Core meltdown may occur in the event of a catastrophic nuclear power plant accident. The reactor pressure vessel will be destroyed by the ultra-high temperature and extremely radioactive core melt, which even poses a risk of contaminating the surrounding area. As the main component of the core catcher, sacrificial concrete may alter the physical and chemical properties of the core melt during nuclear accidents, which is extremely significant for the safety protection of nuclear power plants. To gain a comprehensive understanding of the high temperature properties and failure mechanism of sacrificial concrete, researchers have conducted in-depth research on the high temperature mechanical properties and physical properties of sacrificial concrete, and the interaction between core melt and concrete in order to provide direction for the development and renewal of such materials. This review first introduced the service characteristics of a core meltdown accident as well as the key property requirement of nuclear sacrificial concrete under these extreme conditions. The main research on sacrificial concrete focuses on material modification and the improvement of material performance. The addition of graphene or polypropylene fiber is anticipated to improve the service performance of sacrificial concrete since the majority of researches demonstrate that high temperature circumstances will degrade the mechanical characteristics of sacrificial concrete and increase the danger of spalling. Additionally, simulation experiments and numerical modelling on accident condition response are mostly used to explore the interaction between the core melt and sacrificial concrete due to the high radioactivity of the core melt. Currently, there are still gaps in our understanding of sacrificial concrete that need to be addressed, and results have not been consistent from study to study. Therefore, the main development directions in this field include an in-depth knowledge of the deterioration mechanism during the service process of sacrificial concrete and a thorough understanding of the interaction between core melt and sacrificial concrete.

Based on the mechanism of sulfate attack, a microstructure evolution model of hardened cement paste under sulfate attack was established by using the improved CEMHYD3D hydration model and random probability method. At the microscopic level, the free diffusion, random collision and transformation reaction of sulfate ions in the pore solution of hardened cement paste were simulated, and the microstructure damage and volume expansion induced by the growth of expansive erosion products were analyzed. Meanwhile, the content of gypsum and ettringite and the expansion strain of paste in the process of sulfate attack were calculated, and the model was verified by comparing with the experimental results in present literature. On the basis of the model, the microstructure evolution and expansion process of hardened cement pastes with different water-cement ratios under sulfate attack were numerically simulated. The results show that under the same sulfate concentration, the smaller the decrease in the contact area of calcium hydroxide and phase containing aluminum with pores is, the lower the expansion strain of hardened cement paste is. For hardened cement pastes with water-cement ratios of 0.25, 0.30 and 0.35, their expansion strain begins to increase rapidly when the pore filling degree reaches 9.09%, 9.27% and 9.41%, respectively. As the sulfate concentration increases, the time for rapid expansion of hardened cement paste is advanced.

The effects of two kinds of organic phosphonic acids on the compressive strength, water resistance, and setting time of magnesium oxysulfate cement were explored. The phase composition and microscopic morphology of magnesium oxysulfate cement were characterized by X-ray diffraction, simultaneous thermal analysis, and scanning electron microscopy. The results show that when the content of amino trimethylene phosphonic acid (ATMP) is 0.75% (mass fraction, the same below), the 28 d compressive strength increases by 113.99%, and the softening coefficient increases by 101.86% compared with the blank group. When the content of 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) is 0.75%, the magnesium oxysulfate cement shows the best compressive strength and higher retardation effect, and the softening coefficient reaches 0.93. Compounding of two organic phosphonic acids with a total content of 0.75%, when m(ATMP)∶m(HEDP) is 3∶1, it has the best modification effect on magnesium oxysulfate cement. ［Mg(OH)(H2O)x］+ generated during the hydration of MgO and organic phosphonic acid form a stable chelate, which slows down the hydrolysis of active MgO to Mg(OH)2, thereby delaying the setting time of magnesium oxysulfate cement. The addition of organic phosphonic acid provides feasibility for the application of magnesium oxysulfate cement in practical engineering.

The strength of resistance to chloride ion erosion has a key impact on the service life of cement-based materials. In this paper, the effect of different graphene oxide (GO) content (0%, 0.02%, 0.04%, 0.06%, 0.08%, 0.10%, mass fraction) on chloride ion erosion resistance of cement mortar under dry-wet alternating chloride environment was studied. The relationship between free chloride ion concentration and chloride ion erosion resistance of cement mortar under different GO content was analyzed, and the chloride ion erosion resistance of cement mortar was analyzed from micro perspective by scanning electron microscope. The results show that GO can significantly improve the chloride ion erosion resistance of cement mortar and the optimal content range is 0.04%~0.06%. At the same drilling depth, the free chloride ion concentration in cement mortar decreases first and then increases with the increase of GO content. GO can effectively regulate the microscopic morphology of cement mortar, reduce the generation of internal pores, make the structure more dense, and improve the ability of cement mortar to resist chloride ion erosion.

In this paper, the flexural strength, compressive strength, water absorption and unsteady chloride ion migration coefficient were used to investigate the effect of styrene-butadiene rubber powder (SBR)/nano SiO2 (NS) on strength and impermeability of cement-based materials. The hydration products and microstructure of cement-based materials were analyzed by XRD, DSC-TG, FTIR, SEM-EDS and MIP. Results show that complex SBR/NS significantly improves the early strength degradation of cement-based materials caused by single SBR. Both single SBR and complex SBR/NS reduce the water absorption, water absorption rate and unsteady chloride ion migration coefficient, and the effect of complex SBR/NS is better than that of single SBR. The microscopic test shows that the single SBR reduces the content of Ca(OH)2 and the number of harmful pores and more-harmful pores and increases the integrity of the structure. The complex SBR/NS further reduces the content of Ca(OH)2, promotes the hydration reaction to generate more C-S-H, improves the polymerization degree of C-S-H, decreases the most probable aperture, reduces the amount of less-harmful pores, harmful pores and more-harmful pores, lowers the Ca/Si ratio of hydration products, and thus enhances the flexural strength, and compressive strength and improves the impermeability of the sample.

In order to study the damage evolution characteristics and crack propagation of high temperature cement mortar after local water cooling, a hole was drilled in the middle of cement mortar specimen. The specimen was heated to 200 ℃ and 400 ℃, and then water was injected into the hole for local cooling. The damage behavior of cement mortar specimen under high temperature and local water cooling was studied by low field nuclear magnetic resonance (NMR). The results show that with the increase of the heat treatment temperature, the pore size and content of the small hole of the specimen after local water cooling increase continuously, while the change of the large pore is not particularly obvious, and the damage degree of the specimen increases correspondingly. At the same time, after high temperature and local water cooling treatment, the peak of the probability density distribution of the gray value of magnetic resonance imaging specimens moves to the right with the increase of temperature. And the higher the temperature is, the greater the increase of the gray value corresponding to the probability density distribution function is, which is consistent with the change of T2 spectrum. Finally, the distribution of temperature and temperature stress of cement mortar specimens after high temperature and local water cooling were solved, and the crack germination and propagation range of locally cooled cement mortar specimens after 200 ℃ and 400 ℃ were solved based on the maximum tensile stress criterion.When the temperature is 200 ℃, the temperature stress produced by local water cooling is not enough to cause crack initiation.

Due to the different hydration mechanism of cement mixed with alkaline and alkali-free accelerators, there are obvious differences in application performance. In this paper, the application performance and early hydration process of two accelerators were comprehensively analyzed through the test of macroscopic properties such as setting time and compressive strength of mortar, and the microscopic methods such as hydration heat analysis, XRD quantitative analysis, thermogravimetric analysis and scanning electron microscope observation. The results show that the ［Al(OH)4］- accelerates the consumption rate of gypsum in cement and a large amount of ettringite (AFt) are generated in the initial hydration stage after the alkaline accolerator is added to the cement. At the same time, the alkaline accolerator also promotes the hydration of C3S minerals, shortens the setting time of cement paste and improves the early compressive strength of mortar. However, the accelerated consumption of gypsum also makes the hydration products such as monosulfur-type hydrated calcium sulfoaluminate (AFm) and hydrated calcium aluminate (C-A-H) form in advance, which negatively affects the long-term compressive strength development of cement-based materials. While the alkali-free accelerator is added to the cement, the ［Al(OH)4］- and SO2-4 form a large amount of AFt in the liquid phase, which promotes the hydration of C3A and C3S minerals, and affects the crystallization and precipitation of Ca(OH)2(CH). It is worth noting that SO2-4 from the alkali-free accolerator not only promotes the process of C3A to generate AFt, but also delays the consumption of gypsum in cement and the formation of hydration products such as AFm and C-A-H. Therefore, the 28 d compressive strength is not negatively affected in addition to the obvious improvement of the early compressive strength.

In order to study the particle shape characteristics and characterization method of manufactured sand, the particle shape of five kinds of manufactured sand was tested by aggregate image measurement system (AIMS) and digital image processing (DIP) technology. Based on the shortcomings of existing research, an improved particle shape measurement method was proposed, and the relationship between different particle shape characterization parameters was studied. The results show that the angularity of manufactured sand increases first and then decreases with the particle size range from large to small, while the two-dimensional shape value has no obvious change law. The manufactured sand in the range of 0.3~0.6 mm can reflect the angularity of overall particle size range. The particle shape parameters obtained by single projection image processing have a large fluctuation range, so it is impossible to accurately judge the particle shape of manufactured sand. Aspect has a strong correlation with convexity. Regularity has a strong correlation with aspect, roundness and convexity, while fractal dimension has no correlation with other parameters. The particle shape evaluation conclusion obtained by improved DIP technology is consistent with AIMS, which has certain feasibility and popularization value.

Steel fiber (SF) and macro-polypropylene fiber (MPPF) were used as aggregate to prepare hybrid fiber recycled aggregate concrete (HFRAC) suitable for pavement in order to improve the strength and wear resistance of recycled aggregate concrete (RAC). The Box-Behnken experimental design method was adopted, with the volume content of SF, volume content of MPPF and sand ratio as factors, and the flexural strength, compressive strength and wear amount of HFRAC as evaluation indicators. The prediction model of each evaluation index was established, the influence of each factor on evaluation index was analyzed, and the optimal model of the mix proportion of HFRAC based on NSGA-Ⅱ coupled entropy weight TOPSIS method was constructed to determine the mix proportion scheme when the comprehensive performance was optimal. The results show that the response surface model of each evaluation index has good fitting effect and high prediction accuracy within the test range. Each evaluation index is not only affected by a single factor, but also affected by the interaction between factors. The interaction between the volume content of SF and the volume content of MPPF has a extremely significant effect on flexural strength and compressive strength, and has a significant effect on wear amount. The interaction between the volume content of MPPF and the sand ratio has a significant effect on flexural strength. The optimal mix proportion of HFRAC is obtained. When the volume content of SF is 1.39%, the volume content of MPPF is 0.97%, and the sand ratio is 36.10%, the comprehensive performance of HFRAC is the best. This method can realize the comprehensive improvement of HFRAC performance, and provide a certain theoretical basis and technical support for the popularization and application of HFRAC in road engineering.

In order to study the damage and failure process of steel fiber reinforced concrete and the mechanism of crack development and evolution, based on fractal theory and extended finite element method, the mesoscopic finite element model of steel fiber reinforced concrete cube tensile test and the finite element model of notched beam three-point bending test were established. The reliability of the established finite element analysis model was compared and verified based on the relevant test results. The damage evolution process of steel fiber reinforced concrete was characterized by the fractal dimension of crack, and the effects of different volume content and length of steel fiber, the shape of coarse aggregate and other important factors on the damage evolution process of steel fiber reinforced concrete were investigated. The results show that the damage value based on the fractal dimension of crack can better reflect the damage evolution process and characteristics of steel fiber reinforced concrete. The increase of steel fiber volume content and length and the irregularity of aggregate shape will delay the damage evolution process of steel fiber reinforced concrete cube specimens. The increase of steel fiber volume content and the distance between the initial crack and the midspan, and the reduction of the initial crack height ratio can delay the damage evolution process of steel fiber reinforced concrete notched beams to a small extent.

In order to solve the preparation problem of super-retarding concrete at the construction site of bite pile and explore the mechanism of retarder, the super-retarding concrete was prepared by adding sugar and sodium gluconate with a mass ratio of 7∶3 as composite retarder, and two kinds of preparing process, namely the primary stirring process and secondary stirring process were compared. The mechanical properties, microstructure, adsorption amount and hydration properties of super-retarding concrete were tested and analyzed by compressive and flexural testing machine, environmental scanning electron microscope (ESEM), total organic carbon analyzer and isothermal calorimeter. The results show that the setting time of concrete increases with the increase of retarder content. When the content of retarder is 0.38% (mass fraction), the initial and final setting time of the first stirring group are 31 h and 46 h, respectively, and the initial and final setting time of the second stirring group are 34 h and 50 h, respectively. When the content of retarder is 0.50% (mass fraction), the initial and final setting time of the first stirring group are 61 h and 78 h, respectively, and the initial and final setting time of the second stirring group are 65 h and 84 h, respectively. Under the two dosages, the 56 d compressive strength of concrete is all above 40 MPa, which can meet the construction requirements of the two working conditions. The secondary stiring process is helpful to further prolong the setting time of concrete and improve the fluidity of concrete mixture, but slightly reduce the compressive strength of concrete. The order of adsorption capacity of different retarders on the surface of cement particles is: sodium gluconate>sugar-sodium gluconate>sugar>sugar-sodium gluconate after blending. Mixing retarder can reduce hydration heat and restrain hydration of cement, so as to prolong setting time of concrete.

A high elastic modulus concrete was designed on the base of modified Furnas model and close-packing aggregates test results. In addition, steel microfibers were used to improve the toughness of high elastic modulus concrete. The effect of steel microfiber on fluidity, strength, elastic modulus and bending toughness of concrete under close-packing aggregates state was investigated. The results show that using close-packing aggregates and proper steel microfiber, the static and dynamic elastic modulus of concrete are up to 50.15 GPa and 53.23 GPa, respectively, the fracture energy is about 5 680.45 N/m, and the residual bending toughness ratio increases from 0 to 0.43. Moreover, with the increase of steel microfiber content, the fluidity of high elastic modulus concrete decreases, while the flexural strength, elastic modulus and bending toughness increase. With the increase of steel microfiber content, the compressive strength increases first and then decreases. In close-packing aggregates state, considering fluidity, mechanical properties and engineering economy, the resonable amount of steel microfiber in high elastic modulus concrete is 0.4% (volume fraction).

In order to solve the crack and leakage problem of concrete members such as side walls of underground structures, the green economy sisal fiber-engineered cementitious composite (ECC) was selected to replace concrete to improve the impermeability of members. The optimal ratio of sisal fiber-ECC was obtained by orthogonal experiment. An improved experimental setup was self-designed for realizing synchronous coupling of sustained compressive loading and water transfer by sisal fiber-ECC. The capillary water absorption performance test under sustained compressive loading was carried out on sisal fiber-ECC. The effects of stress levels (10%~40%) on the destruction morphology, cumulative amount of water absorption and capillary water absorption rate of sisal fiber-ECC specimens were analyzed, and compared with that of ordinary concrete specimens. The results indicate that within 10%~40% compressive stress level, the cumulative amount of water absorption and the average water absorption rate of the sisal fiber-ECC both decrease first and then increase with the increase of compressive stress level. The stress threshold for variation of capillary water absorption performance of specimens is 20% of its ultimate compressive strength. When the sustained compressive loading is in the range of 10% to 30% compressive stress level, compared with ordinary concrete, the sisal fiber-ECC can maintain a lower cumulative amount of water absorption and water absorption rate. Sisal fiber-ECC has better impeding effect on water tranfer. It shows that the impermeability of the structure at low compressive stress level (10%~30%) can be significantly improved by sisal fiber-ECC. The research results can provide theoretical support for the application of sisal fiber-ECC in the impermeability of side walls of underground structure.

To study the strength degradation law of reactive powder concrete (RPC) after elevated temperatures, the mass loss and compressive strength as well as split-tensile strength of RPC specimens after elevated temperatures were measured. Besides, the effects of temperature and fiber content on the strength of RPC samples were analyzed. The results show that the apparent color of RPC specimens gradually changes from dark to light, and the mass loss rate gradually increases with the rising temperature. The cubic strength loss rate and split-tensile strength loss rate as well as axial compressive strength loss rate all decrease first and then increase with the increasing temperature, but the critical temperature is different. The critical temperature of cube compressive strength and split-tensile strength is 300 ℃, while the critical temperature of axial compressive strength is 200 ℃. In addition, the loss rate of axial compressive strength is higher than that of cubic compressive strength after 300 ℃, and all the strength loss rates exceed 80% after 800 ℃. Deterioration of matrix microstructure is the root cause of macroscopic strength degradation. Moreover, the strength loss rate of the RPC specimen mixed with polypropylene (PP) fiber is relatively small after elevated temperature. When the steel fiber content is 2%（volume fraction), the optimal content of PP fiber is 0.15% （volume fraction). Finally, the calculation equation between the strength loss rate of RPC and temperature as well as PP fiber content was established through regression analysis.

To study the fatigue performance of nano-modified recycled concrete, the fatigue life was estimated and fatigue equations were developed. Fatigue cycle loading tests at different stress levels (0.75, 0.80, 0.85) were designed with different recycled aggregate replacement rates (0%, 30%, 50%, mass fraction) and nano-CaCO3 content (0%, 1%, mass fraction) as the main influencing factors. The results show that the elastic modulus of concrete decreases with the increase of recycled coarse aggregate replacement rate, and incorporation of nano-CaCO3 can improve the elastic modulus, optimize the damage pattern of concrete and effectively enhance its integrity. The overall fatigue life under cyclic load decreases rapidly with the increase of maximum stress level, and 1% nano-CaCO3 modification can increase the fatigue life by 60%. Establish the fatigue life equation with a two parameters S-N (stress level-fatigue life) curve, and deriving the P-S-N curve considering the life probability. The correlation coefficient obtained decreases rapidly with the increase of recycled coarse aggregate substitution rate and increases after nano-modification. The fatigue strain evolution of recycled concrete basically conforms to the three-stage strain curve development law. A new equation is proposed to describe the second-stage strain curve of recycled concrete, and the relationship equation between deformation volume and cycle ratio is established.

In order to study the tensile fracture characteristics of concrete, the uniaxial tensile test of C80 high-strength concrete prism with precast cuts was carried out, the field displacement of the prism surface was measured by electronic speckle pattern interferometry (ESPI) technology, and the fracture parameters and fracture characteristics of concrete were analyzed during the loading process. For comparative analysis, the deformation of specimen was also measured using a linear displacement meter and a clip-on displacement meter. The comparison results show that the ESPI technology measurement results are in good agreement with the clip-on displacement meter results, which confirms the accuracy and feasibility of ESPI technology to measure the displacement field of concrete surface. The analysis shows that the initial crack point stress is about 82% of the peak stress. The crack mouth opening displacement (CMOD) of the peak load is 11 μm, and the fracture toughness of concrete under uniaxial tension is obtained by combining the formula to obtain a fracture toughness of about 0.41 MPa·m1/2, and the fracture energy is about 24.71 N/m. The experimental stress-strain relationship is fitted by using two fitting formulas, and the fitting results are good. Finally, the crack propagation law under uniaxial tension was obtained by analyzing the crack mouth opening displacement varied with the width of specimen in the displacement cloud map measured by ESPI technology at different loading steps.

In order to study the effect of magnesium oxide expansion agent and hydration heat regulator compounding on the crack resistance of concrete and explore the mechanism of hydration heat regulator, diabetic temperature rise, limited expansion rate, volume deformation, self-shrinkage, elastic modulus of the concrete mixed with magnesium oxide and the concrete mixed with magnesium oxide and hydration heat regulator were tested, and the microstructure was investigated. The results show that the hydration heat regulator can significantly change the cement hydration exothermic process, the temperature suppression rate of the slurry reaches 31.2%, and the temperature suppression effect is enhanced with the increase of the mold temperature. The hydration heat regulator can stimulate the hydration of magnesium oxide and promote the release of expansion energy, and the effect is more obvious with the increase of curing temperature. The hydration heat regulator can change the temperature rise history of concrete, especially reduce the early hydration heat release rate. The combination of hydration heat regulator and magnesium oxide can reduce the self-shrinkage of concrete. When the content of hydration heat regulator is 0.2% and 0.4% (mass fraction), the shrinkage value is reduced by 84 με and 54 με, respectively. The hydration heat regulator will reduce the elastic modulus of concrete in the early age, but it has little effect on the elastic modulus in the long age. The change of cement hydration process, hydration product generation and microstructure compactness caused by hydration heat regulator is the fundamental reason for improving the crack resistance of concrete.

To explore the enhancement effect and modification mechanism of silica powder on the frost resistance of basalt fiber pavement concrete, the decay law of mass loss, relative dynamic elastic modulus and flexural tensile strength of basalt fiber reinforced concrete with different freeze-thaw cycle times were studied by quick freezing method. By means of mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM), the evolution of pore structure and interface structure before and after freeze-thaw cycle were analyzed, and the strengthened mechanism of silica powder reveals from the microscopic level. The research results show that 9% (mass fraction) silica powder has the best effect on improving the frost resistance of basalt fiber pavement concrete, the mass loss reduces by 62.35%, the relative dynamic elastic modulus increases by 14.68%, and the flexural tensile strength is improved 43.89% after 320 times freeze-thaw cycles. The MIP results indicate that the addition of silica powder refines the internal pore structure of the basalt fiber pavement concrete, reduces the number of pores, optimizes the distribution of pores suppresses the growth of mean pore-size and critical pore size. SEM images reveal that the addition of silica powder improves the interface zone structure between fiber-cement stone and aggregate-cement stone, and improves the frost resistance of basalt fiber pavement concrete.

The bond property of the interface between carbon fiber reinforced polymer (CFRP) and clay brick is the key of external CFRP reinforcement technology. In order to understand the degradation law of the bond property of the CFRP-clay brick interface under sulfate erosion, a single shear test was carried out on the specimens strengthened under different sulfate drying and wetting cycles. The results show that the influence of sulfate erosion on the properties of CFRP sheet and impregnating glue is not obvious, but it has a great influence on the bond properties of CFRP-clay brick interface. The shear stress and bearing capacity of the CFRP-clay brick interface increase slightly first and then decrease obviously with the increase of drying and wetting cycles. On the basis of the experiment and the existing theory, the bond slip model of the CFRP-clay brick interface under the action of sulfate drying and wetting cycles is proposed. The model can well reflect the bond property degradation law of the CFRP-clay brick interface by comparing with the experimental value. Based on ABAQUS software, the cohesive force constitutive model was used to simulate the mechanical behavior of the interface. The results show that the cohesive force model can well simulate the nonlinear mechanical behavior of the interface, and the numerical simulation values are in good agreement with the experimental values.

This investigation intends to explore the feasibility for preparing the C40 and above strength grade recycled concrete with incorporation of large amount of coarse and fine recycled aggregates. For this purpose, based on the C45 grade natural aggregate concrete mix ratio, four recycled concretes were prepared with simultaneous incorporation of Class-II coarse recycled aggregate and Class-I fine recycled aggregate. The following replacement ratios for coarse and fine recycled aggregates were considered: 25%, 50%, 75% and 100% by mass. The results show that the mechanical properties of the recycled concrete decrease very little for the replacement ratio of 25%, and the compressive strength of the two recycled concretes with 50% and 75% replacement ratios reaches C45 and C40 grade, respectively. Compared with the natural aggregate concrete, the 28 d various mechanical properties, such as compressive strength, splitting tensile strength, axial compressive strength and elastic modulus of fully recycled concrete with 100% replacement ratio decrease by 12.0%~23.2%, and reach C35 compressive strength grade. The increase of the replacement ratio of coarse and fine recycled aggregates will reduce the durability of concrete, but even the fully recycled concrete still has high durability, and its resistance to carbonation, chloride ion permeability and frost resistance reach T-IV, RCM-IV and F300 grade, respectively. All these results indicate that it is feasible to incorporate 50% or more coarse and fine recycled aggregates into recycled concrete with strength of no less than C40 grade.

In order to study the effect of composite modification of recycled coarse aggregate with various concentrations of sodium silicate solution and silane solution on the mechanical and deformation properties, as well as the microstructure of recycled concrete, cubic compressive strength tests were used to investigate the effect of composite modification on the mechanical properties of recycled concrete. Meanwhile, the effect of composite modification on the deformation properties of recycled concrete was studied by using the digital image correlation (DIC) method. Additionally, scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) were utilized to analyze the internal microstructure of the modified recycled concrete. The results show that, the water absorption of recycled coarse aggregate for 24 h decreases the most when it is modified with 5% （mass fraction） of sodium silicate solution and 10% （mass fraction） of silane solution, and the 28 d compressive strength of recycled concrete made from it is significantly improved, which is 35.80% higher than that of unmodified recycled concrete. The composite modification of recycled coarse aggregate with sodium silicate solution and silane solution can effectively reduce the deformation of recycled concrete, and when the stress is high, it can stop the excessive concentration of stress, resulting in improved overall deformation property of recycled concrete. Furthermore, it can improve the surface sparse structure and roughness of recycled coarse aggregate, and strengthen the performance of the interfacial transition zone (ITZ) between aggregate and mortar, but the improvement in ITZ performance of new and old mortar is not evident.

Coal gasification slag and fly ash are solid wastes produced in the process of coal resource utilization, which can be used in the field of alkali-activation. In this paper, by studying the properties of coal gasification coarse slag, coal gasification coarse slag was modified with fly ash, and the coal gasification coarse slag-fly ash based geopolymer was prepared by alkali-activation technology, and the properties of prepared products were studied. The results show that adding fly ash into the system significantly improves its mechanical properties. When the mass fraction of fly ash is 30%, the 28 d compressive strength of the sample is the highest, which is 44.5 MPa. In addition, through the phase analysis and micro morphology characterization of the sample, it is found that the amorphous product of the sample is mainly N(C)-A-S-H gel, which can form an interconnected spatial network structure and has strong bonding ability, which is the main reason for the high strength of the sample material.

The pumpability of coal gangue slurry is affected by its rheological properties, which are regulated by particle size and water/gangue ratio. The rheological properties, degree of fluidity and flow time of fresh coal gangue slurry were tested in this paper, and the effects of different particle sizes (100 mesh, 150 mesh, 200 mesh, 250 mesh, 300 mesh, corresponding to 150 μm, 106 μm, 74 μm, 58 μm and 48 μm, respectively) and water/gangue ratio (1.0, 1.5, 2.0) on the rheological parameters were discussed. The variation rules of rheological parameters, degree of fluidity and flow time were discussed as well, and some grouting suggestions were put forward. The results show that the water/gangue ratio is the main controlling factor of rheological properties of coal gangue slurry. When the water/gangue ratio is 1.0, the coal gangue slurry conforms to the Herschel-Bulkley model, and the particle size affects both the yield stress and plastic viscosity of coal gangue slurry, and the yield stress is between 2.5 Pa and 3.6 Pa. When the water/gangue ratio is 1.5 and 2.0, the coal gangue slurry conforms to the Bingham model, and the particle size only affects the yield stress of coal gangue slurry, and the yield stress is between 0.1 Pa and 0.7 Pa. In addition, the degree of fluidity of coal gangue slurry with different particle sizes is more than 365 mm, and the flow time is in the range of 27 s to 31 s. Based on these test results, grouting suggestions are put forward that a larger water/gangue ratio (≥1.5) and a longer stirring time (>800 s) are recommended to improve the pumpability of coal gangue slurry.

To reveal the volume variation of hardened cement paste with circulating fluidized bed fly ash (CFBFA), CFBFA was employed to replace cement by mass to prepare the cement paste specimens. The volume expansion of the specimens were studied under different curing conditions. Meanwhile, the micro morphology, mineral composition and thermal effect of the CFBFA and paste specimens were analyzed by using scanning electron microscope (SEM), X-ray diffraction (XRD), mercury porosimeter and TG-DSC thermal analyzer. The results show that the water requirement for standard consistency of the blended paste significantly increases with the incorporation of the CFBFA due to the rough and porous surface of the particles. The water requirement for standard consistency of the blended paste with 80% (mass fraction, the same bellow) CFBFA content is 1.6 times as much as that of the neat cement paste. Moreover, the specimens with CFBFA content less than 40% exhibit shrinkage cured under the closed condition, specimens with over 60% CFBFA present remarkable expansion. The internal hydration of the specimens under the standard curing condition are sufficient, the specimens exhibit expansion which increased with CFBFA content under the standard curing condition. The expansion ratio of the specimens with 80% CFBFA content reaches 0.42% after 28 d. All the specimens presented drying shrinkage when they are exposed to the ambient air. However, the specimens with 80% CFBFA content gained more shrinkage over the expansion induced by the inclusion of CFBFA, which is attributed to the higher water to cement ratio.

In order to improve the comprehensive utilization rate of industrial waste residue, a green and high-performance grouting material was developed. Ultrafine ground granulated blast furnace slag (UFS) and silica fume (SF) were used instead of a certain amount of cement, and the influences of different content of UFS, SF and polycarboxylate superplasticizer (PCE) on properties of grouting materials were systematically studied by orthogonal test and range analysis method under different water-cement ratios. The properties of the optimized slurry and pure cement slurry were compared and the microscopic tests were carried out. The results show that the slurry flow performance is enhanced when the mass fraction of UFS increases from 18% to 20%. SF can improve the compressive strength of stone body and reduce the bleeding rate, and PCE has a significant effect on reducing the viscosity of slurry. Taking 28 d compressive strength and viscosity as the main indexes, the optimal ratio of slurry was obtained as water-cement ratio 0.70, UFS content 20% (mass fraction), SF content 12% (mass fraction), and PCE content 0.16% (mass fraction). The optimized slurry has better bleeding rate, compressive strength and flexural strength than the pure cement slurry. After the addition of UFS and SF, ettringite (AFt) and hydrated calcium silicate (C-S-H) gels filled the pores between particles were generated in the slurry, resulting in the increase of the strength of the optimized slurry stone body.

The supersulfated cement (SSC) with different content of calcined phosphogypsum (CPG), ground granulated blast-furnace slag and slaked lime was prepared in this study. The effect of CPG content on the hydration properties of SSC was investigated by testing the variation of hydration heat, electrical resistivity, chemical shrinkage, hydration products, pore solution pH value, and compressive strength of cement slurry. The results show that the third peak of heat release curves of cement slurry delays when the CPG content increases from 0% (mass fraction, the same below) to 20% . The cumulative heat at 3 d and the chemical shrinkage at 14 d increase with the increase of CPG. However, the electrical resistivity at 3 d decreases with the increase of CPG, and the pore solution pH value decreases from 11.95 to 10.80. The incorporation of CPG promotes the formation of ettringite. When CPG content is 10%, the 28 d compressive strength of specimen reaches the maximum of 23.8 MPa.

Some fine aggregates were substituted for glass sand in the preparation of alkali-activated slag (AAS) mortars. The effects of glass sand content (0%, 10%, 20%, 30%, mass fraction) on compressive strength, flexural strength, drying shrinkage, thermal conductivity, and expansion rate of alkali-silicate reaction (ASR) of AAS mortars were tested, and the microscopic mechanism was analyzed by scanning electron microscope (SEM). The results demonstrate that the early compressive strength of AAS mortars can be significantly improved with 10% to 30% glass sand content, but the 28 d compressive strength can be slightly reduced. The flexural strength of AAS mortars increases first and then decreases with the increase of glass sand content.The 10% glass sand content is most favorable to the 3 d flexural strength, while the 20% glass sand content is most favorable to the 28 d flexural strength. With the increase of glass sand content, the drying shrinkage, thermal conductivity and ASR expansion rate of AAS mortars all decrease. The AAS mortar with 30% glass sand content is discovered that it has 14.4% lower thermal conductivity, 27.6% lower 56 d drying shrinkage, 39.6% lower 14 d ASR expansion rate, and 34.5% lower 28 d ASR expansion rate comparing to the control group. Hydration products are created on glass sand surface, and its binding with cementitious material is tighter than that of quartz sand, according to SEM examination, which makes the microstructure of AAS mortar compact.

Red mud synthetic sand was manufactured by firing and using red mud as the main materials with a small amount of fly ash and bentonite. Alkali activity of red mud synthetic sand was studied by slow alkali-aggregate method. The microzone of interface between red mud synthetic sand and cement was analyzed by SEM-EDS from alkali-aggregate reaction specimen, compared with standard sand and natural fluvial sand specimens. The results show that the expansion rate of specimen is 0.035% in red mud synthetic sand alkali-aggregate reaction on 180 d, which is slightly higher than the expansion rate of specimens in standard sand and natural fluvial sand alkali-aggregate reaction. The expansion rate is less than 0.1% in red mud synthetic sand alkali-aggregate reaction specimen, and meets the requirement as national construction sand. Compared with standard sand and natural fluvial sand in alkali-aggregate reaction specimens, the content of Fe element is highest in the red mud synthetic sand interface on 28 d, and the garnet is generated in the synthetic sand interface. This study can provide a reference for solving accumulation of red mud and shortage of natural sand.

Using ferronickel slag as raw material, adding nitric acid and surfactant to modify its mineral phase, a modified ferronickel slag adsorbent was prepared, and the effects of surfactant type, cetyltrimethylammonium bromide (CTAB) dosage, adsorbent dosage, initial pH value of solution, Cr(VI) concentration on Cr(VI) adsorption were investigated. The results show that amorphous SiO2 with loose structure and high specific surface area of 180.6 m2/g is prepared from ferronickel slag after modification. The adsorption rate of modified ferronickel slag on Cr(VI) reaches 90% within 10 min. The adsorption isotherm conforms to the Langmuir model, the maximum theoretical adsorption capacity is 42.55 mg/g, and the adsorption kinetics conforms to the pseudo-second-order kinetic model. The adsorption mechanism of Cr(VI) by modified ferronickel slag adsorbent is mainly physical adsorption and redox, that is, the Van der Waals force on the surface of adsorbent adsorbs HCrO -4 to the surface of adsorbent, and the electron pair provided by CTAB reduces Cr(VI) to Cr(III). The amorphous SiO2 with high specific surface area obtained by modified ferronickel slag can not only adsorb and purify Cr(VI) effectively, but also realize the resource utilization of ferronickel slag to achieve the purpose of treating pollution with waste, and has good environmental effects and economic benefits.

With the acceleration of industrialization process, how to reduce the emission of nitrogen oxide has received strong attention from people. At present, the complex absorption method has good absorption performance for nitric oxide (NO), which is regarded as an important development direction of denitration technology in the future, but the regeneration of complex solution is still a difficult problem. In this paper, the problem of difficult regeneration of Fe(II)EDTA-NO complex solution in complex denitration and the inability to run continuously were investigated. Pd/NPCs catalysts in granular form were prepared by using nitrogen-doped porous carbon as carrier and palladium nanomicelles as active component. Pd/NPCs catalysts were characterized by X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results show that the palladium nanoparticles are successfully loaded on the carrier, with an average particle size of 2.36 nm and the Pd0 content is 68% (mass fraction), which shows good catalytic activity for the reduction of Fe(II)EDTA-NO. The effects of solution pH, reaction temperature, oxygen content, and liquid-gas ratio on the catalytic reduction of Fe(II)EDTA-NO by catalysts were further explored, and a sustainable fluidized bed test device was built. The evaluation test results show that when the air flow is 200 L/h and the NO content is 0.07% (volume fraction), the denitration rate can maintain above 80% for 3 h.

Alumina-silica aerogel is a three-dimensional nano-porous structure material with low density, high specific surface area, high porosity and low thermal conductivity. It is one of the ideal high-temperature insulation composite and has a broad prospect in aerospace, building thermal resistance, petrochemical and other applications. However, pure alumina-silica aerogel has low mechanical properties and its ability to suppress high temperature radiation heat transfer is weak, which limits its application in the field of thermal insulation. The fiber reinforced alumina-silica aerogel composites are an international hot issue because of their excellent mechanical and thermal insulation properties. In this paper, the preparation methods and research progress of the fiber reinforced alumina-silica aerogel thermal insulation composites were summarized, and further prospects were presented.

SiO2 aerogel has poor mechanical properties and strong thermal insulation properties. In order to make SiO2 aerogel a good thermal insulation material, a preparation method of SiO2 aerogel fiber thermal insulation composites was proposed. SiO2 aerogel fiber insulation composites were prepared under atmospheric pressure condition by ethyl orthosilicate (TEOS) as precursor, glass fiber and ceramic fiber as reinforcers, and silane coupling agents KH550 and KH570 as fiber treatment agents, and the material properties were characterized. The results show that the higher the content of hexadecyl trimenthyl ammonium (CTAB) in precursor is, the lower the thermal conductivity of SiO2 aerogel in composite is, which can be as low as 0.028 W/(m·K). When using silane coupling agent KH550, the interface bonding strength between matrix and fiber is higher. The mechanical properties of SiO2 aerogel reach a high level with the addition of fiber. When the molar ratio of TEOS to CTAB is 1∶0.022, the thermal conductivity of glass fiber/SiO2 aerogel composites treated with KH550 is 0.054 W/(m·K), the mechanical properties are good, and the thermal insulation property is optimal.

Due to the orthogonal-tetragonal and tetragonal-cubic phase transitions of BaTiO3 in the range of -55 ℃ to 150 ℃, the sharp dielectric peaks corresponding to these phase transitions make the dielectric properties of BaTiO3 ceramics difficult to meet the temperature stability requirements of X8R. In this paper, the BaTiO3 based fine-grained ceramics were prepared by using 50 nm nano-BaTiO3 powder and a small amount of cordierite (MgO-Al2O3-SiO2, MAS) glass to meet the dielectric temperature specification of X8R. The results indicate that the crystal structure of BaTiO3 based ceramics at room temperature changes from tetragonal phase to pseudo-cubic phase with the addition of MAS glass. The average grain size decreases significantly from 1.904 μm for pure BaTiO3 ceramics to 183 nm for BaTiO3 based ceramics with 0.5% (mass fraction) MAS glass. Meantime, although the dielectric constant of BaTiO3 based ceramics decreases, the dielectric loss and temperature stability of dielectric properties are greatly improved. When the MAS glass content is 0.5%, the dielectric properties of BaTiO3 based fine-grained ceramics are as follows: the dielectric constant of 984 and dielectric loss of 0.006 5 at 1 kHz and room temperature, meeting the temperature specification requirements of X8R.

Thin ceramic tiles are functional products with low energy consumption, but their application is limited by high breakage rate caused by low strength. In this case, it has become a research hotspot in ceramic industries to strengthen thin ceramic tiles with low cost. In this study, various kinds of fabrics and binders were optimized to prepare fabrics reinforced thin ceramic tiles with layered composite structure, which was proved to have low cost and excellent mechanical properties. Besides, the apparent morphology of cross-section and the fracture mechanism were investigated, respectively. It is observed that the composite thin ceramic tile with carbon fabric and epoxy resin as reinforcements has the best interface bonding strength and mechanical properties. And its bending strength is 85.26 MPa and the impact energy is 1.45 J, which are 22.98% and 141.67% higher than those of thin ceramic tiles green body. There are many positive strengthening and toughening mechanisms, such as microcrack expansion, fiber deflection and so on, which are conducive to improving the mechanical properties of thin ceramic tiles with fabrics and binders.

Silicon nitride ceramic strips were prepared by air pressure sintering process with α-Si3N4 powder as raw material and MgO-La2O3-Lu2O3 as ternary composite sintering aids. The effects of sintering aids and β-Si3N4 on the microstructure and mechanical properties of silicon nitride ceramics were studied. The results show that the ternary composite sintering aids promote the densification of sintering and improve the mechanical properties of the materials. At the highest sintering temperature of 1 750 ℃ and the addition of 8% (mass fraction) composite sintering aids, the silicon nitride ceramics for ice skates with density of 3.172 8 g/cm3, Vickers hardness of 15.85 GPa, fracture toughness and bending strength of 9.69 MPa·m1/2 and 1 029 MPa can be obtained. The fracture toughness of the material is enhanced by adding β-Si3N4, and the maximum fracture toughness is 10.33 MPa·m1/2. The high hardness of Si3N4 ceramics itself and the addition of rare earth oxides improve the hardness and lubricating properties of the prepared ice skates, and the surface properties of ice skates are excellent.

In response to the difficulty of the synthesis of high-entropy carbides (HECs), a pressureless low-temperature sintering strategy was utilized to prepare (Zr,Hf,Nb,Ta)C powders with three different transition metal proportion, which powder mixtures of ZrC, HfC, NbC, TaC and Ni were initially annealed at 1 500 ℃ under a flowing Ar atmosphere, and then etched by the nitric acid solution in order to dissolve the metal matrix. The results show that all samples exhibit cuboid morphology with an average size of 2 μm and the exposure of (100) face. Due to high dielectric constant, (Zr1/4Hf1/4Nb1/4Ta1/4)C microcuboids show good microwave absorption performance, and its minimum value of reflection loss attains -48.86 dB at a thickness of 3.5 mm and a frequency of 6.16 GHz. As-fabricated HECs samples also possess good oxidation resistance at 800~1 200 ℃. Moreover, oxidation products are irrelevant to the transition metal proportion and oxidation temperature, which are composed of orthorhombic Nb2O5-Ta2O5 solid solution (o-(NbxTa1-x)2O5), monoclinic ZrO2-HfO2 solid solution (m-(ZrxHf1-x)O2) and orthorhombic HfO2(o-HfO2). Notably, the synergy effect caused by transition metal elements significantly influences the phase transition process of oxides in comparison with monocarbide. In specific, the existence of Hf inhibits the transition of Nb2O5 from orthorhombic to monoclinic, in the meantime, assists the transition of ZrO2 from tetragonal to monoclinic even at 800 ℃. Moreover, the addition of Nb and Ta accelerates the phase transition of HfO2 from monoclinic to orthorhombic under atmospheric pressure.

Refractories are important supporting materials for high-temperature industry. With the continuous development of related technologies, a large amount of literature has been accumulated. However, it is difficult to read so much literature with traditional methods, and it is more difficult to further analyze and summarize them. Therefore, in the past, personal experience was often based on selecting representative literature for summary and analysis. However, this method is difficult to have a comprehensive, quantitative and in-depth analysis and induction of research trends, which is not conducive to systematically grasp its development status and trends, and has gradually become difficult to meet the future needs of scientific research. This work summarizes the current situation of refractory research from the perspective of knowledge graph. By using CNKI and WOS (Web of Science) core database, the overall development venation of refractory research from the scope of China and the world is introduced, and the research hotspots and trends in the field of carbon containing refractories are introduced. At last, the future development of refractories and knowledge map has prospected.

Photocatalytic technology is considered to have a broad application in the treatment of uranium-containing wastewater. g-C3N4 has become the most studied material of photocatalytic reduction uranium (U(VI)) due to its suitable band structure, excellent stability and optoelectrochemocal properties. In this paper, the advances in research of g-C3N4 based materials in photocatalytic reduction of U(VI) were reviewed. The mechanism of U(VI) removal through photocatalysis, the synthesis technology and the research status of g-C3N4 based photocatalysts were discussed. The practical application challenges of photocatalytic reduction of U(VI) by g-C3N4 based materials were identified and future research orientations were suggested.

Nano materials prepared by using apoferritin have the advantages of controllable size and single structure, and also have great advantages in catalysis. In this paper, apoferritin/lead selenide (apo/PbSe) composites were prepared by template synthesis and two-step method, with the template of apoferritin, the selenium source of selenium urea, the raw materials of ammonium acetate and lead acetate. The materials were analyzed by transmission electron microscopy (TEM), X-ray diffractometer (XRD), energy dispersive X-ray spectroscopy (EDS), ultraviolet visible spectrophotometer (UV-vis) and fluorescence spectrometer (PL). The catalytic degradation performance of apo/PbSe composites for the wastewater dye methyl orange under visible light was measured. The results show that the main mineral core in the protein is PbSe, and the apo/PbSe composite photocatalyst is successfully synthesized. The best experimental conditions of the composite photocatalyst are pH=3.0, H2O2 mass fraction of 9%, and the degradation efficiency of methyl orange can reach 97.10%. The stability of photocatalytic efficiency is proved by five cycle degradation experiments. Based on the above results, it is shown that apo/PbSe has good catalytic activity and stability, and the photocatalytic degradation mechanism of methyl orange by apo/PbSe composite is proposed.

The Al2O3 ceramic filter membrane is easily clogging by dye macromolecules during the process of filtering dye wastewater, resulting in a decrease in the water flux of the Al2O3 ceramic filter membrane. Ti(OH)4-AlOOH composite sol was prepared by the sol-gel method with butyl titanate and aluminum isopropoxide as precursors, and TiO2-Al2O3 composite powder was obtained by heating at a temperature of 450 ℃. The influence of the molar ratio of Ti（OH）4 and AlOOH on the particle size distribution of composite sols and the photocatalytic performance of TiO2-Al2O3 composite powders was characterized by using SEM, nanoparticle size/potential meter. The results show that when the molar ratio of Ti（OH）4 and AlOOH is between 0 and 0.4, the average particle size of the colloidal particles decreases from 67.5 nm to 34.0 nm with the increase of the molar ratio of Ti（OH）4 and AlOOH, and the Zeta potential of the Ti(OH)4-AlOOH composite sol increases from 43 mV to 53 mV. When the molar ratio of Ti（OH）4 and AlOOH is 0.4, the removal rate of crystal violet by composite powder up to 79.3%, and the reaction rate constant increases to 0.018 min-1. The ceramic membrane prepared by TiO2-Al2O3composite powder can effectively degrade the macromolecules deposited on the surface, and solve the problem of clogging of the ceramic membrane.