The solar photovoltaic (PV) technology undergoes a linear decrease in photoelectric conversion efficiency when the PV operating temperature increases. But proper cooling can improve PV efficiency and prolong its service life. Thus, with the annual increase of PV installation, people pay more attention to the cooling of operating PV. Compared with active cooling of PV, recently, passive cooling is widely studied due to its self-sustained nature and energy-saving. Passive cooling based on spectral-selective includes two aspects. One is to selectively shields the sub-bandgap absorption in the solar radiation region (0.3~2.5 μm), reduce the generation of absorption heat, and maintain the high transmittance of photoelectric response light. The other is to improve the emissivity of the mid-infrared region (MIR) (4~25 μm) of the PV surface, and enhance the radiative cooling ability of the parasitic heat. In the view of spectral-selective, the materials and structures of solar spectral-selective, radiative cooling and all-optical spectral-selective to promote the cooling of solar photovoltaics were summarized. The spectral-selective materials on glass were fabricated by etching, sputtering and painting to eliminate sub-bandgap absorption heat and enhance radiative cooling capacity. They can effectively reduce the PV temperature and improve the photoelectric conversion efficiency. In addition, the industrialization potential of passive cooling materials was prospected, which provided reference for related exploration.

A novel microwave heating self-healing functional material (MHSFM) that can quickly repair concrete cracks was prepared by using thermally expandable microspheres, paraffin, and graphite. The effect of the thermally expandable microspheres dosage on the volume expansion rate of MHSFM was studied, and the heating rates of MHSFM and mortar with MHSFM under microwave were tested. The effect of MHSFM dosage on the mechanical property, impermeability and self-healing performance of mortar was evaluated. The results show that the volume expansion rate of MHSFM gradually increases, as the dosage of thermally expandable microspheres increases. Under microwave, the heating rate of mortar increases obviously with the increase of MHSFM dosage. MHSFM has a certain effect on the mechanical property and impermeability of mortar, but it significantly enhances the self-healing performance of mortar. The mortar with 12% (mass fraction) MHSFM can quickly heal 0.53 mm crack under microwave.

The varying principle of workability of ultra-high performance concrete (UHPC) slurry can be theoretically studied with the relationship of its workability and rheological properties. An orthogonal test was designed to study the effects of water-binder ratio (W/B), substituted rate of cement by superfine fly ash and silica fume content on the workability and rheological properties of UHPC slurry. The film thickness on particles was taken as the index to evaluate workability and rheological properties of UHPC slurry. According to the test results of workability and rheological properties, the combined effect of W/B and substituted rate of cement by superfine fly ash on the workability and rheological properties of UHPC slurry were analyzed, and the relationship of workability between paste and mortar was investigated. Based on the film thickness on particles, the relationship between the workability and rheological properties of UHPC mortar was established. The results show that W/B is the most important factor, and as W/B, substituted rate of cement by superfine fly ash and silica fume content substituted increase, the film thickness on particles increases. Flow spread and consistency coefficient of UHPC slurry are correlated due to the combined effect of W/B and substituted rate of cement by superfine fly ash.

To improve the real-time damage monitoring effect of building structures in cold regions, the durability and piezoresistivity of self-sensing cement mortar prepared by using chopped carbon fiber and iron tailings as conductive materials under the sulfate freeze-thaw cycles were studied. Based on the mass loss, relative dynamic elastic modulus and compressive strength loss, the change law of durability performance was studied, the correlation between fractional change in resistivity and compressive stress was used to reflect the development law of piezoresistivity under the sulfate freeze-thaw cycles and the conduction mechanism was explained, the average stress sensitivity coefficient was used to evaluate the stability of piezoresistivity under the sulfate freeze-thaw cycles. The results show that cement mortar combined with 0.4% volume of carbon fiber and 30% (mass fraction) replacement rate of iron tailings reach a better level of durability and piezoresistivity. The fractional change in resistivity-compressive stress shows a first-order exponential decay relationship due to the holes and cracks caused by sulfate freeze-thaw cycles. The Plane model can be used to reflect the good correlation among the attenuation degree of average stress sensitivity coefficient and the number of freeze-thaw cycles and the replacement rate of iron tailings.

Based on the central composite design (CCD) of response surface method, a 3D printing gypsum powder fluidity optimization experiment was designed, and the effect of different dosages of hydrophobic nano silica and soluble starch on the liquidity of 3D printing gypsum powder was analyzed. Tests regarding printer powder coating, surface topography and flow rate for the optimized 3D printing powder were carried out. The results show that the best scheme to improve the fluidity of gypsum is introducing 1% (mass fraction) hydrophobic nano SiO2 and 3% (mass fraction) soluble starch. Compared with unmodified gypsum, the fluidity of gypsum increases by 38%. The nonlinear regression equation between the fluidity of powder and the content of hydrophobic nano silica and soluble starch was obtained, and the relative error between the best optimized predicted value and the measured value is only 0.31%. Under the best optimized condition, the flow rate of the modified gypsum powder is 3.16 g/s, which flows continuously, and the surface of the powder layer is uniform without obvious defects. This research highly improves the accuracy of gypsum-based powder 3D printing, which is beneficial to the application of gypsum materials in 3D printing.

In order to optimize the properties of fiber-reinforced ordinary Portland cement-sulfoaluminate cement composites (OPC-CSA-ECC) and extend the use of nano-SiO2, this study discussed the effects of nano-SiO2 on the setting time, strength and toughness of OPC-CSA-ECC. Microstructure and modification mechanism of OPC-CSA-ECC were analyzed by XRD and SEM. The results show that, nano-SiO2 shortens the setting time of the composite cementitious, and the greater the content, the shorter the setting time. Nano-SiO2 improves the strength and toughness of OPC-CSA-ECC. The appropriate content of nano-SiO2 is 1.5% (mass fraction), the corresponding compressive strength at 7 d and 28 d is 59.1 MPa and 85.4 MPa, and the equivalent flexural toughness is 195.82 kJ/m3 and 256.51 kJ/m3, respectively. Nano-SiO2 doesn’t change the type of hydration products, but promotes the formation of C-S-H gel and consumes some portlandite crystals. SiO2 increases the adhesion between the matrix and fiber by increasing the density of the matrix, which contributes to improve strain hardening ability.

To investigate the electrothermal properties of nickel-plated carbon fiber (Ni-CF) cement-based materials, the Ni-CF was mixed into cement to prepare thermally conductive cement-based composites. The effects of water-cement ratio (W/C), fiber content and length on the heating law of cement paste specimens were studied, and the variation law of the maximum temperature rise and the difference of the electrothermal conversion rate were analyzed. The results show that when the content of nickel-plated carbon fiber increases from 0.3% to 0.6%, the maximum temperature rise of the specimens increase first and then decrease, among them, the sample with 0.4% (mass fraction) Ni-CF content has the best heating effect. With the increase of Ni-CF length from 4 mm to 8 mm, the maximum temperature rise of cement paste specimen decreases gradually. The increase of the water-cement ratio leads to the maximum temperature rise of the nickel-plated carbon fiber cement paste. Under the same intensity of the current, the electrothermal conversion rate of Ni-CF cement specimens reach 71.98%, which is twice as high as that of carbon fiber (CF) cement specimens under the same mix ratio.

To explore the attenuation rules and mechanism of impermeability of basalt fiber reinforced concrete under dynamic fatigue load, the best parameters of basalt fiber were optimized based on impermeability. The fatigue tests were designed with the self-developed loading device, and the variation rules of electric flux under fatigue load were analyzed. The evolution of microstructure was studied to reveal the attenuation mechanism of impermeability. The results show that the impermeability of concrete increases first and then decreases with the rise of basalt fiber length and content. Based on impermeability, the optimal length and content of basalt fiber are 12 mm and 0.08% (mass fraction). With the rise of fatigue times and stress ratio, the increase of electric flux of basalt fiber reinforced concrete is lower than that of reference concrete, which is more suitable for heavy load and heavy traffic areas. Basalt fiber refines the pore structure of concrete, and the proportion of harmless pore increases by 18.51%. The pore size of concrete shows an expansion trend and the pore distribution is coarser under fatigue load. The microcracks mainly extend in the length direction at the early stage of fatigue loading, while the microcracks mainly extend in the width direction at the later stage. Basalt fiber delays the deterioration of pore structure and the propagation of microcracks, so as to reduce the attenuation range of impermeability.

In order to study the variation of mechanical behavior and internal pore structure of concrete under sulfate attack, uniaxial compression tests were carried out on concrete specimens soaked in 0%, 10%, 15% and 20% (mass fraction) sodium sulfate solution for 210 d. The stress field distribution was simulated by PFC2D software to study the crack evolution during the test, and the internal pore distribution was analyzed by nuclear magnetic resonance. The test results show that the peak stress and elastic modulus of the concrete decrease with the increase of immersion concentration. According to the PFC2D simulation results, tensile cracks first appear in the concrete during uniaxial compression, then the cracks continue to expand, and tensile and shear composite cracks appear, finally a shear crack runs through the diagonal. The T2 distribution curve of concrete after sulfate attack shows three peaks, and the internal pores are mainly micro pores and small pores. With the increase of immersion concentration, the micro pores gradually transform into small pores, resulting in the increase of T2 peak 1 amplitude and area of the concrete.

The daily and annual temperature differences in northwest China vary greatly, which leads to thermal fatigue deterioration of concrete. Under the condition of constant environmental humidity, the thermal fatigue tests of concrete with two strength grades were carried out at the temperature difference of 20 ℃, 30 ℃ and 40 ℃ to measure the changes of the macroscopic properties such as compressive strength and splitting tensile strength. The microstructure changes of concrete were measured by ultrasonic nondestructive technology and mercury intrusion porosimetry test. The results show that the thermal fatigue degradation effect is obvious. With the increase of temperature difference and number of temperature difference cycles, the concrete strength decreases obviously. The decrease of C40 concrete is greater than that of C25 concrete, and the splitting tensile strength is more sensitive to thermal fatigue than compressive strength. The ultrasonic velocity decreases, which indicates that the internal defects of concrete increase. The porosity, total pore volume, average pore diameter, medium pore diameter and the most probable pore diameter of concrete increase with the increase of temperature difference and number of cycles, while the total pore surface area decreases, which indicates that the pore structure shows the characteristic of coarsening and a tendency to deteriorate. The porosity of C40 concrete is smaller than that of C25 concrete, but the relative change value of the porosity of C40 is larger, which reveals the internal reason for strength damage of concrete under thermal fatigue from the microscopic level.

The target porosity was prefabricated by adding different content of expanded polystyrene (EPS) particles to simulate different hole defects of concrete, and concrete specimens with different porosity levels of C25 and C30 were prepared to develop the mechanical properties of concrete with hole defects under monotonic and reciprocating loading. In the experimental study, the changes in the shape, strength, strain and elastic modulus of concrete specimens with porosity were analyzed, and the influences of different hole defects on the static and dynamic properties of concrete were discussed. The test results show that under monotonic and reciprocating loading, the concrete specimens without prefabricated hole defects show brittle failure characteristics. However, with the increase of porosity, the strength of concrete specimens decreases significantly, and the stress-strain curve gradually tends to distribute in a fish-maw shape. The specimens change from brittle to ductile failure and gradually show the characteristics of multi-crack propagation, especially for reciprocating loading. Under the two loading methods and two strength levels, the main mechanical properties of the specimens show consistent changes with the increase of the precast porosity. Peak stress and elastic modulus decrease exponentially with the increase of porosity, while peak strain and extreme strain increase linearly. The influence of porosity on the mechanical properties of specimens under reciprocating loading is greater than that of monotonic loading, and this effect decreases with the increase of concrete strength. In the reciprocating loading process, the greater the porosity, the greater the stiffness ratio of the specimen before the peak stress, and the more serious the stiffness degradation after the peak. For the same porosity, the higher the concrete strength grade, the smaller the stiffness growth rate before the peak stress and the less the degree of stiffness degradation after the peak.

In this paper, a new type of ultra-high performance concrete (UHPC) prefabricated cable trench was designed, and its bearing capacity and applicability were studied. The bending performance of the side plate was experimentally studied, and the test results were compared with the calculation results of the current three specifications. The results show that the calculated values of bearing capacity, stiffness and crack width based on “Technical specification for fiber reinforced concrete structures” (CECS 38-2004) are close to the experimental values. This specification can be used as the basis for the design of UHPC prefabricated cable trench components. The reliability of the connection mode between the bottom plate and the side plate was studied. Through the experimental study on the cast-in-situ, the connection mode with bolt constraint on the bottom plate and the cup joint, it is found that the deformation of the side plate of the cup joint specimen under load is obvious, and the bearing capacity is only 6.7 kN. Compared with the cast-in-situ joint specimen, the failure section of the bottom bolt connection is the same, the stiffness is slightly lower, and the ultimate bearing capacity is similar, which is about twice that of the cup joint specimen. It can ensure the overall resistance performance of UHPC prefabricated cable trench.

The basic mixture of ultra-high performance concrete (UHPC) was optimized by the modified Andreasen & Andersen particle packing model, and the effects of steel fibre shape, content and hybridization on the wet packing density of UHPC were evaluated. Moreover, the D-optimal design (DOD) method was employed for modelling of wet packing density of UHPC against hybrid steel fibres. The results reveal that the incorporation of long straight fibres, short straight fibres and hooked-end fibres have varying degrees of effects on UHPC packing system, among which the end hook fibre reduces the density of UHPC the most. In addition, the steel fibre content has obvious effects on wet packing density of UHPC, and especially as the steel fibre content exceeds 2.0% (volume fraction, below is the same), the packing density of UHPC drops dramatically, resulting in significant damage to UHPC packing system. Based on the analysis results of the DOD model, it is concluded that the hybridization of 0.9% long straight fibres and 1.1% hooked-end fibres is optimized mixture and disturbing effect of steel fibre on UHPC accumulation system is minimized.

Phosphogypsum is a kind of industrial solid waste, which is discharged when the phosphoric chemical industry produces phosphoric acid through the wet process. Because phosphogypsum contains a large amount of impurities such as phosphorus, fluorine, and alkali metal salts, it will be disposed of in a landfill, which will cause problems such as occupation of cultivated land and environmental pollution. At present, the most promising and effective treatment method is to convert phosphogypsum to α-hemihydrate gypsum (α-HH). But the harmful impurities such as soluble phosphorus, eutectic phosphorus and soluble fluorine of phosphogypsum are the main obstacles to the preparation of α-HH from phosphogypsum. Therefore, the pretreatment of harmful impurities in phosphogypsum and the adjustment of α-HH crystal morphology are the focus of research on the preparation of α-HH from phosphogypsum. This article comprehensively reviewed the physicochemical properties of phosphogypsum, the influences of harmful impurities on the properties of gypsum, the pretreatment measures, the preparation method of α-HH and the adjustment of crystal micromorphology, and the current research status. Different pretreatment measures and the preparation methods of α-HH were discussed. The advantages and disadvantages of the method were summarized, and the mechanism of the crystal transformation agent regulating the micro-morphology of α-HH crystals was summarized. Finally, the next problem to be solved was put forward.

The influences of sepiolite fiber volume fraction and length on mechanical properties and drying shrinkage of artificial sand mortar with high stone powder content were investigated. A mercury porosimeter and a scanning electron microscope were employed to analyse the characteristic variation of mortar internal pore structure and microscopic morphology. The results indicate that an appropriate quantity of short sepiolite fiber significantly improves the compressive strength, flexural strength and drying shrinkage resistance of mortar. Compared to the blank group, the 28 d compressive strength and flexural strength of specimens with 1.5% volume fraction of 1 mm length fiber increase by 98.9% and 36.2%, respectively. Besides, the 28 d natural drying shrinkage value with 2.0% volume fraction of 1 mm length fiber reduces by 72.1%. A large number of needle-shaped ettringite and flaky calcium hydroxide crystals are observed inside the sepiolite fiber specimen, which effectively improve the compactness of mortar hardening system. The total porosity of mortar is inversely proportional to the fiber volume fraction.

In this paper, a modified alkali-activated slag cementitious material was proposed by applying calcium and alumina mineral phases (Ca(OH)2 and γ-Al2O3) as partial replacement of slag, aiming at promoting the formation of Friedel’s salt (F salt) in the matrix when in the presence of chloride, and improving the chloride binding capacity. The effects of calcium and aluminum mineral phase content on reaction products, chloride binding capacity and mechanical properties were discussed. The results show that the addition of calcium and aluminum mineral phases improves the chloride binding capacity of alkali-activated slag, and the mass ratio of Ca(OH)2 to γ-Al2O3 is highly related to this capacity. XRD analyses show that there exists unreacted Ca(OH)2 within the reaction products, and all those Ca(OH)2 transform into F salt or other phases after chloride attack. It is demonstrated that the enhancement of chloride binding capacity is attributed to the formation of F salt. The compressive strength results indicate that the addition of Ca(OH)2 exhibits a negative impact, while the γ-Al2O3 can compensate for the strength loss due to the Ca(OH)2 addition.

This study is aimed at the differences of physical properties such as specific surface area and particle size distribution of cementitious materials. The P·Ⅱ cement, grade Ⅰ and grade Ⅱ fly ash, grade S95 and grade S105 slag were intermixed. Four combinations of fly ash and slag were designed on the premise of fixed cement dosage. The effect of the combination method on the fluidity of the pure slurry was analyzed through the fluidity experiment, and the particle size curve was compared with the Fuller distribution curve. Tests on workability, mechanical properties and free chloride ion concentration of concrete with different combinations were carried out on the basis of the pure slurry mix proportion. The microscopic morphology and chemical composition of hydration product of hardened slurry were analyzed. The effects of particle size distribution of fly ash and slag on the strength and chloride ion penetration resistance of concrete were discussed, and the influence mechanism was revealed. The research results show that the particle size distribution of mineral admixtures is an important factor in determining the quality of particle gradation. The ball effect of grade Ⅰ fly ash is stronger, which makes it play a key role in improving fluidity. The mechanical properties and durability of concrete are affected by the hydration of fly ash and slag, and the degree of pozzolanic reaction. The grade Ⅰ fly ash has larger specific surface area and higher pozzolanic activity. Therefore, the fluidity, workability, compressive strength and chloride ion penetration resistance of grade Ⅰ fly ash and S95/S105 slag combination group are significantly higher than the combination of grade Ⅱ fly ash and S95/S105 slag combination group. Among all the combinations in this experiment, the particle size distribution curve of cementitious material of the combination of grade Ⅰ fly ash and grade S95 slag is the closest to the Fuller curve. The particle size distribution of this combination is the best, the content of Ca(OH)2 in the hydrated slurry is the lowest, and the pozzolanic reaction is the most sufficient. The corresponding concrete has a dense internal structure, and the chloride ion penetration resistance of concrete is good.

In response to the “carbon peak and neutrality” policy of energy saving and emission reduction, in the present paper, geopolymers were prepared with metakaolin and blast furnace slag as raw materials. The compressive strength was used as the index to optimize the preparation conditions and to explore the factors affecting the strength of geopolymer based on metakaolin. The optimum mixing ratio of geopolymer was determined by orthogonal test. The metakaolin fractions calcined at different temperatures were analyzed by thermogravimetry and XRD. The research results show that when the calcining temperature of kaolin is 800 ℃, the optimum mixing ratio of geopolymer based on metakaolin is that the mass ratio of sodium hydroxide to sodium silicate is 6.5∶1 and the mass fraction of activator is 14.2%. Under these conditions, the 28 d compressive strength of the geopolymers reaches 46.6 MPa. The compressive strength of the geopolymer based on metakaolin increases with the addition of the mass fraction of activator, and increases first and then decreases with the increase of the mass ratio of sodium hydroxide to sodium silicate, and increases first and then decreases with the increase of kaolin calcination temperature.

To investigate the effect of adding silica fume (SF) and fly ash (FA) on the strength and shrinkage performance of cement slurries at various curing ages, five different composite cement slurries (water-binder ratio of 0.29) with different content of SF and FA were designed. The hydration heat release characteristics and pore structure composition of different composite cement slurries were characterized by calorimeter and mercury porosimeter tests, and the changes of hydration heat release and porosity with the increase of SF and FA content were analyzed. The relationships between compressive strength and pore structure, hydration characteristic and shrinkage strain were also established. Results show that FA greatly reduces the early compressive strength of cement pastes, while it is beneficial to reduce the autogenous shrinkage strain and dry shrinkage strain at the same time. The 3 d compressive strength of the cement pastes can be improved obviously by adding SF. However, the autogenous shrinkage strain at 3 d and dry shrinkage strain at 28 d of cement pastes increase significantly once SF content exceeds 10% (mass fraction). The addition of SF advances the start and end time of the induction period of cement hydration, and increases the hydration reaction order and the constant value of reaction rate at each stage, which leads to a significant increase of total hydration heat release amount and heat release rate of cement-silica fume in comparison with cement-fly ash system. SF and FA not only effectively improve the internal pore structure of cement slurries, but also increase the proportion of gel pores and reduce the proportion of large pores. It is found that the total hydration heat release amount of composite slurries at 72 h has positively correlation with 3 d autogenous shrinkage strain, and porosity has negatively correlation with compressive strength of composite slurries.

In order to promote the high-value utilization of iron and steel metallurgical slag and chemical waste slag, steel slag, blast furnace slag, soda residue and desulfurization gypsum were used as raw materials to prepare artificial reef cementitious materials for marine ranching through the combination and synergistic effect between active activator and solid waste materials. By mixing 16% (mass fraction, the same below) steel slag , 64% blast furnace slag, 8% soda residue and 12% desulfurized gypsum, the 28 d compressive strength of the mortar test block reaches 52.6 MPa, which has the potential to replace Portland cement in some cases. The influences of steel slag and blast furnace slag ratios on the compressive strength development of the net slurry test block soaked in seawater of East China sea in the 15 months were studied. Hydration products of the total solid waste cementitious materials system were studied through XRD, SEM and MIP characterization methods. The results show that there is a synergistic hydration between steel slag and blast furnace slag, and the main hydration products are ettringite (AFt), C-S-H gel and Friedel’s salt (FS). The amorphous C-S-H gel, which binds AFt to FS, is the main source of strength of the whole system. The research provides scientific basis for the proper settlement of large amount of solid waste.

Uniaxial compression tests were carried out on four kinds of well-graded rubber concrete with different rubber volume content (0%, 5%, 10%, 20%). The mechanical properties and failure modes were analysed, and the rubber content was determined when the comprehensive performance of rubber concrete was optimal. Then, the uniaxial compression experiments of the optimal dosage group under different strain rates were carried out, and the energy characteristics of rubber concrete under different strain rates were analysed. Results show that the rubber concrete is characterised by ductile failure, rather than brittle failure of ordinary concrete. With the increase in rubber content, the compressive strength decreases significantly, but the deformation ability is enhanced. When the rubber content is 10%, the compressive strength of rubber concrete reaches the standard, and the deformation ability is the best. The typical energy evolution and transformation process of rubber concrete under compression is that the input energy is first converted into elastic energy and stored; then, the conversion rate of dissipated energy begins to increase, resulting in a large number of micro-cracks on the surface of the specimen. Finally, the elastic energy is rapidly released, and the proportion of the conversion rate of dissipative energy is significantly improved, resulting in the overall failure of the specimen. In addition, with the increase of strain rate, the compressive strength and initial elastic modulus of rubber concrete increase significantly, while the peak strain decreases. At the same time, the total input energy, elastic energy and dissipation energy show an upward trend, and the elastic energy increases more obviously.

In order to study the effects of different mass dosage of triethanolamine (TEA) as grinding aid on the particle properties of bagasse ash, the particle properties of bagasse ash were characterized by sieve residue test, BET, particle size distribution test and particle shape test, the effects of bagasse ash particle properties on the strength and chloride resistance of bagasse ash mortar were investigated. The results show that TEA optimizes the particle size distribution of bagasse ash, and the proportion of particles smaller than 32 μm increases by 8.2 percentage point, the specific surface area increases to 5.503 5 m2/g, and the particle shape tends to be spherical under the optimal addition of 0.08% (mass fraction).Meanwhile, the strength and chloride resistance of bagasse ash mortar show a pattern of increase first and then decrease with the increase of TEA content; the compressive strength of bagasse ash mortar increases by 19.88% and the chloride ion diffusion coefficient drops by 79.63% compared with normal concrete when TEA dosage is optimally at 0.08%. The mechanism of the influence of bagasse ash particle properties on the performance of bagasse ash mortar is revealed by X-ray diffraction (XRD) and mercury intrusion porosimetry (MIP). Results show that the pozzolanic activity of bagasse ash optimized by TEA is enhanced, and more hydration products are generated in the bagasse ash mortar matrix to improve the compactness. The optimized bagasse ash particles give full play to the filling effect, reduce the void ratio of bagasse ash mortar, and improve the the mortar strength and resistance to chloride salt erosion.

Ammonium hexafluorosilicate and ammonium bicarbonate as raw materials were used to prepare silica and ammonium fluoride (NH4F). Based on the single factor experiment and Box-Behnken design response surface methodology, a quadratic regression model was established for variance analysis and verification. The influences of four single factors (liquid-solid ratio, ingredient ratio, reaction temperature and reaction time) on silica yield and NH4F concentration were investigated. By the response surface analysis, the better process conditions are as follows: liquid-solid ratio 8, ingredient ratio 5.49, reaction temperature 76.5 ℃, reaction time 49.08 min. Under these conditions, the verification experiment was carried out. The silica yield is 96.90%, and the NH4F concentration is 2.02 mol/L. There is no significant difference between the predicted value and the experimental value, which verifies the reliability of the quadratic regression model. XRD, IR, TG-DSC, SEM, BET characterization, particle size analysis and performance test of the product silica were carried out. The concentration of the product NH4F was measured by the fluoride ion selective electrode method, and its performance was tested. It is confirmed that the particle size of silica product is micron-sized, and silica is a mesoporous material with specific surface area of 316.83 m2/g. The mass fraction of SiO2 is as high as 97.77%, and the appearance, heating loss, ignition loss, pH value, heavy metal content, and oil absorption value all meet industry standards. The content of ammonium fluoride, free acid and fluorosilicate in NH4F product all meets the national standard of the People’s Republic of China.

In this study, calcium oxalate chemically bonded material (COCM) was fabricated through the reaction between calcium oxide-rich blast furnace slag and oxalic acid (OA) at room temperature. The effects of the mass ratios of oxalic acid to blast furnace slag (BFS) on the mechanical properties of COCM were studied, and its solidification effect for heavy metals (Pb, Cd and Cu) was further investigated. The results show that the COCM with an OA/BFS mass ratio of 0.25 has the best mechanical property. The compressive strength at 3 d, 7 d and 28 d reaches 25.70 MPa, 27.86 MPa and 34.79 MPa, respectively. XRD and SEM were used to analyze the phase composition and microstructure of COCM. The results indicate that COCM is mainly composed of calcium oxalate (CaC2O4·H2O) and has tense microstructure. When the mass fraction of heavy metals (Pb and Cu) is 8%, COCM still has good solidification effect on heavy metals (Pb and Cu), and the toxic concentration of solid leaching is lower than the national standard limit. The results provide reference for preparing COCM from blast furnace slag.

In recent years, microbial induced calcium carbonate precipitation (MICP) has become an efficient and environmentally friendly technology for repairing concrete cracks. In this paper, a mineralization microorganism that grows in a low temperature environment was selected, and then the changes of Ca2+ concentration, pH value and calcification rate were studied in alkaline solution to reveal the dynamic process of microbial induced mineralization. Subsequently, the microorganism was applied to the self-healing of concrete cracks, and the crack healing ratio and permeability coefficient were used to characterize the self-healing effect of concrete cracks. The results show that the microorganism quickly reduces the Ca2+ concentration in the solution and increases the calcification rate. Meanwhile, the mineralization products are mainly spherical calcite CaCO3. For the early concrete cracks with the width of less than 0.50 mm, the surface of the crack basically fills with white precipitations after 28 d healing time at the curing temperature of 10 ℃, and the permeability coefficient drops by two orders of magnitude. In addition, the healing products at the crack mouth are mainly spherical calcite CaCO3 with different sizes.

In order to effectively reduce the collapsibility of loess areas in contact with water, a study was conducted on the collapsibility of loess using microbial induced calcium carbonate precipitation (MICP) in Lanzhou loess. The unconfined compressive strength and coefficient of collapsibility of the loess before and after MICP treatment were evaluated. The microscopic characteristics of loess modified by MICP were analysed by CT scanning technology, and the improvement mechanism of MICP was further explored. The test results show that the unconfined compressive strength of the loess specimens modified by MICP increases significantly, up to 150 kPa, and the collapsibility of the loess is effectively reduced; the amount of calcium carbonate production continues to increase with the increasing concentration of the cementing fluid, but decreases when the concentration of the cementing fluid is greater than 1.25 mol/L; the porosity and pore equivalent diameter of the modified loess specimens are decreased. The porosity and pore equivalent diameter of the modified loess specimens are all reduced.

In order to improve the effects of cement and fly ash on the solidification of waste soft clay with high water content, sodium silicate and quick lime were selected as additive and dispersing agent, respectively. The unconfined compressive strength test (UCS), X-ray diffraction (XRD), and scanning electron microscope (SEM) were used to research the influences of mixing ratio and age on the water stability, strength behavior, solidification mechanism of solidified waste soft clay. The results show that 3% (mass fraction) cement combined with 7% (mass fraction) fly ash, 2% (mass fraction) quick lime and 2% (mass fraction) sodium silicate significantly improve the strength and water stability of solidified soft clay. The strength of solidified soft clay reaches 1 MPa, and meets the strength requirements of the cement-fly ash base layer. With the same mixing ratio of cement, fly ash and water glass, the mass fraction of quick lime increases from 0% to 2%, and its strength increases about 375 kPa. Adding the quick lime is conducive to the uniform mixing of the other curing agents. It indicates that the water absorption and dispersion effect of quick lime play a vital role in the solidified soil. In addition, SEM images show that after adding the composite curing agent, the large aggregates disappear, a large number of sheet structures generate, the large pores between the particles are filled, and the strength of soft soil is also improved.

Jizhou kiln in Song Dynasty is a typical kiln for producing black porcelain in ancient China, and it has a history of more than 1 200 years. Among them, the most representative black porcelain is the leaf-temmoku porcelain produced by Jizhou kiln. Leaf-temmoku porcelain represents the decoration of natural wood leaves on the black glaze, and the leaf ash reacts with the glaze layer to form leaf patterns with distinct stems and leaves in the firing process. At present, the research on the leaf-temmoku porcelain mainly focuses on the testing analysis of composition and imitation angle, but there are few relevant reviews on the overall technology and development view. Hence, chemical composition, leaf species, porcelain making process and color formation mechanism were summarized and analyzed in this paper, which play a positive role in analyzing the Jizhou kiln leaf-temmoku porcelain and its inheritance.

At present, the application of artificial bone is greatly limited due to its poor mechanical properties. Therefore, it has become a research interest to obtain the artificial bone with improved mechanical properties, while its original piezoelectric and biological properties are maintained. In this paper, in order to improve the mechanical properties of the composite while keeping the electrical properties unchanged, the carbon fiber/barium titanate-hydroxyapatite (Cf/BT-HA) composite was prepared by traditional solid-phase sintering method using barium titanate-hydroxyapatite (BT-HA) composite as matrix and carbon fiber (Cf) with 5% (mass fraction) as reinforcement. The results show that the electrical properties remain unchanged and the mechanical properties are greatly improved after adding Cf into the composite. The samples possess excellent ferroelectric properties, the piezoelectric constant d33 is 37 pC/N, and the Curie temperature is 170 ℃, which is higher than the artificial bone service temperature. The bending strength is 121.7 MPa, and the hardness is 3.56 GPa, both of which are three times of the original. The fracture toughness is also doubled, reaching 1.21 MPa·m1/2. Cf/BT-HA composites have no cytotoxicity and good osteoinduction. It is found that Cf/BT-HA composites would be a promising bone substitute material.

Using polyacrylonitrile (PAN) based carbon fiber weft free cloth and short-cut mesh fiber interactive laminated acupunture, the BaTiO3 with different mass fractions (0%, 5%, 15%, 25% and 35%) was introduced in the preparation process to prepare the longitudinal fiber arranged ring carbon fiber preforms. The method of chemical vapor deposition (CVD) and liquid phase impregnation was combined. BaTiO3 modified carbon/carbon composites were prepared. The mechanical properties of the composite were tested in both vertical and parallel directions, and the microstructure and morphological characteristics of the fracture were observed. The results show that the introduction of nano-BaTiO3 accelerates the nucleation and growth of pyrolytic carbon, and changes the structure of pyrolytic carbon, the single smooth layer is transformed into smooth layer and rough layer. With the increase of BaTiO3 content, the vertical compressive strength of the composite is basically unchanged first and then gradually increases, while the parallel compressive strength first increases and then decreases. The fracture mode of the composite under vertical compression is brittle fracture, and the fracture mode under parallel compression is brittle fracture with the characteristics of interlaminar fracture.

In recent years, the massive consumption of fossil fuels has led to increasingly serious environmental pollution. Solid oxide electrolysis cell (SOEC) has attracted more and more attention because it can efficiently and environmentally convert CO2 into CO and other high value-added chemicals. Electrode materials with excellent performance are crucial to the development of efficient and stable SOEC. La0.7Sr0.3Cr0.5Fe0.5O3-δ(Sto-LSCrF)perovskite oxide has attracted widespread attention due to its excellent oxidation-reduction stability. In order to further improve the performance of Sto-LSCrF fuel electrode materials for CO2 electrolysis, the A-site doping Ce strategy in Sto-LSCrF was adopted to improve the content of mobile oxygen vacancies in Ce-LSCrF, so as to increase its adsorption and activation ability of CO2 and then enhance its electrochemistry properties. At the same time, the phase structure, oxygen vacancies content and CO2 adsorption and desorption capacity of the materials were characterized and analyzed in detail. In addition, the electrochemical performance of Ce-LSCrF was explored. Compared with Sto-LSCrF, Ce-LSCrF fuel electrode not only exhibits higher electrolysis performance, but also shows better constant voltage discharge stability. The enhancement of electrolytic performance is attributed to more mobile oxygen vacancies in Ce-LSCrF lattice that can effectively absorb and activate CO2. These results indicate that Ce-LSCrF is an excellent fuel electrode material for CO2 electrolysis in SOEC.

Aiming at the urgent demand of the new generation of sonic logging tools for their core components, piezoelectricceramics, which have high Curie temperature, high voltage electrical coefficient and high stability, 0.06BiYbO3-0.94Pb(Zr0.48Ti0.52)O3(BY-PZT) ternary piezoceramics with addition of different oxide additives were prepared by traditional solid-state reaction method. The effects of oxide additives on the phase structures and electrical properties of the BY-PZT ternary piezoceramics were investigated. XRD and SEM analysis show that all samples are pure tetragonal perovskite structure. When doped with Cr2O3, the average grain size of the samples has a maximum value. Dielectric temperature spectrum and resonance spectrum analysis illustrated that doping of four kinds of oxide improved the temperature stability of dielectric properties respectively. The lanthanum-doped sample got the lowest temperature coefficient of dielectric constant (Tkε). The mechanical quality factor (Qm) has a maximum value when MnO2 are doped; but the samples doped with CeO2 have the best thermal depolarization resistance. The analysis of high temperature complex impedance (Cole-Cole) shows that Cr2O3 doping significantly improve the high temperature resistivity of the ceramic. It is found that the electrical conduction behavior of the ceramics at high temperature is dominated by the grain-boundary response. The lanthanum-doped sample has both high Curie temperature (TC=397 ℃) and high piezoelectric constant (d33=290 pC/N), and after annealed at 300 ℃ for 4 h, the d33 value of the sample still retains above 270 pC/N, which provides great promising for application in the high-temperature piezoelectric devices with an extreme operating temperature of 300 ℃.

Magnesium phosphate coating belongs to a new type of high temperature resistance inorganic fireproof material, and also an excellent inorganic anti-corrosion material for industrial steel structures. This article focused on the mechanical properties of magnesium phosphate coatings after high temperature action. Through the experiments, the changes in mechanical properties such as hardness and bonding strength of magnesium phosphate coatings after high temperature (100 ℃, 200 ℃, 300 ℃, 400 ℃, 500 ℃, 700 ℃, 900 ℃) action, as well as the microscopic mechanism of the changes in mechanical properties were systematically studied. The results show that the magnesium phosphate coating has good integrity after high temperature action, and there are no defects such as powdering, blistering, peeling and cracking. Compared with room temperature, the mechanical properties of magnesium phosphate coatings after high temperature action decrease slightly. The magnesium phosphate coatings treated at 300 ℃ have the lowest bonding strength and the most obvious decrease in hardness. With the temperature increasing above 300 ℃, the mechanical properties of the coatings improve in different degree. Based on the microscopic characterization and thermogravimetric analysis at different temperatures, the four-stage high temperature evolution mechanism that caused the changes of the high temperature mechanical properties of the magnesium phosphate coatings was suggested.

Sintering is one of the key processes in preparing low temperature co-fired ceramic (LTCC) substrate, which plays an important role on the properties of LTCC substrate. In this paper, the effects of different sintering heating rates on the dielectric properties, warpage, film adhesion and flexural strength of LTCC substrate were studied, and the reasons for the changes of substrate properties were analyzed. The results show that when the heating rate is 8 ℃/min, the dielectric constant of the substrate is 5.788 and the dielectric loss is 8.21×10-4. The substrate basically has no warpage, high density, strong adhesion, and the flexural strength of the substrate is up to 175 MPa。

During vitrification of high-level liquid waste with high content of sulfur and sodium, Na2SO4 is very easy to decompose and separate from the glass melts. In this paper, it was proposed that Na2SO4 in the high-level liquid waste was converted into PbSO4 by addition a proper amount of Pb(NO3)2 solution, and then the borosilicate glass solidified body was prepared by melting method. The dissolution characteristics of PbSO4 in glass melt was observed in situ for the first time by high temperature confocal scanning laser microscope, which has been widely used in steel materials. The thermal stability of PbSO4 mixed with borosilicate glass at different temperatures (800 ℃ to 1 150 ℃) and the sulfur content in glass were investigated. The results show that borosilicate glass samples with 6% (mass fraction) SO3 introduced in the form of PbSO4 are homogeneous glass-ceramics at both 800 ℃ and 900 ℃. The glass-ceramics mainly possess SiO2 phase along with a small amount of BaSO4 and PbSO4 phases at 800 ℃. The content of SiO2 crystal decreases while the BaSO4 crystal content increases, and PbSO4 phase disappears and CaMgSi2O6 phase appears at 900 ℃. A white separated phase begins to appear on the glass surface composed of PbO, BaSO4 and LiNaSO4 crystals at 1 000 ℃. In addition, the round shape PbO crystals grow gradually and BaSO4 crystals change from block to strip shape with the temperature increasing from 1 000 ℃ to 1 100 ℃. The sulfur content in the glass remains unchanged at 800 ℃ to 1 000 ℃, and decreases obviously with further increasing the temperature.

As an important carrier of clean energy, NH3 is a necessary raw material for the production of various chemicals, which is closely related to the rapid development of human society. The photocatalytic nitrogen fixation technology has attracted extensive attention of researchers in recent years, since it uses clean solar energy as the only energy input toward directly converting N2 and H2O to NH3 under mild conditions. Although the advantages of photocatalytic nitrogen fixation technology are environmentally friendly, energy conservation and easy to operate, the traditional semiconductor photocatalyst used for nitrogen fixation cannot fully exert its activity due to the restriction in light harvest and utilization of photogenerated carriers. In order to efficiently enhance the nitrogen fixation performance, thus, it is necessary to design the corresponding catalysts to improve the adsorption and activation of inert N2 molecules. In this paper, first of all, a brief overview of photocatalytic nitrogen fixation was given and two possible reaction mechanisms of photocatalytic nitrogen fixation were introduced. Then, the focus was put on the influence of semiconductor materials containing oxygen, nitrogen and sulfur vacancies on photocatalytic nitrogen fixation. Finally, some practical opinions on the current challenges and future development in the field of photocatalytic nitrogen fixation were given.

Antimony selenide (Sb2Se3) has become one of the most popular solar cell materials because of its high abundance and good photoelectric properties. At present, among many preparation methods of Sb2Se3, vapor transfer deposition (VTD) has attracted much attention because of its simple process and large area preparation. There are many factors affecting the preparation of Sb2Se3 films by VTD, such as chamber pressure, reaction temperature, the position of evaporation source and substrate, substrate inclination and so on. Sb2Se3 thin films were prepared by VTD at different substrate inclinations (30°, 45°, 60°, 90°) and characterized by XRD, Raman, SEM and near infrared-ultraviolet (NI-UV) reflection. The results show that different substrate inclinations have obvious effects on the structure and optical properties of the films. The grain size first increases and then decreases with the increase of substrate inclination. At the same time, the morphology of the film changes from rod to sheet. When the substrate inclination is 90°, the film becomes dense. The NI-UV reflection spectrum shows that the sample with an inclination of 60°, has the lowest reflectivity in the range of wavelength less than 1 100 nm. The FTO/CdS/Sb2Se3/C device prepared at this angle has a conversion efficiency of 2.38%.

Electrochemical biosensors with ultra-high sensitivity and specificity are of great significance in the fields of environmental risk substances monitoring and biomedical detection. The key to the application of electrochemical biosensors is to construct a high biocompatibility, simple preparation process and low cost detection electrode. In this paper, three-dimensional graphene electrodes with good reproducibility were prepared by 3D printing technology, and then the morphology and oxidation groups of graphene on the surface were regulated by electrochemical oxidation. The electrochemical biosensor shows high sensitivity in the detection of environmental pollutant microcystin (MC-LR). The linear detection range is 4×10-6 μg/L to 1 μg/L, and the detection limit is 1.5×10-7 μg/L. At the same time, the electrochemical biosensor presents highly sensitivity for dopamine, heavy metal Hg2+, tetracycline and so on by changing the aptamer detection probe. This study provides a new idea for the application of electrochemical aptamer biosensors, and provides some basic data for the development of ultra-high sensitivity environmental monitoring and biomedical detection sensors.

Aluminum nitride (AlN) nanowires have been studied extensively by scholars due to their excellent thermal conductivity. Aluminum nitride nanowires were prepared by direct nitriding method using melamine and yttrium fluoride as additives. The crystal structure and microscopic morphology of the reaction product were carried out by X-ray diffraction (XRD), scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM) and energy spectrometer (EDS). The promoting effects of melamine and yttrium fluoride on nitriding reaction were analyzed. The effects of different melamine content and different reaction temperatures were studied on the preparation of aluminum nitride nanowires. The results show that the addition of melamine increases the nitridation reaction rate and promotes the formation of nanowires. When the reaction temperature is 1 200 ℃, the mass ratio of aluminum powder to melamine is 1∶4, and the content of yttrium fluoride is 5% (mass fraction), aluminum nitride nanowires with high aspect ratio are successfully prepared.

Styrene butadiene rubber (SBR) active emulsified asphalt can activate aged asphalt of old pavement. However, the engineering application is limited due to its poor high-temperature stability and insufficient adhesion. To solve the performance shortcomings of SBR active emulsified asphalt performance, waterborne epoxy resin (WER) was used for composite modification. The evaporation residue was obtained by the modified low-temperature evaporation method. The effects of WER dosage on the basic physical properties, adhesion, dynamic rheological properties, low-temperature creep properties and reducibility of SBR active emulsified asphalt were analyzed. The results show that with incorporation of WER, the penetration of SBR active emulsified asphalt decreases significantly, the softening point increases significantly, but the ductility decreases. WER can significantly improve the high-temperature stability of SBR active emulsified asphalt, but has an adverse impact on its low-temperature ductility properties. In addition, WER significantly enhances the adhesion of SBR active emulsified asphalt. The complex shear modulus (G*) and rutting factor (G*/sin δ) increase, while phase angle (δ) decreases with the increase of WER dosage, implying that the high-temperature rutting resistance of SBR active emulsified asphalt is improved. Furthermore, with the increase of WER dosage, the stiffness modulus (S) and the creep rate (M) of SBR active emulsified asphalt show an increasing and decreasing trend, respectively. The incorporation of WER has little effect on the reducibility of SBR active emulsified asphalt. Based on the experimental results, the dosage of WER should be controlled in 10%~15% (mass fraction).

In order to explore the effect of segregation on the long-term water stability of asphalt mixture in hot and humid area, two simulation schemes of gradation segregation and temperature segregation were designed respectively. The void ratio of the asphalt mixture was tested by the drainage method, and the residual stability of the asphalt mixture was tested by the immersion Marshall test. Based on the nonlinear fitting method, the datas of residual stability of the asphalt mixture with different dry-wet cycles were analyzed, and the decay curves and the law of water stability of asphalt mixture were obtained under different states of segregation. The research results show that with the dry-wet cycles progress, the void ratio of asphalt mixtures with different types of segregation increases, but the increase is limited. After ten times of dry-wet cycles, the residual stability is 81.8%, indicating that the fine aggregate segregation is not easy to cause strength loss under the dry-wet cycles. Under the condition of severe segregation, the residual stability decreases to 79.8% after the first dry-wet cycle, and then decreases to 67.4% after the 10th dry-wet cycles. Whether there is segregation or not, the effect of dry-wet cycles has a turning point, that is, the effect of dry-wet cycles in the early stage is obvious, and the effect significantly slows down after reaching the turning point. As the degree of segregation increases, the turning point of the residual stability gradually moves forward, indicating its long-term water stability becomes worse.

Mineral admixtures are important part of cement-based grouting materials for semi-flexible pavement. The coordination of mineral admixtures plays an important role in improving the fluidity and mechanical properties of grouting materials. In this paper, blast furnace slag powder, cenosphere and silica fume were selected. The effects of the three mineral admixtures on the fluidity and mechanical properties of grouting materials for pavement were investigated by the orthogonal experimental design method, and the hydration product composition and morphology of hardened paste of grouting materials were analyzed by means of XRD and SEM. The results show that the order of influencing factors of the cooperative optimization of three mineral admixtures on the fluidity and mechanical properties of grouting materials is cenosphere, silica fume and blast furnace slag powder.Among them, cenosphere has the most significant effect on improving the fluidity of grouting materials, and silica fume and blast furnace slag powder have the obvious effect on promoting the mechanical properties of grouting materials. According to the evaluating indicator of the fluidity and early strength of grouting materials, the optimum content of cenosphere, silica fume, and blast furnace slag powder is 15.0%, 1.5% and 5.0% (both are mass fraction) respectively. In addition, the synergistic addition of three mineral admixtures has little effect on the composition and morphology of early hydration products of grouting materials. It shows that the improvement of early mechanical properties of grouting materials by three mineral admixtures is mainly caused by the improvement of hardened slurry materials compactness through physical filling.