste incineration bottom ash.

In this paper, municipal sewage treatment plant sludge and Dexing copper mine tailings were used as the main raw materials to prepare ceramsite by high temperature sintering. The ratio of raw materials and sintering process parameters were determined by experiments. The physical properties (bulk density, apparent density, 1 h water absorption rate, void ratio) of ceramsite, heavy metal content in leaching solution, and the adsorption of lead ions by ceramsite were analyzed. The ceramsite was used to replace the gravel in ordinary concrete to varying degrees (0%, 20%, 40%, 60%, 80%, 100%, mass fraction), and the changes of cube compressive strength and splitting tensile strength of concrete were studied. The results show that the raw materials are mixed and granulated according to m(sludge)∶m(tailings)∶m(clay)=2∶3∶1, and the sintering process is drying at (105±5) ℃ for 3 h, preheating at 400 ℃ for 15 min, and sintering at 1 000 ℃ for 12 min. Then the bulk density of the prepared ceramsite is 528 kg/m3, the apparent density is 1 004 kg/m3, the 1 h water absorption rate is 7.64%, and the void ratio is 47.37%. The content of heavy metals in ceramsite leaching solution is lower than the limit of national standard. The adsorption rate of lead ions by ceramsite sintered at 960 ℃ reaches 93.57% under the condition of 30 ℃ constant temperature water bath. After adding ceramsite, with the increase of ceramsite replacement rate, the cubic compressive strength and splitting tensile strength of ceramsite concrete increase first and then decrease. When the ceramsite replacement rate is 60%, the compressive strength of the cubic test block cured for 28 d reaches the maximum of 35.38 MPa. When the ceramsite replacement rate is 40%, the splitting tensile strength reaches the maximum of 5.8 MPa.

A design method of solid waste-based self-foaming expanded ceramsites was studied, and the gas produced by the decomposition of hematite in red mud at high temperature was used to realize self-foaming. In this study, the ceramsites were produced by sintering the raw materials (95% of which were solid wastes) at 1 200 ℃ for 60 min, and the obtained ceramsites have the characteristics of light weight and high strength. The ceramsites particle strength is 4.86~6.75 MPa, water absorption is 0.72%~1.11%, and bulk density is 0.53~0.71 g/cm3. The influence of red mud content on the physical properties, microstructure, phase components and chemical structure of ceramsites was investigated by SEM, XRD, FTIR, TG-DSC and XPS. The results show that with the content of red mud increases from 10% to 25% (mass fraction), the expansion index and water absorption decrease, the bulk density increases, and the particle strength first increases and then decreases. The main reason of the solid waste-based expanded ceramsites with self-foaming behavior is that hematite decomposed at high temperature to released gas, and the gas is entrapped by the liquid phases.

The autoclaved aerated concrete is prepared by using red mud-gypsum to excite blast furnace slag (BFS) and fly ash, which is of great significance to promote the resource utilization of red mud, reduce the consumption of Portland cement, and achieve CO2 reduction. The autoclaved aerated concrete with strength grade A3.5 and density grade B06 was taken as the design goal, and the influences of red mud, gypsum, BFS, and quicklime on the compressive strength of autoclaved aerated concrete were analyzed. The results show that when the mass ratio of fly ash, red mud, gypsum, BFS and quicklime is 60∶10∶3∶7∶20, the dry density and compressive strength of autoclaved aerated concrete are 623.4 kg/m3 and 3.6 MPa, respectively. The analysis of hydration products shows that the hydration product before autoclave reaction is mainly ettringite, and the hydration products after autoclaved reaction are tobermorite and katoite.

In order to study the activation effect of chemical excitation, heat treatment and their coupling on recycled powder, the mechanical properties, mineral composition and reaction product types of recycled powder were studied by means of compressive strength test, X-ray diffraction test and infrared spectroscopy, etc. The results show that chemical excitation provides alkaline environment and reactive ions, and high temperature calcination changes the mineral structure of original material. Both methods make recycled powder have rehydrating and cementing ability. After high temperature thermal activation, the aluminosilicate structure of recycled powder is reorganized or destroyed. The groups in the mineral are more easily dissolved during chemical excitation to participate in the reaction to form cementitious products. At this time, the 3 and 28 d compressive strength of recycled powder reach 27.0 and 48.6 MPa, respectively, which increase by 10.3 times and 5.8 times compared with original specimen. The coupling effect makes recycled powder have higher activity and strength.

Recycled fine powder (RFP) is difficult to be effectively utilized due to its low activity, resulting in a great waste of resources. To stimulate the activity of RFP, the effects of traditional alkali activators (sodium hydroxide, calcium hydroxide, magnesium hydroxide, sodium silicate), alcohol amine activators (polyisomeric alcoholic amine, triethanolamine) and nanocrystalline nuclear activator on the compressive strength of mortars mixed with RFP were investigated. Meanwhile, the effects of chemical activators on the hydration heat release, hydration products and microstructure of RFP-cement pastes were analyzed to reveal their promotion mechanism. The results show that sodium hydroxide and sodium silicate can further reduce the compressive strength of mortars mixed with RFP, and the relationships are linear inverse with their dosage. Calcium hydroxide, magnesium hydroxide, triethanolamine and nanocrystalline nuclear activator can improve the early strength under certain dosage conditions, but can not improve the later strength. Polyisomeric alcoholic amine can significantly improve the compressive strength of each age through promoting the hydration of mineral phases tricalcium aluminate (C3A) and tetracalcium aluminoferrite (C4AF), accelerating the hydration process of RFP-cement pastes, improving the compactness of the interfacial bond between cement matrix and sand. The activity index of RFP increases from 62.8% to 74.8% at the optimal dosage of 0.2% (mass fraction). The research results can provide reference for improving the utilization rate of RFP and achieving the goal of energy conservation and emission reduction in the construction industry.

In order to investigate the effect of ceramic polishing waste (CPW) on the durability of ultra-high performance concrete (UHPC), the CPW was used to replace part of cement, fly ash and silica fume to prepare UHPC, and the effect of CPW on the pore structure, mechanical properties, volume stability, chloride penetration resistance, and sulfate attack resistance of UHPC was investigated. The results show that the porosity of UHPC increases with the increase of CPW replacing cement, fly ash and silica fume, respectively, and then the chloride penetration resistance of UHPC decreases. The replacement of fly ash by CPW improves the autogenous shrinkage of UHPC, while the replacement of cement and silica fume by CPW leads to reduce the autogenous shrinkage of UHPC. The replacement of cement by CPW reduces the compressive strength of UHPC, but the corrosion resistance coefficient and compressive strength of UHPC are improved after sulfate attack. When the cement replacement rate by CPW is 20% (mass fraction), the compressive strength of UHPC after sulfate attack for 90 d reaches the highest value.

In order to investigate the effect of heat activated oil shale semi-coke on the durability of concrete, and promote the application of cement-oil shale semi-coke concrete, the effects of different activation and calcination temperatures (300, 400, 500 and 600 ℃) and different content (0%, 5%, 10%, 15%, 20% and 25%, mass fraction) of oil shale semi-coke on the durability of concrete were investigated using the concrete carbonation test, chloride ion penetration resistance test and frost resistance test. The nuclear magnetic resonance (NMR) test was used to analyze the pore size distribution and porosity of concrete, and the influence mechanism of oil shale semi-coke on the durability of concrete was revealed from the pore size distribution characteristics. The results show that compared with the activation and calcination temperature of oil shale semi-coke, the effect of content on the concrete durability is more significant. The incorporation of oil shale semi-coke reduces the carbonation resistance of concrete, but it still meets the requirements of the standard design value at 25% content. And the carbonation depth is far less than 20 mm. The chloride ion penetration resistance also decreases with the incorporation of oil shale semi-coke, and it is still in the low permeability range when the content is not higher than 25%. 5 kinds of oil shale semi-coke content of concrete can meet the requirements of 150 times freeze-thaw cycles, overall having good durability. In addition, the incorporation of oil shale semi-coke significantly changes the pore size distribution and pore number inside concrete, thus affecting the durability of concrete to varying degrees.

The composition of radionuclide in high-level radioactive waste is complex resulting in an issue of strong selectivity in ceramics solidification. In this study, a novel method was proposed to simultaneously immobilize fission products and actinides in a simple process. Based on the ceramizable geopolymer design theory, a high-level radioactive liquid waste multiphase ceramics-based form was prepared by mixing simulated high-level radioactive liquid waste with metakaolin, slag, silica fume and nano-zirconia as main raw material and 1.5-modulus potassium water glass as activator. After mixing of high-level radioactive liquid waste, raw materials and activator, and curing at room temperature for 7 d, the hardened cement waste form was transformed into a geopolymer-based multiphase ceramics high-level radioactive liquid waste form by heat treatment at 1 100 ℃. The leaching resistance properties of waste form were tested by static leaching method. XRD, SEM-EDS, XPS and other analytical techniques were employed to explore the mechanism of geopolymer ceramization conversion process, nuclide immobilization mechanism and Ce element oxidation status. The results show that the immobilization mechanisms of simulated nuclides are both chemical and physical forms. Large amounts of the simulated nuclide transfer into the crystal structure of leucite (cubic), zirconia (cubic), zircon lattice or form ceramic phases. Small amounts of nuclide are wrapped in glass phases. Cs and Sr are uniformly distributed, and Ce and Nd are enriched in the glass phase. Leaching results show that the geopolymer-based multiphase ceramics high-level radioactive liquid waste form has excellent leaching resistance property for immobilizing simulated nuclide of various valences and radii. The 28 d normalized element leaching rates of Cs and Sr are 10-2g/(m2·d), and those of Nd and Ce are 10-4~10-5 g/(m2·d). This paper provides a design and preparation method of high-level radioactive waste form that can simultaneously solidify multiple nuclide by combining cement, glass and ceramics solidification methods with simple process, which casts a new light on the effective solidification of high-level radioactive waste.

The main component of existing high-level radioactive sludge in China is phosphomolybdic heteropolyacid salt. Due to the low solubility of phosphorus and molybdenum in borosilicate glass, beyond certain solubility limit, phosphomolybdic heteropolyacid salt causes phase separation on the surface of glass and affects the efficiency and safety of vitrification. In this paper, the effect of PM content on the phase composition, microstructure and leaching resistance of borosilicate glass was mainly investigated. The results show that when PM content is 0%~4% (mass fraction, the same below), the sample is transparent glass. When PM content is higher than 5%, the sample is glass ceramic containing calcium molybdate and barium molybdate phases. With the increase of PM content from 0% to 6%, the ［SiO4］ structure in glass network structure gradually depolymerizes, the ［MoO4］2-structure gradually increases, the content of ［BO4］, Q3 and Q4 units in glass network decreases, and the compactness of glass network structure decreases. With the increase of PM content, the normalized leaching rates of Si, B and Na decrease first and then increase after 28 d, while the normalized leaching rate of Mo increases first and then decreases after 28 d.

Gahnite-diopside glass-ceramics were prepared with SiO2, Al2O3, ZnO, CaO and MgO as main raw materials, and the mechanical properties of glass-ceramics were improved by self-toughening technology. The influences of heat treatment parameters on the mechanical properties of glass-ceramics were studied by orthogonal test, and the relationships between the proportion of crystal phase, microscopic morphology and mechanical properties of glass-ceramics were discussed. The results show that the fracture toughness of glass-ceramics increases significantly with the increase of diopside phase ratio, but the bending strength of glass-ceramics decreases when diopside phase ratio is too high. Therefore, in order to prepare glass-ceramics with high fracture toughness and bending strength, columnar crystals are required to crisscross and granular crystals are required to fill the gaps, which together play a synergistic strengthening role. When the basic glass with heat treatment at 750 ℃ for 2 h+810 ℃ for 2 h+880 ℃ for 2 h+950 ℃ for 2 h, the fracture toughness of glass-ceramics can up to 5.1 MPa·m1/2, the bending strength can up to 255 MPa, and the vickers hardness is 8.3 GPa.

Cordierite silicon glass-ceramics with different nucleating agents were prepared by melting. The effects of different nucleating agents on the crystallization and properties of glass-ceramics were studied by DSC, XRD, FE-SEM, UV-VIS-NIR and other test methods, and the crystallization kinetics of glass-ceramics with different nucleating agents were analyzed using the classical kinetic equation (Johnson-Mehl-Avrami). The results indicate that the crystallization mechanism of glass-ceramics with P2O5 or P2O5+ZrO2 as nucleating agent is controlled by surface crystallization. However, the glass-ceramics with P2O5+ZrO2+TiO2 as nucleating agent has the tendency to be bulk crystallization. With the crystallization temperature increases from 950 ℃ to 980 ℃, the μ-cordierite in the three groups of glass-ceramics begins to transform into α-cordierite. While the introduction of TiO2 increases the α-cordierite content, the precipitated crystals become dense. With the extension of crystallization time, compared with other nucleating agent, the glass-ceramics with P2O5+ZrO2+TiO2 as nucleating agent obtain higher crystallinity within the same crystallization time, the increase of α-cordierite content significantly improves the mechanical properties of glass-ceramics, but decreases the light transmittance. Under the heat treatment system of 800 ℃/10 h+980 ℃/3 h, the elastic modulus of glass-ceramics with P2O5+ZrO2+TiO2 as nucleating agent reaches 103 GPa, the fracture toughness is 1.27 MPa·m1/2 and the light transmittance is 82.3%, which meet the performance requirements of mobile terminals.

The effect of ZnO content on structure and properties of ZnO-B2O3-SiO2-BaO glass as a research object for copper paste was studied by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), raman spectroscopy (Raman), 27Al nuclear magnetic resonance aluminum spectroscopy (27Al NMR), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results show that with the increase of ZnO content, the molar ratio of BO/NBO, the average bridge oxygen number and the molar ratio of ［ZnO4］/［ZnO6］ all increases first and then decreases, the molar ratio of ［BO4］/［BO3］ increases, the molar proportion of ［AlO6］ and ［AlO5］ increases and the molar proportion of ［AlO4］ decreases in glass samples, which results in the trend first dense and then loose in the connection degree of network structure of glass samples. Among them, the network structure is the densest when the ZnO content is 36% (mass fraction). With the increase of ZnO content from 32% to 42% (mass fraction), the glass transition temperature Tg, initial sintering temperature TS1 and the coefficient of thermal expansion (CTE) decrease first and then increase, and the CTE value range is 6.0×10-6~6.3×10-6 K-1. It meets the requirements of thermal expansion and sintering temperature for sealing copper paste with Ca1-xSrxZrO3 ceramic substrate.

Lightweight of refractories is an important direction for high-temperature industry energy conservation. Lightweight M60 mullite materials were prepared via an in-situ decomposition pore-forming route using tertiary raw bauxite and fly ash as main raw materials. The effect of fly ash on the structure and properties of lightweight M60 mullite materials at different firing temperatures was studied. The results show that at the firing temperature of 1 400 and 1 500 ℃, the introduction of fly ash reduces the bulk density of materials, increases the total porosity of materials, and greatly increases the compressive strength of materials. The thermal conductivity of sample sintered at 1 500 ℃ decreases obviously. When the firing temperature reaches 1 600 ℃, the total porosity of material decreases, the bulk density increases slightly, and the thermal conductivity increases obviously. The introduction of fly ash also reduces load softening temperature of materials. After the introduction of 34.0% (mass fraction) fly ash, the bulk density of prepared mullite materials decreases by 8%~13%, and the total porosity increases by 23%~37%. After firing at 1 500 ℃, the compressive strength of materials reaches (122.6±2.2) MPa, and the thermal conductivity tested at 1 000 ℃ is only 0.616 W/(m·K).

The slag resistance test of MgO-CaO bricks in slag line area of AOD furnace was carried out by means of static crucible method after high temperature heat treatment at 1 700 ℃ for 3 h in air atmosphere. The corrosion mechanism of two kinds of AOD furnace slags on MgO-CaO bricks in slag area of AOD furnace was analyzed by means of XRD, SEM and EDS. The results show that the oxidation period slag with low alkalinity has obvious corrosion on MgO-CaO bricks. Under the action of surface tension and capillary force, the slag enters MgO-CaO bricks and reacts with CaO to form dicalcium ferrite (2CaO·Fe2O3, C2F) with low melting point, which promotes the dissolution of CaO and destroys the origin compact structure. The structure of reaction layer becomes loose, cracked and easy to peel off. The periclase crystal cluster in MgO-CaO bricks absorbs iron oxide, chromium oxide and manganese oxide in liquid slag and forms a composite spinel structure within and between its crystals in order to improve the viscosity of liquid slag on the surface of MgO-CaO bricks and slow down the corrosion of slag on MgO-CaO bricks. The alkalinity of reduction period slag is high and the corrosion effect on MgO-CaO bricks is weak, which is mainly manifested in the corrosion and penetration of SiO2 into the bricks, and the volume effect and temperature gradient cause the peeling of small periclase crystal cluster on the surface of MgO-CaO bricks into slag.

Using yttrium nitrate hexahydrate and calcium carbonate as yttrium and calcium sources, and urea as fuel, the Y2O3 coating CaO powder were prepared by low temperature self-spreading combustion synthesis (LCS) method. The CaO-Y2O3 composites were prepared by calcination, pressing, drying and sintering. The effects of the molar ratio of calcium to yttrium on the structure and properties of composites were investigated. The results show that the prepared Y2O3 coating CaO powder has good coating property. When the molar ratio of calcium to yttrium is 2∶1, the physical properties of the material are the best, the relative density is 96.56%, the apparent porosity is 1.32%, the compressive strength at room temperature is 270.0 MPa, the residual strength retention rate of the sample after 5 thermal shock cycles is 88.39%, and the hydration weight gain rate of the sample after 21 d in the atmospheric environment is 0.75%.