Table of Content

15 September 2023, Volume 42 Issue 9

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Cement and Concrete

Research Progress of Chloride Ions on Corrosion of Marine Concrete Reinforcement

LIU Yumei, YANG Lang, RAO Feng, ZHANG Kaiming, SUN Chuanlin

2023, 42(9):  3059-3074. 

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In the marine environment, most of the marine concrete will be corroded and destroyed before reaching the designed service life, resulting in serious national marine engineering safety risks and marine environment pollution. The corrosion of steel bar caused by chloride ions is the main reason for the deterioration of the structural performance of marine concrete. Based on the characteristic of polychlorinated salts in marine environment, starting from the process of chloride ion erosion on marine concrete, this paper reviews and summarizes the corrosion path and mechanism of chloride ions from the process of chloride ions eroding marine concrete. It focuses on the path of chloride ions entering concrete through penetration, diffusion and electrochemical migration, and the corrosion mechanism of chloride ions destroying passivation film, forming corrosion battery, depolarization and conductivity. On this basis, aiming at the latest research on chloride ions corrosion resistance of marine concrete at home and abroad, this paper introduces the mechanism of chloride ions solidification, and focuses on the fundamental measures such as improving the compactness of marine concrete, reducing cracks in marine concrete and increasing the thickness of marine concrete. At the same time, it summarizes the supplementary measures of concrete surface protection, steel bar protection and adding rust inhibitor, crack repairing to improve the chloride ions corrosion resistance of marine concrete. Finally, it raises that there is a big gap between the single chloride ions corrosion process in the current research and the concrete in the actual seawater. Low-carbon and environmentally friendly anti-chloride ions corrosion concrete materials and technologies need to be further developed.

Research Progress on Properties of Cement-Based Materials under Medium or High Vacuum Environment

GUO Zheng, MU Song, ZHUANG Zhijie, ZHANG Hao, ZHANG Lei

2023, 42(9):  3075-3082. 

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Constructing a vacuum pipeline maglev high-speed train system with low vacuum operating environment to reduce air resistance and noise is an important direction for the development of higher speed rail transit technology in the future. Concrete, as an important representative of cement-based materials, is an important alternative structural material in vacuum magnetic levitation pipeline scheme and needs to address new challenges in vacuum service environment. This paper summarizes the influence of medium/high vacuum environment on characteristic peak of hydration products of hardened cement paste, the influence of medium/high vacuum environment on water transmission, shrinkage deformation and pore structure of cement-based materials, and the change law of mechanical properties of cement-based strength of materials in medium/high vacuum environment. Finally, the application direction of cement-based materials in vacuum environment is discussed and prospected in order to provide reference for the development of high-performance cement-based materials suitable for vacuum environment.

Effect of Zeolite Powder on Hydration Properties of Potassium Magnesium Phosphate Cement

DENG Yonggang, DAI Tingting, SUN Chen, YANG Yuanquan

2023, 42(9):  3083-3088. 

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In order to improve the hydration property of magnesium phosphate cement, potassium magnesium phosphate cement was prepared by replacing part of magnesium oxide with zeolite powder. The influence of adding zeolite powder on the basic properties of potassium magnesium phosphate cement was studied by combining setting time test, mechanical properties test, hydration heat, phase identification and micro-morphology analysis. The results show that the hydration setting time of potassium magnesium phosphate cement is extended to 10.17 min when the content of zeolite powder is 8% (mass fraction), but at the same time its 7 d compressive strength and flexural strength are reduced to 44.6 and 8.0 MPa. With the increase of zeolite powder content, the amount of K-type struvite decreases. When the content of zeolite powder is not exceed 12% (mass fraction), the total hydration heat of potassium magnesium phosphate cement increases, but further adding zeolite powder can reduce the magnesium oxide in potassium magnesium phosphate cement and the hydration heat of potassium magnesium phosphate cement.

Influence Mechanism of Limestone Powder on Chloride Ions Transport of Cement-Based Material

SHAN Yalong, YANG Shengjie, HE Gongrui, SUI Shiyu, LI Shaochun, GENG Yongjuan

2023, 42(9):  3089-3099. 

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The partial replacement of cement with supplementary cementitious materials such as limestone powder can effectively reduce carbon emissions in the field of construction materials. However, its impact on durability still needs further exploration. The effects of limestone powder content, raw material fineness and water/binder ratio on chloride ion transport of cement-based materials were investigated by testing compressive strength, natural immersion of chloride ion and electromigration acceleration chloride ion transport. According to the phase composition and pore structure characteristics, the effect of limestone powder on the microstructure of system was studied. Combined with the macroscopic properties and microscopic analysis results, the relationship between chloride ion transport resistance and phase composition, pore tortuosity and critical pore size of system was discussed. The results show that in cement-limestone powder system, when the content of limestone powder is less than 15% (mass fraction), the influence of limestone powder on chloride ion transport resistance of system is small, and the formation factors can effectively measure the chloride ion transport resistance of system. In addition, the phase composition and pore tortuosity exhibit little correlation with chloride ion transport, and the critical pore size is the most important factor affecting chloride ion transport.

Strength Characteristics and Mechanism of Low-Heat Portland Cement at High Temperature

SHEN Xin, WANG Min, HUANG Wen, ZHANG Kunyue, GUO Suihua, WEN Zhaijun

2023, 42(9):  3100-3108. 

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Low-heat Portland cement has the characteristic of stable strength growth at high temperature. In this paper, the strength development of mortar and phase composition, pore development and micromorphology of cement paste under thermal curing (50~80 ℃) after forming and thermal curing after standard curing for 1 d were studied by comparing Portland cement and low-heat Portland cement. The results show that the cement strength collapses under high temperature conditions due to the microstructure deterioration in the later stage of hydration, but this behavior is closely related to the heat in the early stage of hydration. The slow hydration rate of low-heat Portland cement at high temperature makes the hydration products uniform and dense, and the pore structure of paste does not deteriorate with the increase of temperature and the change of heating way. Therefore, its strength can maintain a steady increase at high temperature. The decomposition of ettringite caused by high temperature in the later stage of Portland cement does not directly lead to strength collapse, but the quickly hydration rate of Portland cement in the early stage leads to more holes and defects in the cement paste, accelerates the precipitation and growth of AFm and Ca(OH)₂ caused by high temperature in the later stage, and induces the increase of porosity.

Effect of Carbon Dioxide Concentration on Performance of Low-Calcium Carbon Sequestration Cementitious Materials and Its Mechanism

LI Shuai, ZHOU Fengjiao, TAN Xinyu, ZHANG Bin, LIN Yongquan, TAO Congxi, HUANG Mingjun

2023, 42(9):  3109-3116. 

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In order to achieve the national strategic goals of “peak carbon dioxide emission and carbon neutrality” in the building materials industry, a type of low-calcium carbon sequestration cementitious materials (LC-CSCM) was prepared by calcining industrial calcareous and siliceous raw materials at 1 350 ℃. The influences of different concentrations of CO₂ on the carbonation degree and the carbonation hardening performance of LC-CSCM were investigated. XRD, FT-IR, TG, SEM and EPMA were used for the evolution of product analysis, microanalysis and mechanism analysis of carbonated LC-CSCM. The results show that with the increase of CO₂ concentration, the carbonation degree and the carbonation hardening performance of LC-CSCM increase significantly. When the CO₂ concentration is 99.99% (volume fraction), the compressive strength reaches 132.2 MPa after 8 h of LC-CSCM carbonation curing; compared with the concentration CO₂ of 25%, the compressive strength increases by 260%.

Effects of Humidity and Temperature on Electrical Conductivity of MXene Cement-Based Composites

LIN Zhengxiang, TANG Xiaodan, YU Changsheng, BAI Zhipeng, ZHI Fangfang, JIN Weizhun, WANG Liang, JIANG Linhua

2023, 42(9):  3117-3124. 

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Two-dimensional transition metal carbon/nitride (MXene) cement-based composites were prepared to study a new type of cement-based material intrinsic sensor. The effects of MXene content, humidity and temperature on resistivity of composites were studied by four-electrode method. The microstructure of composites was observed by scanning electron microscope (SEM). The results show that the variation of electrical resistivity of MXene cement-based composites with content of MXene conforms to the percolation theory. The increasing of relative water content and ambient temperature decreases the electrial resistivity of composites, and composites has good temperature-sensitive performance after multiple rising and cooling cycles. SEM results show that the electrical resistivity of MXene cement-based composites is mainly determined by distribution and contact of MXene conductive network.

Flexural Performance of Steel-PVA Hybrid Fiber Engineered Cementitious Composites

ZHANG Pinle, DENG Rang, HU Jing, WU Lei, TAO Zhong

2023, 42(9):  3125-3134. 

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In order to remedy the defects of existing steel-polyvinyl alcohol (PVA) hybrid fiber engineered cementitious composites in terms of high cost and narrow engineering applications, in this paper, a new multicomponent hybrid fiber engineered cementitious composite (MFECC) was prepared by partially replacing Japanese PVA fibers with cheap domestic PVA fibers. The flexural performance and damage morphology of MFECC sheet specimens were studied, the flexural toughness and cost-effectiveness of specimens were evaluated, and the ultimate flexural performance prediction model was established by multiple non-linear regression method of SPSS software. The results show that the strain-hardening mechanical behavior and multiple cracking phenomenon of MFECC sheet after the introduction of domestic PVA fibers are reduced compared with that when only Japanese PVA fibers are mixed, but it still has high strength and ductility. When the volume admixture of steel fiber, Japanese PVA and domestic PVA fiber are 0.2%, 0% and 2.0%, MFECC ultimate tensile strain is 4.4%, compressive strength is 46.39 MPa, and ultimate flexural deflection reaches 12.697 mm, which has the highest cost-effectiveness. The established model for predicting ultimate flexural performance of MFECC sheet specimens has a good fit to the test values.

Effects of Two Modifiers on RheologicalProperties of Grouting Materials

HU Yang, LIU Yawei, WU Yinghui, LU Liulei, HUANG Wenhao, NIU Weifeng, LI Shengsheng, WANG Junfeng

2023, 42(9):  3135-3142. 

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In order to improve the grouting quality of reinforcement, anti-seepage plugging and other projects, it is necessary to adjust rheological properties of grouting materials by adding modifiers. The effects of two modifiers (early strength grouting modifier SX-ZJ-Z and high strength grouting modifier SX-ZJ-G) on rheological properties of grouting materials were studied, and their setting time, fluidity, plastic viscosity and yield stress were tested at different content (10% and 20%,mass fraction) and water-to-binder ratios (W/B=0.25, 0.30, 0.35 and 0.40), and the degree of fitting of Bingham model and Modified Bingham model to their rheological curves was analyzed. The results show that the addition of SX-ZJ-G significantly prolonges coagulation time of grouting materials, while the addition of SX-ZJ-Z shortenes setting time of grouting materials. The addition of SX-ZJ-G exerts the “ball” effect and greatly improves fluidity of grouting materials, but the addition of SZ-ZJ-Z has almost no effect on fluidity of grouting materials. The addition of modifier changes the cement slurry from Newtonian fluid to yield-stress-fluid, showing a nonlinear shear stress curve, and Modified Bingham model had a good fitting effect compared with the Bingham model. When W/B=0.30, 0.35 and 0.40, the addition of SX-ZJ-Z has little effect on plastic viscosity and yield stress of grouting materials. The addition of SX-ZJ-G greatly reduces plastic viscosity and yield stress of cement slurry by more than 90%, and improves rheological properties of grouting materials.

Frost Resistance Durability and Damage Model of Fiber Concrete in Tibet Plateau Area

DENG Xianghui, ZHANG Peng, WANG Rui, WU Qiyuan, WANG Xu

2023, 42(9):  3143-3153. 

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In order to investigate the frost resistance durability and evolution law of freeze-thaw damage on different fiber concrete under environmental conditions of the Tibet Plateau area, this paper relies on a concrete road project in the Naqu area of Tibet, the freeze-thaw cycle test and related mechanical tests were conducted on ordinary fiber concrete (NC), abrasion fiber concrete (CM) and expansive fiber concrete (PZ). On the basis of the experimental study, a freeze-thaw damage model was established under low pressure environment of the plateau. The results show that abrasion fiber concrete (CM) has the best frost resistance durability based on the results of freeze-thaw cycle test, while the three kinds of fiber concrete are ranked as CM>NC>PZ in terms of frost resistance durability. According to the freeze-thaw damage model and the predicted flexural strength equation based on the model which are established in this paper, the test data of high cold air-entraining concrete from a high-speed project in the Tibet Plateau area are used for verification. It is found that the trend of the test values of flexural strength after freeze-thaw cycles are similar and coincided with the predicted values. Therefore, the freeze-thaw damage model for the flexural strength of the Tibet Plateau which is established in this paper can be probably reasonable and feasible.

Synergistic Effect of Multi-Scale MgO Expansion Agent and SAP on Mechanical and Shrinkage Properties of UHPC

WEI Yaping, LI Shaocheng, WANG Youzhi, TIAN Changjin

2023, 42(9):  3154-3165. 

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Due to its low water-to-binder ratio and high content of cementitious materials, ultra-high performance concrete(UHPC) produces large autogenous shrinkage at early age, which easily causes shrinkage cracking of UHPC. Therefore, multi-scale MgO expansion agent and super absorbent polymer (SAP) internal curing material were mixed to solve this problem. The effects of multi-scale MgO expansion agent and internal curing material on mechanical, shrinkage and hydration characteristics of steam-free UHPC were investigated, and then the synergistic mechanism of mixing multi-scale expansion agent and internal curing material was revealed by SEM, XRD, MIP and TG-DTG microscopic methods. The results show that mixing multi-scale MgO expansion agent is more conducive to the development of mechanical properties of UHPC than single-scale MgO and nano MgO, and at the same time provides a stable expansion source for the whole process of hydration of UHPC system. On the basis of adding muti-scale expansion agent,the introduction of SAP can improve the working performance of UHPC, while further reducing the autogenous shrinkage of UHPC at early age. The research results can provide data support and theoretical guidance for solving the problem of large autogenous shrinkage in the early stage of UHPC.

Influence of Age on Error of Concrete Member Tested by Ultrasonic-Rebound Combined Method

YUN Jianzhou, CHEN Shunchao, ZHENG Weilong, NIE Liangpeng, YUAN Shengtao

2023, 42(9):  3166-3175. 

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In order to study the error rate between calculated compressive strength and measured compressive strength of concrete members by ultrasonic-rebound combined method, concrete members of strength classes C20, C30 and C40 were designed and poured. The rebound value, ultrasonic wave velocity and compressive strength of three grades were tested under natural conditions with test age up to 730 d, and calculated compressive strength of concrete was estimated. The effect of age on rebound value, ultrasonic wave velocity, calculated compressive strength and measured compressive strength were compared and analyzed, and the relationships between rebound value, ultrasonic wave velocity and measured compressive strength of concrete members were linearly fitted according to test results. The results show that the development of rebound value of concrete members of three grades is similar to that of compressive strength. Ultrasonic wave velocity can be clearly divided into three stages with age, such as at long ages (after 180 d), the strength of concrete members with higher design grades (C40 and above) may be higher (within 10%) by using the ultrasonic-rebound combined method, and the strength of concrete members with lower design grades (C30 and below) may be lower (within 10%) by using the ultrasonic-rebound combined method. At long ages, ultrasonic wave velocity and rebound value are good at characterizing the compressive strength of concrete members from 10 to 70 MPa, and have high linear correlation with correlation coefficients of 0.95 and 0.93, respectively.

Solid Waste and Eco-Materials

Preparation and Mechanism of Food-Grade Vaterite Calcium Carbonate by Limestone

MENG Mei, XIE Yan, LU Jingjing, FENG Lunwei, LIU Yan

2023, 42(9):  3176-3185. 

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Limestone was used as raw materials, Ca(NO₃)₂ solution was obtained by HNO₃ acid hydrolysis and Ca(OH)₂ precipitation purification, and food-grade vaterite calcium carbonate was prepared by CO₂ carbonization in the ammonia atmosphere. The effects of carbonization process parameters on the regulation of calcium carbonate crystal form were discussed, and the products were characterized by scanning electron microscopy, X-ray powder diffractometer and Fourier transform infrared spectroscopy. The mechanism of NH⁺₄ and NH₂COO^- co-regulating the formation of vaterite crystal form was proposed. The results show that the ammonia atmosphere is helpful to the stable nucleation of vaterite-type calcium carbonate. When the concentration of NH₃·H₂O is 13% (mass fraction), the flow rate of CO₂ is 0.5 L/min, the reaction temperature is 25 ℃, and the reaction time is 25 min, the single phase vaterite calcium carbonate microspheres of 2~5 μm are prepared. The purity of the product is 99.5% (mass fraction), and the quality meets the requirements of food safety national standard food additive calcium carbonate. The research provides a theoretical basis for the high-value utilization of limestone and the preparation of metastable vaterite calcium carbonate.

Research on Basic Properties and Mechanism of Carya Cathayensis Peels Biochar Mortar

ZHOU Wenjian, XUE Wen, XU Dan, LI Ying

2023, 42(9):  3186-3195. 

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The use of biochar in cement-based materials can improve their basic properties and achieve carbon sequestration while enriching the ways of resource utilization of biomass solid waste. To study the effect of carya cathayensis peels biochar on mortar's performance, including fluidity, microstructure, basic mechanical properties and thermal insulation, mortar samples whose fine aggregates were partially or completely replaced by carya cathayensis peels biochar were prepared. The experiment results suggest that: 1) the best workability of the mix is found with extra water addition at the rate of 25% of biochar by mass. 2) The highest flexural and compressive strength are found in mortar with 25% biochar-sand-replacement by volume fraction, which has a better interfacial transition zone and paste-wrapping around the aggregates particles, beyond this addition. With the increase of sand substitution rate, the strength of mortar specimens decreases step by step. 3) The thermal conductivity of cement mortar presents a significant decreasing trend with the increase of biochar addition. The native pores of biochar prolong the heat transporting path and exhibit the effect of slowing down thermal conduction which significantly improve the thermal insulation and heat preservation performance of cement mortar.

Effect of Calcium Carbide Residue on Mechanical Properties and Microstructure of Composite Cementitious Material

CHEN Youzhi, WU Xiuqi, YIN Weisong, LI Wanmin, TANG Shichang

2023, 42(9):  3196-3203. 

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Calcium carbide residue, as an industrial by-product with high Ca(OH)₂ content, can accelerate the hydration process of alkali-activated composite cementitious material in cooperation with sodium carbonate. In this paper, fly ash and mineral powder were used as precursors of composite cementitious material, the effects of different ratios of calcium carbide residue (CCR) and Na₂CO₃ on the pore solution pH value and mechanical properties of composite cementitious material were investigated. In addition, the effect of co-activation of CCR-Na₂CO₃ on hydration process and microstructure of composite cementitious material was investigated by heat of hydration, X-ray diffraction, thermogravimetric analysis and scanning electron microscopy. The results show that with the increase of calcium carbide residue content, the pore solution pH value and mechanical properties of composite cementitious material increase first and then decrease. When the content of CCR and Na₂CO₃ are 6% and 9%(mass fraction), respectively, the pore solution pH value at 3 d and compressive strength at 28 d of alkali-activated composite cementitious material reach the maximum value, 12.95 and 26.8 MPa, respectively. The microstructure shows that alkali-activated composite cementitious material can generate more C-(A)-S-H gels under co-activation of CCR and Na₂CO₃, which makes the structure more dense.

Effect of Carbide Slag on Carbonation Resistance of Alkali-Activated Fly Ash-Slag

LIU Yang, XIAO Xinxin, CHEN Xiang, WANG Bowen, LUO Dong, LU Naiwei

2023, 42(9):  3204-3211. 

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To achieve the secondary utilization of industrial waste, alkali-activated fly ash-slag composite gel material (AAFSC) was prepared by partially replacing fly ash with carbide slag and mixing it into alkali-activated fly ash-slag (AAFS). The carbonization resistance of AAFSC with different carbide slag content was investigated, and the microstructure of materials was analyzed by mercury intrusion porosimetry, thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy. The results show that after the rapid carbonization process, the pore structure of AAFSC develops towards harmful pores, resulting in a significant decrease in compressive strength after carbonization. Compared with AAFS, AAFSC exhibits superior carbonization resistance in the early and middle stage before carbonization. However, this advantage gradually decreases or even disappeares with the prolongation of carbonization age. AAFSC with 6% carbide slag content has the best carbonization resistance in the early and middle stage before carbonization and still has the maximum compressive strength of 39.92 MPa in the later stage after carbonization. With the increase of carbide slag content, Ca(OH)₂ content in AAFSC increases, and these Ca(OH)₂ are consumed during carbonization, resulting in the formation of calcite, aragonite and other carbonates.

Effects of Water Reducing Agents on Performance of Red Mud-Fly Ash Based Geopolymer

PAN Rongxiang, YANG Min, YUAN Hong

2023, 42(9):  3212-3220. 

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For the problem of high water demand and high viscosity of geopolymer, the effects of sodium lignosulfonate (SL), polycarboxylate superplasticizer (PC), naphthalene surperplasticizer (N) and melamine superplasticizer (M) on the performance of red mud-fly ash based geopolymer were investigated. The stability of water reducing agents in alkali solution and the effects on the phase, morphology and structure of red mud-fly ash based geopolymer were analyzed by FTIR, XRD and SEM-EDS. The results show that all the four water reducing agents could improve the fluidity of slurry with the same liquid-solid ratio, and the degree of fluidity improvement is N, M, SL, PC in the order from high to low. SL and N have an improved effect on the compressive strength when the dosing is not higher than 0.50% of the dry basis mass, and the effects on the compressive strength are N, SL, M, PC in order from excellent to poor. The addition of water reducing agents does not change the phase composition of geopolymer. SL and N are relatively stable in alkali solution, but PC and M are less stable in alkali solution. The optimum admixtures of SL, PC, N, M are 0.50%, 0.75%, 0.50%, 0.50% (mass fraction), respectively.

Influence Mechanism of Coal-Series Metakaolin on Mechanical Properties and Microstructure of Concrete

LI Xueliang, ZHAO Qingchao, LI Weiguang, LI Yong, ZHU Yangge, SONG Houbin, YANG Hao, ZHANG Yanping

2023, 42(9):  3221-3230. 

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Coal-series metakaolin of 600 mesh (23 μm) and 1 000 mesh (13 μm) was tested according to the concentration of 0%, 5%, 10% and 15% (mass fraction) mix into concrete, and the influences of coal-series metakaolin fineness and content on the mechanical properties and microstructure of concrete were studied by strength, XRD, TG-DTG, SEM-EDS and nitrogen adsorption tests. The results show that the incorporation of metakaolin significantly improves the mechanical properties of concrete. When the fineness of metakaolin is 1 000 mesh and the content is 15%, the compressive strength of concrete is the largest, and the 90 d compressive strength reaches 81 MPa. The hydration products are mainly composed of calcium hydroxide, ettringite, hydrotalcite and calcium silicate hydrate (C-S-H) gel, etc. The addition of metakaolin do not change the type of hydration product, but increases the content of C-S-H gel in the hydration product, while reduces the content of calcium hydroxide. Metakaolin and cement hydration product calcium hydroxide undergo secondary hydration to form C-S-H gel and improve the compactness of concrete, which is the main reason that metakaolin can enhance the mechanical properties of concrete.

Influence of Gold Tailing Composite Sand on Properties of Different Strength Grade Concrete

TONG Xiaogen, ZHANG Kaifeng, MENG Gang, ZHU Wangke, WANG Min, FU Wanzhang

2023, 42(9):  3231-3239. 

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The gold tailing composite sand was used as fine aggregate to replace natural sand, the effect of gold tailing composite sand replacement rate on workability, compressive strength and durability of C30~C50 concrete were studied, and the microstructure of group with better mechanical properties was analyzed. The results show that when the replacement rate of gold tailing composite sand is lower than 50%(mass fraction), the composite sand has better gradation. When the replacement rate of gold tailing composite sand increases from 0% to 50%(mass fraction), it is necessary to adjust admixture amount to ensure the good workability of gold tailing composite sand concrete. When the replacement rate of gold tailing composite sand is 20%~30%(mass fraction), the compressive strength, carbonization resistance and freezing resistance of C30~C50 concrete at different ages are significantly improved compared with the reference group without gold tailing composite sand, and the interweaving microstructure hydration products enhances the structural compactness.

Effect of GGBS on Properties and Chloride Binding of Cement Paste

ZHANG Tao, WANG Teng, ZHANG Yan, TAN Hongbo, LIU Jialong, DONG Chao

2023, 42(9):  3240-3247. 

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In order to solve the problem of chloride erosion in reinforced concrete, the effects of different dosages of ground granulated blast furance slag(GGBS)on working performance, mechanical properties and chloride binding capacity of cement paste were studied, and the chloride binding mechanism was characterized and analyzed by phase composition, thermogravimetric analysis, pore structure distribution and thermodynamic simulation. The results show that the GGBS can improve the working performance of cement-based materials, and effectively improve the compressive strength and chloride binding capacity of cement paste at the later stage. The comprehensive performance is the best when the GGBS content is 30% (mass fraction). The GGBS can chemically combine with chloride ions to promote the formation of Friedel's salt and Kuzel's salt, and the pozzolanic effect can increase the content of C-S-H and refine the pore structure of hardened slurry to improve the compactness. The chloride binding capacity of the cement paste with GGBS is affected by the chemical binding, physical adsorption and migration resistance of chloride ions. With the increase of the content of GGBS, the chloride chemical binding and physical adsorption ability of the cement paste gradually increase, and there is an optimal content of GGBS for migration resistance. This study provides technical and theoretical support for using GGBS cement based materials in offshore islands.

Effect of Fluoride on Structure and Properties of Gypsum-Based Cementitious Materials

GUO Zhixiang, WANG Qin, ZHANG Qiuchen, ZHENG Haiyu, LIU Kejun

2023, 42(9):  3248-3257. 

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The different fluorine impurities in phosphogypsum have varying effects on the microstructure and properties of hardened gypsum paste, and their mechanisms are not yet clear, which affects the recycling of phosphogypsum resources. In this paper, through testing methods such as setting time, in-situ hydration heat, ion concentration, mechanical properties, mercury intrusion, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy, the effects of four types of fluorine impurities (CaF₂, NaF, Na₂SiF₆, and Na₃AlF₆) on the hydration process, microstructure, and mechanical properties of calcined gypsum were systematically studied. The results show that, soluble fluorine impurities can promote the hydration of calcined gypsum, showing a certain effect of promoting coagulation. The higher the solubility of fluorine impurities is, the more significant the promotion effect on the hydration process of calcined gypsum (NaF>Na₃AlF₆>Na₂SiF₆) is. Insoluble CaF₂ has little effect on the hydration process of calcined gypsum. However, excessively fast hydration rate can lead to premature hardening of the slurry, preventing some calcined gypsum from hydrating promptly. Consequently, these calcined gypsum may gradually transform into plate-like crystals during subsequent slow hydration, increasing the porosity of the hardened gypsum paste and impairing its mechanical properties. This study provides certain guidance for the efficient utilization of phosphogypsum in building materials.

Effect of Polyvinyl Alcohol Fiber on Properties of Phosphorus Building Gypsum Matrix Composites

HUANG Ronggui, TAO Zhong, WU Lei, SHEN Jinjin, XU Weijie

2023, 42(9):  3258-3266. 

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In order to improve the poor characteristics of low strength and poor toughness of phosphorus building gypsum, polyvinyl alcohol fibers of different diameters with different content were added to phosphorus building gypsum matrix composites. And the effects of polyvinyl alcohol fibers on the working and mechanical properties of phosphorus building gypsum matrix composites were explored through experimental analysis. The results show that the incorporation of polyvinyl alcohol fiber can significantly reduce the fluidity of the slurry and shorten the setting time of the slurry. At the same time, incorporating polyvinyl alcohol fiber can significantly improve the mechanical strength of the composite when the fiber diameter is 15 μm and the volume content is 1.6%. In the same composition, the composites mechanical properties are the best, the flexural strength, compressive strength, bending strength and tensile strength are 10.071, 13.25, 10.73 and 2.89 MPa, respectively. In addition, the microscopic morphology of the material structure was observed by SEM, and it is found that polyvinyl alcohol fiber can be dispersed in the pores and cracks of phosphorus building gypsum, which makes the interior structure of the composite more solid and improves the mechanical properties.

Experimental Study on Performance of Metakaolin-Phosphogypsum-Based Composite Gelling Materials

QIU Wei, KONG Dewen, CUI Gengyin, HUANG Yingying, WANG Lingling

2023, 42(9):  3267-3276. 

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In order to expand the comprehensive utilization of phosphogypsum, raw phosphogypsum (RPG) and β-hemihydrate phosphogypsum (HPG) were used as main raw materials. Besides, metakaolin (MK) and alkaline activators (quicklime, water glass) were used to modify and prepare a kind of phosphogypsum-based composite gelling materials. The effects of MK content, water glass content and the relative ratio of RPG and HPG on mechanical properties, water resistance and dry and wet resistance of metakaolin-phosphogypsum-based composite gelling material (MKPGBM) were investigated by single-factor tests. The mechanism was also analyzed at last. The results show that the strength of MKPGBM can be effectively improved by increasing the content of MK, water glass and HPG. The mechanical properties and water resistance of MKPGBM are optimal when the content of MK and water glass (by mass fraction) are 7%~9% and 21%~24%, respectively. When the relative ratio of RPG and HPG is 5∶5 (mass fraction ratio), the 28 d compressive and flexural strength of MKPGBM are the best, which are 19.58 and 7.44 MPa, respectively. The overall performance of MKPGBM is better when the relative ratio of RPG and HPG is 6∶4, and its 28 d softening coefficient reaches 0.796. The incorporation of MK and admixtures can effectively promote the formation of hydration products and fill the pores between matrix, and can also improve the mutual contact strength of RPG internal particles, thereby improving the mechanical properties,water resistance and dry and wet resistance of phosphogypsum-based composite gelling materials.

Effect and Mechanism of Low Water Absorption Ceramic Recycled Sand on Mechanical and Drying Shrinkage Properties of Mortar

YANG Yibo, LIANG Songsuo, LIU Fucai, XIE Rui, OU Jinsheng, GUO Wenying, WANG Hengchang

2023, 42(9):  3277-3285. 

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In order to solve the problem of waste ceramic recycling and river sand shortage, a study on the properties of low water absorption ceramic recycled sand (prepared from waste low absorption porcelain ceramic tiles, referred to as ceramic sand) and the effect of equal volume fully replacing of river sand on the mechanical and drying shrinkage properties of mortar was carried out. The results show that ceramic sand has a low water absorption, apparent density and crushing index, which is a light and high strength fine aggregate. Under the same water-binder ratio, cementitious material composition and working performance, compared with river sand mortar, the mechanical properties of three ceramic sand mortars with water-binder ratio of 0.45, 0.35 and 0.25 are significantly improved, in which the 28 d compressive strength increases by 39.1%, 26.8% and 24.6%, and the 28 d drying shrinkage value decreases by 45.7%, 17.9% and 5.3%, respectively. The larger the water-binder ratio is, the greater the increase in compressive strength, flexural strength and elastic modulus of ceramic sand mortar are, and the greater the decrease in drying shrinkage value is. The performance improvement is due to the properties of ceramic sand with high strength, rough surface, containing micropores from 1 μm to 20 μm and a large number of micro-powders from 1 μm to 5 μm, which improve the interfacial transition zone and the microstructure of cement stone in mortar after replacing river sand with ceramic sand.

Experimental Study on Mechanical Properties of Scrap Steel Fiber Reinforced Rubber Concrete

PENG Man, GAO Yongtao, HAN Yang, CHEN Xiuli, KOU Xiongjun

2023, 42(9):  3286-3294. 

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To improve the strength loss caused by the incorporation of rubber particles into concrete, the mechanical properties of three kinds of rubber concrete (RC) were enhanced by adding scrap steel fiber with volume content of 0.5%~2.0%. The cube compressive strength, splitting tensile strength, four-point flexural strength, and axial compressive strength of each scrap steel fiber reinforced rubber concrete (SSFRC) at 28 d were tested. To measure the compressive toughness of SSFRC, the tensile-compressive ratio, flexural-compressive ratio, and toughness index were introduced. Macroscopic test results and SEM were used to analyze the mechanism of strengthening and toughening of RC mechanical properties by scrap steel fiber. The results show that adding rubber decreases the mechanical properties of concrete with various matrix strength. Adding steel fiber admixture causes a trend in the mechanical strength of SSFRC with various matrix strength to increase first and then decrease, getting the greatest compressive strength at 1.0%, the greatest tensile and flexural strength at 1.5% of steel fiber. Steel fiber and rubber particles can cooperate at a specific admixture amount to increase the toughness of RC. The local hydration of scrap steel fiber may have taken place, according to the microscopic morphology of the transition zone at the interface between the matrix and scrap steel fiber. In conclusion, the best mechanical strength enhancement effect and the best toughness of SSFRC are achieved at 10% of rubber and 1.5% of scrap steel fiber.

Preparation of Manganese Oxide Membrane Coated Zeolite and Characteristics of Treating Manganese Containing Water

JIN Xing, FU Jinxiang, ZHANG Li, HE Xiang

2023, 42(9):  3295-3305. 

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Quartz or manganese sand filters are widely used in water purification plants, however, there are problems such as poor adsorption performance of filter materials and a long time of “start-up period” in the process of contact oxidation manganese removal. In view of this phenomenon, manganese oxide membrane coated zeolite (MOMCZ) was prepared by using zeolite as the matrix material, and potassium permanganate and manganese sulfate were used to generate manganese oxide and then deposit on the surface of zeolite. MOMCZ was combined with the adsorption properties of zeolite and the catalytic oxidation characteristics of manganese oxide. SEM, EDS, XPS, XRD, BET, and Zeta potential analyses were used to observe surface morphology and chemical composite of MOMCZ. The response surface model was used to analyze the effect of adsorption performance of MOMCZ on manganese ions. The results show that manganese oxide membrane on surface of MOMCZ exhibits a three-dimensional complex network structure. The existing forms and molar ratio of Mn element are 51.28% for Mn (Ⅲ) and 48.72% for Mn (Ⅳ). Na_0.55Mn₂O₄(H₂O)_1.5 is the main component of manganese oxide membrane. The specific surface area of MOMCZ is 38.76 m²/g, and the pore size distribution is concentrated in the range of 3～40 nm and the isoelectric point pH value is 2.36. The order of four influencing factors for adsorption of manganese ions by MOMCZ is pH value> load> adsorption time> adsorption temperature. Through model optimization, it is found that the maximum manganese ion removal rate reaches 70.82% at the load of 0.8 mg/g, pH=8.5, adsorption temperature of 23.40 ℃, and adsorption time of 6.58 min. The relative error between the predicted values of experimental model and the actual data values is less than 2.5%. The response surface model of MOMCZ adsorption manganese ion has a high degree of fitting and accurate prediction, and has high feasibility and reference value.

Ceramics

Tape Casting and Microstructure Controlling of Fine Grained Al₂O₃ Ceramic Substrate

DENG Jiawei, XIONG Xinrui, XU Xiewen, LIU Peng, YANG Xianfeng, XIE Zhipeng

2023, 42(9):  3306-3314. 

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The submicron Al₂O₃ composite powder was obtained by sand milling process, which was used to prepare fine grained Al₂O₃ ceramic substrates. The effect of slurry composition on rheological properties of slurry, bulk density and stress-strain behavior of green tape was investigated, and the influence of sintering schedule on average grain size and flexural strength of ceramic substrate was also studied. The results show that key factors such as solid content, R value (mass ratio of plasticizer to binder) and dispersant dosage determine the rheological properties of slurry. The increase of R value leads to the reduction of tensile strength and density of green tape, and the increase of solid content is beneficial to increase the possible maximum casting thickness. Under the optimized process conditions, 0.16~1.20 mm green sheets can be prepared. At a sintering temperature of 1 550 ℃, a heating rate of 2.5 ℃/min and a holding time of 60 min, the average grain size of the prepared ceramic substrate is about 1.1 μm, the grain size distribution is uniform, and the flexural strength reaches (440±25) MPa.

Evolution of Composition, Structure and Mechanical Properties of High Alumina Porcelain with Sintering Temperature

YUAN Zhiyong, ZHANG Xueri, LI Kai, XU Chengming, WU Jiali, LIAO Cangdong, ZHENG Meng, WU Yinghao, YAN Faqiang

2023, 42(9):  3315-3323. 

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When the formula and raw materials are fixed, the composition, structure and properties of high alumina porcelain largely depend on the firing system. Changes of phase composition, microstructure and mechanical properties of high alumina porcelain with sintering temperature were systematically studied, and the reasons were analyzed. The results show that with the increase of sintering temperature from 1 160 ℃ to 1 310 ℃, the amount of fused corundum and quartz particles in porcelain increases, the content of corundum phase decreases from 37.85% (mass fraction, the same below) to 35.02%, and the content of quartz phase decreases from 7.60% to 1.94%. The fused corundum and some quartz precipitate in the form of mullite, and the content of mullite phase in porcelain increases from 7.49% to 11.41%. As sintering temperature increases from 1 160 ℃ to 1 280 ℃, the content of glass phase in porcelain increases from 47.06% to 51.63%, while the true porosity of porcelain decreases from 12.50% to 5.59%. However, when sintering temperature reaches 1 310 ℃, the porcelain are overburning, therefore the true porosity increases to 6.99%. When sintering temperature is 1 160 ℃, the porcelain is undersintering with open pores, and the bending strength is only 151 MPa. When sintering temperature increases to 1 190 ℃, the bending strength reaches a maximum value of 181 MPa. As sintering temperature continues to rise to 1 310 ℃, the total content of crystalline phases in pocelain decreases from 52.94% to 48.37%, indicating that the crystalline particles which play a dispersion enhancing role in porcelain decrease, thus the strength of porcelain gradually decreases from 181 MPa to 158 MPa. These research results have important reference significance for optimizing the formulation, firing system and material properties of high alumina porcelain.

Effects of Different Fluxes on Properties of Anorthite-Based Daily Porcelain

CHENG Zhenyu, MIAO Lifeng, BAO Zhenhong

2023, 42(9):  3324-3333. 

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Anorthite-based daily porcelain was prepared by using calcite, kaolin and alumina as the main raw materials, feldspar, burnt talc and dolomite as fluxes. The effects of different fluxes and their addition amounts on properties of anorthite-based daily porcelain were studied. The results show that the fluxing effect is poor when feldspar is served as single flux. At the same time, excessive feldspar will lead to the significantly reduction of bending strength. With burnt talc and feldspar as composite fluxes, the fluxing effect is not obvious at a low addition amount of burnt talc. When the addition amount of burnt talc increases to 4%(mass fraction), the water absorption of sample obviously decreases and the bending strength is improved dramatically. The fluxing effect is good when the dolomite and feldspar are served as composite fluxes. With the increase of the addition amount of dolomite, the bending strength of sample increases first and then decreases. When the addition amount of dolomite is 6%(mass fraction), sample has the best comprehensive properties, which has a water absorption of 0.27%, bending strength of 101 MPa and good transparency.

Water-Sensitive Aging Mechanism of Low-Density Ceramic Proppant

CHEN Jianing, HAO Jianying, WANG Shengchang, LIANG Tiancheng

2023, 42(9):  3334-3341. 

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Good performance of low-density ceramic proppant is particularly important during the exploration of unconventional energy. In view of the performance degradation of low-density ceramic proppant upon serving in the formation water, two specifications of proppant were selected to be soaked in the formation water for different time. The proppant before and after soaking was characterized by XRF, XPS, XRD, SEM and TEM, and its aging mechanism was explored. The results show that the content of ClO₂ in the proppant increases, while the content of Al₂O₃ and SiO₂ decreases, and the content of Cl^- and HCO^-₃ in the formation water decreases. The peaks of Cl 2p and Cl 2s appear by XPS, and the new phase SiCl₄ is detected by XRD. These results confirm that Cl^- in the formation water diffuses to the proppant surface and reacts with SiO₂ to form SiCl₄, which further hydrates to generate silicone gel or silicic acid gel and coats the proppant surface. Al₂O₃ in the proppant can react with H⁺ (acidic environment) of the formation water to form Al³⁺, and then Al³⁺ reacts with HCO^-₃ to form Al(OH)₃ precipitating into the formation water. A large amount of Cl^- and H⁺ in the formation water erode the proppant from the surface, reducing the densification within the structure and making the structure loose, which reduces the proppant crushing resistance and degrades its performance.

Performance of 3M^TM Solid Ceramic Microspheres in Porcelain Replenishment

SONG Zixian, WEN Jianhua

2023, 42(9):  3342-3349. 

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The composite materials used in the restoration of porcelain cultural relics are called porcelain materials. At present, the porcelain materials commonly used in the restoration of porcelain cultural relics generally have the problems of poor aging resistance and insufficient mechanical properties. 3M^TM solid ceramic microsphere is a spherical ceramic material with high hardness, high whiteness and corrosion resistance, which can effectively enhance the aging resistance and mechanical properties of material. In this paper, three commercially available ceramic microspheres (W-210, W-410 and W-610) were used as research object, and the commonly used porcelain replenishment material calcium carbonate was used as control group. Under the four experimental conditions of strong ultraviolet irradiation aging, weak ultraviolet irradiation aging, wet-heat dry-cold alternating aging and non-aging, the samples were subjected to bending test, tensile test, impact test, hardness test, color difference test and gloss test. The results show that the aging resistance and mechanical properties of 3M^TM solid ceramic microspheres are better than those of calcium carbonate, and the aging resistance and mechanical properties of ceramic microspheres W-410 are the best. Compared with the calcium carbonate control group, the mechanical properties of the experimental group are comprehensively improved by 25%~30%, and the aging resistance is comprehensively improved by 50%. It can be used as a new replenishment material for porcelain restoration.

Glass

Microstructure and Properties of Glass-Ceramics Containing Cu₂O Nanocrystallines

WU Yuxin, LYU Jieheng, RUAN Jian, TIAN Chen, LIU Chao, HAN Jianjun

2023, 42(9):  3350-3358. 

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Novel glass-ceramics containing Cu₂O nanocrystallines with features of high Cu loading amount, low cost and easy large scale production is a potential substitute for silver loaded antibacterial glass. In this study, SiO₂-Al₂O₃-K₂O-ZnO-P₂O₅-B₂O₃-CuO glass-ceramics with different ZnO/K₂O were investigated. Their microstructures were characterized by XRD, Raman spectroscopy, XPS, FESEM and TEM. The structure-performance relationship was also discussed. The results indicate that there is an enrichment of Zn and P elements around the region where Cu element locates in the glass-ceramics. An appropriate amount of ZnO makes sure the particles size of Cu₂O crystallines precipitated in glass-ceramics be in nano-scale and regulate the leaching rate of Cu element. Glass-ceramics containing Cu₂O nanocrystallines exhibit significant antibacterial effects on Escherichia coli and Staphylococcus aureus. They also show photocatalysis activity for degradation of Victoria blue B solution under visible light. It should be a novel functional glass-ceramics material with great potential.

Design and Electromagnetic Shielding Performance of New Triple-Band FSS Laminated Glass

TAN Tian, CHEN Ruizhe, ZHANG Ze, HOU Xinyu

2023, 42(9):  3359-3366. 

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This paper presents a laminated glass for GSM shielding and WLAN isolation, a frequency selective surface (FSS) with a layer of ring and tripole slot elements embedded in the middle, capable suppress transmission in the 1.94, 3.55 and 4.98 GHz bands. The structural parameters of FSS laminated glass were analyzed by using the equivalent circuit model. The 2 GHz frequency point will move forward with the increase of the radius of the ring. After the tripole is hollowed out to become a three-level sub-slit, two stop bands will be generated, and the length of the tripole will affect the frequency point. But the line width and the third-level sub-slot width have little effect. The extraction and calculation process of the parameters of the equivalent circuit components was introduced. The transmission response of the FSS structure was simulated by using electromagnetic simulation software, and the influence of the geometric parameters of the structure and the incident angle on the transmission characteristics of the structure were analyzed. It still has a good shielding effect when the incident angle reaches 60°. The experimental samples were made by screen printing method, and the wave transmittance and light transmittance tests were carried out. The test results are in good agreement with the software simulation results, so it has good application potential in electromagnetic radiation protection, GSM shielding and WLAN isolation.

Influencing Factors of Thermal Insulation Performance of Bodyside Window Glass of High-Speed Electric Multiple Unit

PANG Shihong, CHEN Xi, YANG Xuedong, YANG Ailian, TAN Lei, HAN Lei

2023, 42(9):  3367-3371. 

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The air-conditioning system of high-speed electric multiple unit (EMU) provides a comfortable environment for the occupants, but also consumes a lot of energy. The bodyside window glass accounts for about 30% of bodyside wall area, which has a great influence on the load of air-conditioning system. In this paper, the thermal insulation performance of bodyside window glass under stationary and motion status of train was studied. At the same time, the influences of glass composition and emissivity on thermal insulation were also studied. The results show that under the stationary state of train, as the emissivity of glass increases from 0.070 to 0.837, the thermal transmittance coefficient of laminated-hollow glass increases by 105% and laminated-hollow vacuum composite glass increases by 209%. While under the high-speed motion status of train, the thermal transmittance coefficient of laminated-hollow glass increases by 120% and the laminated-hollow vacuum composite glass increases by 228%.

Effects of Pillar Parameters on Equivalent Stress and Deformation of Fully Tempered Vacuum Glass

YUAN Zhaoyang, HU Dongfang, LI Yanbing

2023, 42(9):  3372-3378. 

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Fully tempered vacuum glass (FTVG) is a new type of high-end architectural glass material that has excellent thermal insulation, sound insulation, safety performance and other advantages, which are highly valued in modern architecture. As an important component of FTVG, the parameters of the pillars have a significant influence on their equivalent stress and deformation properties. Numerical analysis was conducted on the effects of spherical, cylindrical and annular pillars with different spacing and arrangement on the equivalent stress and deformation of FTVG. The research results show that regardless of the shape or arrangement of the pillars, the maximum equivalent stress and deformation are positively correlated with the spacing. Under other conditions being equal, the equivalent stress and deformation of FTVG with circular pillar and equilateral triangle arrangement are the least. This study has obtained reasonable pillar spacing for different shapes and arrangements through simulation results, providing a theoretical basis for the manufacture of FTVG.

New Functional Materials

Effect of Ni-Doping on Optical and Electrical Properties of FTO Thin Film and Its Mechanism Analysis

WU Baoqi, ZHANG Qin, LIU Qiying, SHI Guohua, ZHAO Hongli

2023, 42(9):  3379-3386. 

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Ni-doped FTO thin films were prepared by aerosol-assisted chemical vapor deposition (AACVD) using monobutyltin trichloride (MBTC) as tin source, ammonium fluoride (NH₄F) as fluorine source, methanol as solvent, and nickel chloride hexahydrate (NiCl₂·6H₂O) as nickel source. The optical and electrical properties of FTO thin films were characterized and analyzed by spectrophotometer, four-probe resistor meter and Hall effect tester. The electronic structure of doped system was calculated based on first principles as well. The results indicate that the Ni-doped FTO thin films are tetragonal rutile structure, and the conductivity is improved. When Ni/Sn is 2%(atomic fraction), the quality factor Φ_TC reaches 3×10^-2 Ω^-1, the resistivity ρ is 3.79×10^-4 Ω·cm, the average transmittance of visible light is about 80%, the carrier concentration n is 6.88×10²⁰ cm^-3, and the mobility μ is 13.31 cm²·V^-1·s^-1.

Electrochemical Performance of Lithium-Rich Manganese-Based Cathode Materials Improved by Polymorphic MnO₂

YUAN Zhongchun, LI Jia, YAO Mengqin, LIU Fei, MA Jun, GENG Shuo

2023, 42(9):  3387-3394. 

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Lithium-rich manganese-based cathode materials are known as one of the most promising cathode materials for next-generation lithium batteries due to their high theoretical specific capacity. However, there are problems in the cycle process, such as low specific capacity, poor magnification performance, and fast decay rate. Based on this, polymorphic MnO₂ materials were prepared by hydrothermal method, and the lithium-rich manganese-based cathode materials were modified of surface coating by wet chemical grinding combined and heat treatment. Electrochemical performance of the obtained materials was tested by cyclic voltammetry, constant current charge and discharge and electrochemical impedance spectroscopy, and the effect of polymorphic MnO₂ on electrochemical performance of lithium-rich manganese-based cathode materials was studied by the changes of electrochemical performances of the materials before and after coating. The results show that β-coated has the best electrochemical performance, and its initial specific capacity reaches 292.2 mAh·g^-1 at 0.1 C, the capacity retention rate is 56.3% at 0.1~5.0 C, and the capacity retention rate is 81.6% at 1 C for 50 times cycles. The coating of β-MnO₂ by EIS test improves electrochemical kinetics of original sample during the electrochemical reaction.

Fabrication of Quartz Crystal Resonator by Inductively Coupled Plasma Etching Method

CHEN Jingbai, ZHANG Xinhai, LIU Feng

2023, 42(9):  3395-3401. 

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In order to fabricate quartz crystal resonators, the step morphology was prepared on the quartz substrate by photolithography and inductively coupled plasma etching. The influences of the process parameters such as the excitation power, the bias power and the heat-conducting substance on the etching effect were studied. The surface morphology of etched pattern was observed using scanning electron microscope, and the process parameters which meet the requirements of industrial production were obtained through experiment and analysis. Finally, the vertical step morphology with a height of about 22 μm was obtained using optimized processing parameters. The characteristics of dry etching and the feasibility of dry etching for industrial production of quartz crystal resonators were demonstrated by comparing with wet etching.

Road Materials

Strength Index and Dynamic Characteristics of Low Content Cement Stabilized Laterite Granules

LI Qianqian, WANG Xudong

2023, 42(9):  3402-3411. 

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The aim of this study is to find a more reasonable evaluation method for the strength index and dynamic characteristics of cement stabilized laterite granules. Different strength indexes and dynamic characteristics of cement stabilized laterite granules with low content (2.5% and 4.0%, mass fraction) were investigated. Compressive, tensile strength and dynamic modulus tests of low content cement stabilized laterite granules were carried out. The laws of strength, dynamic modulus and phase angle influenced by different factors were analyzed. The relational model with different strength indexes and dynamic modulus dependence model of cement stabilized laterite granules were developed. The results show that there are significant differences in the tensile and compressive strength of cement stabilized laterite granules under different stress modes, and the compressive strength is significantly greater than the tensile strength. For cement stabilized laterite granules, the compressive strength > flexural strength > splitting strength > direct tensile strength, and there is a significant linear relationship between strength indexes. It is possible to evaluate the tensile strength properties of cement stabilized laterite granules using compressive strength, flexural strength or splitting strength instead of direct tensile strength. The low content cement stabilized laterite granules is a kind of non linear elastic material, and its dynamic parameters have significant dependence on stress and frequency. Specifically, with the increase of stress and frequency, the dynamic modulus increases in S-shape, while the phase angle decreases gradually and increases first and then decreases, respectively. The dynamic modulus dependence model of cement stabilized laterite granules base on stress level and loading frequency reflects the nonlinear response characteristics more realistically and accurately obtains the modulus values of such materials.

Preparation and Pavement Performance of High Dosage Coal Gasification Slag Stabilized Base Mixture

LI Xiaodong, TENG Yiwei, ZHAO Jianning, YAN Sheng, YANG Jianrong, JIA Xiaolong

2023, 42(9):  3412-3420. 

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In order to solve the problem of insufficient supply of traditional sand and gravel aggregate and large storage of industrial solid waste coal gasification slag, this paper uses coal gasification slag and gravel soil to prepare pavement base materials, and explores the best proportion of coal gasification slag, cement content and gravel soil blending. The feasibility of the application of coal gasification slag pavement base material in highway engineering was studied from the aspects of mechanical properties, road performance and durability of the mixture. The results show that the optimal ratio is that the mass ratio of coal gasification slag to gravel soil is 40% to 60% and the cement content is 7%. Under this ratio, the 7 d unconfined compressive strength, splitting strength and flexural tensile strength of cement stabilized coal gasification slag pavement base material can reach above 3.0, 0.5 and 1.5 MPa, which has good vertical deformation resistance ability. After five freeze-thaw cycles, the compressive strength loss rate B of specimens is above 90%, the mass change rate is less than 5%, and the water stability is good. After 180 d of dry shrinkage test, the cumulative dry shrinkage of a group (coal gasification slag content of 35 % and cement content of 7%) and C group (coal gasification slag content of 40% and cement content of 7%)specimens are less than 2.5 mm, showing good dry shrinkage strain. The formation mechanism of coal gasification slag strength is put forward by observing the types and spatial distribution characteristics of hydration products of cement stabilized coal gasification slag base material with SEM and XRD. It is concluded that calcium silicate hydrate (C-S-H) gel and Ca(OH)₂ are the main hydration products, which is conducive to the formation of strength of base mixture.