Table of Content

15 August 2024, Volume 43 Issue 8

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Cement and Concrete

Research Progress on Carbonation Resistance of Calcium Sulfoaluminate Cement-Based Materials

ZHOU Jian, LI Weihua, PI Zhenyu, XU Mingfeng, LI Hui, NIE Song

2024, 43(8):  2711-2725. 

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Carbonation is a complex physical and chemical process, which mainly includes the diffusion and dissolution of CO₂ in cement concrete and the reaction with carbonizable substances, which eventually leads to the decrease of alkalinity of cement concrete and the corrosion of steel bars, which significantly affects its durability. Calcium sulfoaluminate cement (CSA) has the characteristics of fast hardening, high early strength and excellent sulfate corrosion resistance. However, its poor carbonation resistance can easily lead to the change of chemical composition of hydrates and the deterioration of microstructure, which will seriously endanger the normal service of infrastructure. Therefore, it is of great engineering and scientific significance to clarify the factors affecting CSA carbonization and reveal the mechanism of CSA carbonization. Firstly, starting from the hydration products of CSA, this paper introduces the carbonation mechanism of calcium trisulphoaluminate hydrate (AFt), calcium monosulfoaluminate hydrate (AFm) and calcium silicate hydrate (C-S-H). Secondly, the influences of material factors on the carbonation resistance of CSA are analyzed. Finally, the effect of CO₂ mineralization curing on the performance of CSA is reviewed, and the shortcomings of current CSA carbonization research are summarized, and suggestions for further research on methods of improving the carbonization resistance of CSA and the utilization of carbonization are put forward.

Research Status on Shear Capacity of Concrete Beams with FRP Rectangular Stirrup

WANG Jinhui, LU Chunhua, FENG Chenyang, ZHU Xuewu

2024, 43(8):  2726-2736. 

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Steel bars are prone to corrosion in harsh environments, resulting in degradation of mechanical properties of concrete members. Replacing steel bars with fiber reinforced polymer (FRP) stirrup can effectively avoid this problem. However, the low elastic modulus of FRP stirrup makes the beams easy to produce brittle shear failure. And the anisotropy makes the bending strength of FRP stirrup much lower than that of the straight section, resulting in the shear capacity of concrete beams with FRP rectangular stirrup being lower than that of reinforced concrete beams. In the past 20 years, in order to explore the practical application value of concrete beams with FRP rectangular stirrup, domestic and foreign scholars have carried out a series of experimental research and theoretical derivation, and put forward the calculation methods of shear bearing capacity and bending strength of FRP stirrup. In this paper, the above research results are summarized comprehensively, and the future research direction is prospected, in order to provide reference for the application and development of this kind of structural members.

Research Developments on Microbial Self-Healing Concrete

WEI Shuangni, WANG Yinghui, LAI Junxiang, WEI Chaoshuai, HUANG Aiguo, YAO Shengxun, ZHAI Xiaofan, SUN Congtao

2024, 43(8):  2737-2747. 

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Microbial induced calcium carbonate deposition(MICP) self-healing technology is an environmental friendly and long-term feasible repair method, which has attracted much attention in the field of concrete crack repair. Based on the research in recent years, this paper summarizes the deposition mechanism of calcium carbonate induced by different kinds of microbial, and compares and analyzes the differences of microbial carrier materials currently used. It is recommended to consider the effects of biocompatibility, immobilization ability, repair effect and other factors when selecting microbial carrier materials. Secondly, the characterization methods of microbial self-healing concrete are summarized, and the crack repair effect is comprehensively evaluated from the aspects of compressive strength recovery rate, crack surface healing rate, concrete durability and microscopic analysis. Finally, combined with the research progress of microbial self-healing concrete, suggestions for future research and development are given.

Research Progress on Effect of Tertiary Alkanolamine on Hydration of Cementitious Materials

ZHOU Yongfang, ZHANG Dajiang, JIANG Liangzhi, HUANG Wen, WANG Lei, WANG Jianfeng

2024, 43(8):  2748-2757. 

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Tertiary alkanolamine is a kind of admixture commonly used in cementitious materials. It can significantly change the hydration process of cementitious materials, and affect the strength of cementitious materials. However, the differences of performance and mechanism of tertiary alkanolamine with different molecular structures have not been uniformly explained. In this paper, the influence of tertiary alkanolamine on the strength and hydration of cementitious materials is summarized, and the reasons for the different mechanical properties of cementitious materials caused by tertiary alkanolamine with different molecular structures are explored. Finally, the future research and development trend of tertiary alkanolamine is prospected.

A Step-by-Step Analytical Solution for Predicting Elastic Modulus of Leached Cement Paste

QI Fengyan, ZHANG Jian, SONG Wenbing, WANG Hailong, GAO Yun

2024, 43(8):  2758-2767. 

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The leaching of calcium ions from the interior of concrete in a low alkalinity environment is an important factor causing a significant increase in the internal porosity of concrete, leading to a deterioration in its mechanical properties. In order to investigate the degradation law of the elastic modulus of cement paste after calcium leaching, this paper establishes a step-by-step analytical solution for predicting elastic modulus of leached cement paste. Firstly, the hydrated cement particles are regarded as a three-phase composite sphere composed of unhydrated cement particles (UC), high-density hydrated gel (H-HL), and low-density hydrated gel (L-HL). By introducing an equivalent inclusion phase (EQ) composed of UC and H-HL, the three-phase composite sphere model can be simplified into an equivalent hydrated cement particle model composed of the inclusion phase and L-HL. Finally, the elastic modulus of the two-phase composite sphere composed of the equivalent hydrated cement particles and the porosity of partially leached cement paste is solved using elasticity theory. The effectiveness of the step-by-step analytical solution is verified by comparing with third-party numerical results. Based on the analytical method established in this paper, the effects of hydration degree, volume ratio of calcium hydroxide (CH) to hydrated calcium silicate (C-S-H), and volume ratio of high-density hydrated calcium silicate (C-S-H_a) to low-density hydrated calcium silicate (C-S-H_b) on the elastic modulus of leached cement paste were analyzed. The results show that among the three influencing parameters, the hydration degree has the greatest impact on the elastic modulus of eroded cement paste. This study provides an analytical method for predicting the regression of the elastic modulus of cement paste after calcium leaching, which can provide some reference for the durability design of concrete after calcium leaching.

Effect and Mechanism Analysis of Carboxylic Acid Type Hydrophobic Agent on Cement Hydration

ZHANG Jinfei, MA Qi, MU Song, GUO Zheng, ZHUANG Zhijie, QIAO Hongxia, HONG Jinxiang

2024, 43(8):  2768-2777. 

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The hydrophobic corrosion inhibitor makes the concrete have an excellent hydrophobic effect and inhibits the medium transmission in the corrosive environment. However, the mechanism of action is not clear. In this paper, the hydration behavior of cement paste with different content of carboxylic acid type hydrophobic agent (CAHA) was studied, and its effects on the hydration heat, hydrate phase, surface contact angle, and compressive strength of cement were investigated. The results show that CAHA reduces the first hydration exothermic peak of cement paste and delays the hydration of cement. In the early stage of hydration, CAHA inhibits the formation of ettringite and calcium hydroxide, which is more significant at high dosage. CAHA reduces the early compressive strength of mortar to a certain extent and has no obvious effect on 28 d compressive strength. CAHA significantly reduces the water absorption of mortar and makes it hydrophobic. Through comparison, the optimum dosage of CAHA is recommended to be 6% of the mass of cementitious material, at which time the loss of compressive strength of the cement mortar is smaller and the erosion resistance is significantly improved.

Early Drying Shrinkage Analysis of Vinyl Acetate-Ethylene Modified Plastering Mortar

CHEN Chengwen, SHAO Lirong, WANG Jinguang, SHAN Junwei, JING Hongjun, GUO Meirong, YE Wanjun

2024, 43(8):  2778-2787. 

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To alleviate the early drying shrinkage of plastering mortar, vinyl acetate-ethylene (VAE) modified plastering mortar was used in this paper. The effects of VAE, water-binder ratio, fly ash and ground calcium carbonate on early drying shrinkage of cement mortar were discussed by orthogonal test. The influences of various factors on the early drying shrinkage were analyzed by grey correlation degree, and the pore structure distribution of VAE modified plastering mortar was analyzed by nuclear magnetic resonance. The results show that the influence degree of various factors on the early drying shrinkage of mortar in descending order is water-binder ratio, VAE content, ground calcium carbonate content and fly ash content, and the best combination is 0.45 water-binder ratio, 3% (mass fraction, the same below) VAE content, 0% ground calcium carbonate content and 20% fly ash content. When VAE content is about 3%, the peak value of ‘three peaks’ of mortar decreases, and the integral area of T₂ spectrum is the smallest, which mainly reduces the number of harmful holes and multi-harmful pores, and the distribution of mortar pore structure is uniform and the morphology is complex. Under the influence of VAE, the early drying shrinkage value of mortar has a negative correlation function with the fractal dimension of pore structure. The more uniform the pore size distribution is, the more complex the morphology is, the stronger the mortar resistance to early drying shrinkage is. In practical engineering, the early drying shrinkage of mortar can be controlled by water-binder ratio and VAE content, and the cost input can be controlled by fly ash and ground calcium carbonate content.

Influences of Additives on Alkali-Activated Cementitious Materials Drying Shrinkage Performance

FAN Xiaochun, YANG Dongsheng, ZHANG Yu, GAO Xu, YU Liju

2024, 43(8):  2788-2796. 

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In order to further improve the shrinkage characteristics of alkali-activated cementitious materials, the effects of single-doped organic shrinkage reducing agents (polyethylene glycol and latex) and inorganic expansion agents (CaO, MgO and gypsum) on hydration products composition, pore structure and shrinkage characteristics of alkali-activated slag fly ash (AASF) system were explored. The results show that among all the additives, polyethylene glycol has the most significant shrinkage reduction effect. The 91 d drying shrinkage of AASF samples with 1% (mass fraction) polyethylene glycol is only 1 683 με, which is 29.7% lower than that of control group, mainly due to the significant coarsening of pore structure. Polyethylene glycol and latex have a certain negative impact on the compressive strength of AASF, mainly due to the decrease of hydration reaction and the increase of overall porosity. The shrinkage compensation effect of three expansion agents in AASF system is not strong, but there is a significant increase in flexural strength.

Enhancement Mechanism of Mechanical Properties of Steam-Cured UHPC by Nano-C-S-H/PCE

WU Yonghua, YI Ang, HE Juan, KUANG Yufeng, YUAN Yibing

2024, 43(8):  2797-2805. 

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At present, the mechanical properties of ultra-high performance concrete (UHPC) products need to be further improved, and the use of nano-C-S-H/PCE to enhance UHPC is a feasible technical way in theory. The effect of nano-C-S-H/PCE on the mechanical properties of UHPC under steam-cured condition was studied. The influence mechanism was analyzed by measuring hydration heat, hydration products, microstructure and pore structure. The results show that the incorporation of 3.0% (mass fraction) nano-C-S-H/PCE significantly increases compressive and flexural strengths of steam-cured UHPC. The addition of nano-C-S-H/PCE can promote the hydration in early age of UHPC and form more C-S-H gel, and increase the exothermic temperature peak of hydration and shorten time to reach the hydration temperature peak. Also, the pore structure of steam-cured UHPC can be improved effectively by adding nano-C-S-H/PCE, and the total porosity and harmful pore proportion are the lowest at 3.0% (mass fraction) nano-C-S-H/PCE. This study can provide a theoretical reference for the application of nano-C-S-H/PCE in steam-cured UHPC.

Compressive Failure and Energy Evolution Characteristics of Rubber-Manufactured Sand UHPC

GE Jinjin, GAO Xiaoyu, CHEN Peiyuan, HUANG Wei, ZHANG Liming, DU Suyong

2024, 43(8):  2806-2816. 

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In order to reduce the amount of river sand in ultra-high performance concrete (UHPC) and improve its compressive fracture characteristics, the effects of manufactured sand, rubber particles, water-binder ratio and steel fiber on the fluidity and compressive strength of UHPC at different levels were analyzed through the design of four-factor and four-level orthogonal tests, and the optimal group with the best comprehensive performance was obtained. The energy evolution characteristics of compressive failure of rubber-manufactured sand UHPC were investigated. The results show that: 1) among the factors, the greatest influence on the fluidity and compressive strength of UHPC mix are water-binder ratio and steel fiber respectively. The fluidity of UHPC increases significantly with the increase of water-binder ratio, while the compressive strength has a positive effect on steel fiber content. 2) When rubber content and manufactured sand replaces river sand by 10% and 40% respectively (rubber replaces river sand with equal volume, and manufactured sand replaces river sand with equal quality, which is equivalent to saving 50% of river sand), the compressive strength of UHPC reaches 118.5 MPa. 3) From the view of failure morphology and energy evolution, the UHPC shows brittle-elongation transformation mechanical characteristics after mixing steel fiber and rubber particles. UHPC in the optimal group maintained better integrity than those in the control group when the stress peak was reached.

Effect of MgO Expansion Agent on Performance of Ultra-High Performance Concrete (UHPC) and Its Mechanism

LI Jianhua, ZHOU Kai, DENG Qiang, ZHAO Zhongjun, ZHANG Wei, TANG Guowang, ZOU Jie, LI Tingyi, YUAN Huikai

2024, 43(8):  2817-2826. 

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Ultra-high performance concrete (UHPC) has wide application prospect in engineering field because of its excellent performance. However, due to large shrinkage, the further promotion and development of UHPC were limited. Magnesium oxide (MgO) expansion agent has the characteristics of stable expansion, controllable activity, and is suitable for UHPC, so it is regarded as a UHPC expansion agent with great potential. The purpose of this study was to investigate the effects of different activity and dosages of MgO expansion agent on the performance of UHPC, and to further explain the mechanism of different activity of MgO expansion agent on the performance of UHPC by means of XRD and SEM. The results show that in UHPC mixed with MgO expansion agent, shear thickening is observed at low speed, while shear thinning is observed at high speed. Compared with cement particles, MgO expansion agent particles have stronger adsorption capacity to water. Therefore, the higher the activity of MgO expansion agent is, the more significant the decrease in the fluidity of UHPC is. And the dynamic yield stress of UHPC increases, which requires more pumping energy in practical engineering.

Numerical Simulation of Cementitious Composites Stool with Digitally Distributed Steel Fibers

MU Ru, FAN Chunhao, WANG Xiaowei, CHEN Xiangshang, QING Longbang, MEI Shaolin, CAO Chengxiang, LIU Haiyang

2024, 43(8):  2827-2834. 

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The addition of steel fibers into cementitious composites can improve the tensile performance and toughness. The direction and volume fraction of steel fibers are designed according to the distribution of tensile stress, which is defined as digitally distributed steel fiber, and can maximize the reinforcement of steel fibers on cementitious composites. In this paper, a stool was chosen as case study. The relationship between the magnitude and direction of tensile stress with the distribution of steel fibers was established by numerical simulation, and the digitally distributed steel fibers in the stool were determined. The mechanical properties of critical cross-sections of the stool were analyzed. In the midspan of the top slab of the stool, the amount of digitally distributed steel fibers is 187% and 514% higher than that of aligned and randomly distributed steel fibers, and the resultant force undertaken by the digitally distributed steel fibers increases by 276% and 888%, respectively, compared to that by aligned and randomly distributed steel fibers. The amount of digitally distributed steel fibers is 113% and 355% higher than that of aligned and randomly distributed steel fibers in the top normal section of side slab of the stool, and the resultant force undertaken by the digitally distributed steel fibers increases by 218% and 775%, respectively, relative to that by aligned and randomly distributed steel fibers. The results show that the reinforcement effect of digitally distributed steel fibers is significantly improved compared with aligned and randomly distributed steel fibers, and the midspan cross-section of the top slab and the top normal section of side slab are characterized by an increasing number of steel fibers, which leads to a higher steel fiber resultant force.

Dynamic and Static Mechanical Properties and Microstructure of Frozen Shaft Lining Imitation Steel Fiber Reinforced Concrete

WANG Rui, YAO Zhishu, FANG Yu, WANG Jiaqi

2024, 43(8):  2835-2847. 

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In order to improve the brittleness characteristics of high-strength concrete in frozen shaft lining, and improve its crack resistance and toughness, the imitation steel fiber reinforced concrete was proposed as lining building material of frozen shaft lining. Through the optimization of materials and orthogonal tests, theimitation steel fiber reinforced high-performance concrete with different mixing ratios was obtained, and the static and dynamic mechanical properties and microstructure were experimentally studied. The results show that the tensile and flexural strength of concrete is increased by 29.46% and 26.72%, and its brittle characteristics are significantly improved by adding 15% (mass fraction) fly ash and 0.54% (volume fraction) polypropylene imitation steel fiber (PPTF) to the benchmark concrete. Compared with the benchmark group, the toughness of imitation steel fiber reinforced concrete with the best mix ratio is significantly enhanced, the toughness index increases by 40.83% in the strain range of 0~0.012, and the failure patterns after failure is more complete. The addition of PPTF and fly ash effectively inhibits the generation and expansion of micro-cracks in frozen shaft lining concrete, and the concrete shows a denser microstructure and higher macroscopic mechanical properties.

Performance of High Performance Concrete Based on Magnetic Field Oriented Steel Fiber

LIU Tongjun, ZHANG Chong, XU Dujun, ZHANG Jicai, LI Fang, ZHANG Xiuzhi

2024, 43(8):  2848-2857. 

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In this paper, a directional method of steel fiber in high performance concrete was designed by using magnet. The working performance of concrete was adjusted by changing the amount of water reducing agent. The relationship between the directional effect of steel fiber and the rheological properties and mechanical properties of concrete was studied. The results show that with the increase of mass fraction of polycarboxylate superplasticizer, the yield stress and plastic viscosity of concrete decrease gradually, and the fluidity increases. When the mass fraction of water reducer is greater than 2.5%, the yield stress and fluidity gradually tend to be stable, but the plastic viscosity still maintains a decreasing trend. The lower the yield stress and plastic viscosity is, the better the fiber orientation effect is. The directional coefficient of unoriented steel fiber is 0.479~0.526, while the directional coefficient of steel fiber under magnetic field is 0.815~0.912. The flexural strength of concrete with oriented steel fiber increases by 24.0%~43.3%, and the toughness index I₂₀ increases by 38.4%~69.9%. In addition, the magnetic field has no obvious effect on the dispersion of steel fiber, and there is no significant difference in compressive strength between oriented specimen and unoriented specimen.

Negative Poisson Ratio Design and High-Speed Impact Resistance of Reinforced Concrete

LIU Jin, ZHANG Yun, MA Yanxuan, LI Mengyao, WANG Peng, ZHANG Jian, WANG Gongbin, ZHANG Peng, GAO Song

2024, 43(8):  2858-2870. 

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To enhance the high-speed impact resistance of reinforced concrete, a negative Poisson ratio design was implemented on the internal framework of the concrete. This design resulted in two variations of concrete specimens with different numbers of internal concave angles: one with six-ribbed and another with star-shaped steel reinforcement. Additionally, square reinforced concrete and plain concrete were used as control groups. Split Hopkinson pressure bar (SHPB) test was conducted to assess the high-speed impact resistance of these various types of reinforced concrete. Furthermore, a digital speckle correlation method (DSCM) was employed to analyze the field variations and microscale Poisson ratio. The results show that the negative Poisson ratio of reinforced concrete can be achieved by designing the structure of reinforced skeleton. The negative Poisson ratios of six-ribbed and star-shaped reinforced concrete under high-speed impact are -0.50 and -1.00, respectively. Under the high-speed impact, the trend of surface cracks of the three kinds of reinforced concrete is related to the shape of the steel skeleton. According to the strain field, the maximum strain values of both six-ribbed and star-shaped reinforced concrete occur in the vicinity of the internal concave angles, gradually decreasing outward from these internal concave angles. With the increase of the number of internal concave angles, the deformation ability and energy dissipation ability of reinforced concrete are significantly enhanced. The energy consumption of six-ribbed and star-shaped reinforced concrete is 1.76×10⁵ and 1.86×10⁵ J/m³, respectively, which is 1.17 times and 1.23 times that of square reinforced concrete. These results indicate that reinforced concrete with negative Poisson ratio is superior in energy dissipation, and these capabilities could be further strengthened with the increase in the number of internal concave angles.

Effects of Aluminium Oxide Fiber Content and Length on Mechanical Properties and Microstructure of Concrete

LYU Yuanfang, YAN Tiecheng, YANG Yongdong, LU Tongping

2024, 43(8):  2871-2878. 

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Aluminium oxide fiber (AOF) is a new type of polycrystalline ceramic fiber material with good hydrophilicity. Aluminium oxide fiber modified concrete (AOFMC) was prepared by using AOF as modified material. By testing AOFMC compressive strength, flexural strength and splitting tensile strength, the effects of AOF content and length on the mechanical properties of concrete were analyzed, and the optimum content and length of AOF were determined. On this basis, the strengthening effect of AOF on the mechanical properties of concrete with different strength grades(C40, C50, C60) was studied. In addition, the effects of AOF on the microstructure of concrete were analyzed by scanning electron microscopy and mercury intrusion test. The results show that the effect of AOF content and length on the improvement of mechanical properties of concrete is mutually restricted. When the length of AOF is 12 mm and the volume content is 0.2%, the mechanical properties of AOFMC are the best. With the increase of strength grade, the improvement effect of AOF on the mechanical properties of concrete is increasing. AOF is well combined with concrete matrix, thus improving the mechanical properties of concrete. In C50 concrete, AOF is mainly pulled out, while in C60 concrete, AOF is partially pulled off. When the length of AOF is small, AOF can fill the internal pores of concrete.

Mechanical Properties of Strain-Hardening Alkali-Activated Composites with Hybrid PE/PP Fibers

WANG Yanzhao, LYU Jinghui, WANG Yingchang, GUO Yongchang

2024, 43(8):  2879-2887. 

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Strain-hardening alkali-activated composites (SHAAC) is featured by both low carbon footprint and high toughness, but the high cost has limited the engineering applications. To reduce costs, this study explored the substitution of PE fibers with PP fibers to develop a hybrid PE/PP fibers SHAAC. Through axial compression and tension tests, along with cost analysis, the study investigated the influences of different replacement ratios of PP fibers (0%, 25%, 50%, 75% and 100%, volume fraction) on the axial compressive, axial tensile performance, and cost of the hybrid PE/PP fiber SHAAC. The results indicat that the axial compressive and tensile strength of SHAAC decrease when PE fibers are replaced with PP fibers, along with its crack control ability. However, SHAAC can still exhibit pseudo-strain hardening and multiple-cracking phenomenon when the PP fiber replacement ratio is below 75%. When the PP fiber replacement ratio is 50%, SHAAC shows the highest ultimate tensile strain (8.40%) while maintaining high axial compression and tension strength. Moreover, costs can be reduced by 29.00%, and the ratio of tensile parameters to cost is maximized.

Thermal Conductivity and Pore Structure of Foam Concrete Based on Orthogonal Test

LI Lin, WANG Yu, MA Yuying, SHEN Hanqi, LUO Jianghong

2024, 43(8):  2888-2896. 

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With sulphoaluminate cement and fly ash as cementitious materials, the effects of foaming agent, water reducer and thickener on the thermal conductivity of foam concrete were studied by orthogonal experiment to determine the optimal combination. Five groups of foam concrete with different densities (300, 400, 500, 700, 900 kg/m³) were prepared, and the cross-sectional views of the samples were binarized by Photoshop image processing software. The pore structure characteristics such as porosity, roundness value and pore size distribution were analyzed by Image-Pro Plus (IPP) software. The results show the primary and secondary order of the factors affecting the thermal conductivity of foam concrete is thickener content, foaming agent content, water reducer content. The density grade is negatively correlated with porosity and R² is 0.91. As the density increases, the pores proportion with roundness value of 1 also increases. The pore size distribution of foam concrete with different density grades follows the log-normal distribution approximately, the pore size mainly concentrates at 200 μm, and the proportion of large pore size gradually decreases with density increases.

Performance and Hydration Mechanism of Polymer Double Slurry for Shield Tunnel

ZHANG Shuhao, JIN Li’an, LI Zongqi, SHEN Lu, CUI Sheng’ai

2024, 43(8):  2897-2904. 

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In order to solve the problems of large loss and poor stability of grouting slurry during shield tunnel construction, three polymers of polyacrylamide (PAM), styrene-butadiene latex (SBR) and sodium carboxymethyl cellulose (CMC-Na) were selected as raw materials to develop polymer double slurry grouting material for shield tunnel. The basic properties and water dispersion resistance of polymer double slurry were measured. Combined with CT test and hydration heat test, the pore structure and hydration mechanism of different kinds of polymer double slurry were analyzed. The results show that the early retarding effect of 0.5% (mass fraction) PAM is the most obvious, and the water dispersion resistance is the best. CMC-Na has the effect of increasing the strength growth rate in later stage. The incorporation of polymer increases the pore size, expands the pore size distribution range, and reduces the number of pores. SBR has a significant effect on the dissolution reaction of C₃A, while CMC-Na plays a controlling role in the formation of C-S-H in accelerated hydration stage.

Internal Curing Effect of Water-Saturated Hollow Glass Microspheres

QU Yanan

2024, 43(8):  2905-2911. 

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The internal curing mortar was prepared by water-saturated hollow glass microspheres in this paper. The water release characteristics and shrinkage retardation effects of water-saturated hollow glass microspheres were studied. The role of internal curing water in cement hydration process was investigated, and the internal curing mechanism of water-saturated hollow glass microspheres was illustrated. The results show that the pore size on the surface of hollow glass microspheres is 1~20 μm. When the relative humidity is 97.5%, the water release percentage of water-saturated hollow glass microspheres is greater than 95%. When the internal curing water is introduced through water-saturated hollow glass microspheres, autogenous shrinkage of internal curing mortar decreases gradually with the increase of internal curing water-binder ratio. The internal curing water can improve the relative humidity inside cement paste and the hydration degree of cement, and significantly extend the humidity saturation period of cement paste, so as to reduce the early autogenous shrinkage of concrete or mortar.

Solid Waste and Eco-Materials

Process, Heavy Metal Transformation Behavior of Typical Solid Waste-Based Sintering Ceramsite and Its Application Status Analysis

KE Guopeng, XU Hao, YANG Ruzhu, CHEN Zhibin, DONG Shuyu, ZHUANG Guanzheng, ZENG Wu, LI Yaohuang, LIU Jingyong, ZHONG Sheng, YANG Zuoyi, LI Lei

2024, 43(8):  2912-2923. 

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At present, there are still a lot of solid wastes that can’t be properly treated, and using solid wastes to sinter ceramsite not only conforms to the concept of sustainable development, but also can turn waste into treasure, which is a feasible way of resource utilization. Firstly, the differences of three typical processes for sintering ceramsite from solid waste and some key processes in the sintering process were expounded. And then, the solidification and volatilization processes of seven heavy metals Cr, Zn, Cu, Cd, Ni, Pb and As in the product ceramsite during the sintering process of the above solid waste were analyzed, and six factors that may affect this process were summarized. Finally, the research and application status of ceramsite products in four main fields, such as concrete, water treatment, sound absorption materials and ceramsite proppants, and other emerging directions were summarized. Besides, some problems and prospects in the current migration and solidification of ceramsite heavy metals and the research and application of ceramsite were put forward, which can provide reference for the prevention and control of heavy metal pollution in the process of sintering ceramsite from solid waste and the subsequent use of the ceramsite products.

Influence Mechanism of Sodium Aluminate on Properties of Phosphogypsum Slag Dry-Hard Cement

TANG Pei, WEN Jiaqi, CHEN Wei

2024, 43(8):  2924-2932. 

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Phosphogypsum slag cement is a low-carbon cement. The dissolution rate of slag in this system is slow, resulting in low early-age strength and long setting time. Reducing the water-cement ratio and using dry pressing molding method can improve its early-age properties by dense packing of particles. However, the very low water-cement ratio of dry-hard cement slows down the hydration process in long term. Therefore, the use of the additional sodium aluminate to promote the production of hydration products in early age and the hydration of slag in later age was proposed in this study. The effect of sodium aluminate on the compressive strength, hydration process, phase assemblages and micromorphology of phosphogypsum slag dry-hard cement were studied. The results show that the hydration process is promoted, and more hydration products are produced in early age resulting in the increasing compressive strength. The hydration of slag in late age is improved and the strength of sample with sodium aluminate is higher than reference sample in all curing ages. The optimized content of additional sodium aluminate is 0.5% (by mass of total powder).

Effect of Desulfurization Gypsum on Properties and Microstructure of Alkali-Activated Cementitious Materials

NI Zhenkun, XUE Lili, DING Yanling, LIU Hongfei, LIU Kaifu

2024, 43(8):  2933-2940. 

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The rapid setting characteristic of alkali-activated cementitious materials (AACM) has restricted its wide application in engineering, especially at high alkali dosage. In this study, an industrial by-product desulfurization gypsum was introduced into AACM to solve this problem. Meanwhile, mechanical properties and hydration reaction characteristics were investigated to study the effect of desulfurization gypsum on the properties of AACM, and microscopic analysis methods such as XRD and SEM were used to explore the action mechanism of desulfurization gypsum on AACM. The results indicate that the incorporation of desulfurization gypsum can effectively prolong the setting time of AACM, and that the content of desulfurization gypsum is positively correlated with the setting time, but negatively correlated with the strength, hydration heat flow and total heat, the content of desulfurization gypsum should not exceed 9% (mass fraction) of the cementitious materials. The incorporation of desulfurization gypsum does not produce a large number of ettringite crystals in matrix of AACM, however, the microstructure is loosened which resulted in a decrease in strength.

Influence of Acid Activator on Activation Effect ofSolid Waste Materials

ZHANG Huifang, GONG Linyang, CHEN Jie, ZHANG Yudong, CAO Hui, LIU Zheying, LI Yukuan, WEI Wenbo, LIU Kaihong

2024, 43(8):  2941-2951. 

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In order to investigate the effect of different types and concentrations of acid activators on the activation effect of solid waste, the controlled variable method was used. Three acid solutions were selected as activators to activate fly ash and slag. The activated fly ash and slag were mixed as cementitious materials to replace 30% (mass fraction) of cement. Two types of fine aggregates, all iron tailings sand and all recycled aggregates, were selected as grouting material specimens for testing. The experimental results show that the activity of solid waste materials stimulated by soaking in an appropriate concentration of acid activator is improved to varying degrees. Comparing the strength of the all iron tailings test group and the fully recycled fine aggregate test group, it is found that the acid activator has a better effect on improving the strength of the recycled aggregate test group. For the experimental group of the same type of fine aggregate, hydrochloric acid has a better effect on improving the strength of the specimens. When the types of acid solutions are the same, oxalic acid solution with a concentration of 1% (mass fraction), acetic acid solution with a concentration of 1% (mass fraction), and hydrochloric acid solution with a concentration of 2% (mass fraction) have a better improvement effect on the iron tailings test group. The experimental group of recycled aggregates with a concentration of 1% (mass fraction) oxalic acid solution, 3% (mass fraction) acetic acid solution, and 1.5% (mass fraction) hydrochloric acid solution show better improvement effects. Through X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis, it is found that the use of acid excited cementitious materials resulted in an increase in the relative content of quartz and ettringite in the specimens, indicating that acid excitation can promote the progress of hydration reactions.

Feasibility Study on Using Coal Gasification Slag as a Substitute for Blast Furnace Slag to Prepare Super Sulphated Cement

DOU Zhanshuang, WEI Li, WANG Mengmeng, WANG Chong, JIA Xiaolong, MEN Guangyu, LI Ruijie

2024, 43(8):  2952-2960. 

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Coal gasification slag (CGS) is rich in silicon and aluminum elements, which has the potential to be used as a precursor of cementitious materials. However, the particle morphology of CGS is rough and the activity is low. In this study, in order to solve the issues of low activity and difficult utilization of CGS, the technical feasibility of using CGS as a partial substitute for blast furnace slag (BFS) in the preparation of SSC was explored. The microstructure of the hydrated products of SSC was characterized and analyzed using Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, energy dispersive spectrometry and other microscopic testing techniques. The results show that CGS as a raw material for the preparation of SSC, can provide the silicon and aluminum elements needed for initial hydration and drive the hydration reaction of SSC. With the increase of the dosage of CGS, the compressive strength of SSC sand shows a gradual decrease, while the effect on flexural strength is small. The optimum dosage of CGS is 20% (mass fraction), under this dosage, the 28 d flexural strength of cement sand specimen is the largest, and the compressive strength also reaches 43.9 MPa. The hydration products of SSC are mainly hydrated calcium silicate, hydrated calcium sulfoaluminate and other gels. The results show that CGS can be used to prepare SSC by partially replacing BFS.

Immobilization of Electroplating Sludge by Lead-Zinc Smelting Slag-Based Cementitious Material

SHI Yaoming, LI Dongwei

2024, 43(8):  2961-2974. 

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Electroplating sludge (ES) is a hazardous waste containing various heavy metals. This study aims to evaluate the solidification effectiveness of a geopolymer material prepared from lead-zinc smelting slag (LZSS) on electroplating sludge and elucidate the impact mechanism of organic polymers on this process. The results demonstrate that under the conditions of 3.5% (mass fraction) alkali content, a water glass modulus of 1.4, and a liquid-to-solid ratio of 0.22, the lead-zinc smelting slag-based geopolymer material can safely immobilize 2.5% (mass fraction) electroplating sludge. The addition of organic polymers enhances the immobilization amount of composite geopolymer material twofold and increases the compressive strength by 27.45%. At this stage, the total leaching concentration of Cr decreases from 20.05 mg/L to 13.65 mg/L, which is lower than the limit specified in the Identification Standards for Hazardous Wastes-Identification for Extraction Toxicity (GB 5085.3—2007). Mineral composition analysis, microstructure observation, chemical bond analysis, and oxidation state characterization of the solidified matrix indicate that the combined effect of Fe(II) in the lead-zinc smelting slag and organic polymers effectively reduces the toxicity of Cr and enhances the fixation rate of heavy metal ions. This study provides a new approach to the safe disposal and comprehensive utilization of electroplating sludge and lead-zinc smelting slag.

Solid Waste and Eco-Materials

Influence of Iron Tailings Mud on Strength and Early Shrinkage Performance of Full Tailings Concrete

MA Xinrui, XIAO Linlin, CUI Jiaqi, YU Zikang, YANG Mingjing, SUN Jianheng

2024, 43(8):  2975-2983. 

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In order to maximize the utilization of iron tailings resources and achieve green and sustainable development of concrete, this article uses iron tailings mud as admixture, iron tailings crushed stone and iron tailings sand as coarse and fine aggregates to prepare full tailings concrete with a strength grade of C30. Using 20%, 30%, and 40% (mass fraction) iron tailings mud with a specific surface area of 320 and 432 m²·kg^-1 as total tailings concrete admixture, the effects of iron tailings mud content and fineness on the workability, mechanical properties, and early shrinkage performance of concrete were studied. The results show that when the fineness of iron tailings mud is 320~432 m²·kg^-1 and content is 20%~30%, compared with conventional concrete with fly ash as admixture, the splitting tensile strength of full tailings concrete is increased by 6.6%~12.8%, and 7 d shrinkage rate is reduced by 10.4%~26.3%. Microscopic analysis shows that when the content is between 20%~30%, iron tailings mud as an admixture can improve the compactness of concrete and reduce the early shrinkage of full tailings concrete.

Effect of Recycled Fine Aggregate on Mechanical Properties and Carbonation Durability of High Ductility Cementitious Composites

WU Yinjia, WANG Xinjie, ZHU Pinghua, SUN Weihao, XIONG Lei

2024, 43(8):  2984-2995. 

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In order to promote the application of recycled fine aggregate (RFA) in high ductility cementitious composites (HDCC), the effect of RFA replacement rate (0%, 25%, 50%, 75%, 100%, mass fraction) on compressive strength, tensile properties, four-point flexural strength and carbonation durability of HDCC was studied. The results show that with the increase of RFA replacement rate, the compressive strength of HDCC decreases gradually, but the tensile properties and flexural strength increase significantly. Under 100% RFA replacement rate, the peak strain of HDCC reaches 3.06%, and the flexural strength reaches 7.9 MPa, which is 31.33% and 11.27% higher than that of natural fine aggregate HDCC, respectively, showing good ductility. When the replacement rate of RFA is higher than 50%, it is helpful to improve the carbonation durability of HDCC. Based on the fitting of test results, a HDCC carbonation depth prediction model related to RFA replacement rate is established.

Performance of Fully Recycled Aggregate Rockfill Concrete

DENG Xin, LI Jun, LU Zhongyuan, LI Xiaoying, HOU Li, JIANG Jun, YOU Ya, ZHANG Junjin, HE Kewen

2024, 43(8):  2996-3004. 

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As the emission of construction solid waste increases year by year, the traditional treatment methods are facing problems such as resource waste and environmental damage. Self-compacting mortar prepared from recycled fine aggregate and recycled fine powder was utilized to fill the gaps between waste concrete blocks, ultimately creating recycled aggregate rockfill concrete. Research results indicate that the incorporation of recycled powder reduces the slump flow and bleeding rate of self-compacting mortar by 6.1%~16.7% and 7.7%~30.8%, respectively. Replacing cement with recycled powder reduces the 7 d flexural strength of self-compacting mortar and has little effect on 28 and 60 d flexural strength. The replacement of recycled fine aggregate with recycled powder increases the compressive strength of mortar at 7 and 28 d, when the water-cement ratio is 0.45. The compressive strength and splitting tensile strength of rockfill concrete decrease gradually as the curing age increases. Replacing recycled fine aggregate with recycled powder increases the compressive strength and splitting tensile strength of concrete under a low water-cement ratio. The mechanical strength and frost resistance of concrete are affected by water-cement ratio, cementitious material content and aggregate gradation.

Analysis of Pore Structure and Mechanical Properties of Recycled Concrete with Full Replacement of Coarse Aggregate

ZHANG Yudong, ZHANG Jiashuai, JIA Jilong, LI Xiaochen, HUO Gang, XIE Long, MENG Zhipeng, GAO Yuzeng, CAO Yingzhuo

2024, 43(8):  3005-3016. 

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In order to improve the utilization rate of construction waste, large liquidity recycled concrete was prepared using recycled coarse aggregates with significant differences in properties from two sources to meet engineering needs. The effects of different quality recycled coarse aggregates and mineral admixtures on workability, mechanical properties and pore structure of recycled concrete were studied under the full replacement of coarse aggregates, and the optimal ratio was determined. The results show that recycled coarse aggregates contain more cracks than natural aggregates. After adding fly ash and mineral powder, some particles fill the gaps inside aggregates, which is beneficial for improving workability of concrete, but not conducive to development of concrete strength. The analysis of pore structure shows that the smaller percentage of bubble volume and the larger percentage of beneficial bubbles, the more favorable it is for concrete. Taking into account various performance factors, it is recommended that the optimal mix ratio is 10% (mass fraction, the same below) fly ash and 5% mineral powder. The workability of recycled concrete meets the requirements of large liquidity and the strength meets the requirements of C30 strength grade.

Ceramics

Preparation and Properties of MgAlON-Al₂O₃ Composite Ceramics by Hot Pressing Sintering

XU Yong, JING Zhengyang, CHEN Hao, CHEN Bowen, TU Bingtian, WANG Hao

2024, 43(8):  3017-3025. 

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MgAlON and α-Al₂O₃ have comparable optical refractive indices, and the composite ceramics composed of two materials are expected to obtain optimized microstructures, mechanical and thermal properties while maintaining reasonable optical properties. In this study, the optical transmittance behavior of MgAlON-Al₂O₃ composite ceramics were predicted based on Van-de-Hulst theory, and it is found that the theoretical in-line transmittance increases with the decrease of content and grain size of α-Al₂O₃, and it can reach 86% at the wavelength of 2 μm. In the composite ceramics prepared by hot-press sintering, α-Al₂O₃ effectively inhibites the grain growth of MgAlON through grain boundary pinning effect. As the sintering temperature increases, α-Al₂O₃ content in the composite ceramics decreases. At the same time, the optical transmittance of ceramics increases, while the mechanical properties and thermal conductivity decrease. The maximum in-line transmittance of sintered samples with 1 mm thickness from 1 500 ℃ to 1 650 ℃ is greater than 72.6% at a wavelength of 4 μm. Among them, 1 600 ℃ sintered sample shows the maximum in-line transmittance of 76.1%, elastic modulus of 321.69 GPa, hardness of 15.93 GPa, four-point fracture strength of 268.09 MPa, fracture toughness of 2.41 MPa·m^1/2, and thermal conductivity of 13.98 W·m^-1·K^-1.

Effects of Sintering Temperature and Mechanically Activated Time on Ceramic Tiles Preparation with Ceramic Solid Waste

NING Gaopeng, ZHOU Zhengyuan, XIA Guanghua, WU Wenxing, CAO Tianyi, CHEN Yushan

2024, 43(8):  3026-3033. 

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The production, using and disposal process of ceramics will produce a large amount of solid waste. Most of these ceramic solid wastes can only be disposed of open piles or landfills, with a low degree of resource utilization. In this paper, ceramic solid waste was mechanically activated with triethanolamine and millimeter zirconia balls as main raw material. The effects of different mechanical activation times and sintering temperatures on sintering performance of waste ceramic powder were investigated. The experimental results show that the most suitable mechanical activation time is 6 h, which can reduce the medium particle size D₅₀ of waste porcelain powder from 4.329 μm to 0.141 μm. The mechanical activation can break the ordered Si—O tetrahedral structure of waste porcelain powder, deepen its amorphization, and then improve the sintering activity of powder. The increase of sintering temperature not only increases the generation of liquid phase to fill inter-particle pores and improves densities of samples, but also promotes the generation of tremolite, which improves the physical properties of samples. The most suitable sintering system is sintering temperature 950 ℃ and holding time 0.5 h. The sintered sample has a flexural strength of 51.63 MPa, a water absorption rate of 0.386%, and a bulk density of 2.342 g/cm³, which can meet the BIa class standard (average flexural strength ≥35 MPa, water absorption ≤0.5%) in Ceramic Tiles (GB 4100—2016). This paper provides a new method of ‘from waste to resource’, which achieves the effective recycling of waste ceramics.

Glass

Preparation and Corrosion Resistance Performance of Graphene Oxide/SiO₂ Coatings on LAS Glass

CHANG Xizheng, ZHANG Jihong, HE Jianxiong, LI Junge, XIE Jun

2024, 43(8):  3034-3044. 

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In the present work, the graphene oxide (GO)/tetraethyl orthosilicate (TEOS) aqueous solution was prepared by the sol-gel method after investigating the dispersibility of GO in water and ethanol, the complex dispersion of GO powder and its water solution in the hydrolysate of TEOS. The surface and cross section morphology, element distributions of the composite film were analyzed. The influence of GO/SiO₂ film on the corrosion resistance of the glass was studied. The results show that 0.05 g GO can be well dispersed into 15 mL deionized water, and a uniform coating solution can be obtained with further TEOS hydrolysate addition. After heat treatment at 600 ℃ for 2 h and under N₂ atmosphere, dense GO/SiO₂ film can be obtained. The carbon element analysis shows graphene oxide was homogeneously distributed in the film. The corrosion behavior comparison of non-coated, SiO₂ film coated and GO/SiO₂ composite film coated LAS glass in HCl (1 mol/L) solution and NaOH (5％, mass fraction) solution confirmed that GO/SiO₂ composite film can improve the acid corrosion resistance of LAS glass.

Crystallization Behavior of Ag-Doped Alkali Borosilicate Glass with Different K Values

WANG Liang, FENG Jinyang, LI Bohan, ZHAO Xiujian, MA Xiao, WU Donghua, HE Yongtao, HU Yuhao

2024, 43(8):  3045-3052. 

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Based on the K₂O-B₂O₃-SiO₂ ternary system glass, different glass composition parameters K values of Ag-doped alkali borosilicate glass were designed based on a fixed glass composition parameter R values. The base glass was prepared by melting method, and a one-step heat treatment within the crystallization temperature range resulted in the precipitation of spherical AgCl crystallites in all samples. The study indicates that the different glass composition parameters K values have a significant impact on the precipitation of AgCl crystallites within the Ag-doped alkali borosilicate glass. For the designed weak phase separation system glass, the variation of the glass composition parameter K values can affect the network polymerization of the glass, but the phase separation of the glass is not the main factor affecting the glass crystallization. Through glass structure analysis, the change in the glass composition parameter K values can affect the existence state of ZrO₂ in the glass network, thereby reducing the solubility of ZrO₂ in the glass network, increasing the nucleation sites in the base glass, and thus exerting a significant influence on the AgCl crystallization behavior in the Ag-doped alkali borosilicate glasses.

New Functional Materials

Synthesis of Silicon/Silicon Carbide Nanocomposites from Silica Fume and Investigation of Its Lithium Storage Performance

HUANG Haiming, DU Jing, XIE Jieyang, CHEN Qingze, ZHU Runliang

2024, 43(8):  3053-3062. 

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The volumetric expansion of silicon anodes in lithium-ion batteries leads to a shortened cycling life and rapid capacity decay. Consequently, it is imperative to enhance the cyclic stability of silicon anode materials. In this study, we employed a molten salt-assisted magnesiothermic reduction method and successfully devised a silicon nanomaterial reinforced with silicon carbide (SF-Si) by utilizing silica fume containing elemental carbon, which is an industrial solid waste. The resulting SF-Si sample not only retained the SiC present in the silica fume but also converted the elemental carbon into SiC, achieving a SiC content of 16.4% (mass fraction). Comparative analysis with silicon material prepared from heat-treated silica fume without elemental carbon removal (H-SF-Si) revealed that SF-Si exhibited superior cyclic and rate performance. It attained a high specific capacity of 2 584.76 mAh·g^-1 in the first cycle, maintained an 83% capacity retention after 100 cycles, and even at a high current density of 5 A·g^-1, the average capacity remained at 877.28 mAh·g^-1. These enhancements were primarily attributed to the higher SiC content. The study underscores the potential application of silica fume in the domain of silicon anodes for lithium-ion batteries, with its carbon element playing a constructive role in the preparation of silicon-based nanomaterials.

A Theoretical Study of Enhancing Electrical Performance of TCO-Based Ultra-Thin Cu(In,Ga)Se₂ Solar Cell via Back-Interface Nanophotonic Structure

LI Hangyu, SONG Hao, TU Ye, PEI Hanning, YIN Guanchao

2024, 43(8):  3063-3070. 

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Transparent conductive oxide (TCO)-based ultra-thin Cu (In, Ga) Se₂ (CIGSe) solar cell have the potential for building photovoltaic integration. However, due to the presence of a back Schottky junction, increasing the back recombination rate S_b not only improves hole transport but also increases photo generated electron back recombination, thereby suppressing its performance improvement. This article uses 1D-SCAPS software to theoretically explore how back interface nanophotonic structures (NPs) can improve the performance of cells. The research results indicate that the introduction of back interface NPs generates complex electrical effects. On the one hand, NPs themselves do not absorb light energy, thereby reducing the effective light absorption volume near the back interface, resulting in a decrease in the concentration of photogenerated carriers at the back interface and a significant decrease in back recombination of back interface. On the other hand, the introduction of NPs increases the thickness of the absorption layer, causing the space charge region (SCR) to move away from back interface, reducing its collection efficiency for photo generated electrons and leading to an increase in back recombination. At a high back recombination rate (S_b=1.0×10⁷ cm·s^-1), the decrease in photogenerated carrier concentration leads to a greater decrease in back recombination than the increase in back recombination caused by SCR movement, resulting in an overall decrease in back recombination. At the same time, the reduction of back recombination also alleviates the photogenerated electron loss at high S_b, thereby relieving the inhibition of back recombination on battery performance that increases with S_b. These findings provide reference for the design and optimization of TCO-based ultra-thin CIGSe solar cell.

Preparation and Thermal Properties of KGM/CNC Carbon Aerogel Shaped Eutectic Salt Mirabilite Composite Phase Change Material

SUN Zengbao, LIU Xin, TIE Shengnian

2024, 43(8):  3071-3078. 

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In order to solve the leakage problem of hydrated salt phase change material (PCM) and explore a lower-cost and environmentally friendly carbon aerogel to encapsulate hydrated salt phase change material, KGM/CNC carbon aerogel was successfully prepared by directional freezing-casting and high temperature carbonization using konjac glucomannan (KGM) and cellulose nanocrystal (CNC) as raw materials. Konjac glucomannan/cellulose nanocrystal phase change material (KGM/CNC PCM) was prepared by vacuum impregnation method using Na₂SO₄·10H₂O-Na₂HPO₄·12H₂O eutectic salt (EHS) with 0.2% (mass fraction) nano-carbon particles as phase change matrix. The structure composition of KGM/CNC carbon aerogel was analyzed by SEM, EDS, XRD, Raman, FTIR, XPS and BET. The thermal properties of KGM/CNC PCM were studied by DSC and TG. The results show that KGM/CNC carbon aerogel has good compatibility with EHS. KGM/CNC PCM could load 98.3% (mass fraction) EHS, and the melting enthalpy and crystallization enthalpy could reach 273.3 and 239.1 J·g^-1, respectively. After 5 000 solid-liquid cycles, the melting enthalpy and crystallization enthalpy decrease by 1.4% and 2.8%, respectively. This paper solves the problem of poor cycle stability of hydrated salt phase change material, which is helpful to further promote the application of hydrated salt phase change energy storage material.

Preparation of Mesoporous La_1-xSr_xMnO₃ Catalysts via COK-12 Nano-Casting Method

HUANG Xuehui, HU Xiang’ao, CHEN Wenzhen, DENG Penghui

2024, 43(8):  3079-3088. 

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Perovskite-type catalysts show promising potential in the purification of automobile exhaust. This paper discussed the synthesis of mesoporous material COK-12 using surfactant P123 as a soft template and inexpensive sodium silicate as the silicon source under nearly neutral conditions. Building on this, the mesoporous COK-12 was modified with p-xylene as a swelling agent, resulting in large-pore, ordered mesoporous materials. Subsequently, for the first time, modified mesoporous materials were used as templates for the preparation of mesoporous La_0.8Sr_0.2MnO₃ catalysts through nano-casting combined with the sol-gel method. The results demonstrate that the catalyst synthesized at 550 ℃ possesses a larger specific surface area (72.11 m²/g) and the highest molar ratio of Mn⁴⁺/Mn³⁺ and O_ads/O_lat on the surface. Additionally, CO catalytic performance tests of samples indicate that those synthesized at 550 ℃ exhibit the best catalytic activity and excellent high-temperature stability. Their characteristic temperatures T₅₀ and T₉₀ are 180 and 218 ℃, respectively.

Ni-Loaded Composites as Microwave Absorption Materials by Recycling of Coal Fly Ash

ZHU Baoshun, TIAN Yuming, MU Weipeng, GAO Yunfeng, FENG Ming, LI Huiyu

2024, 43(8):  3089-3097. 

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The recycle of coal fly ash (CFA) is of momentous value to relieve the growing levels of the serious environment pollution. To achieve the preparation of low-cost microwave absorption materials and the recycling of CFA resources, the Ni-loaded CFA composites (Ni/CFA-x) used as microwave absorption materials were synthesized by a facile “one-pot” method using solid waste CFA as the raw material. The results show that with the increase of the concentration of nickel nitrate precursor solution, the microwave absorbing properties improve first and then decrease. The effective combination between the dielectric and magnetic components of the material exhibits significantly enhanced microwave absorption performance, through loading an appropriate amount of metal Ni particles. When the concentration of nickel nitrate precursor solution is 1.0 mol/L, the microwave absorption performance of Ni/CFA-1.0 is best. At a coating thickness of 2.0 mm, the minimum reflection loss reaches -47.9 dB, and the corresponding effective absorption bandwidth is 4.2 GHz. The excellent microwave absorption performance can be attributed to the conduction loss caused by the metal Ni particles and a certain degree of graphitization of carbon, and the interface polarization loss among the Ni particles, carbon and CFA matrix.

Interface Mechanism and Mechanical Properties of Micron PS Epoxy Resin Toughened Steel-CFRP

CHEN Zhuoyi, YAN Zizhuo, LIU Yan, PENG Lan

2024, 43(8):  3098-3108. 

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To strengthen the strength and toughness of epoxy resin at the steel-carbon fiber reinforced polymer (CFRP) adhesive interface, polystyrene (PS) microspheres were added to enhance the mechanical properties of epoxy resin. The tensile, bending and impact properties of micron PS toughened epoxy resin under normal temperature curing process were studied. The micromorphology of the tensile cross section of epoxy resin was observed using scanning electron microscope (SEM). The strengthening and toughening mechanism of micron PS particles on epoxy resin was analyzed, and the mechanical property test of the steel-CFRP adhesive interface was carried out. The results show that: the tensile strength, tensile modulus of elasticity, flexural strength, flexural modulus, elongation at break, flexural deflection and impact strength of the adhesives show a tendency to increase and then decrease with the increase of PS dosage when the mass fraction of PS increases from 0% to 5.00%. When the matrix breaks, the PS particles produce large deformations or hinder the development of microcracks, thereby achieving the purpose of toughening. The larger amount of PS particles will adhere and agglomerate in epoxy resin, resulting in a decrease in the mechanical properties of epoxy resin. As the PS content increases from 0% to 2.50%, the failure mode of the steel-CFRP bonded specimens gradually transitions from steel plate debonding and adhesive layer cohesive failure to CFRP plate delamination. The tensile strength of the double-lap specimen gradually increases, and the micron PS toughened epoxy resin with mass fraction of 2.50% shows good mechanical properties in the steel-CFRP adhesive interface.