Table of Content

15 September 2022, Volume 41 Issue 9

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Cement and Concrete

Research Progress on Frost Resistance Property of Recycled Coarse Aggregate Concrete

LIU Enming, LIN Mingqiang, XIE Qun

2022, 41(9):  2963-2978. 

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The application of recycled coarse aggregate in the field of concrete production effectively reduces environmental pollution, and realizes building waste recycling. However, due to the inherent defects such as surface wrapping by existing mortar and initial imperfection, recycled coarse aggregate concrete (RCAC) has a relatively high water absorption rate and inferior interface bond which will lead to poor frost resistance of RCAC structures exposed to subzero environment. Based on the review of both domestic and overseas researches for frost resistance of RCAC, it is found that the interfacial transition zone in freezing RCAC presents complexly vulnerable character. The development of micro-crack and pores causes the deterioration of RCAC under the freeze-thaw cycles. The growth of recycled coarse aggregate replacement percentage accelerates the degradation of frost resistance, and the mass content of recycled coarse aggregate should be controlled within 50% for optimum consideration. Mass loss, relative dynamic elastic modulus and compressive strength are usual parameters for damage level evaluation of recycled concrete. The mass loss shows negative growth at the initial stage of test, and the relative dynamic elastic modulus is less sensitive under limited freeze-thaw cycles. By contrast, the compressive strength better reflects the freeze-thaw damage level of RCAC. In the future, it is necessary to pay more attention on more systematic and in-depth research into the freeze-thaw damage mechanism of recycled concrete, and to explore reasonable non-destructive test indices that work well, as well as specific evaluation of the frost resistance behavior of recycled concrete for specific engineering environments based on standard freeze-thaw tests, in order to promote more widespread use of RCAC.

Research Progress on Activation of High Belite Calcium Sulphoaluminate Cement

ZHANG Wuyi, NIE Song, XU Mingfeng, ZHOU Jian, LI Hui

2022, 41(9):  2979-2992. 

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Cement industry should set out its plan for decarbonization, for its massive carbon emissions, to realize the “dual carbon” goal proposed by the Chinese government. Therefore, the design and application of low carbon cement are in great need. High belite calcium sulphoaluminate cement is a new type of low carbon cement, that not only saves energy and reduces carbon emissions, but also utilizes aluminium containing solid waste in its production. Besides, it is also a low-cost cement with high strength in long term. Based on these features, the development of high belite calcium sulphoaluminate cement shows great promise for the sustainability of cement industry. However, high belite calcium sulphoaluminate cement faces challenges to improve its early-age strength as it contains limited content of ye’elimite in cement clinker. Research on the activation of the cement at an early age improves its strength and broaden its application. This paper reviews the composition, characteristics and research status of the high belite calcium sulphoaluminate cement. Activations of high belite calcium sulphoaluminate cement are summarized in the three aspects of dicalcium silicate, ye’elimite and the design optimization of cement mineral composition. The aim is to provide a theoretical guidance for development of high performance cement.

Review on Effect of Microbial Colony System on Self-Healing of Concrete Cracks

HAN Qiangqiang, LU Wei, JIANG Lu, WANG Yamei

2022, 41(9):  2993-3007. 

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Cracking is the most common disease in concrete structure engineering. The crack provides a channel for external water and corrosive media, and the corrosive media will lead to accelerated deterioration of concrete durability and seriously affect the service life of engineering structure. In order to effectively prevent the intrusion of harmful ions and prolong the service life of structures, timely repair of cracks is a common problem faced by the construction industry. Microbial self-healing concrete has received extensive attention from researchers. Unlike traditional concrete, microbial self-healing concrete endows structural cracks with the function of self-diagnosing and self-healing. And there are two main repair systems, namely the one-element repair system and the multi-element repair system. This paper analysed the repair effect of microbial self-healing concrete from the perspective of different repair systems, summarised the key problems faced under each system, compared the advantages and disadvantages of the self-healing effect under both systems, and proposed the development direction of the research on self-healing of concrete cracks based on microbial-induced carbonate precipitation (MICP).The study finds that if a core bacterium with mineralisation function is used as the basis and anaerobic bacteria are added to assist mineralisation, deep crack repair can be achieved, and this new mineralisation system provides an innovative idea for the research of self-healing concrete based on MICP.

Effect and Mechanism of Sodium Lactate on Strength of Supersulfate Cement

WU Shuanglei, JI Junrong, ZHOU Weijie, CHEN Yu, ZHOU Runduo, ZHOU Zhou, CHEN Huxing

2022, 41(9):  3008-3015. 

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Supersulfate cement is a kind of resource saving and environmentally friendly cementitious material, but its application is limited because of its low strength in early stage. In order to improve its early strength, the effect of sodium lactate content on the strength of supersulfate cement was studied, the ion concentration, hydration products and microstructure were analyzed by ICP-OES, MIP, XRD and SEM, and the related mechanism was discussed. The results show that the strength of supersulfate cement, especially the early strength, is improved by adding a small amount of sodium lactate, but it is detrimental to the strength when adding too much. Considering the increasing effect of early strength and late strength, the suitable content of sodium lactate is about 0.25% (mass fraction). The main reasonwhy sodium lactate improves the strength of supersulfate cement is that sodium lactate can promote the dissolution of slag, accelerate the formation of ettringite and C-S-H, and thus improve the microstructure of cement.

Modification of Cement-Based Anchoring Grouting Material by Nano-Al₂O₃ Synergistic with Waterborne Epoxy Resin

FU Hongyuan, FU Sini, QIU Xiang, JIANG Huangbin, WANG Jiangying

2022, 41(9):  3016-3027. 

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The anchoring grouting material hasgood performance and can effectively improve the service life of the anchoring structure. In order to solve the problems of insufficient stability and mechanical properties of traditional cement-based anchoring grouting material in slope engineering, nano-Al₂O₃ and waterborne epoxy resin were used to modify cement-based anchoring grouting material to obtain composite modified cement slurry. Through orthogonal experiment, scanning electron microscope and X-ray diffraction test, the basic properties and modification mechanism of composite modified cement slurry under different water-cement ratios and mix ratios were studied. The results show that the fluidity, setting time and compressive strength of composite modified cement slurry are more affected by the content of waterborne epoxy resin than that of nano-Al₂O₃. But the funnel viscosity and water seperation rate are more affected by the content of nano-Al₂O₃ than that of waterborne epoxy resin. The composite modified cement slurry has the characteristics of high stability, low water separation rate and high compressive strength, which effectively solves the problems of insufficient stability and mechanical properties of traditional cement-based anchoring grouting material. And there exists the best performance mix ratio: water-cement ratio is 0.5, nano-Al₂O₃ content is 5% (mass fraction, the same below), waterborne epoxy resin content is 20%, and curing agent content is 2.0%.

Effect of Flocculant on Properties of Portland Cement Mortar

WANG Chuanlin, ZHANG Siyi, HUANG Junxuan, JIANG Tao, LIANG Ping, ZHOU Zhibing, WANG Yihong

2022, 41(9):  3028-3035. 

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The residual flocculant in manufactured sand produces adverse impact on properties of concrete. The effects of three types of flocculants, which are anionic polyacrylamide (APAM), nonionic polyacrylamide (NPAM) and polyaluminium chloride (PAC), and four dosages (0%, 0.015%, 0.030%, 0.050%, mass fraction) on the fluidity, setting time and mechanical properties of Portland cement were examined. X-ray diffraction (XRD) detection and scanning electron microscope (SEM) examination were conducted to explore the affecting mechanism of flocculants. In additions, the effects of water reducing agent, retarder and dispersant on the fluidity and mechanical strength reduced by flocculant were studied. The results show that APAM affects the fluidity of paste most significantly, and NPAM secondly, while PAC the least. Both APAM and NPAM slightly shorten the setting time, while PAC slightly prolongs the setting time of paste. Three flocculants all reduce the strength of mortar, and the higher the dosage is, the greater the decline is. Three flocculants all hardly change the hydration products of Portland cement, while APAM and PAC promote cement hydration, and NPAM inhibits the hydration. The combined use of water reducing agent and retarder significantly improves the fluidity and compressive strength of mortar mixed with flocculant.

Effect of Moisture State of Recycled Fine Aggregate onProperties of Mortar

XU Xin, ZHANG Hongru, JI Tao, ZHAO Baojun, YAO Jie

2022, 41(9):  3036-3046. 

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The recycled fine aggregate (RFA) was used to replace 30% (mass fraction) of the river sand to prepare mortar. The water content of RFA was set to be 0%, 30%, 70% and 100% of the value measured under the saturated-surface-dried state, by pre-treating RFA in water. The influence of the moisture states of RFA on the properties and microstructure of mortar was experimentally investigated, by taking two types of water control methods, i.e., to keep a consistent supply of mixing water and total water, respectively. Test results show that at the given mixing water supply, the fluidity of recycled mortar increase as the water content of RFA increase, and the influence of the moisture states of aggregate on the 28 d mechanical properties is insignificant. In contrast, given a consistent total water supply. The fluidity of recycled mortar decrease as the water content of RFA increase, the mortar group prepared with the oven-dried RFA present the best 28 d mechanical properties among all the mortar groups. Besides, it is found that the resistance to chloride ion ingress of recycled mortars prepared with the oven-dried RFA is the greatest among all the mortar groups, and comparable or even higher than natural mortar counterpart, regardless of the water control methods. Test results on the micro scale show that the moisture states of RFA can influence the microstructure of mortar significantly. The pre-wetting treatment of RFA led to enlarge porosity and diminished average microhardness of the new interfacial transition zones, which thereby has a negative effect on the mechanical properties and durability of mortar on the macro scale. It is suggested that the RFA at a low water content should be used to prepare the cement mortar for practical use, given that the fluidity of mortar could be ensured.

Structural Analysis and Comparison of the Ming Dynasty Great Wall Mortar in Beijing Yanqing and Huairou

SHAN Sihan, ZHANG Ruifeng, WANG Qin, ZHU Yuhua, QI Guodong

2022, 41(9):  3047-3058. 

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The Great Wall is a world cultural heritage, and mortar is the key material in its conservation and restoration. In this study, the composition, crystal structure and microscopic morphology of the Great Wall masonry mortar in Yanqing and Huairou areas and the mortar in different parts of the Great Wall of Yanqing were systematically analyzed by microscopic analysis and testing methods such as X-ray fluorescence spectroscopy, X-ray diffractometry, thermogravimetric analysis, scanning electron microscopy and Fourier infrared spectroscopy. The results show that the composition of the Great Wall masonry mortar in Yanqing and Huairou areas is quite different. The content of Mg, Si and organic matter in Huairou mortar is much higher than that in Yanqing mortar. This is because Huairou mortar stone material may contain more magnesite, and Huairou mortar contains a small amount of sand. The masonry mortars in both areas contain glutinous rice, which results in a smaller crystal grain size of CaCO₃ and a denser structure. There are also differences in the composition of mortar for different parts in the same area. The grouting mortar is quite different from other types of mortar, and contains more sand and stone. And the stone joint mortar contains a small amount of fine sand. The pavement masonry mortar is not fully carbonized, and contains a small amount of Mg(OH)₂ and Ca(OH)₂. The presence of glutinous rice is detected in brick masonry, jointing, and pavement masonry mortar, but no glutinous rice is detected in grouting and stone joint mortar. This study will provide a theoretical basis for the formulation of the Great Wall repair mortar.

Effect of Combined Activation Multiple Supplementary Cementitious Material on Performance of Steamed Concrete

SHE Liang, FU Pingfeng, DENG Wei, CHEN Yuqi, WANG Xiancong

2022, 41(9):  3059-3067. 

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Highly active supplementary cementitious materials (SCM) were prepared using fly ash microspheres, granulated blast furnace slag and silica ash via mechanical activation-chemical activation method. The effects of multiple SCM activated by different methods on activity index and hydration products of mortar were studied. The effect of multiple SCM addition on the compressive strength and sulfate corrosion resistance of steamed concrete was discussed. The hydration products and pore structure of materials were analyzed by X-ray diffraction (XRD), thermogravimetric method (TG-DSC) and mercury pressure method (MIP). The results show that by using multiple SCM to replace 30% (mass fraction) of cement, the 3 d, 7 d and 28 d activity index of mortar reach 137.54%, 140.06% and 143.97% after steam curing treatment with resting for 6.0 h and 90 ℃ curing for 4.5 h, respectively. The porosity of the hardened paste is 6.78%, and the decrease ratio of mortar fluidity is 3.94%. When the resting time is 7.5 h and the steam curing time at 90 ℃ is 4.5 h, the compressive strength of concrete for 1 d increases by 17.7% compared with cement group and the sulfate resistance coefficient of concrete increases by 5.8%. When the resting time is 6.0 h, and the steam curing time at 90 ℃ is 4.5 h, 7.0 h and 12.5 h, the compressive strength of concrete for 1 d increases by 13.4%, 16.2% and 15.3%, and the compressive strength for 7 d increases by 16.3%, 16.0% and 15.2% compared with cement group, respectively. The sulfate corrosion resistance coefficient of concrete reaches 90.1%. After the combined mechanical, chemical and hot steam high-temperature activation, the secondary reaction occurs between highly active components in SCM and Ca(OH)₂ in cement, promoting the generation of calcium silicate hydrates (C-S-H) gel. Thus, it improves the performance of streamed concrete.

Effects of Sand Ratio and Machine-Made Sand Characteristics on Concrete Fluidity and Film Thickness of Particles

XIAO Shiyu, PENG Bingjie, WU Tao, LUO Xiaodong, TAO Jun

2022, 41(9):  3068-3076. 

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Different kinds of mix proportion of concrete, e.g. sand ratio and sand mix, were designed. By testing the concrete slump flow, slump-flow time (T₅₀₀) and combining with the calculation of paste film thickness (PFT) and water film thickness (WFT), the relationships between PFT, WFT and fluidity of fresh concrete were analyzed in detail. The results show that the fluidity of concrete is greatly effected by PFT and WFT, and the fluidity, PFT and WFT of concrete prepared with different kinds of sand are quite different. The slump flow of concrete increases with the increase of PFT and WFT, and the correlation is high between the fluidity and, and WFT. The T₅₀₀ decreases with the increase of PFT and WFT, but the correlation is poor between T₅₀₀ and PFT, WFT. The changes of PFT and WFT are mainly due to the changes of the fine content, fineness modulus of machine-made and aggregate porosity. When the fine content of sand is too high, although more slurry will be introduced to improve PFT, it will also reduce the volume water binder ratio and improve the specific surface area, resulting in the decrease of WFT and the deterioration of concrete fluidity.

Effects of Silica Fume and Shrinkage Reducing Admixture on Autogenous Shrinkage and Porosity of Concrete

HUANG Zhengfeng, OU Zhongwen, LUO Wei, WANG Fei, WANG Tingfu

2022, 41(9):  3077-3083. 

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Silica fume and low water-binder ratio will reduce the total porosity of concrete, but increase the autogenous shrinkage of concrete and lead to microcracks. In this paper, the effects of silica fume and shrinkage reducing admixture (SRA) on autogenous shrinkage and pore size distribution in micro and macro scale of concrete with different water-binder ratios were studied. The results show that the autogenous shrinkage of concrete increases by 27.3%~28.8% with the addition of 10% (volume fraction) of silica fume, while the autogenous shrinkage of concrete decreases by 68.0%~85.1% with the addition of SRA, and even more to the concrete samples containing silica fume. In addition, the addition of silica fume and SRA reduces the total porosity of concrete by 5.1%~6.0% and 35.9%~39.7%, respectively, but silica fume increases the proportion of pore volume below 100 nm and above 100 μm, while SRA has the opposite effect on the volume of these two types of pores. At the same time, there is a significant positive correlation between autogenous shrinkage and pore volume fraction above 100 μm.

Influence of Calcium-Aluminum Hydrotalcite on Salt-Frost Resistance of Concrete

SHAN Jixiong, LI Jun, HOU Yongsheng, HU Yanmin, LIU Chang

2022, 41(9):  3084-3090. 

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Deicing salt with chlorine salt as main component can cause salt-frost damage to concrete, while Ca-Al hydrotalcite (CAHL) can adsorb and solidify chloride ion. In order to study the influence of CAHL on the salt-frost resistance of concrete, CAHL with the mass fraction of 0%, 0.5%, 1.0%, 1.5% and 2.0% of cementing material was added into C30 concrete, and the influence of different CAHL content on compressive strength, electric flux, salt-frost spalling mass and free chloride ion concentration of concrete was tested. The results show that when the content of CAHL is ≤1.5%, the compressive strength of concrete increases gradually with the increase of CAHL content, while the electric flux decreases gradually, indicating that CAHL can improve the compactness of concrete better under the appropriate content of CAHL. The diffraction peak of Friedel's salt increases gradually with the increase of CAHL content, indicating that CAHL can solidify chloride ion well. By improving the compactness of concrete and solidifying chloride ion, the content of free chloride ion in concrete under salt-frost condition is effectively reduced after adding CAHL. Compared with the blank sample, the mass loss of concrete with CAHL content of 1.5% decreases by 22.9% after 28 times single-sided salt-frost spalling.

Multi-Factor Prediction Model for Chloride Diffusion Coefficient Considering Material Parameters and Stress Level

YU Bo, HUANG Junhui, WANG Jialiang, QIN Hecheng

2022, 41(9):  3091-3099. 

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In order to overcome the shortcomings of low prediction accuracy for traditional model that cannot effectively consider the effect of material parameters and external load, a multi-factor prediction model for chloride diffusion coefficient was proposed by considering material parameters and stress level. Firstly, the influences of water-binder ratio, sand ratio, mineral admixture (fly ash, slag, silica fume) and stress level on diffusion coefficient were investigated based on 311 sets of rapid chloride migration test data. Then a multi-factor prediction model for chloride diffusion coefficient was established by using the two-phase analysis method and stepwise regression method. Finally, the effectiveness and accuracy of the prediction model were verified by comparing with traditional models and experimental data. The coefficient of determination of the model is 0.90.

Wear Law of Natural Pumice Concrete under Ice Friction

WANG Xiaoxiao, FENG Rongrong, JING Lei, LIU Shuguang, YAN Changwang, JIANG Lin

2022, 41(9):  3100-3106. 

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Ice wear is one of important factors affecting the damage of hydraulic concrete. In order to investigate the wear law of natural pumice concrete under ice friction, natural pumice in Inner Mongolia was used as coarse aggregate, and the effects of volume fraction of pumice aggregate, water-binder ratio and cementitious material hardness on the wear of natural pumice concrete were studied. The significance of different influencing factors on the wear amount of natural pumice concrete was analyzed. The apparent morphology of natural pumice concrete under ice wear was observed by super depth of field microscope. The results show that the wear amount of natural pumice concrete increases with the increase of pumice aggregate volume fraction and water-binder ratio, and decreases with the increase of cementitious material hardness. The volume fraction of pumice aggregate and water-binder ratio have significant effects on the wear amount of natural pumice concrete. The surface material of natural pumice concrete falls off under the action of cutting and fatigue wear mechanisms. The hole wall of the worn surface is damaged and the holes are enlarged.

Experimental Study on Double K Fracture Characteristics of Wet Concrete Based on Wedge-Splitting Method

LOU Jianmin, ZHANG Guohui, YANG Zhendong, SUN Junchong, LI Hu

2022, 41(9):  3107-3114. 

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Using wedge-splitting method, the changes of moisture content and double K fracture mechanical properties of three strength grades (C20, C30 and C40) concrete immersed in free water environment for 0 h, 2 h, 5 h, 24 h and 120 h were studied, so as to provide support for the safety evaluation of concrete structure in water environment. The results show that the higher the concrete strength grade is, the slower the water absorption rate is, the lower the moisture content is, and the longer soaking time it takes to reach saturation state. The initial cracking fracture toughness and unstable fracture toughness of concrete decrease linearly with the increase of moisture content. The initial cracking fracture toughness of C20, C30 and C40 concrete in saturated state is 29.6%, 23.2% and 33.4% lower than that in dry state, and the unstable fracture toughness of C20, C30 and C40 concrete in saturated state is 22.7%, 23.9% and 33.8% lower than that in dry state, respectively. Under the same moisture content, the initial cracking fracture toughness and unstable fracture toughness of C20, C30 and C40 concrete decrease similar basically. The P-CMOD curves obviously have a linear elastic non-crack initial stage, a stable expansion stage and an unstable expansion stage. With the increase of moisture content, the slope of linear elastic stage and stable expansion stage gradually decreases, and the curve of unstable expansion stage drops more and more gently. The critical crack opening displacement decreases gradually with the increase of moisture content, the deformation capacity and toughness of concrete decrease gradually.

Determination Method of EVA by Thermal Gravimetric Analysis Coupled with Mass Spectrometry

ZHANG Jie, LIU Yongjia, HOU Jingwen, LI Yan

2022, 41(9):  3115-3120. 

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Ethylene-co-vinyl acetate (EVA) is widely used in daily life and the development of its detection technology is very important. In this study, thethermal gravimetric analysis coupled with mass spectrometry (TGA-MS) was applied to develop a method for the direct quantitative analysis of EVA without further sample pretreatment. The degradation of EVA as measured by the combination of TGA with Fourier transform infrared spectrometer (FTIR) and gas chromatograph-mass spectrometer (GC/MS) consists of three steps. The results show that a large amount of acetic acid produced in the deacetylation step of second stage can be clearly identified, while (CH)_n fragments and acetone produced in this step. With the increase of pyrolysis temperature, benzene derivatives and large (CH₂) fragments are detected. This indicates the chain scission reactions occurring at the end of the polymer main chain during deacetylation. Isothermal deacetylation reaction is monitored by MS which determines that the formation of ketones does not affect deacetylation. MS signal intensities of acetic acid linearly responding to EVA concentrations, therefore the quantitative analysis of EVA can be clearly identified by acetic acid. This method is easier operation and rapid to test the concentration of EVA, at the same time it can be a viable complement to existing methods.

Solid Waste and Eco-Materials

Research Progress on Preparation of Cement and Concrete from Gold Tailings

ZHANG Xiao, WANG Huangqi, WANG Dongmin

2022, 41(9):  3121-2128. 

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Gold production has the characteristics of high value, high cost, high pollution and high emission. The greening of the gold industry is of great significance to sustainable development. The ore content of gold ore is low, and a large number of tailings will be produced during the production process. These tailings occupy a lot of land and cause huge environmental burdens. Therefore, the resource utilization of gold tailings is of great significance. Gold tailings are rich in silicon, and the tailings have fine particles and potential pozzolanic activity. Using gold tailings to produce cement concrete is an ideal way to realize the utilization of tailings as building materials. This paper theoretically analyzes the possibility of using gold tailings to prepare cement clinker, mortar and concrete products from the aspects of physical-chemical properties, particle characteristics and macroscopic particle group properties of gold tailings, and summarizes the use of gold at home and abroad. The research progress of tailings production of cement and mortar concrete aims to provide reference for the efficient utilization of gold tailings as building materials resources and related research.

Research Status of Phosphogypsum Pyrolysis

WU Yonglin, ZHANG Wei, DIAN Bo, CHEN Jianjun

2022, 41(9):  3129-3137. 

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Pyrolysis is the key of resource utilization of phosphogypsum. However, in the absence of reducing agents and catalysts, the disadvantages of phosphogypsum utilization include high energy consumption, high cost and low decomposition rate. Therefore, it is an important challenge to find the reducing agents and catalysts which can reduce the decomposition temperature of phosphogypsum and improve the decomposition rate. In this paper, the research status of the pyrolysis process of phosphogypsum was reviewed in the presence of reducing agents and catalysts. Traditional fuel-based reducing agents, e.g. CO and coke, have more advantages in practical application, which can effectively reduce the initial decomposition temperature of phosphogypsum and improve the decomposition efficiency. The addition of non-traditional reducing agents (sulfur, H₂S) and catalysts can not only reduce the cost of phosphogypsum pyrolysis, but also reduce the emission of greenhouse gas CO₂ during the pyrolysis of phosphogypsum. However, this method is still in the experimental research. Searching for suitable reducing agents and catalysts with higher decomposition efficiency and lower energy consumption and cost in the pyrolysis process is crucial for achieving green, low-carbon and efficient resource utilization of phosphogypsum.

Influence of Red Sandstone Aggregate on Strength and Softening Resistance Performance of Cement Stabilized Base

CHEN Fuling, WEN Yubin, SHAN Junhong, WEI Jie, ZHOU Mingkai, GAO Peng

2022, 41(9):  3138-3147. 

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Red sandstone has the characteristic of water softening. By comparing with limestone aggregate, the hardness and softening resistance performance of coarse and fine aggregate of red sandstone were studied. Then the influence law of red sandstone aggregate on the strength and softening resistance performance ofcement stabilized base were studied. The mineral composition and microstructure of red sandstone and limestone aggregate before and after immersion were compared by boundary moisture content measurement, XRD and SEM examination. The results show that the weight and hardness of red sandstone aggregate decrease after immersion, and the softening resistance performance becomes worse. The strength and softening coefficient of cement stabilized red sandstone base are lower than those ofcement stabilized limestone base, but the decreasing degree of strength and softening coefficient of cement stabilized red sandstone coarse aggregate base is less than those of cement stabilized red sandstone fine aggregate base. The main reason for the decrease of strength and softening coefficient of cement stabilized red sandstone base is that clay minerals in red sandstone aggregate are disintegrated and expanded in water. This study provides theoretical reference for the composition design and application of red sandstone in pavement base.

Effect Mechanism of Curing Temperature on Mechanical Properties of Tuff-Based Cementitious Materials

ZHANG Ping, MA Xudong, HAN Shijie, GU Longlong, WANG Zhangyan

2022, 41(9):  3148-3153. 

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Tuff is a kind of volcanic ash clastic rock which is scattered on the ground through volcanic eruption and solidified through compaction and hydration cementation, and it has certain pozzolanic activity. In this paper, the effect of curing temperature on the mechanical properties of tuff-based cementitious materials was studied, and the microstructure of hydration products of tuff-based cementitious materials was analyzed by means of FTIR, TG, SEM and MIP. The results show that the increase of curing temperature has a certain promotion and enhancement effect on the mechanical properties of tuff-based cementitious materials, which can not only improve the early strength, but also improve the later strength. The optimal curing temperature of tuff-based cementitious materials is 50 ℃. With the increase of curing temperature, no new hydration products are formed in the tuff-based cementitious material, but the content of hydration products such as AFt and C-S-H increases, and the content of Ca(OH)₂ decreases. The increase of curing temperature is beneficial to increase the proportion of gel pores and transition pores in the tuff-based cementitious material, refine the pore size structure, reduce the porosity, and improve the density of matrix structure.

Influence of Calcium Formate/Nano C-S-H Composite on Early Hydration of Fly Ash-Cement System under Steam Curing

ZHOU Lanlan, MEI Junpeng, LI Hainan, NIU Yinlong, LI Yunong, XU Zhidong, WANG Zhixin, HE Xiangxiang

2022, 41(9):  3154-3161. 

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The effect of calcium formate/nano C-S-H (NC) composite on the early compressive strength of fly ash-cement system under steam curing was studied, and the influence mechanism was analyzed by XRD, DSC-TG, MIP, SEM and FTIR. Results show that doping calcium formate can significantly improve the early compressive strength of fly ash-cement system under steam curing, and the effect is the best when the dosage is 1.5% (mass fraction). Calcium formate can promote the hydration of cement and fly ash, accelerate the formation of hydration products, and reduce the porosity and total pore volume of the fly ash-cement system. Incorporating NC on the basis of calcium formate can further improve the compressive strength of the system, and the strength increases with the increase of NC content. NC can further promote the formation of hydration products, improve the degree of hydration, refine the pore structure, and improve the density of the system.

Melt Properties of Melting-Separated Red Mud Slag During Fiberization

XING Lei, DU Peipei, LONG Yue

2022, 41(9):  3162-3169. 

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Taking melting-separated red mud as the research object, the change law of melt properties was explored in the process of melting-separated red mud slag fibrosis. The melting process and melting temperature of melting-separated red mud were studied by slag melting point and melting rate tester. FactSage thermodynamic software was used to simulate the mineral precipitation type, content and initial crystallization temperature during the cooling process of melting-separated red mud slag. X-ray diffractometer and field emission scanning electron microscope were used to study the mineral composition and micro-morphology of melting-separated red mud slag at different temperatures. The viscosity change of melting-separated red mud slag during the cooling process was studied by using the comprehensive tester of melt physical properties. The results show that the melting temperature of melting-separated red mud is 1 236 ℃. During the cooling process of melting-separated red mud slag, crystals begin to precipitate at 1 300 ℃. At first, magnesium aluminate spinel (MgAl₂O₄) is precipitated. In addition, after comprehensive analysis of melt properties of melting-separated red mud slag, it is clear that the temperature of preparing inorganic fiber by fiberizing melting-separated red mud slag should be higher than 1 433 ℃.

Influences of Mineral Admixtures on UHPC Performance

ZHAO Yaming, ZHANG Zhen, WANG Pan, ZHANG Mingfei

2022, 41(9):  3170-3175. 

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For traditional ultra-high performance concrete (UHPC), the dosage of silica fume is generally high, resulting in high production cost and large autogenous shrinkage, which has a certain impact on its practical engineering application. In this paper, UHPC was prepared by partly or completely replacing silica fume with fly ash and mineral powder. The working performance, mechanical properties, autogenous shrinkage and pore structure characteristics of UHPC were studied. The results show that the replacement of silica fume by fly ash or mineral powder improves the fluidity of UHPC mixture. The higher the replacement rate is, the greater the fluidity of the mixture is. When 50% (mass fraction) silica fume is replaced by fly ash or mineral powder, the influence on 28 d compressive strength is small under standard curing, while for high temperature steam curing, the 28 d compressive strength decreases. When the replacement rate reaches 100% (mass fraction), the 28 d compressive strength is significantly reduced under standard curing or high temperature steam curing. Fly ash or mineral powder instead of silica fume reduces the proportion of fine pores, increases pore size and reduces autogenous shrinkage, and the inhibitory effect of fly ash on autogenous shrinkage is better than that of mineral powder.

Experimental Study on Road Performance and Durability of Iron Tailings-Steel Slag Aggregate Micro-Surface Mixture

LIU Mingyang, ZHOU Bin, YAN Feng, CHEN Longjiang, HOU Meiqing

2022, 41(9):  3176-3189. 

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Aiming at a series of problems such as insufficient road surface durability at the existing micro-surface, low comprehensive utilization rate of tailings and environmental pollution caused by long-term stacking of steel slag, the feasibility of replacing traditional high quality aggregate with steel slag and iron tailings with different particle sizes was discussed. The material characteristics of steel slag and iron tailings were revealed by material analysis technology, physical and mechanical properties test. The micro-surface mixture with iron tailings-steel slag aggregate was prepared. Taking cohesion, wear resistance, water stability, slip resistance and rutting resistance of the prepared mixture as indicators,the durability of the micro-surface mixture mixed with steel slag and iron tailing was evaluated by cohesion test, wet wheel wear test, freeze-thaw cycle wet wheel wear test, long-term slip resistance test and wheel rutting deformation test.The results show that iron tailings and steel slag have significant enhancing effect on the wear resistance, long-term slip resistance and rutting resistance of the micro-surface mixture. The incorporation of iron tailings adversely affects the cohesion and water damage resistance of mixture, and the impact increases when the dosage is 20% (mass fraction), while the addition of steel slag effectively improves the problem of poor adhesion caused by iron tailings. Using steel slag coarse aggregate instead of traditional aggregate, and adding 15% (mass fraction) iron tailings fine aggregate can effectively improve the durability of micro-surface pavement, so as to prolong the service life of micro-surface pavement.

Mechanical Properties of Fly Ash-Silicon Manganese Slag Recycled Concrete Based on Orthogonal Test

WANG Chenchen, WANG Xuezhi, CHEN Donglin, HE Jingjing

2022, 41(9):  3190-3201. 

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To study the applicability of solid waste replacement of concrete raw materials and the effect on concrete properties, through the orthogonal test of 16 groups of fly ash-silica manganese slag recycled concrete test blocks, the effects of fly ash volume substitution for cementitious material, silicon manganese slag volume substitution for sand, and recycled aggregate mass substitution for coarse aggregate on concrete slump, cube compressive strength and splitting tensile strength were studied under different substitution amounts. The results show that when the substitution amount of fly ash is 40% (volume fraction), theincreasing rate of concrete slump is the largest, which is 14.5%, and the cube compressive strength and splitting tensile strength are reduced, and the reduction rate are 7.2% and 22.8%, respectively. The substitution of silicon manganese slag reduces the slump of concrete, and when the substitution amount of silicon manganese slag is 80% (volume fraction), the reduction rate of the compressive strength and splitting tensile strength is the smallest, which are 0.5% and 11.5%, respectively. The substitution of recycled aggregate reduces the slump of concrete, and when the substitution amount of recycled aggregate is 100% (mass fraction), the reduction rate of the cube compressive strength is 1.9%, and the reduction rate of splitting tensile strength is 12.4%. The cube compressive strength of concrete is predicted by the optimized model NSGM(1,4). The average relative error of model simulation is 0.542%, and the average relative error of model prediction is 2.727%.

Effect of Filtrate Circulation on Preparation of Desulfurization Gypsum Whiskers in H₂SO₄-NaCl-H₂O System

LIU Qiang, WANG Xiao, JIN Biao, LIN Xingtong, ZHANG Jianwu, WANG Yubin

2022, 41(9):  3202-3207. 

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The pretreated desulfurization gypsum was used as raw material,the sulfuric acid was used to adjust the pH value of the reaction solution, and the desulfurization gypsum whiskers were prepared by hydrothermal method to realize green production. Through the recycling of filtrate with or without reagent compensation, the effect of cycle number of filtrate on the quality of whiskers, pH value of solution and concentration of Na⁺ was studied. The results show that, with the increase of cycle number of filtrate, the pH value of filtrate gradually increases, but the concentration of Na⁺ decreases and its loss is from 27.3% to 34.6% in the condition of no reagent compensation. When H₂SO₄ and NaCl are used to compensate the reaction solution, the effect of cycle number of filtrate on the concentration of Ca²⁺ is slight before and after reaction. However, the cycle number of filtrate has an obviously effect on the crystal morphology, aspect ratio and quality of whiskers. When the cycle number of filtrate is less than 5, the quality of prepared whiskers is relatively good.

Effect and Mechanism of Waste Glass Powder as Supplementary Cementitious Material on Mortar Properties

LI Fang, YANG Jian, LI Lihui

2022, 41(9):  3208-3218. 

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Incorporating waste glass powder (WGP) into concrete as supplementary cementitious materials (SCMs) offers a potential method for recycling glass. To facilitate the effective application, it is necessary to research the effect and mechanism of waste glass on mortar properties. In this paper, the effect of WGP with different particle sizes of 0~0.075 mm, 0.075~0.15 mm and 0.15~0.3 mm as SCMs on the mechanical properties of mortar and expansion of alkali-silica reaction (ASR) was studied. The results show that the 28 d compressive strength of mortar increases by 5%~15% and ASR expansion rate decreases by 20.2% when the size of WGP is 0~0.075 mm. The 28 d compressive strength of mortar decreases by 5%~8% and the ASR expansion rate increases by 39.7% when the size of WGP is 0.15~0.3 mm. To further explore the mechanism of performance change, thermogravimetric analysis, inductively coupled plasma and electron microscope and energy dispersive spectrometer were used to examine the resulting products, pore solution, microstructure and composition. The alkali aggregate activity of coarse WGP is strong, easy to ASR, resulting in ASR expansion rate increased. The pozzolanic reactivity of fine WGP is strong, the pozzolanic reaction produces calcium silicate hydrate gel with a low Ca/Si ratio and a low expansion rate. The product absorbs Na⁺ and K⁺, reducing the number of reactants needed for ASR, and the resulting mortar is denser than the plain mortar, which is beneficial for reducing porosity, reducing water infiltration, and resisting expansion pressure.

Effect of Waste Glass Powder on High Temperature Compressive Strength and Microstructure of Cement Stone

LI Cheng, GENG Chenzi, DAI Dan, WANG Chunyu, SONG Weikai, YAO Xiao

2022, 41(9):  3219-3226. 

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Waste glass powder, as a kind of solid waste with high content of SiO₂, can effectively prevent the strength retrogression of oil well cement stone at high temperature, thereby improving the long-term sealing integrity of cement sheath in deep and ultra-deep wells. The effect of waste glass powder on compressive strength and microstructure of cement stone at 150 ℃, 21 MPa was studied in this paper. The results show that the 180 d compressive strength of neat cement stone is 8.57 MPa, which is 76.04% lower than 1 d compressive strength. The incorporation of waste glass powder improves the long-term stability of cement stone compressive strength. When 40% (mass fraction) cement is replaced by waste glass powder with a particle size of 45 μm, the 180 d compressive strength of cement stone is 31.85 MPa, which is only 3.95% lower than 1 d compressive strength. In addition, the 180 d permeability of cement stone is 1.28×10^-2 mD, which is 16.88% lower than 1 d permeability. The incorporation of waste glass powder changes the phase composition of cement stone. The neat cement stone is composed of portlandite and hillebrandite. The cement stone incorporating 40% waste glass powder with a particle size of 45 μm is made up of xonotlite and tobermorite. The grain size of xonotlite and tobermorite in cement stone is stable after incorporating 40% waste glass powder with a particle size of 45 μm. More large pores are produced in neat cement stone with the increase of curing age, while the structure in cement stone incorporating 40% waste glass powder with a particle size of 45 μm is denser, and gel pores are dominated within 180 d.

Effect of Plasticizer Type on Properties of Construction Spoil Based High-Fluid Backfill Materials

TAN Zhengri, TAN Hongbo, LYU Zhouling, KONG Xianghui, JIAN Shouwei, MA Baoguo

2022, 41(9):  3227-3233. 

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Construction spoil based high-fluid backfill material has the advantages of high fluidity, self-leveling, self-compaction and so on. Compared with the traditional backfill materials, it can effectively avoid the engineering problems caused by insufficient compaction. However, construction spoil based high-fluid backfill material is easy to settle and bleeding, which limits its engineering application. In this paper, polycarboxylate superplasticizer (PCE), sulfonated acetone formaldehyde (SAF), naphthalene superplasticizer (FDN) and melamine superplasticizer (PMS) were used to reduce water consumption and optimize fluidity. Meanwhile, the effects of four plasticizers on the properties of construction spoil based high-fluid backfill materials were compared. The results indicate that under the same fluidity, the water reducing effect of four plasticizers decreases in order: PCE>SAF>PMS>FDN. In terms of temporal fluidity, FDN system has better fluidity within 1 h than other plasticizer systems. The fluidity retention of four plasticizers systems decreases in order: FDN>PCE>PMS>SAF. Four plasticizers significantly reduce the bleeding rate of construction spoil based high-fluid backfill materials and shorten the setting time.

Ceramics

Research Progress on High Temperature Oxidation Resistance of SiC Fibers

XIANG Yu, YU Jinshan, WANG Honglei, ZHOU Xingui

2022, 41(9):  3234-3242. 

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As an important load-bearing part of SiC_f/SiC composites, the microstructure and performance evolution of SiC fibers under high temperature oxidative environment directly affect their practical application. This paper reviewed the oxidation mechanism and oxidation model, as well as the influencing factors of oxidation behavior of SiC fibers. The approaches to improve the oxidation resistance of SiC fibers were also summarized and introduced. The oxidation behavior of SiC fibers is divided into passive and active oxidation according to the oxygen partial pressure. The high temperature oxidation in the water-oxygen environment accelerates the increase of the SiC fibers oxide layer thickness and the generation of cracks, resulting in the degradation of the mechanical properties. The composition and microstructure also have different effects on the oxidation results. This paper is intended to provide some reference for the application of SiC fibers under high temperature oxidative environments.

Research Status and Development of Proton Exchange Membrane Fuel Cell

TONG Xin, XIONG Zhe, GAO Xinyu, HOU Junwei, LIU Yiying, LIAO Kaifeng, WU Weichuang, WU Weibin, QI Long, WANG Hailin, CAI Weizi

2022, 41(9):  3243-3258. 

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The proton exchange membrane fuel cell (PEMFC) is an efficient and clean power generation technology with the characteristics of fast reaction kinetics and low start-up temperature. The current rapidly development of PEMFC technology is expected to be widely popularized. A brief overview of the development of PEMFC was given in recent years, starting from the core components of PEMFC. The core components were classified from the perspective of key materials. The research status and technical features of proton exchange membranes (PEM), catalysts and gas diffusion layers (GDL) were introduced in detail. The research methods, improvement methods and progress of each component were summarized, and the research direction and development trend of PEMFC were prospected. Based on various advantages in high temperature environments, PEM with short side chains and low equivalent weight values will continue to be the focus of research under high temperature and low humidity environments. PEMFC will further develop towards the situation of low Pt or even no Pt, and achieve water balance under humidification-free.

Research Progress on Oxygen Control Technology During Preparation of Czochralski Single-Crystal Silicon

ZHANG Mengyu, LI Tai, DU Shanlin, HUANG Zhenling, ZHAO Liang, LYU Guoqiang, MA Wenhui

2022, 41(9):  3259-3271. 

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The single-crystal silicon prepared by Czochralski (CZ) method is showing a development trend toward larger size, higher quality, and lower cost with the rapidly development of China's photovoltaic industry. Nevertheless, the issue of high oxygen impurity content in single-crystal silicon is increasingly drawing attention as the size of the single-crystal silicon size increases. In this paper, based on the introduction of oxygen impurity transport mechanism during the process of preparing single-crystal silicon by CZ method, the current state of oxygen control technology in the production of single-crystal silicon was summarized. Furthermore, the influence laws of thermal field structure optimization, process optimization, doping elements, argon flow field optimization and new CZ technology on the oxygen impurity content of single-crystal silicon were analyzed, and the development direction of oxygen control technology in the future was put forward.

Preparation and Electrochemical Properties of K⁺ Doped LiNi_1/3Co_1/3Mn_1/3O₂ Materials

GUO Lifang, XIE Yulong, BEN Cuoji

2022, 41(9):  3272-3278. 

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LiNi_1/3Co_1/3Mn_1/3O₂, a cathode material for Li-ion battery, has the advantages of large discharge specific capacity, good thermal stability, low cost, and good safety performance, but its rate performance needs to be further improved. Therefore, K⁺ doped LiNi_1/3Co_1/3Mn_1/3O₂ materials (LNCM-xK) were prepared by hydrothermal method in this paper.The morphology and structure of LNCM-xK were characterized by X-ray diffraction spectrum, field emission scanning electron microscopy and X-ray photoelectron spectroscopy, and its electrochemical properties were tested by electrochemical workstation and blue electric test system. The results show that K⁺ doping can effectively reduce the cation mixing degreeand effectively improve the electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ materials, among which K⁺ doped LiNi_1/3Co_1/3Mn_1/3O₂ (LNCM-0.125K) of x=0.125 has the lowest cation mixing degree. The LNCM-0.125K sample has the best electrochemical performance. The capacity retention rate is 96.15% after 50 cycles at 0.2 C. The rate performance is carried out at different current density (0.2 C, 0.5 C, 1 C, 2 C, 5 C), and the capacity retention rate is 97.00% after 30 cycles of continuous charge and discharge.

Preparation and Properties of Ta, Ba Co-Doped Garnet-Type Li₇La₃Zr₂O₁₂ Electrolyte

SHEN Ao, ZHOU Jiacheng, XIE Dianchen, JIANG Xue, MA Shucheng, LUO Yali

2022, 41(9):  3279-3287. 

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Conventional lithium-ion batteries using organic liquid electrolytes suffer from limited energy density and safety risks. To improve energy density and safety, all-solid-state lithium battery are developed using solid electrolytes. Among various inorganic solid-state electrolytes, the garnet-type Li₇La₃Zr₂O₁₂ electrolytes have attracted a great deal of attention, owing to high ionic conductivity and the excellent stability against Li metal. In order to further improve the conductivity, the garnet-type electrolytes Ta and Ba co-doped Li₇La₃Zr₂O₁₂ (Li_7-x+yLa_3-yBa_yZr_2-xTa_xO₁₂) were prepared using solid-state synthesis method. The crystal structure, morphology and ionic conductivity of Li_7-x+yLa_3-yBa_yZr_2-xTa_xO₁₂ (0.4≤x≤0.6, 0≤y≤0.05) electrolytes were systematically investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS), respectively. The results show that Ta⁵⁺ doping stabilizes the cubic phase. Meanwhile, Ba²⁺ as dopand and sintering agent can decrease the total resistance by promoting the growth of grains and ceramic densification. Notably, the Li_6.45La_2.95Ba_0.05Zr_1.4Ta_0.6O₁₂ sample presents a total conductivity of 1.07×10^-3 S·cm^-1 at room temperature and an activation energy of 0.378 eV. Ta⁵⁺/Ba²⁺ co-doping strategy is conducive to the preparation of garnet-type electrolyte materials with high density and high conductivity.

Preparation and Characterization of Monodisperse Mesoporous Silicon Dioxide Microspheres with Large Particle Size

GUAN Tong, JIN Zhao, SHAO Huafeng, SUN Jinrui

2022, 41(9):  3288-3295. 

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Using tetraethyl orthosilicate (TEOS) as silicon source and N,N-dimethylformamide (DMF) as emulsified porogen, partially condensed poly(ethoxy)siloxane (PES) was obtained by acid-catalyzed method. PES was further catalyzed by alkali to obtain mesoporous silicon dioxide microspheres. The effects of the amount of acid catalyst, spin temperature on the viscosity and degree of polymerisation of PES and the effect of PES viscosity on the particle size of silicon dioxide microspheres were investigated. The effects of the amount of ammonia water, the type of emulsified porogen, the amount of emulsified porogen, the stirring speed and the post-treatment method on the properties of silicon dioxide microspheres were also studied. The microspheres were characterized by scanning electron microscopy, rotational viscometer, nitrogen blow adsorption and Fourier infrared spectroscopy. The results show that the prepared mesoporous silicon dioxide microspheres are spherically intact, with uniform particle size distribution and high purity. The average pore size of microspheres is 10.164 4 nm, the pore volume is 1.023 023 cm³/g and the specific surface area is 396.528 1 m²/g.

Discrete Element Simulations on Compressive Fragmentation of Alumina Ceramics

QIU Meifang, ZHANG Qingyan, ZHENG Yuxuan

2022, 41(9):  3296-3303. 

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The compressive failure of ceramics is always accompanied by an explosive fragmentation process that creates lots of fragments flying away at high speed. Due to experimental limitations, the details of compressive fragmentation occurred inside the specimen are not clear. In this paper, the compression crushing process of alumina ceramics was numerically reproduced by discrete element method. The size distribution of fragments under different strain rates, the average splash velocity of fragments and the variation law of fragment velocity in different areas within the specimen were analyzed. The simulation results show that as follow: (1) Both the compressive strength of ceramics and the average splash velocity of fragments increase with the increase of loading strain rate. (2) The dispersion velocity of debris is related to its initial position. The dispersion velocity of peripheral debris is the largest. With the decrease of distance between initial position and central axis of the specimen, the dispersion velocity of debris decreases gradually. (3) With the increase of loading strain rate, the number of fragments produced by fragmentation increases gradually, and the corresponding average size of fragments decreases. The energy conservation and conversion mode in the compression crushing process of the specimen were further discussed, and the average velocity of debris splashing was theoretically analyzed.

Refractory Materials

Hazardous Waste Slag Corrosion Resistance of Cement Bonded Al₂O₃-Cr₂O₃ Castable

LIAO Zixin, LI Yawei, LIAO Ning, LIU Huilin

2022, 41(9):  3304-3314. 

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Al₂O₃-Cr₂O₃ castable is one of the important lining materials of hazardous waste incinerators. However, the sources of hazardous waste are extensive and very complex, which lead to the difference of slag composition, thus affecting the service life of hazardous waste incinerators. In this paper, calcium aluminate cement (CAC) bonded Al₂O₃-Cr₂O₃ castable was taken as the research object. Three typical hazardous waste slags rich in CaO, Fe₂O₃ and SiO₂ were selected,and the effects of the above hazardous waste slags on the erosion/penetration behavior and Cr(Ⅵ) formation of chromium corundum castables before and after firing were investigated. The result shows that the slag corrosion resistance and infiltration resistance of materials are related to the chemical composition of slag, viscosity, interfacial reaction between slag and materials and pore structure of materials. As far as infiltration is concerned, the high SiO₂ slag and high Fe₂O₃ slag react with the material interface to form phases such as nepheline with low melting point, which promote the slag infiltration, while the high CaO slag reacts with the material to form phases such as CaAl₁₂O₁₉ with high melting point, which slow down the slag infiltration. As a result, the order of slag infiltration depth: high SiO₂ slag>high Fe₂O₃ slag>high CaO slag. In contrast, heat treatment of the material can significantly reduce the reactivity of CaO in the matrix, microporation can be achieved, and the infiltration behavior of slag is inhibited, especially the infiltration of high SiO₂ slag is significantly reduced. The corrosion resistance of static crucible slag is related to the infiltration behavior of slag liquid. Because of the obvious infiltration behavior of slag, the corrosion index of slag is reduced. After the high CaO slag reacts with the sample, the viscosity of slag liquid increases, and the calcium aluminate phase with high melting point is formed to slow down the penetration of slag liquid, and the time for slag to act on the material interface increases, which leads to the high corrosion index of high CaO slag.

Preparation and Properties of Lightweight Insulation Materials of Ceramic Phase Bonded Fly Ash Cenosphere

DONG Bo, MIN Changsheng, CHEN Bo, DENG Chengji, XIE Zhe, YANG Qianqiu, DING Jun, ZHU Hongxi, YANG Xinyu, YU Chao

2022, 41(9):  3315-3323. 

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Potassium feldspar and fly ash cenosphere (FAC) were used as raw materials, and bauxite was used as a texturizer for the preparation of lightweight insulation materials at 900~1 150 ℃ for 1 h in the air atmosphere. The influence law and action mechanism of sintering temperature and bauxite content on the service performance of lightweight insulation materials were studied. The results show that the cold physical properties of lightweight insulation materials are effectively optimized by the increase of sintering temperature or bauxite content. The sample containing 20% (mass fraction) bauxite has the best physical properties after sintering at 1 100 ℃. The bulk density, true porosity, and cold crush strength of sample are (0.97±0.01) g·cm^-3, (63.7±0.5)%, and (9.42±0.21) MPa, respectively. Besides, the sample has good thermal insulation performance with thermal conductivity of 0.147 W/(m·K) at 300 ℃ and thermal conductivity of 0.229 W/(m·K) at 600 ℃. Compared with general lightweight insulation materials, the porous potassium feldspar-FAC lightweight insulation material has excellent service performance and lower preparation cost.

New Functional Materials

Preparation of Ion Imprinted Magnetic Micromotor by Biological Template and Dynamic Removal of Pb²⁺ from Sewage

MA Guihong, ZHANG Qing, GENG Zhong, YU Haibao

2022, 41(9):  3324-3334. 

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Ion Imprinted polymer (IIP) is a traditional material for selective removal of ions, but its low adsorption capacity and high cost limit widely practical application. Exploring a novel material with high adsorption capacity and low cost to capture Pb²⁺ is necessary but very challenging. Herein, a novel Pb²⁺ imprinted Janus magnetic micromotor was successfully fabricated by hydrothermal, impregnation calcination, photoreduction and ion imprinted method using naturally available and low-cost lotus pollen as biological template. Theresults show that the asymmetric spherical micromotor was able to have a highly selective adsorption ability to Pb²⁺ in sewage and the maximum adsorption value reaches 67.12 mg/g. The adsorption process of the kinetics and thermodynamics of Pb²⁺ follow well in line with pseudo-second-order kinetic model and Langmuir isotherm model. In addition, the prepared samples not only have good magnetism for direction control and recycling, but also exhibite excellent reusability in practical application. This work provides an effective strategy for effcient and selective removal of Pb²⁺ from sewage.

Electromagnetic Wave Absorption Performance of Yolk-Shell Structure NiCo/C Composites Derived from MOF

JIN Hongdu, HONG Qu, LIN Jun, LI Jun, LING Yujia, LI Menghe, CHEN Taiping, WEN Huimin, HU Jun

2022, 41(9):  3335-3343. 

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Due to having large surface area and pore volume, the porous metal/carbon composites derived from the metal organic framework (MOF) have attracted widespread attention in the field of electromagnetic wave absorption. In this paper, bimetal NiCo-MOF was synthesized by the solvothermal method, and NiCo/C composite with Yolk-shell structure was prepared by calcination. The effects of different mass ratios of Ni and Co on the absorption performance of NiCo/C composites were investigated by SEM, XRD, Raman spectroscopy and VSM analysis.The results show that with the change of mass ratio of Ni and Co, the absorption performance is changed significantly. The performance of Ni₁Co₁/C composite is the best state, which has a minimum reflection loss of -56.8 dB and an effectively absorbing bandwidth of 5.5 GHz under the frequency of 9.4 GHz. By analyzing the absorption mechanism, it is found that multiple reflection, interfacial polarization loss, natural resonance and exchange resonance are the important reasons for improving the absorption performance of the composite. It provides an inspiring method for the preparation and properties of nano-porous bimetal MOF composites.