Table of Content

15 February 2024, Volume 43 Issue 2

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Cement and Concrete

Problems Faced by Plant Fiber Reinforced Cement-Based Composites and Research Status of Its Related Modification

JIANG Demin, XU Haodong, KANG Honglong, HU Siyu

2024, 43(2):  387-396. 

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As a new type of green environmental protection building materials, plant fiber reinforced cement-based composites have been favored by many researchers, but there are still many problems. Three main problems in the study of plant fiber reinforced cement-based composites were summarized, namely, the high water absorption of plant fiber, the deterioration of plant fiber and the anticoagulation effect of plant fiberin cement-based composites. The main causes of these problems were analyzed. The common modification methods were listed and the corresponding modification mechanism and research status were described in detail. In the end, the research prospect of plant fiber reinforced cement-based composites was prospected, which provides reference for the resource utilization of plant fiber in the future.

Experimental Research on Bonding Performance of Interface Between Ultra-High Performance Concrete and Stone

HUANG Wei, HUANG Yaying, CHEN Xueli, WU Yingxiong, ZHENG Xinyan, ZHANG Hengchun

2024, 43(2):  397-406. 

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In the reinforcement and repairmen of existing stone structures by ultra-high performance concrete (UHPC), the excellent bonding performance between UHPC and stone is the key to ensure the reinforcement effect. Therefore, in order to explore the interface bonding performance between UHPC and stone, the effects of different interface treatment methods were investigated by splitting tensile test and double L-shaped shear test. The results show that the failure modes of the interface between UHPC and stone are mainly divided into three types. The interface bonding strength is the largest when mode C failure (stone UHPC failure) occurs. The interface groove treatment method significantly improves the interface bonding strength and interface shear stiffness of UHPC-stone specimens. Simultaneously, the interface groove treatment method effectively improves the ductility of specimens while changing the failure mode. When the groove depth is 20 mm, specimens show better interface bonding performance. In addition, the shear load-displacement curve of specimen includes the pre-slip stage and the post-slip stage, and the chisel specimen does not experience plastic deformation in the post-slip stage. Under the same interface treatment method, the interface shear strength between UHPC and stone is positively correlated with the interface splitting tensile strength.

Effect of Mineral Admixture on Hydration Behavior and Mechanical Properties of Shotcrete at Different Temperatures

YUAN Jian, WANG Qin, ZENG Fanchao, GUO Zhixiang, WANG Hongwei

2024, 43(2):  407-417. 

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The effects of fly ash, slag and silica fume on hydration behavior and mechanical properties of shotcrete at different temperatures are still unclear. The effects of three mineral admixtures on the hydration behavior of shotcrete at different temperatures and ages were characterized by XRD quantitative analysis, thermogravimetric analysis and SEM test, and the compressive strength of mortar was tested. The results show that silica fume and slag can improve the early and late strength of shotcrete at different temperatures, while fly ash is not conducive to the development of early strength. The 6 h compressive strength of fly ash mortar is lower than reference value at 20 ℃. At 6 h and 1 d ages, the effect of temperature on the compressive strength of test blocks is very significant, and the 6 h compressive strength of silica mortar at 60 ℃ is as high as 13.39 MPa. With the increase of age, the strengthening effect of temperature on the strength of test block decreases. The increase of temperature stimulates the pozzolana effect of mineral admixture, generates C-S-H gel to fill the internal pores and improve the compressive strength of mortar test block. At the same temperature and age, the content of C-S-H gel in hydration products of silica fume system is high, resulting in the highest compressive strength.The slag system has the highest degree of hydration, resulting in higher compressive strength. Although AFt content of fly ash system is the highest, C-S-H gel content is low, resulting in the lowest compressive strength.This paper provides guidance for the application of mineral admixtures in shotcrete under special environment.

Frost Resistance of Marine Concrete Containing Air-Entraining Agent and Its Beam Bending Capacity

LU Chunhua, ZHU Xuewu, PING An, YANG Yuting

2024, 43(2):  418-427. 

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In order to study the effect of air-entraining agent on the frost resistance of marine concrete and its beam bending capacity, a total of 100 rapid freeze-thaw tests were carried out on six marine concrete beams of two mix ratios and the corresponding freeze-damaged test blocks. The mass loss rate, the dynamic elastic modulus damage degree and the compressive strength loss rate were used to efficiently evaluate the degree of freeze-thaw damage of concrete. The degradation of the compressive strength of concrete as well as the changes in the coefficients of the equivalent rectangular stress diagrams were considered, and the formula for calculating the bending capacity of normal cross-section of marine concrete beams under freeze-thaw action was proposed. The results show that the addition of air-entraining agent can enhance the frost resistance of marine concrete and slow down the degradation rate of the cracking moment of beams, but the concrete strength and the ultimate moment of beams will be reduced. The proposed model can predict the bending capacity of the cross-section of marine concrete beams under freeze-thaw action better within 150 freeze-thaw cycles.

Uniaxial Compressive Damage Comparison of Concrete under Sulfate Salt and Dry-Wet Cycles, Freeze-Thaw Cycles

TANG Zixiang, YANG Shuyan, GAO Haihai, XU Ningyang

2024, 43(2):  428-438. 

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In order to study the damage characteristics of concrete under typical service environment in Ningxia, common action and coupled action of three factors, such as sodium sulfate, dry-wet cycle and freeze-thaw cycle were used to investigate different stress-strain curves of concrete uniaxial compressive. Mass loss rate, relative dynamic elastic modulus and stress-strain curves of samples under different concentrations of sodium sulfate solution and differentcorrosion times were measured. The results show that with the increase of corrosion times, the mass loss rate and relative dynamic elastic modulus of coupled action increase first and then decrease, and that of the common action gradually decreases. With the increase of the concentration of sodium sulfate solution, the slopes of upward section of stress-strain curves of samples under the two corrosion systems are gradually decreasing, and the peak stress is gradually decreasing, as a result, the common action deteriorates more than coupled action. With the increase of corrosion times, the slope of rising section of stress-strain curve of specimen under both corrosion regimes decreases gradually, and the peak stress under the coupled action increases first and then decreases, that under the common action gradually decreases. The peak strain under both corrosion systems increases gradually, and the common action deteriorates faster than the coupled action. The prediction models of concrete stress-strain curve under two corrosion systems are established, which can provide a basis for the life prediction of concrete structure under service environment in Ningxia.

Prediction Model of Chloride Erosion Concrete Based on Artificial Intelligence Algorithm

CUI Jifei, BAI Lin, RAO Pingping, KANG Chenjunjie, ZHANG Kun

2024, 43(2):  439-447. 

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Some prediction models of chloride ion concentration in concrete of the transmission tower pile foundations were established based on machine learning algorithm. These models were tested through correlation coefficient, root mean square error, mean absolute error and variance ratio, and the robustness of the models were analyzed according to Monte Carlo simulation. At the same time, the models were optimized based on sea-horse optimizer. The results show that the support vector machine (SVM) model, the random forest (RF) model and the gradient boosting decision tree (GBDT) model can accurately predict the chloride ion concentration in the concrete of the transmission tower pile foundations. The correlation coefficient R² is greater than 0.880, the root mean square error is less than 0.009, the mean absolute error is less than 0.006, and the variance ratio is greater than 0.890 for all these prediction models. According to the results of error and robustness analysis, it is recommended to prioritize the use of the GBDT model and SVM model for the prediction of chloride ion concentration in concrete. According to the optimization results, the sea-horse optimizer can significantly improve performance of model.

Prediction Model of Impact Splitting Tensile Strength of Concrete after Freeze-Thaw Cycle

XU Ye, TAO Junlin, LI Hongxiang

2024, 43(2):  448-455. 

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In order to predict the impact splitting tensile strength of concrete materials after freeze-thaw cycle, this paper conducted 0, 25, 50, 75 and 100 times freeze-thaw cycle tests on the concrete standard freeze-thaw specimens and the concrete splitting tensile specimens, and tested the dynamic elastic modulus of the concrete standard freeze-thaw specimens through the dynamometer. Electro-hydraulic servo universal testing machine and split Hopkinson pressure bar system were used to perform splitting tensile tests at 0.5, 0.5×10⁶, 1.0×10⁶ and 2.0×10⁶ kN/s, respectively. The effects of freeze-thaw damage and force loading rate on impact splitting tensile strength of concrete were analyzed. The results show that the apparent condition, mass and relative dynamic elastic modulus of standard freeze-thaw specimens deteriorate continuously with the increase of freeze-thaw times. When the freeze-thaw times are constant, the impact splitting tensile strength of concrete specimens increases with the increase of force loading rate. On the basis of the above tests, a prediction model of impact splitting tensile strength of concrete after freeze-thaw cycle is established, which can provide a theoretical basis for the prediction of impact splitting tensile strength of concrete after freeze-thaw cycle.

Energy Dissipation Characteristics and Damage Pattern Law of Basalt Fiber Concrete under Dynamic Load

WANG Li, JIANG Shichao

2024, 43(2):  456-465. 

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The damage behavior and energy dissipation characteristics of basalt fiber concrete with four different fiber content were investigated under four strain rates based on the split Hopkinson pressure bar test apparatus. The results indicate that with the increase of strain rate, the fractal dimension of concrete with varying basalt fiber content linearly increases. The addition of fibers tends to reduce the rate of growth of fractal dimension. The incident energy, reflected energy and dissipated energy of concrete exhibit a linear growth trend, while the transmitted energy shows a slight decrease. With the increase of fiber content, the fractal dimension of basalt fiber concrete increases first and then decreases at different strain rates, and the dissipated energy density follows an "S"-shaped trend, increasing first, decreasing, and then increasing again. As the fractal dimension grows, the dissipated energy density of concrete with different basalt fiber contents linearly increases. The best optimal performance is achieved when the fiber volume fraction is 0.1%, resulting in the maximum tolerance to damage.

Multi-Factor Orthogonal Test Analysis of Mechanical Properties and Fluidity of Steel Fiber Sprayed Mortar

PAN Huimin, ZHANG Hao, LI Mengyi, XIE Shaokang, ZHAO Qingxin

2024, 43(2):  466-477. 

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In order to explore the influence of matrix factors on the mechanical properties and fluidity of steel fiber sprayed mortar, the mechanical properties and fluidity of mortar specimens were tested based on orthogonal test method. The results show that the ratio of sand to cement (A) has a great influence on the splitting tensile strength, and has a certain influence on 7 d compressive strength, and has a particularly significant effect on later flexural strength. The influence of steel fiber content (B) on splitting tensile strength, early flexural strength and early and middle compressive strength is particularly significant, significant and insignificant, respectively. The content of accelerator (C) has a significant effect on compressive strength before 7 d and the splitting tensile strength in middle and late stages. The content of fly ash (D) has significant influence on compressive strength in late stage. The four factors have no significant influence on fluidity. The optimal mix ratio of compressive strength, flexural strength, splitting tensile strength and fluidity are obtained by analytic hierarchy process as A₁B₃C₃D₁, A₃B₃C₁D₂, A₃B₃C₃D₁, A₂B₁C₁D₃, and the optimal mix ratio is obtained by efficiency coefficient method as A₂B₃C₁D₂. The steel fiber plays a bridging and anchoring strengthening role in matrix. During the hydration process, the accelerator consumes a large amount of Ca(OH)₂ and generates ettringite, which is the main reason for the rapid increase in early strength of sprayed mortar.

Effect and Performance of Microbial Healing Technology on Mortar Through Injection Method at Low Temperature

NI Yongjun, LI Wenrong, SONG Weichang, ZHANG Shenghua, LI Jun, TIAN Qian, GUAN Bowen

2024, 43(2):  478-486. 

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To address the issue of reduced growth activity of common microorganisms in low-temperature environments, which leads to a decrease in their ability to repair concrete, the healing effects of mesophilic and cold-resistant bacteria and their combination on the prefabricated crack in mortar specimen were investigated through injection method and quantitatively evaluated by comparing the flexural and compressive strength of mortar specimens before and after healing. The results show that the healing effect of microorganism on mortar cracks is related to its growth activity at different temperatures. Compared with Sporosarcina pasteuri fwzy14, which can only grow well at room temperature, the cold-resistant Brevibacterium frigoritolerans A779 has the capacity of growing at both room and low temperature, and therefore shows more balanced repairing ability. In addition, A779 can metabolize through both aerobic respiration and nitrate reduction with calcium nitrate as precursor, which enables it to grow inside the crack that is anoxic and repair the crack in depth.

Effect of Poplar Fiber on Flowability, Mechanical Property and Auto-Shrinkage of Mortar

ZHU Haohua, YANG Li, LIU Jianhui, SHI Caijun

2024, 43(2):  487-494. 

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The effects of size and volume fraction of poplar fiber on flowability, mechanical properties (compressive strength, flexural strength), and auto-shrinkage of mortar were studied by using control variable method. The results indicate that the volume fraction of poplar fiber has a more significant effect on flowability of mortar than its size. When the volume fraction of poplar fiber increases from 1.0% to 3.0%, the flowability of mortar decreases by 49.56%. Increasing the size and volume fraction of poplar fiber reduce the flexural strength of mortar, while increasing the volume fraction of poplar fiber is conducive to improving the compressive strength of mortar. The volume fraction of poplar fiber is more significant than its size on the effect of reducing shrinkage of mortar, and the addition of 3.0% poplar fiber of 0.30~1.25 mm reduces the auto-shrinkage of mortar by 45.6% at 72 h.

Carbon Nanocomposite Cement-Based Materials for Geothermal Drilling and Production Based on Response Surface Method

XIANG Jie, WANG Sheng, LI Yujie, WANG Wenjie

2024, 43(2):  495-508. 

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A novel carbon nanocomposite cement-based material for geothermal drilling and production (CNTs-CC) was developed to solve the problem of insufficient performance of existing thermal cementing cement. Firstly, with graphite and silicon nitride as main thermal conductivity filler, silicon powder as heat stabilization material and carbon nanotubes as co-reinforcing filler, the nano composite cement material base liquid was preliminarily developed. Secondly, based on the Box-Behnken experiment design of response surface method, 17-sets of ratio optimization experiments were carried out, and a quadratic polynomial prediction model with 28 d compressive strength and thermal conductivity as the response indexes was constructed. The influences of various factors on the response indexes were investigated by combining analysis of variance and response surface, and the optimal ratio of cementable materials was obtained. Finally, the engineering properties of the cement-based composite materials were evaluated, and the hydration mechanism of the cement-based composite materials was studied by XRD and SEM. The results show that the thermal conductivity and compressive strength of cement-based composite materials are influenced by the interaction of many factors, in which the interaction between early strength agent and water reducing agent is significant. The 28 d compressive strength of CNTs-CC cement stone is 8.15 MPa, and the thermal conductivity is 2.236 W/(m·K). The thermal conductive filler does not participate in the hydration process, and the carbon nanotube powder can play a "filling" and "bridging" effect, and the admixture regulates the hydration process.

Preparation of BMIMBr Cement-Based Electrolyte and Its Application in Structural Supercapacitor

LI Jiandong, YANG Zhenying, DING Yangfei

2024, 43(2):  509-516. 

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To improve the ionic conductivity and electrochemical performance, a cement-based composite electrolyte with high ionic conductivity and good mechanical strength was synthesized by using room temperature ionic liquid 1-butyl-3-methylimidazole bromide (BMIMBr) as redox active additive, which can be applied to construct structural supercapacitor. The results show that the ionic conductivity of cement-based composite electrolyte containing 20% (mass fraction) BMIMBr reaches the highest value of 35.91 mS·cm^-1. BMIMBr can provide Br^- which can produce reduction reactions and increase the number of free ions, which is beneficial for ion transport in electrolyte and obtains higher specific capacitance. The structural supercapacitor shows a high specific capacitance of 20.07 F·g^-1 at a current density of 0.05 A·g^-1. After 1 000 cycles of galvanostatic charge-discharge, the capacitance retention rate reaches 83.6% and coulomb efficiency is 97.56%, demonstrating an excellent cycle lifespan.

Solid Waste and Eco-Materials

Research Progress on Preparation and Comprehensive Utilization of Solid Waste Based Calcium Silicate Hydrates

ZHU Yinyuan, ZHU Ganyu, QI Fang, LI Huiquan, CHEN Yan, LI Shaopeng, GUO Yanxia

2024, 43(2):  517-533. 

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Bulk solid waste is a variety of solid waste generated in the process of industrial production, and most of the solid waste contains many silica resources and a variety of valuable resources. Calcium silicate hydrates (C-S-H) is a kind of loose and porous material with strong surface activity, which is widely used in cement activation, thermal insulation material preparation and heavy metal adsorption, etc. Combining the efficient extraction of valuable resources of bulk solid waste with the efficient utilization of silicon resources to prepare C-S-H is a good way to improve solid waste resources and realize the large-scale utilization of C-S-H materials. Therefore, this paper analyzes the synthesis method, structure and performance characteristics of solid waste C-S-H, discusses the application of C-S-H materials in building materials, environment, chemical industry, biology and other fields, and further prospects its future development direction, so as to provide reference for the utilization of bulk solid waste silicon resources and the controllable preparation of C-S-H materials.

Research Progress on Comprehensive Utilization of Phosphogypsum and Its Application in the Field of Building Materials

ZHOU Wu, LI Yang, FENG Weiguang, SU Yi, JIE Weizhe, ZHANG Hua, NI Hongwei

2024, 43(2):  534-542. 

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Phosphogypsum is a byproduct in the wet process of phosphate fertilizer production, with its main phase being CaSO₄·2H₂O. Despite China being the world's largest producer of phosphogypsum, its comprehensive utilization rate is below 50%. The accumulated stock has reached 800 million tons, causing severe ecological damage. Therefore, exploring effective utilization methods for phosphogypsum is urgently needed. This article analyzes the current research status of the comprehensive utilization of phosphogypsum in various fields. Currently, the utilization rate of phosphogypsum in the chemical industry is only 5%, and in agriculture is a mere 2%, while the building materials sector remains its primary application field. Industrial applications such as using phosphogypsum as a cement retarder, gypsum block, and cement mortar have been industrialized. However, its application in cementitious materials and subgrade materials has not been widely adopted due to concerns about leaching toxicity. The use of phosphogypsum as a filler is still in the experimental exploration phase due to the relatively low strength of material. The paper concludes by envisioning the future trends in the research on environmental friendly utilization of phosphogypsum, aiming to provide references for resolving the stockpile issue of phosphogypsum.

Dynamic Mechanical Properties of White Sandstone under Hydrostatic Pressure

LYU Shaopin, ZHENG Guang, ZHENG Yuxuan, NIE Hong, ZHOU Fenghua

2024, 43(2):  543-554. 

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The dynamic mechanical properties of deep rock in high underground stress environment have an important influence on the development of deep mine engineering. Therefore, it is of great significance to study its dynamic mechanics. The effects of hydrostatic pressure on the dynamic mechanical properties, energy absorption and damage of white sandstone from a coal mine in Pingdingshan were investigated, using 3D Hopkinson bar experiments and finite element simulations based on the Holmquist-Johnson-Cook (HJC) constitutive model. The results show that as the hydrostatic pressure increases, the peak stress of white sandstone increases. Conversely, the peak strain decreases with the increase of hydrostatic pressure. Furthermore, the hydrostatic pressure can restrain the crack propagation and enhance the strength of white sandstone. Additionally, it was found that the HJC constitutive model can simulate the damage failure of white sandstone well. These expected results provide a valuable reference for the study of dynamic mechanical properties of deep rock and a theoretical basis for the implementation of deep rock engineering.

Properties of High Toughness Engineered Cementitious Composites with Granite Porphyry Rock Powder

SUN Binqiang, TIAN Maosheng, XIE Chao, LI Yanxiao, AN Jianmin

2024, 43(2):  555-563. 

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High toughness engineered cementitious composites (ECC) have been used in large size plate and beam structures due to their excellent mechanical properties and crack control, but its further application is limited by high cost. The production process of mechanism sand will produce a large amount of rock powder, which will seriously pollute the environment if not handled properly. In order to achieve the dual objectives of reducing the cost of ECC and environmental protection, granitic porphyry rock powder high toughness engineered cementitious composites (GP-ECC) with rock powder instead of river sand was prepared, its properties were studied, and the self-shrinkage prediction model for GP-ECC was established. The results show that the GP-ECC specimens exhibit the characteristics of multi-seam cracking and strain hardening, and compressive strength and flexural strength decrease first and then increase with the increase of granite porphyry rock powder replacement rate, and the best performance is achieved when completely substituted. The 28 d tensile stress peak value reaches 4.4 MPa, the ultimate strain exceedes 4.2%, the compressive strength exceedes 50 MPa, and the flexural strength exceedes 18 MPa. The early self-shrinkage value of GP-ECC increases with the increase of rock powder replacement rate, in which the self-shrinkage value when rock powder completely replaces river sand is 3 133.3 μm/m, which is 117.3% higher than that of the benchmark specimen. So it is necessary to suppress the self-shrinkage of GP-ECC. Meanwhile, the self-shrinkage prediction model proposed in this paper can effectively predict the change of self-shrinkage of GP-ECC. The SEM test results show that the PVA fibers are uniformly dispersed in the granitic porphyry rock powder cement matrix and can work together.

Effects of Composition and Content of CFBFA on Hydrated Cementitious Properties

YAN Kezhou, SUN Xiangyang, ZHANG Xinze, WEN Kai, GUO Yanxia, CHENG Fangqin

2024, 43(2):  564-571. 

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The chemical composition of circulating fluidized bed fly ash (CFBFA) are significantly affected its hydrated cementitious properties. Based on the effects of composition and content on the hydrated cementitious properties for CFBFA, it is helpful to further clarify the hydrated cementitious mechanism of CFBFA. The effects of composition and content on the hydrated cementitious mechanical properties, phase composition, micro morphology and elemental distribution for CFBFA were investigated by mechanical properties testing, X-ray diffraction analysis and scanning electron microscopy-energy spectroscopy analysis. The results show that the hydrated cementitious properties are obviously different for CFBFA mortar test block with the different chemical compositions. When the mass contents of aluminum and silicon exceeds 75%, the 28 d compressive strength of CFBFA mortar test block is about 38 MPa. When the mass content of calcium and sulfur exceeds 28%, the 28 d compressive strength of CFBFA mortar test block decreases to about 14.5 MPa. The high content of aluminum and silicon are beneficial to the formation of dense blocks with the large percentage of hydrated calcium silicate, while the high content of calcium and sulfur will result in the appearance of rod-shaped calcium alumina, which is not conducive to the development of mechanical property. In addition, with the increase of cement mass fraction from 50% to 90%, the 28 d compressive strength of CFBFA mortar test block increases by 27.2 MPa. The compressive strength of CFBFA mortar test block is positively correlated with the additional amount of cement in hydrated cementitious system, due to the hydration effect of cement itself and its promoting effect on the reaction of CFBFA. This study can provide a theoretical guidance for the application of CFBFA in the field of construction materials.

Effect of Organic Ethanolamine TEA-M-Inorganic Salt System on Activation of FBC

WU Yuanting, WANG Yuanchen, WANG Zhao, LIU Hulin, WANG Wei, REN Siqian, HUA Chunfeng

2024, 43(2):  572-583. 

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The treatment of fluidized bed combustion ash and slag (FBC) and the development of environmentally friendly activator material are the effective way to prevent environmental secondary pollution. An organic ethanolamine TEA-inorganic ethanolamine M-inorganic salt composite activator was developed, and the performance of the material was optimized. And the micromorphology, chemical composition and performance changes of the materials were analyzed by SEM, FTIR, XRD and other characterization methods. The influences of three series of activators, M, TEA-M and TEA-M-inorganic salt on the fluidity ratio and compressive activity index of cement slag were explored. The results show that the grinding effect of TEA improves the particle size. The inorganic activator M can affect the content of Ca(OH)₂ participating in hydration reaction. The inorganic salt CaSiO₃ may produce more C-S-H in the later stage and provide alkaline condition. The synergistic effect of different materials in the composite activator increases the compressive activity index of cement slag by 29 and 18 percentage points at 7 and 28 d (compared with the blank sample), respectively, while maintaining the fluidity ratio of cement mortar at a high level. This study provides an environmentally friendly activator composite material to promote the green application of FBC.

New Method and Effect Verification for Synthesizing Sodalite from Fly Ash Using Solvent-Free Method

GUO Wei, PANG Laixue, WANG Wenchao, ZHANG Jiali, WANG Hua, BAI Shuxia

2024, 43(2):  584-592. 

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Due to its high silicon and aluminum content, low silicon and aluminum ratio, fly ash is often used to synthesize low silicon pure phase sodalite. In order to improve the high-value utilization of fly ash, sodalite was synthesized from fly ash using solvent-free method. The effects of ash-alkali ratio, crystallization time and crystallization temperature on sodalite phase formation, microstructure and crystallinity were studied. The results show that crystaline pristine sodalite is prepared from fly ash with ash-alkali ratio of 1∶0.8 (mass ratio), crystallization time of 16 h and crystallization temperature of 160 ℃. The ash-alkali ratio has a significant effect on relative crystallinity. The synthesized sodalite has microporous and mesoporous composite pore structure. The N₂ adsorption-desorption isotherm of sodalite isotherm reveals a typical IV isotherm with a type III hysteresis loop. Sodalite has high aluminum content, and has good thermal stability. Compared with the hydrothermal method for synthesizing sodalite, this experimental method utilizes fly ash with high efficiency, and provides a new way for the utilization of fly ash.

Flexural Performance of PVA-Iron Ore Tailings Concrete

ZHU Lishuai, XIE Qun, HUI Jing, ZHAO Peng, LI Junfeng

2024, 43(2):  593-602. 

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In order to achieve the recycling and utilization of solid waste, iron ore tailings were partially replaced with fine aggregates and added with PVA fibers to prepare PVA-iron ore tailings concrete with good workability. The influences of different iron ore tailings replacement rates and PVA fiber content on the flexural performance of concrete were studied through standard flexural tests. The result show that when the PVA fiber content is 0% and 0.1% (mass fraction, the same below), the specimens undergo through type brittle cracking failure. When the PVA fiber content is 0.2% and 0.3%, the crack width of specimens significantly decreases and does not penetrate. When the iron ore tailings replacement rate is 30% and the PVA content is 0.3%, the mid-span and flexural strength of specimen reach their maximum values, which has increased by 22.04% and 6.57% compared to ordinary concrete, respectively. When iron ore tailings replacement rate exceeds 30%, the flexural strength and deflection will significantly decrease. Compared to the single addition of PVA fiber, the deformation ability of specimens mixed with PVA fiber and iron ore tailings is more significantly enhanced. It can be seen from the XRD pattern that the C-S-H gel and ettringite are the most abundant under the 30% iron ore tailings replacement rate, which can significantly improve the strength of material.

Formula Design and Mechanical Properties of Three Kinds of Modified Raw Soil Materials Mixed with Solid Waste

ZHANG Kun, FU Zhiyong, ZHANG Linghan, YANG Wenhao, LAN Guanqi, ZHU Xiyu

2024, 43(2):  603-616. 

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In order to improve the mechanical properties of raw soil materials, iron tailings, gangue, calcium carbide slag, oil sludge and cement were used as admixtures to modify raw soil. On the basis of the monomorphic lattice method, the effects of different factors on the failure morphology, compressive strength and data discreteness of the specimen were studied through compressive test of 180 modified raw soil specimens of three modified formulas. Using the frequency analysis method, the optimal formula of solid waste modified raw soil material was studied. Then, the fractal and pore structures inside the loaded material were analyzed at a microscopic level through CT scanning. The results show that the compressive failure forms of different admixture-modified raw soil specimens are basically the same, but the admixture significantly affects the limit displacement. Gangue and calcium carbide slag, iron tailings and cement, oil sludge and cement as raw soil admixtures can greatly improve the mechanical properties of modified raw soil specimens, the type and the amount of admixture have a significant impact on the strength and data discreteness of modified raw soil specimens. After frequency optimization, the ideal strength admixture ratios for the three formulas are 1) iron tailings 12.1%~19.5% (mass fraction, the same below), cement 13.9%~19.1% and raw soil 65.5%~69.9%; 2) calcium carbide slag 6.7%~14.1%, coal gangue 8.9%~11.8% and raw soil 76.7%~81.8%; 3) oil sludge 11.4%~14.4%, cement 17.4%~19.4% and raw soil 67.1%~70.5%. The fractal and pore characteristics inside the material are stable, exhibiting small fluctuations and good compactness.

Mechanical Property and Resistance to Water Dispersion of Solid Waste Shield Inert Synchronous Grouting Materials

HONG Qiaoheng, HE Xiongfei, ZHANG Minglang, TANG Gang, HUANG Wei

2024, 43(2):  617-626. 

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As typical solid wastes, slag powder, fly ash and silica fume were used as raw materials to fabricate solid waste shield inert synchronous grouting materials. The mechanical property and resistance to water dispersion of grouting materials were investigated by using six-factor and five-level orthogonal test. The results show that the compressive strength of slurry decreases with the increase of alkali activator modulus and the decrease of dosage. The water-binder ratio and bentonite-water ratio exhibit great influence on the hydrodynamic erosion resistance of slurry. The dosage of alkali activator and the water-binder ratio are the main factors affecting the water land strength ratio of slurry. According to the range analysis of orthogonal test and comprehensive performance balance, the optimal mix ratio of grouting material is determined as follows: water-binder ratio 1.00, binder-sand ratio 0.45, bentonite-water ratio 0.35, dosage of water reducer 1.5% (mass fraction), alkali activator modulus 1.6, dosage of alkali activator 20% (mass fraction), and grouting material exhibits compressive strength (28 d) of 13.02 MPa, water land strength ratio of 80.83% and hydrodynamic erosion mass loss rate (3 h) of 5.62%. Furthermore, performance tests such as consistency, setting time, bleeding rate and stone rate were conducted, and the indexes all met the requirements of active slurry. The above research provides a certain research and experimental basis for the application of industrial solid wastes in the field of shield grouting technology.

Hydration Properties of Metakaolin Composite Grouting Materials for Anti-Seepage of Grottoes Rock Fissures

CHEN Jiaqi, WANG Jinhua, YAN Shaojun, TIAN Yechenxi, DU Zhiyan, JIANG Shu, HUO Xiaotong

2024, 43(2):  627-636. 

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Metakaolin composite grouting material is an inorganic grouting material mixed with a large proportion of metakaolin in cement, which is used for anti-seepage grouting engineering of rock fissures in grottoes. In this paper, the hydration and product characterization of binary and ternary metakaolin composite grouting material were studied by means of hydration heat, XRD, FTIR, and SEM-EDX test. The feasibility of applying this material to grotto fissure grouting was analyzed by mechanical properties and water-solube salt test. The results indicate that the reaction degree of cement materials with is low. But the dilution effect and pozzolanic reaction of metakaolin and the charge compensation effect of active Al have a significant advantage in reducing the salt and alkali content in leaching solution. The addition of silica fume can enhance the hydration degree and mechanical strength of ternary composite grouting material. However, the decrease in Al/Si of hydrated products is not conducive to the adsorption of K⁺ and Na⁺. The metakaolin composite grouting material is a safer material than ordinary Portland cement in grotto protection, and it exhibits better compatibility with grottoes environment. Additionally, metakaolin, as a supplementary cementitious material, has more advantages over silica fume in reducing K⁺ and Na⁺ leaching.

Ceramics

Research Progress of Porous Ceramic Insulation Material

WANG Mengmeng, SUI Xueye, QI Kaiyu, XU Jie, LIU Ruixiang, ZHOU Changling, TANG Wenzhe, DUAN Xiaofeng, LI Zhanfeng

2024, 43(2):  637-648. 

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Porous ceramics have a large number of interconnected or closed pores. Microstructural characteristics such as pore size, pore distribution and connectivity, play a crucial role in physical properties of material. In this paper, we present the remarkable properties and broad application prospects of porous ceramic insulation materials, including applications in aerospace, construction, industrial energy efficiency, biomedical (for bone defect repair materials), ceramic electrochemical devices in batteries, catalyst carriers (for exhaust gas purification in gasoline engines), and various other fields such as sound insulation, liquid separation, and sensors. It also summarizes the preparation methods and research progress of porous ceramic thermal insulation materials in recent years. The content mainly covers the selection of raw materials, technological methods, and key material properties. Finally, it outlines the current development status and common challenges faced by porous ceramic materials, along with suggesting strategies for improvement, aiming to provide references for the development of more high-performance porous ceramic thermal insulation materials in the future.

Research Progress of Barium Titanate and Potassium Sodium Niobate Lead-Free Piezoelectric Ceramics

XU Minghao, HUA Kaihui, ZENG Qun, DI Bo, ZHENG Yu, WANG Hongxiang, ZHANG Guoxiang

2024, 43(2):  649-658. 

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Barium titanate (BaTiO₃) and potassium sodium niobate (K_0.5Na_0.5NbO₃) piezoelectric ceramics have become the forefront of international high-tech materials research due to their environmental friendliness, excellent electrical properties and proper curie temperature, and were expected to replace some lead-based piezoelectric ceramics in electronic devices in the fields of national defense, aerospace and communications, etc. In this paper, the latest research progress of BaTiO₃ and K_0.5Na_0.5NbO₃ piezoelectric ceramic materials was reviewed, the aspect of constructing phase boundary to regulate the piezoelectric performance, designing the material system of BaTiO₃-based piezoelectric ceramics, the thermal stability and improvement of K_0.5Na_0.5NbO₃-based piezoelectric ceramics and the new molding and sintering process of piezoelectric ceramics were analyzed and summarized objectively. Finally, future development trend of the two kinds of materials was discussed, and a reference for the development of high-performance lead-free piezoelectric ceramics was provided.

Thermal Shock Resistance of AlN/YAlO₃ Composite Ceramics

LYU Xuming, ZHANG Yunhan, SHI Guohua, WANG Jiawei, SUN Xiaohong

2024, 43(2):  659-665. 

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AlN ceramics have high hardness and brittleness, and it is difficult to be sintered and dense. As a smelting vessel, it is damaged by high-temperature deformation or thermal shock caused by temperature change. AlN/YAlO₃ composite ceramics were prepared by pressureless sintering method by adding YAlO₃ as a particle reinforcement phase, and the thermal shock resistance of AlN/YAlO₃ composite ceramics at different temperatures was investigated. The phase structure, fracture morphology, and surface morphology of AlN/YAlO₃ composite ceramics before and after thermal shock were analyzed, and the mechanism of thermal shock damage was elucidated. The results show that the addition of YAlO₃ can promote the sintering and increase the density to 98.37% of AlN ceramics. The flexural strength and thermal shock resistance of AlN/YAlO₃ composite ceramics are improved due to the grain refinement. Especially in thermal shock experiments at higher temperatures, when the thermal shock temperature rises to 600 ℃, the flexural strength and residual strength ratio of AlN/YAlO₃ composite ceramics are significantly higher than those of AlN ceramics, indicating that the addition of YAlO₃ can effectively improve the thermal shock resistance of AlN ceramics. It is mainly attributable to microcrack toughening, crack deection and branching behavior slow down the reduction of flexural strength of AlN/YAlO₃ composite ceramics. Moreover, when the thermal shock temperature reaches 1 000 ℃, Al₂O₃ oxidated by AlN reduces severely the flexural strength of AlN/YAlO₃ composite ceramics.

Analysis of Influencing Factors on Dielectric Properties of Fused Quartz Ceramics

CUI Tangyin, WANG Peng, LIU Ruixiang, WANG Hongsheng, CAO Junchang, CHEN Dongjie

2024, 43(2):  666-672. 

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Fused silica ceramics were prepared by gel-casting molding process. The crystal structure, micro-morphology and dielectric properties of ceramic samples were analyzed by XRD, SEM and electrical network analyzer, and the influencing factors on dielectric properties of fused silica ceramics were studied to provide basis for screening the optimal preparation technology of fused silica ceramics. The results show that quartz ceramic slabs of different thicknesses are prepared and sintered horizontally with certain material preparation, the density of the same square slab decreases from top to bottom along the vertical direction, and the density has a positive correlation with the dielectric constant, for every 0.01 g/cm³ increase in density, the dielectric constant increases by 0.01~0.02. And the density has little effect on the tangent value of the loss angle. For the same slab of the same thickness, the density of the edge and the middle position barely unchanged. For the same slab and the same thickness direction, the dielectric constant does not change much. The rosin in the quartz ceramic slab makes the sample denser and the dielectric constant increases with the increase of the density, the calculated permittivity has a deviation of about 0.03.

Preparation and Performance of Gas Reservoir Ceramic Proppant with Low Density

XING Li, SUN Xiaosi, BAI Pinbo, WANG Kaiyue, TIAN Yuming

2024, 43(2):  673-681. 

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In the process of extracting coalbed methane, shale gas and other gas reservoir resources, the product performance of ceramic proppants is particularly crucial. Low synthetic density and high strength of proppant are important indicators for achieving high gas reservoir productivity. On the basis of traditional ceramic proppants, by adding raw coal gangue (RCG), sodium carboxymethyl cellulose (CMC), and dolomite (DOL) for solid state sintering, the matrix pore distribution characteristics of the proppants were improved, the structural density of the proppants was reduced, and the matrix strength was enhanced, with the help of the multi temperature pyrolysis effect of the pore forming agents and the high-temperature liquid phase rapid filling mechanism. When a mass fraction of 15%RCG+1%CMC+1%DOL additive is added, the proppant exhibits the best comprehensive performance and meets the parameter requirements for gas reservoir resource extraction.

Glass

Review of Structural Relaxation and Influencing Factors of Inorganic Glass

LI Jingwei, LI Jingchao, ZHENG Ruipeng, WANG Chen

2024, 43(2):  682-694. 

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In this paper, the fictive temperature and relaxation dynamics theories of structural relaxation are introduced at first, and their establishment, development and research progress are discussed as well. The fictive temperature theory focuses on the thermal history of glass, and provides a thermodynamic criterion for determining the direction and velocity of relaxation process, while the relaxation dynamics theory places emphasis on glass transition phenomenon and aims to reveal microscopic mechanism and evolution process of structural relaxation. The thermal history, glass composition, impurities, defects, temperature, stress, moisture and size are key factors affecting the structural of inorganic glass. These factors are important issues of structure tailoring and safety analysis for manufacture and application of glass. Although the structural relaxation theories of glass have been rapidly developed, there are still many gaps in experimental studies, particularly for inorganic glass with complex composition, and the specific microscopic mechanism still needs further improvement. In addition, the structural relaxation of glass-ceramics and glass matrix composites has not received deserved attention. The breakthrough of such problems is expected to support long-term safety and reliability of inorganic glass under more stringent conditions.

Effect of Melt-Pressing Temperature on Bending Strength of Fiber Optic Plate

SUN Yong, ZHAO Jinkai, HUANG Yonggang, WANG Wei, WANG Caili, KONG Zhuang, SONG Puguang, MENG Fanyu

2024, 43(2):  695-701. 

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Fiber optic plate is widely used in fields such as low-light level night vision, space detection, nuclear diagnosis, medical diagnosis and treatment, and has certain requirements for strength in application. However, there is currently a lack of relevant research. In this paper, the effect of melt-pressing temperature on the bending strength of fiber optic plate in x, y, and z directions by three point bengding method was studied. When the melt-pressing temperature is 660 ℃, the secondary multi-fiber fusion is insufficient, leading to gaps. The bending strength of fiber optic plate is low, with values in x, y and z directions of 107, 93 and 114 MPa, respectively. As the melt-pressing temperature increases, the gap between the secondary multi-fiber disappears at 670 ℃, but there is still an interface, and the bending strength is improved, with values in x, y and z directions of 110, 109 and 125 MPa, respectively. At the melt-pressing temperature of 680 ℃, the secondary multi-fiber is fully fused, and the bending strength of fiber optic plate meets the rule of mixture of composite in x and z directions, which is 123 and 127 MPa, respectively. Meanwhile, the core glass in y direction plays a reinforcing role to the cladding glass, and the bending strength is 113 MPa. This study is of great significance in improving the strength of fiber optic plate to meet the requirements of installation and use.

Effect of n(Bi₂O₃)/n(SiO₂) on Microstructure and Reflectivity of Bi₂O₃-B₂O₃-SiO₂ System Photovoltaic Glass Backplane Inks

WANG Wei, ZHAO Tiangui, MENG Zihao, LIU Li, DONG Weixia, XU Heliang, BAO Qifu

2024, 43(2):  702-709. 

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With the rise of passivated emitter and rear cell double-sided glass components industries,the need for photovoltaic ink for photovoltaic glass backsheet is growing annually. After the photovoltaic ink is prepared for the coating, the degree of its density will have a direct impact on the reflectivity of photovoltaic ink coating and conversion efficiency ulteriorly of photovoltaic cell. By changing the n(Bi₂O₃)/n(SiO₂), the crystallization of glass flux and its effect on the photovoltaic ink prepared by Bi₂O₃-B₂O₃-SiO₂ glass flux were investigated. The different characteristics of glass flux were analyzed by using DSC and Raman. The microstructure and reflectance of various photovoltaic ink coating were studied by using XRD and SEM, and the mechanism for the enhancement of light reflection was proposed. The results show that the increase of n(Bi₂O₃)/n(SiO₂) leads to an increase in [BiO₃] and [BiO₆] ionic groups. Thus, the destruction ability of the [SiO₄] glass network is enhanced, and the transition temperature and crystallization peak temperature of glass flux gradually decrease. The crystallization ability of glass flux gradually increases. A large number of flaky Bi₂SiO₅ crystals are gradually precipitated from photovoltaic ink coating in a short period of time. After preparing them as photovoltaic ink coating, the reflectivity of the coating gradually increases with the elevation of n(Bi₂O₃)/n(SiO₂). With n(Bi₂O₃)/n(SiO₂) of 30∶60, the reflectance of photovoltaic ink coating can be enhanced to 82.66% in the near-infrared wavelength range. This is mainly due to the fact that the pores and cavities in photovoltaic ink coating act as heterogeneous interfaces, prompting the precipitation of Bi₂SiO₅ crystals and filling them into the pores and cavities of photovoltaic ink coating, resulting in an increase in the densification of photovoltaic ink coating and thus an enhancement of the reflective ability of photovoltaic ink coating to light.

Effect of Composition on Crystallization Properties of Yttrium Zirconate Nanocrystals in Sodium-Aluminum-Silicate Glass

TIAN Yingliang, HAN Jinlong, XU Bo, WEN Yulin, LI Peihao, HE Feng, ZHAO Zhiyong

2024, 43(2):  710-718. 

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The influences of the molar ratios of Al₂O₃/Na₂O (M_AN) and SiO₂/Al₂O₃ (M_SA)on the crystallization properties of the glass were studied in this work based on the sodium-aluminum-silicate glass system containing Y₂O₃ and ZrO₂. The results show that, when M_AN<1, sodium nepheline crystals precipitate on the surface of the glass after heat treatment. When M_AN>1, yttrium zirconate nanocrystals can be formed in the whole bulk glass, and the glass-ceramics can maintain a high visible light transmittance of 90%. For glass with fixed M_AN, adjusting its M_SA can also achieve the precipitation of yttrium zirconate nanocrystals, and the size of the precipitated crystals decreases as M_SA increases. Furthermore, as the heat treatment temperature rises, the size of nanocrystals in glass-ceramic nanocrystals as well as Vickers hardness increases.

Refractory Materials

Effect of MgCl₂·6H₂O Solution on Properties of Periclase-Magnesia Alumina Spinel Refractories

WANG Xin, HAN Bingqiang, MIAO Zheng, CHEN Junfeng, YAN Wen

2024, 43(2):  719-726. 

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Fused magnesia and fused magnesia alumina spinel were used as raw materials to prepare periclase-magnesia alumina spinel refractories, with three different concentrations of MgCl₂·6H₂O solution at 18 °Be′, 24 °Be′ and 30 °Be′ and phenolic resin as bonding agent. The effect of MgCl₂·6H₂O solution on cold modulus of rupture, cold crushing strength, sintering properties and thermal shock resistance of refractories was investigated by using phenolic resin as control group. The mechanisms of MgCl₂·6H₂O solution action on refractories were elucidated. The results show that MgCl₂·6H₂O solution reacts with magnesia to generate magnesium oxychloride cement (MOC) at room temperature, and the microstructure of MOC is interwoven interlocked whiskers, which makes the refractories show supervise mechanical strength after drying. The cold crushing strength of refractories reaches 79.1 MPa when the fire temperature is 1 700 ℃ and the solution concentration is 24 °Be′,which is 58.2% higher than that of phenolic resin. The apparent porosity of refractories reduces to 16.8% when the firing temperature is 1 700 ℃ and the solution concentration is 18 °Be′, which is 13.4% lower than that of phenolic resin. The increase of MgCl₂·6H₂O solution concentration is beneficial to improve fracture toughness of material. MOC and Mg(OH)₂ decompose to produce reactive MgO during firing process, which promotes the sintering of refractories. In addition, the quasi-spherical MgO produced by decomposition disperses and fills in the internal cracks of magnesia particles, forming a microporous structure inside refractories, which is conducive to mitigating thermal stress impact during thermal shock.

New Functional Materials

Preparation of CdS Nanospheres on Titanium Meshes with Photocatalytic H₂ Evolution under Visible Light

CHEN Zhiqiang, CUI Lei, DONG Jing, LI Haixia, XIA Weiwei

2024, 43(2):  727-733. 

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It is an interesting topic to improve the photocatalytic H₂ evolution activities of catalysts. In this parper, CdS nanospheres on titanium meshes have been synthesized by a simple hydrothermal method. The composition, microstructure and morphology of samples were investigated using X-ray diffractometer (XRD), scan electron microscopy (SEM), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS).And the photoelectrochemical properties and photocatalytic properties under visible light were studied. The results show that, each CdS nanosphere on titanium meshes is self-assembled with nanorods. Then, the samples were used as photoelectrochemical photoanodes and photocatalytic water-splitting processes, the samplewith a Cd/S amount of substance ratio of 1∶1 (CdS-1) has a good photoelectric response, and has a maximal photocurrent of ~140 μA. At the same time, the results show that the sample has a good H₂ evolution activity with the rate of 212.6 μmol·h^-1·cm^-2 and recycling convenient, reusable, which can be an ideal photocatalyst.

Preparation of NiMgAl-Hydrotalcite and Its Inhibition Property on Water Eutrophication

ZHOU Liangqin, WANG Rong, FAN Jinlong, WANG Jiani, XU Tengfei, TAN Wenyuan, FU Dayou

2024, 43(2):  734-745. 

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The discharge of wastewater containing phosphorus will lead to eutrophication and threaten ecological environment. In this article, a kind of NiMgAl-HTLC was synthesized by orthogonal experiment, which was used to remove phosphorus from wastewater. The properties of materials were characterized by SEM, EDS, TEM, XPS and BET. The adsorption mechanism was revealed by studying thermodynamics, kinetics and influencing factors in adsorption process. Finally, in order to evaluate the inhibition ability of NiMgAl-HTLC on water eutrophication, duckweed was cultured by wastewater after phosphorus removal. The results show that the optimum preparation conditions of NiMgAl-HTLC are as follows: the molar ratio of metal ions (Ni∶Mg∶Al) is 3∶1∶3, the dosage of urea solution is 20 mL, the reaction time is 10 h, and temperature is 150 ℃. The thickness of NiMgAl-HTLC nanosheets is about 10 nm, and the specific surface area is 84.98 m²·g^-1. The maximum phosphorus adsorption capacity of NiMgAl-HTLC is 61.162 1 mg·g^-1, and the adsorption process conforms to second-order kinetics and Langmuir thermodynamic model. The reproduction rate of duckweed in wastewater after phosphorus removal is slower significantly, indicating that NiMgAl-HTLC possess obvious inhibition on water eutrophication.

Road Materials

Road Performances and Mechanical Properties of Multi-Gravel Polyurethane Concrete

SUN Min, HOU Derui, GENG Litao, YAN Zhuoran, BI Yufeng, HUANG Zhaoliang, REN Shuaiyu, WANG Benyi

2024, 43(2):  746-756. 

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To investigate the road performance and mechanical properties of polyurethane mixture with dense skeleton structure, the design theory of multi-gravel asphalt concrete was used to design the composition of polyurethane concrete. A variety of performance tests were carried out to evaluate the road performance of multi-gravel polyurethane concrete, and the mechanical properties were evaluated based on uniaxial penetration test, uniaxial compressive test and uniaxial tensile test. The results show that the dynamic stability of multi-gravel polyurethane concrete is 53.4 times and 17.8 times that of matrix asphalt mixture and asphalt mastic gravel mixture. The maximum bending strain at low temperature is 2.26 times and 1.95 times respectively, and the fatigue life is 26.0 times and 12.7 times, respectively. In terms of mechanical properties, temperature has little effect on the uniaxial penetration strength and penetration amount of multi-gravel polyurethane concrete. The compressive and tensile elastic modulus of multi-gravel polyurethane concrete are much smaller than that of cement concrete, but larger than that of asphalt mastic gravel concrete. Multi-gravel polyurethane concrete has excellent road performance. Temperature has little effect on the shear mechanical properties of multi-gravel polyurethane concrete. The multi-uniaxial tensile and compressive mechanical properties are between asphalt mixture and cement concrete, which can be applied to pavement structure paving.

Effect of Excitation Stirring on Compressive Strength of Cement Stabilized Crushed Stone and Coal Gangue

WANG Jiliang, GUO Wenbin, SONG Qingkai, XU Weidong, LIU Peng

2024, 43(2):  757-765. 

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In order to study the influence of excitation stirring process on the performance of cement stabilized coal gangue mixture, based on cement stabilized crushed stone, the effects of conventional stirring and excitation stirring on the unconfined compressive strength of cement stabilized base materials with different cement dosages were compared and analyzed. The results show that increasing the excitation stirring in the dry mixing state has a significant effect on the compressive strength of the base mixture. The 7 d unconfined compressive strength of the mixture reaches the best under the conditions of 0.4 MPa air pressure, 30 s of vibration dry mixing and 30 s of ordinary wet mixing. The average increase of the strength of cement stabilized crushed stone and cement stabilized coal gangue mixture is about 20%, the strength improvement of coal gangue mixture is more significant, and the less the cement dosage, the greater the increase. The SEM results show that the distribution of hydration products in the mixture is more uniform and the structure is more compact after the excitation stirring. According to the linear fitting calculation, when the cement dosage is 2.0%～7.0% (mass fraction, the same bellow), the vibration mixing can save 8.9%～26.3% cement for the gravel mixture and 12.9%～30.8% cement for the coal gangue mixture. And the saving rate is inversely proportional to the cement dosage.

Pavement Performance of Industrial Solid Waste Phosphogypsum Pavement Base Material

ZONG Wei, WANG Yuanhui, XU Liang, LIU Cheng, ZHENG Wuxi

2024, 43(2):  766-773. 

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In order to promote the large-scale utilization of phosphogypsum in highway engineering, the comprehensive road performance of phosphogypsum pavement base material was evaluated by typical mechanical test, bubble swelling test, shrinkage test, freeze-thaw cycle test, delayed formation test and low temperature natural curing test. The results show that the mechanical properties of phosphogypsum pavement base material are comparable to those of ordinary cement stabilized crushed stone. The 28 d cumulative expansion rate is only 0.086%, indicating good water stability. The dry shrinkage coefficient is 116.64 με/%, the temperature shrinkage coefficient is 5.15 με/℃, and the compressive strength ratio after freeze-thaw cycles is 81.13%, demonstrating significant shrinkage resistance and frost resistance. Both the delayed formation time and low-temperature curing have adverse effects on the strength of mixture, with a 24% strength decrease after 4 h delay and 33% strength decrease under 5 ℃ curing condition.

Mechanical Properties and Frost Resistance of Cement Stabilized Recycled Aggregate Mixture

SHAN She, GUO Haizhen, WEI Dingbang, LIU Hui, RUAN Zhiqi, REN Guobin

2024, 43(2):  774-780. 

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In order to promote the application of recycled aggregate in semi rigid base layers and achieve the resource utilization of construction waste in highway engineering, this article uses equal mass replacement method to systematically analyze the effect of recycled aggregate content (mass fraction) at 0%, 30%, 50%, 70%, and 100% on maximum dry density, optimal moisture content, unconfined compressive strength, and frost resistance of inorganic mixtures, and explains its internal influencing mechanism from a microscopic perspective. The results show that the addition of recycled aggregate reduces the maximum dry density of inorganic mixtures and increases the optimal moisture content. Recycled aggregate can effectively improve the unconfined compressive strength and frost resistance of inorganic mixtures. The best effect is achieved when recycled aggregate content is 70%. At this moment, the unconfined compressive strength of recycled aggregate inorganic mixtures is 4.6 and 6.8 MPa after 7 and 28 d, and the residual compressive strength ratio after 28 and 90 d of freeze-thaw cycles can reach 82.4% and 85.5%.