Table of Content

15 December 2020, Volume 39 Issue 12

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Research and Application Progress of Ce-Y(Ca)-TZP Ceramics and Ce-TZP/Al₂O₃ Composite Ceramics

LI Nan, XIE Zhipeng, YI Zhongzhou, ZHAI Fengrui

2020, 39(12):  3729-3742. 

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Ceria-stabilized tetragonal zirconia polycrystalline ceramics (Ce-TZP) have excellent low temperature degradation (LTD) resistance and high fracture toughness (K_IC>20 MPa·m^1/2). However, its application has been limited by the low flexual strength (~500 MPa). How to improve the strength of Ce-TZP ceramics while retaining their LTD resistance and high fracture toughness is a common concern. As revealed by large amounts of research works, by adding other solutes (such as Y³⁺) for co-stabilization and introducing an immiscible second phase (such as Al₂O₃) for grain refinement, the flexural strength of Ce-TZP ceramics can be improved significantly, and their mechanical properties can be comprehensively improved. In this paper, the research progress of ZrO₂ co-stabilized by CeO₂ and other oxides, and Ce-TZP/Al₂O₃ composite ceramics was reviewed, and their applications were introduced by taking dental implant and additive manufacturing as examples.

Review on Mechanical Properties and Durability of Seawater and Sea-Sand Concrete

LI Shicai, YU Yong, JIN Zuquan

2020, 39(12):  3743-3752. 

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Problems such as corrosion of reinforced concrete, lack of river sand and fresh water cause difficulties in the construction of offshore projects. Due to the rich resources of seawater and sea-sand, experts and scholars at home and abroad put forward to use seawater and sea-sand instead of fresh water and river sand to prepare concrete. Workability, mechanical properties and durability of seawater and sea-sand concrete were studied. Chlorine salts of seawater and sea-sand accelerate the setting and hydration of cement, leading to early setting and increasing the early strength of the concrete. However, the strength of seawater and sea-sand concrete grows slowly in the later period, and its final strength is similar to that of ordinary concrete. A small amount of shells in sea-sand has little effect on the workability and mechanical properties of concrete. Different from doped chloride ion, the mechanisms of chloride transmission and binding capabilities of seawater and sea-sand concrete are more complex. As a result, the mechanism of reinforcement corrosion in seawater and sea-sand concrete is changed. However, supplementary cementitious materials, compound rust inhibitor and fiber reinforced polymer bar provide guarantee for the application of seawater and sea-sand concrete structures.

Review on Effect of Mineral Admixture on Concrete Creep

HAN Chao, HE Zhihai, ZHAN Peimin, ZHANG Xiaoxiang, WOLDERUFAEL Yirgalem Fissiha

2020, 39(12):  3753-3762. 

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Mineral admixture is one of the main measures to improve the properties of concrete, which has attracted the widespread attention of researchers. At present, a large number of studies have shown that the incorporation of mineral admixtures has a positive effect on the creep of concrete, but there is a lack of literatures to review and compare the effect of different types of mineral admixtures on creep of concrete. From the creep mechanism, the effects of single and compound mineral admixtures on creep of concrete, etc., the literatures were summarized and analyzed in order to provide references for further research.

Effects of Retarders on Hydration and Properties of High-Belite Calcium Sulphoaluminate Cement

TANG Ruifeng, WANG Ziming, LAN Mingzhang, CHEN Zhifeng

2020, 39(12):  3763-3769. 

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High-belite calcium sulphoaluminate (HB-CSA) cement is a new type of low-carbon cement with low shrinkage characteristics. Aiming at the problem that the setting and hardening of HB-CSA cement is difficult to control, the effects of two retarders, aminotri methylenephosphonic acid (ATMP) and sodium gluconate (SG), on the hydration and retardation response of HB-CSA cement were investigated. Each of the retarder compounded has a different effect on the early-age hydrate assemblage, as shown by quantitative X-ray diffraction, thermal conductivity isothermal calorimeter, scanning electron microscopy. The results show that ATMP significantly retards hydration of HB-CSA cement, prolongs the setting time, and improves HB-CSA cement mid-late strength, while the retardation effect of SG is limited. The combination of two retarders with PCE delays the hydration heat release rate differently to inhibit the early hydration product (ettringite)-forming reaction. Furthermore, the morphology of ettringite is altered depending on the type of retarder used.

Effect of Triethanolamine Maleate on Cement Hydration

JI Xuping, JIANG Yaqing, ZHANG Fengchen, PAN Tinghong

2020, 39(12):  3770-3774. 

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In order to overcome the negative effect of triethanolamine on the flexural strength and later strength of cement, triethanolamine maleate was synthesized, and the hydration degree, the amount of C-S-H and the 28 d fractal dimension of cement hydration products were studied through BSE and BET analysis. The results show that triethanolamine maleate promotes the hydration of cement, especially the silicate phase in cement. The addition of triethanolamine maleate and polycarboxylic acid water reducer significantly increases the amount of C-S-H in cement hydration products. Triethanolamine decreases the fractal dimension of cement stone at the age of 28 d.The effect of mixing triethanolamine maleate alone and mixing triethanolamine maleate and polycarboxylic acid water reducer together increase the fractal dimension of cement stone at the age of 28 d. It can be seen that triethanolamine maleate has broad application prospects as an enhanced cement early strength agent.

Water Transport and Permeability Coefficient Calculation for Unsaturated Cement-Based Materials Based on X-CT

YANG Lin, ZHANG Yunsheng, ZHANG Chunxiao

2020, 39(12):  3775-3782. 

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The technique of X-CT combined with Cs ion enhancing was used to detect the movement of water transport in unsaturated cement-based materials. From that, the relationship between the distance of water uptake and exposed time was established, and the capillary coefficient was obtained. What’s more, a theoretical model for calculating the intrinsic permeability coefficient based on capillary coefficient and pore structure was provided. Effects of water to cement ratio, fly ash content, ground granulated blast furnace slag content and volume fraction of sand on the capillary coefficient and intrinsic permeability coefficient were investigated systematically. The results show that the capillary coefficient increases from 2.07×10^-4 m/s^1/2 to 3.22×10^-4 m/s^1/2 with the water to cement ratio increasing from 0.35 to 0.55, and the intrinsic permeability coefficient increases by one order of magnitude. The addition of fly ash effectively decreases the property of water transport in cement paste, and the ideal content is 30% (mass fraction). The intrinsic permeability coefficient of cement paste with 30% (mass fraction) ground granulated blast furnace slag is one order of magnitude higher than that with 30% (mass fraction) fly ash. For water transport in mortars, both of the capillary coefficient and intrinsic permeability coefficient decrease with the sand volume fraction increasing from 0% to 40%. It also concludes that the ITZ of mortar connect completely when the volume fraction of sand comes up to 42.4%.

Effect of Fly Ash Content on Properties of PVA-ECC

LI Xiaoqin, ZHOU Xu, LI Shihua

2020, 39(12):  3783-3790. 

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The mechanical properties, toughness and impermeability of polyvinyl alcohol fiber reinforced cement-based composites (PVA-ECC) were studied by replacing part of cement (40%, 50%, 60% and 70% (mass fraction)) with fly ash. The correlation between the compressive strength of PVA-ECC and its ultimate tensile strength, bending load, flexural toughness index, deflection and impermeability was established. At the same time, the relationship between the compressive strength of PVA-ECC and its ultimate tensile strength, bending load, flexural toughness index, deflection and impermeability was established statistical data probability distribution analysis. The results show that with the increase of fly ash content, the strength decreases gradually, the ultimate tensile strain increases, the toughness index, energy absorption capacity and mid span deflection increase gradually, the impermeability of each group is improved compared with the 40% fly ash content group. The correlation between compressive strength and other indexes is established, and a complete correlation theoretical system of strength, toughness and impermeability is obtained. The normal distribution is used to analyze the frequency distribution histogram of water seepage height of PVA-ECC, and the probability distribution of seepage height is obtained, and the 95% confidence interval of the average seepage height is calculated.

Experimental Study on Interfacial Bonding Property of New and Old Cement Mortar

MENG Fanqiang, XUE Shanbin, ZHANG Peng, WANG Junjie, GAO Shizhuang

2020, 39(12):  3791-3798. 

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Under the load and environmental factors, concrete structures suffer from varying degrees of deterioration. In order to ensure the safety and durability of the structures, it is necessary to repair the damaged cement-based materials. The bonding strength between repair mortar and matrix was influenced by the moisture state of old mortar, the roughness of interface, the water cement ratio of repaired mortar and the curing condition. Old mortars with different moisture states (0%, 30%, 70% and 100%) were selected as the matrix and then new mortars with water cement ratio of 0.4 and 0.6 were poured. The composite specimens were cured in sealing condition for 28 d. The shear test results show that when the water cement ratio of new mortar is 0.6 and the moisture states of old mortar change in the order of 70%, 30%, 100%, 0%, the shear strength gradually decreases. When the water cement ratio of new mortar is 0.4 and the moisture states of old mortar change in the order of 30%, 0%, 70%, 100%, the shear strength gradually decreases. Moreover, when the water cement ratio of new mortar is 0.4, the interfacial shear strength is generally greater than that when the water cement ratio of new mortar is 0.6. The interfacial roughness was changed by grooving method, and then the new mortar with water cement ratio of 0.6 was poured. The composite specimens were cured in standard condition. The shear test results show that when the interface is rough, the shear strength is 1.26 times of that when the old mortar is smooth. Old mortars with different moisture states (0% and 100%) were selected as the matrix and then new mortars with water cement ratio of 0.4 and 0.6 were poured. The specimens were cured in sealing and standard condition respectively. The experimental results show that when the moisture states of old mortar and water cement ratio of new mortar are the same, the shear strength in standard condition is obviously higher than that in sealing condition.

Characterization of Gas Permeability of Hardened Cement Paste

SONG Yang, LI Jinyuan, LI Junfeng, CHEN Wang, WU Haiyang

2020, 39(12):  3799-3805. 

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Permeability directly determines the transport speed of harmful substances in porous volume of cement-based materials (such as concrete). Thus, it is the key to influence the durability of cement-based materials. Based on 3D pore structure and MIP (Mercury intrusion porosimetry) result of cement paste, the permeability of cement paste was calculated by Katz-Thompson equation and lattice Boltzmann method (LBM), respectively. Then, the calculated values were compared with those by gas permeability test. Results show that the tested gas permeability of cement paste is of 3.82×10^-18 m² to 7.29×10^-18 m². The Katz-Thompson equation only has the accuracy of order of magnitude and cannot accurately predict the permeability of cement paste. In contrast, the lattice Boltzmann method accurately predicts the intrinsic permeability of cement paste, 4.88×10^-19 m² to 15.48×10^-19 m², which is about 2 to 10 times smaller than the tested ones. This implies that the capillary pores in cement paste are still the main path of gas flow, whereas the air holes and micro cracks only locally improve the gas permeability.

Effect of New Composite Early Strength Agent on Mechanical Performance of Cement Mortar

LIU Chunying, REN Guosheng, GAO Xiaojian

2020, 39(12):  3806-3811. 

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In this paper, the effects of two new composite early strength agents (calcium formate-crystal embryo and methacrylic acid-crystal embryo) on the fresh properties and mechanical performances of cement mortar were studied, and the samples were micro-analyzed by X-ray diffraction (XRD) and scanning electron microscope (SEM). The results show that with the increase of the early strength agent content, the fluidity of the fresh cement mortar decreases slightly, and the setting time advances. Both two composite early strength agents accelerate the early hydration of the cement and significantly improve the early strength of the cement mortar. Calcium formate-crystal embryo and methacrylic acid-crystal embryo composite early strength agents increase the 12 h compressive strength of cement mortar by 96.7% and 89.3%, and the flexural strength by 192.2% and 211.1%, respectively. At the same time, the 28 d compressive strength of cement mortar still increases by about 50.0%, indicating that the two types of early strength agents have no negative impact on the later strength development of cement mortar. XRD and SEM analysis both confirm that adding two kinds of composite early strength agents improve the hydration degree of cement, increase the hydration products, and improve the structure compactness.

Analysis of Major Influence Factors and Multi-Factor Calculation Model of Abrasion Resistance of Manufactured Sand Concrete

XIE Jicheng, ZHANG Yun, DU Yueming, CHEN Zheng, LUO Tingyi, TANG Yasen

2020, 39(12):  3812-3822. 

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The influences of sand type, sand rate, stone powder content and compressive strength on the abrasion resistance of manufactured sand concrete were studied and a multi-factor calculation model of abrasion loss was established. The results show that the abrasion resistance of C30 and C40 concrete prepared from limestone manufactured sand and diabase manufactured sand increase by more than 20% compared to that of river sand because manufactured sand has stone powder, higher roughness and soundness. Better abrasion resistance of concrete obtains by selecting lower sand rate in the range of 0.40 to 0.44. The concrete is prepared by using the manufactured sand with 5% to 11% (mass fraction) stone powder content, and the abrasion resistance of concrete shows the best when the stone powder content is 9%, because the compactness of concrete achieves the best at this time through microscopic analysis. The grey system theory is utilized to determine the influence degree of the factors affecting the abrasion resistance, and the influence degree is ranked as follows: sand rate R₃> crushing value R₂> roughness R₁> compressive strength R₅> stone powder content R₄>0.6. The comparison and verification indicate that the proposed multi-factor calculation model of the abrasion loss of concrete has higher prediction accuracy and more excellent applicability.

Stress-Strain Test of Manufactured Sand Concrete

XIE Kaizhong, LIU Zhenwei, GE Bingzhou, ZHU Maojin, XIN Ying

2020, 39(12):  3823-3831. 

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In order to study the mechanical properties of manufactured sand concrete (MSC) under uniaxial load. The prism specimens of MSC were tested with the stone powder content (0%, 4%, 8%, 12%, 16% and 20%, mass fraction) and the concrete design strength grade (C20, C30 and C40) as variable parameters the compressive complete stress-strain curves were investigated and the uniaxial compression constitutive equations of MSC were fitted, compared with the river sand concrete(RSC). The results indicate that the stress-strain curves of MSC are similar with that of RSC. In the rising stage of the curve, MSC and RSC have basically coincident curve. However, in descending stage, the curves of MSC are much steeper than RSC. In addition, the peak stress and peak strain of the MSC specimens increase firstly and then decrease with the increase of stone powder content. When the mass fraction of stone powder is 8%, the peak strain of three different strength grades of MSC reaches the maximum value. The peak stress and elastic modulus of MSC increase with the increase of concrete design strength grade. The complete stress-strain curve of MSC based on the model of Sargin is in good agreement with the test curve.

Effect of Sand Combination on Strength of UHPC Based on Toufar Model

LIN Xiaosong, HUANG Zhibin

2020, 39(12):  3832-3836. 

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In order to investigate the influence of sand gradation on the strength of ultra-high performance concrete (UHPC), sand was divided into 5 grades by screening test, and the particle size ranges of grade 1 to grade 5 of sands are 1.25 mm to 2.5 mm, 0.63 mm to 0.63 mm, 0.315 mm to 0.63 mm, 0.16 mm to 0.315 mm and 0.08 mm to 0.16 mm, respectively.Based on the test data of sand combination of 3&4 and 3&4&5, the Toufar model was modified and verified, respectively.Then, the modified Toufar model was used to determine the maximum characteristic compactness of 4&5, 2&3&4&5 and 1&2&3&4&5. The four kinds of sand combinations (4&5, 3&4&5, 2&3&4&5, 1&2&3&4&5) were used in the mix proportion design of UHPC, and their strengths were measured. The research results show that the modified Toufar model can be used to calculate the maximum characteristic compactness of sand combination and the mass ratio of different grade of sands in UHPC mix proportion design. When the mass ratio of 3, 4 and 5 grade of sands is 1:0.35:0.473, the compactness of the sand combination is the maximum, and the correponding flexural strength and compressive strength of UHPC are the largest.

Anti-Early Plastic Cracking Properties of Concrete Bridge Deck Pavement with Internal Curing

XIE Zhengzhuan, ZHOU Shengbo, WEI Wanfeng, LIU Weidong, JIAO Xiaodong, WANG Bin

2020, 39(12):  3837-3843. 

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In order to improve the anti-early plastic cracking properties of concrete bridge deck pavement. Influence of internal curing materials on the anti-early plastic cracking properties of concrete was investigated with slab restraint method and on-site entity engineering of bridge deck pavement. The results indicate that internal curing materials effectively delay the early cracking of concrete, and theanti-early plastic cracking properties of concrete are improved with the increase of the content of internal curing materials. When the content of internal curing materials is 0.2% (mass fraction), the unit cracking area of concrete decreases from 1 219 mm²/m² to 47 mm²/m² through the slab restraint method. Compared with ordinary concrete, the number of cracks, maximum length, maximum width, and cracked area per unit area decrease by 91.7%, 55.8%, 37.5%, 90.7% with 0.2% internal curing materials, the internal curing materials significantly improve theanti-early plastic cracking properties of concrete bridge deck pavement.

Stress-Slip Model of Steel Bar for Freeze-Thaw Concrete in Severe Cold Regions and OpenSEES Finite Element Simulation

WU Wei, FENG Hu

2020, 39(12):  3844-3850. 

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On the basis of the local bond-slip model of freeze-thaw concrete and steel bar in severe cold regions, based on the analysis of the force mechanism of steel bar along anchorage length in the freeze-thaw concrete and the analysis of the iterative process, a calculation method for the steel bar stress-slip in the freeze-thaw concrete was established. The skeleton curve of stress slip relationship for steel bar in freeze-thaw concrete was proposed. Then, based on the finite element calculation software OpenSEES, the deduced stress-slip curve of steel bar in the freeze-thaw concrete was nested in the zero-length section element, and the element was applied to the beam column fiber model. The three existing freeze-thaw reinforced concrete frame columns were simulated and then compared with the test results. The results show that the numerical results of the freeze-thaw reinforced concrete column finite element model are in good agreement with the test results. It is verified from the component level that the deduced stress-slip curve of steel bar in the freeze-thaw concrete has good accuracy and reliability. The research results provide a theoretical reference for the derivation and finite element simulation for the stress slip of steel bar in freeze-thaw concrete in severe cold regions.

High Temperature Performance of Graphite Modified Concrete

ZHENG Huijun

2020, 39(12):  3851-3857. 

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The influence of graphite and graphene oxide combined with basalt fiber on the high temperature performance of concrete was studied by mechanical properties and microstructure of concrete after heat treatment. The results show that the addition of graphite reduces the mechanical stability of concrete, while graphene oxide greatly improves the mechanical stability of concrete and effectively reduces the deterioration effect of heat treatment. The combination of basalt fiber with graphite and graphene oxide not only fails to form a synergistic effect, but also reduces the mechanical properties of the specimens. The micro-analysis show that graphite disperses in the material system formed interface transition zone defects, but graphene oxide forms a close and continuous cross-linking structure in the material system, which effectively improves the high temperature mechanical properties of concrete.

Analysis of Basalt Fiber Raw Material Characteristics

LIU Changjiang, TONG Xiaocong, LIU Zhong, YANG Chuncheng, LI Hongchao, JIANG Letao

2020, 39(12):  3858-3865. 

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Basalt fiber is a kind of continuous fiber material prepared by melting and followed fast drawing process from raw basalt ore, whose properties depend strongly on its raw materials, and not all of basalt is suitable for fiber production.The present work aims to provide useful information for the optimization and standardization of the raw materials for basalt fiber production. Based on the chemical composition of 14 fibers and 20 rocks, the characteristics of chemical components, mineralogy, lithology, melt properties and structure were analyzed comprehensively in this work. A series of limited conditions, including classes and molar fraction of the oxide components, acidity coefficient, mineral composition, types of alkaline rocks, saturation of alumina, relations between depolymerization degrees and viscosity of the melts were generalized. The result shows that the amorphous or cryptocrystalline, calc-alkaline, and metaluminous rock composed of plagioclase and clinopyroxene without quartz, olivine, corundum is suitable for fiber production. Moreover, oxides molar fraction and acidity coefficient of the raw rock are RO₂=0.58 to 0.75, R₂O₃=0.15 to 0.20, RO=0.18 to 0.30 (R stands for cations), and 3.5 to 5.8, respectively. For the silicate melts, NBO/T is 0.2 to 0.4, and lgη is 0.5 Pa·s to 1.4 Pa·s, respectively.

Strength Influence Analysis of Slag-Cement-Unclassified Tailings Cemented Filling Based on Stepwise Regression Analysis

ZHANG Shengyou, SUN Wei, LI Jinxin

2020, 39(12):  3866-3873. 

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In order to reduce the filling cost of a copper mine, the influence of single factor or multi factor interaction on the strength of filling body was explored. 24 groups of different proportions were designed to analyze the influence of slag content, mass concentration and cement-sand ratio on the uniaxial compressive strength of filling specimens. The slag content, mass concentration and cement-sand ratio were set as the explanatory variables X₁, X₂, X₃ respectively, and the uniaxial compressive strength was set as Y, and the experimental data was stepwise regression analyzed by software SPSS,and the accuracy of regression was verified by response surface method. The results show that: slag content and uniaxial compressive strength of specimens are positively correlated, the higher the cement-sand ratio, the greater the strength growth. The maximum growth rate of 28 d strength is 138.2%. The influence weight of single element on uniaxial compressive strength is mass concentration and cement-sand ratio, and slag content has no significant influence. Two or more factors have influence on uniaxial compressive strength under the interaction, only the slag content and cement interaction have a significant effect on the strength. The equation expressions of the two methods are basically consistent, which proves the reliability of the regression. The regression fitting degree is 97.76%, and the fitting value is very close to the experimental value, so the regression equation can be applied to the filling experiment of the mine.

Effect of Glass Powder on Mechanical Properties of Recycled Concrete

YANG Zhenying, ZHOU Changshun

2020, 39(12):  3874-3880. 

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In order to realize the recycling of waste glass, a kind of solid waste in the urban area, this paper studied the mechanical properties such as compressive strength, splitting tensile strength and elastic modulus of recycled concrete with different content (0%, 5%, 10% and 20%, mass fraction) of glass powder (GP) in cement. The internal microstructure of recycled concrete was analyzed by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). The results show that glass powder reduces the mechanical properties of recycled concrete in the early stage, but the addition of an appropriate amount of glass powder is beneficial to improve the mechanical properties of recycled concrete in the later stage. The compressive strength, splitting tensile strength and elastic modulus of the sample containing 10% (mass fraction) glass powder at 90 d are higher than that of ordinary recycled concrete, and the total porosity reduceds by 19.3%. The secondary pozzolanic activity of glass powder and the filling effect of micro-aggregates improve the microstructure of recycled concrete.

Preparation of Rice Husk Ash and Its Effect on Mechanical Properties of Geopolymer

LIU Zhenzheng, XIE Chunlei, WANG Xueying, GUO Liang, WU Yueyue, CHEN Qin, DUAN Ping

2020, 39(12):  3881-3888. 

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Using rice husk (RH) as raw material, the differences of properties and structures of rice husk ash (RHA) prepared under different treatment conditions and the effects on the mechanical properties of metakaolin-based geopolymer were studied. The optimum preparation conditions of RHA were determined. The results show that hydrochloric acid pretreatment significantly improves the purity of amorphous SiO₂ in RHA as high as 98.354% (mass fraction). The RH pretreated by acid is calcined completely by calcining 60 min at 550 ℃ and the reaction activity of RHA is the highest. RHA treated by acid makes the pore structure of geopolymers denser and the 28 d compressive strength of 550 ℃ RHA geopolymer (10% (mass fraction) RHA+90% (mass fraction) metakaolin) is the highest, which is 53.3 MPa. Through comprehensive impact analysis, the optimum preparation conditions of RHA are as follows: immersed in 2.5% (mass fraction) hydrochloric acid for 1 h and calcined at 550 ℃ for 1 h.

Experimental Study on Proportion of Room Temperature Alkali-Activated Low-Calcium Fly Ash Geopolymer

WEI Wei, GAO Yanbin, CHEN Zhongqing, ZHU Wentao, ZHU Zewei

2020, 39(12):  3889-3896. 

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In order to investigate the influence of the mass ratio of fly ash to alkali activator, the mass ratio of water glass to sodium hydroxide solution, and the molar concentration of sodium hydroxide solution on the mechanical properties of fly ash geopolymer at room temperature, low-calcium fly ash were used as raw material to prepare geopolymer cementing material. Orthogonal test method was used to analyze the compressive strength of fly ash geopolymers and to discuss the influence of the ratio of alkali activator on the mechanical properties of fly ash geopolymers. SEM, XRD and FTIR were also carried out to characterize the geopolymer samples, and the stress-strain relationship of the material was studied. The results show that the compressive strength of fly ash geopolymer increases with the decrease of activator content, and the ratio of water glass in activator is positively correlated with the compressive strength. When the mass ratio of fly ash to alkali activator is 1.8, the mass ratio of water glass to sodium hydroxide solution is 2.5, and the concentration of sodium hydroxide solution is 10 mol/L, the compressive strength of the obtained geopolymer after curing for 120 d reaches to 51.98 MPa. The stress-strain curves show that the amount of activator has a greater impact on the failure strain and elastic modulus of fly ash geopolymer to some extent. Moreover, the results of SEM, XRD and FTIR show that the structure of the cementitious material system become denser with the increase of curing time, and more aluminosilicate gels are mainly generated.

Excitation Pretreatment of Phosphogypsum and Preparation of Non-Burning Building Materials

TIAN Jiayu, WANG Haifeng, YOU Xiaoyu, CHEN Xiaoliang, WANG Jiawei

2020, 39(12):  3897-3904. 

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Phosphogypsum has poor cementitious activity, which hinders its large consumption in the field of building materials. By studying the phase and microstructure of phosphogypsum pretreated by alkali excitation, and the compressive strength, phase and microstructure of the non-burning building materials prepared with the high content phosphogypsum, the process parameters of preparing high content and high compressive strength non-burning building materials with phosphogypsum were obtained. The result shows that, when 100 g phosphogypsum is added with 100 mL activator, after 24 h of excitation under room temperature, the main crystalline phase CaSO₄·2H₂O of phosphogypsum has smaller grains and lower crystallinity. Microstructure analysis shows that the size of calcium sulfate particles increases and the amount of fine particles decreases significantly after pretreatment. Thus, its gelation activity is improved. When the content of phosphogypsum is 80% (mass fraction), compared with the untreated phosphogypsum, the compressive strength of the prepared non-burning building materials after maintening for 7 d, 28 d and immersion in water are significantly improved, which are 13.79 MPa, 18.22 MPa and 11.44 MPa, respectively. Its micromorphology shows that there is no obvious boundary between the calcium sulfate particles, they are almost integrated with high density, which is very beneficial to the strength of the materials.

Influence of Temperature on Carbonation Effect of Refining Slag

FANG Minghang, YI Yuanrong, MA Wenqing, MA Zhongle, BAI Shuqi, LIN Yue, DU Yuncong

2020, 39(12):  3905-3912. 

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With the orthogonal tests, the refining slags carbonation process to improve their stability and compactness effectively were researched. In the experiments in which the temperature was the dependent variable, the size distribution of carbonation was investigated. XRD, SEM, FT-IR, and TG-DTA were used to study the refining slags carbonation effect. The results show the factors in the carbonation of refining slags with descending significance: particle size, CO₂ ventilation, reaction temperature, rotating speed, and liquid-solid ratio. After carbonation, f-CaO, Ca₂SiO₄, Ca₃SiO₅, and 12CaO·7Al₂O₃ in the refining slags disappeare, which are replaced with calcite-dominated crystalline CaCO₃. After carbonation at different temperatures (20 ℃, 40 ℃, 60 ℃, and 80 ℃), the total percentage of weight loss in the thermal decomposition of refining residue are 35.26%, 35.24%, 34.36%, and 27.29%, respectively.

Study on Preparation of Sodium Silicate from Red Mud

SHI Guoyi, PAN Aifang, MA Yuzhao, SUN Yue, CHANG Jie, YANG Ling, DUAN Yuyu

2020, 39(12):  3913-3917. 

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In order to extract and utilize the silicon element in red mud, a new raw material was found for the preparation of sodium silicate. In this paper, the chemical composition and mineral composition of red mud of Chalco Shanxi New Materials Co., Ltd. were analyzed by chemical analysis and XRD. The results show that the red mud is an ideal silicon source for the preparation of sodium silicate, because of its high content of amorphous silica and high reactivity. Silica gel with purity of 92% is obtained by acid leaching red mud. The optimum technological parameters of sodium silicate prepared by silica gel wet method are NaOH mass concentration of 15%, liquid-solid mass ratio of 3, system temperature of 95 ℃, reaction time of 15 min. The dissolution rate of silica under the optimal parameters is 91%, and the utilization rate of silicon in the red mud is 84.6%. This study provides a new idea and basis for the resource recovery of red mud and raw material selection of sodium silicate.

Experiment and Kinetics of Dealkalization from Red Mud by Leaching with Titanium Dioxide Waste Acid

ZHU Xiaobo, WANG Tao, LI Wang

2020, 39(12):  3918-3923. 

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Red mud is a tailing produced during alumina smelting of bauxite, in which the content of free alkali and structural alkali is high. Titanium white waste acid is the acid waste liquid produced during the production of titanium white powder by vanadium-titanium magnetite, which contains a large amount of sulfuric acid. According to the strong basicity of red mud and the acidity of titanium dioxide waste acid, the dealkalization from red mud by leaching with titanium white waste acid was put forward. The effect of stirring rate, liquid to solid ratio, leaching temperature and leaching time on dealkalization rate were investigated. Furthermore, the theoretical analysis and leaching kinetics of the process of red mud demineralization were studied with X-ray diffraction (XRD) and the unreacted shrinking core model (USCM). The results show that the dealkalization rate of red mud is higher than 99% and the pH value of the leaching solution is 6.2 under the conditions of leaching temperature of 70 ℃, stirring rate 400 r/min, liquid to solid ratio 5 mL/g and reaction time 60 min. The leaching process of red mud with titanium white waste acid not only achieves the high demineralization rate, but also enriches the iron grade in the demineralization residue, which is used as a secondary mineral resource for extraction and recovery of iron. The titanium white waste acid significantly destroies the crystal structure of cancrinite in the red mud, which results in complete dissolution of the alkali. The diffraction peaks of anhydrite and hematite are obvious in the demineralization residue according to the analysis of XRD. The leaching process is controlled by the internal diffusion by the analysis of leaching kinetics, and the linear correlation coefficient is more than 0.99. The rate constant increases with the increase of temperature and the apparent activation energy (E_a) is 13.12 kJ/mol.

Influence of Basalt Fiber on Properties of Traditional Sticky Rice-Lime Mortar and Its Mechanism Analysis

YANG Lingming, ZHANG Weixiang, ZHOU Shaoqing

2020, 39(12):  3924-3931. 

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Application of sticky rice-lime mortar (SRLM) in the restoration of ancient buildings is restricted by its properties of early strength, shrinkage and freeze-thaw. The influence of basalt fiber content and sticky rice paste concentration on the mechanical properties of sticky rice-lime mortar and its mechanism were studied by means of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that the position, size and morphology of calcium carbonate crystals are controlled by sticky rice paste concentration, and has a great influence on the early strength, shrinkage, temperature resistance, freeze-thaw properties of sticky rice-lime mortar. The mechanical properties are the best when the mass fraction of sticky rice paste is 6.5%. Characteristics of cavity structure and mini-diameter of the basalt fiber improves the mechanical properties of sticky rice-lime mortar. The 28 d compressive strength and flexural strength increase by 436% and 150%, respectively, 7 d shrinkage rate decreases by 65%, and the freeze-thaw times increase obviously. Basalt fiber sticky rice-lime mortar has the best comprehensive performance when the mass fraction of basalt fiber is 5%. In practical application, it is feasible to improve the performance of sticky rice-lime mortar by adding a certain amount of basalt fiber.

Research on Coal-Series Kaolin Micropowder Prepared by Ultrasonic Assisted Intercalation-Exfoliation Method

ZHANG Tao, YAN Lei, GONG Keyu, LI Jiaquan, HE Hongwei, MIAO Yang, GAO Feng

2020, 39(12):  3932-3938. 

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Chinese coal-series kaolin is rich in reserves. To meet the needs of industries such as papermaking and textiles, it usually needs to be further processed. The optimum conditions for the preparation of coal-series kaolin/DMSO intercalated composites were explored using Shanxi Shuozhou coal-series kaolin as raw materials under constant temperature magnetic stirring and ultrasonic waves. Ultrasonic assisted stripping of coal-series kaolins was carried out on the basis of intercalated composites to prepare kaolin fine powder and XRD, SEM, BET, TG-DSC and other methods were used to analyze and characterize the sample. Orthogonal experimental results show that the amount of DMSO, intercalation time and intercalation temperature all have certain effects on the intercalation rate under magnetic stirring conditions. The ultrasonic wave is beneficial to the process of intercalation of kaolin. The thickness of the grains of the intercalation composites after ultrasonic assisted exfoliation are significantly reduced. The lamellar structure and edges of few kaolinite with large lamellar structure are both fragmented, and the the tendency of cracking is obvious. The specific surface area and pore size of exfoliated sample has been increased twice, providing new ideas for the exfoliation of hard kaolin and the preparation of ultrafine powder.

Adsorption of Mercury in Aqueous Solution by Zeolite Prepared from Coal Fly Ash Using Alkali Fusion-Hydrothermal Method

YAN Kechong, LI Zipeng, LI Yangmin, WANG Pingzhi

2020, 39(12):  3939-3944. 

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Mercury is regarded as one of the most hazardous heavy metals. A variety of water treatment technologies are used to remove mercury in water. However, they may not be achieved large-scale industrial application, largely due to their high implementation costs. In this paper, zeolite was synthesized from industrial solid waste coal fly ash by alkali fusion-hydrothermal method and it was applied to the adsorption of mercury in aqueous solution. The results show that the stable mullite, quartz and amorphous minerals in coal fly ash are transformed into sodium aluminosilicate, sodium silicate and nepheline, which are dissolved in sodium hydroxide solution to form alkaline solution with plenty of sodium, aluminum and silicon. NaA zeolite with high purity is synthesized by adjusting the ratio of aluminum to silicon under a suitable hydrothermal conditions. The zeolite synthesized by this method adsorbs Hg (II) in aqueous solution effectively, and the adsorption removal rate reaches about 95%. The kinetic studies show that the pseudo second-order rate equation fits the experimental data well, and the reaction rate is affected by internal and external diffusion at the same time.

Effects of Calcareous Flocculants on Strength of Cemented Construction Waste Slurry with High Water Content

SONG Miaomiao, ZHU Peng, XU Guizhong, WANG Fengzhen, TANG Peng

2020, 39(12):  3945-3951. 

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In this study, a series of unconfined compression tests were conducted to investigate calcareous flocculant effects on strength behavior of cemented construction waste slurry with high water content containing calcareous flocculants. Changes in strength behavior of cemented waste slurry under different properties and dosage of accelerator were studied. For cemented waste slurry, calcareous flocculants significantly enhance its unconfined compressive strength (q_u), and about onefold increase in the q_u is found at the appropriate content of flocculants. The q_u of cemented slurry at different curing time increases firstly and then decreases with increase in the CaCl₂ content. While for the cemented slurry with Ca(OH)₂, its q_u increases at first, then decreases before the last increase with the increasing Ca(OH)₂ content. Compared with the CaCl₂, the increase in the q_u caused by adding Ca(OH)₂ is relatively smaller at the same content. In addition, the failure strain ε_f and deformation coefficient E50 of cemented slurry vary with flocculant type and content. For cemented construction waste slurry with calcareous flocculants, the equation (E50≈(30~100)q_u) is used to predict the value of E50.

Preparation of Porous Carbon Materials from Construction WasteSawdust

XIE Zhu

2020, 39(12):  3952-3957. 

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In order to study the application of construction waste sawdust in environment protection, nitrogen doped porous carbon materials were prepared by one-step pyrolysis method with NaNH₂ as activator and nitrogen source. The samples were characterized by X-ray diffraction, X-ray photoelectron, N₂ adsorption-desorption isotherm and other methods. It is found that the samples are mainly composed of micropores. Synergism of the large specific surface area and high nitrogen content provide abundant catalytically active sites and CO₂ reactant for electrochemical CO₂ reduction reaction. The electrochemical test suggests that CO is the main product in CO₂ electrochemical reduction, the Faraday efficiency of CO is up to 82% at the overpotential of -0.7 V (reversible hydrogen electrode, RHE). More importantly, the electrolysis can be maintain as long as 18 h. The results indicate that construction waste sawdust derived porous carbons effectively reduce CO₂ and realize the application in the field of environment protection.

Research Progress of Bismuth Ion Doped Cathode Materials for Solid Oxide Fuel Cell

SUN Ning, LIU Xiaowei, LIU Xianglin, JIN Fangjun

2020, 39(12):  3958-3963. 

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Solid oxide fuel cell (SOFC) is one of power generation device which can directly convert chemical energy in fuel into electric energy, with the advantages of flexible fuel selection, high efficiency, and environmental friendliness. Reducing operating temperature has become a hot topic in current research to fulfill the requirement of the running cost and long-term stable operation of solid oxide fuel cell systems. The low catalytic activity of traditional SOFC cathode materials restricts the development of SOFC technology. Therefore, it is very important to develop cathode materials with good catalytic activity. Many studies have shown that bismuth ion doping in materials can effectively improve the conductivity and oxygen catalytic activity. Bismuth ions have unique electronic structure. From the perspective of bismuth ion doping, the effect of bismuth ion doping on the preparation, structure, conductivity and electrochemical performance of cathode materials was reviewed, and development trend of bismuth ion SOFC cathode materials was prospected.

Effect of Glaze Phase Separation on Lead-Free CuO-MnO₂ System Metallic Luster Glaze

CAO Zhimin, LUO Ting, FANG Yijin, WU Junming, LIU Qing, SONG Yawen

2020, 39(12):  3964-3970. 

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The lead-free CuO-MnO₂ system metallic luster glaze was prepared by adding crystallizer CuO and MnO₂ based on calcium raw glaze. The phase composition and microstructure were characterized by XRD and SEM-EDS, and the influences of adding TiO₂, V₂O₅ and glass powder on the phase separation of metallic luster glaze were systematically investigated. The results show that a certain amount of TiO₂ and V₂O₅ effectively promotes the phase separation of the glaze.The high temperature viscosity of the glaze melt is reduced by partially replacing the potassium feldspar in the base glaze with glass powder, further aggravates the glaze phase separation, promotes the precipitation and enrichment of CuMn₂O₄copper manganese spinel on the glaze surface. When the amount of TiO₂ is 2%, V₂O₅is 1%, and the amount of glass powder is 25% (both are mass fraction), the effect of glossy glaze is the best.

Preparation and Microstructure Characterization of Flower Shaped Crystalline Glaze

WANG Chao, ZHANG Li

2020, 39(12):  3971-3976. 

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In view of the traditional problems of crystalline glaze, such as high sintering temperature, long holding time and difficult continuous production, crystalline glaze of K₂O-Na₂O-CaO-ZnO-SiO₂-Al₂O₃ system was successfully prepared at 1 220 ℃. Ceramic raw materials such as potassium feldspar, calcite, zinc oxide and glass powder were used in the experiment. The effects of kiln cooling system and coloring agent on glaze surface were mainly studied. The results indicate that during the cooling process of 3 h “heat preservation” at fixed1 100 ℃, the combination of 2% (mass fraction) NiO and 2% (mass fraction) CuO makes the surface of glaze produce coarse grains. These grains are about 4.5 cm in diameter with white flower lace and green inner clusters. While during the cooling system of “slowly cooling” rate of 125 ℃/h, beautiful and natural plum blossom shaped crystals are also generated, which present in a micro size of 8 mm and display internal green radial clusters and clear boundaries. By the combining use of field emission scanning electron microscope(FESEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) analysis, the microstructure and chemical composition were investigated. It is found that there are internal hexagonal columnar and acicular isomorphic zinc silicate crystals in the plum blossom crystal. Hexagonal columnar crystals are mainly concentrated in the center of plum blossom. Due to the space limitation in the vertical direction of glaze layer, they grew slowly and generally exist in a size of 2 μm. The acicular crystals are mainly parallel to the glaze layer and grew radically toward the petal. There are a large number of nanoscale microsphere structures in the amorphous glass phase of bottom glaze, which present the effect of green opacification. The pairwise combinations of Fe₂O₃, CuO, MnO and NiO make the ceramic glaze present a multi-color and variable crystallization effect, the combination of Fe₂O₃ and MnO, NiO and CuO are best.

Fabrication of Hydroxyapatite-Modified Ag⁺ and Its Property for Defluorination and Bacteriostasis Activity

ZHAO Jinyun, HU Jiapeng, LIN Hao, LIU Ruilai, LIU Junshao, FU Xingping, MU Jilin

2020, 39(12):  3977-3984. 

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Hydroxyapatite-modified Ag⁺ (Ag-HAP) adsorbent was prepared by in-situ co-precipitation method. The effect of Ag⁺/Ca²⁺ molar ratio on defluorination and bacteriostasis was investigated. The infrared spectroscopy and XRD results show that Ag⁺ displaces Ca²⁺ into HAP lattice, forming a new Ag⁺-Ca²⁺ lattice.Both models including Langmuir and Freundlich can predict experimental data conducted. However, Langmuir model has better correlation coefficient than Freundlich model. The adsorptions of fluoride on Ag-HAP adsorbent are more agreeable with monolayer adsorption mode. The thermodynamic and kinetics parameters of adsorptions were obtained. The ΔG⁰＜0, ΔH⁰＞0 and ΔS⁰＞0 indicate that adsorption of fluoricle is a spontaneous and endothermic process with increased entropy, and an increase in temperature benefits adsorption. Activation energy of adsorption E_a=12.645 kJ/mol and migration energy E=7.331 kJ/mol indicate that adsorption is mainly physical adsorption. Kinetic adsorption data show that adsorption process follows the pseudo-second-order kinetic. The dynamic adsorption process of Ag-HAP adsorbent for defluorination and bacteriostatic inhibition was simulated by using a bibcock type water purifier. The bacteriostatic experiments show that the addition of Ag-HAP adsorbent greatly improves the bacteriostatic performance of drinking water.

Grinding Force and Surface Quality of Inner Circle of Ceramic Bearing Outer Ring

HAO Huiling

2020, 39(12):  3985-3990. 

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In order to explore the grinding force of the inner circle of the ceramic bearing outer ring (abbreviated as outer circle) and the influence mechanism of the grinding force on the surface quality, firstly, the influence rules of different grinding parameters on the grinding force of the outer circle were obtained through grinding experiments. Secondly, the relationship among the rotary grinding force, the surface roughness and surface removal method was obtained. The results show that as the wheel speed decreases, the feed rate and the workpiece speed increase, both the normal and tangential direction grinding forces of ceramic cylindrical grinding increase. The normal direction grinding force is about 3 times of the tangential direction grinding force. When the grinding force increases, the grinding surface changes from plastic removal to brittleness removal, the surface roughness value increases, and the surface quality deteriorates. In the cylindrical grinding of ceramic bearings, higher grinding wheel speed, smaller feed rate and workpiece speed are appropriately selected to ensure the surface processing quality and processing efficiency.

Research Progress on Service Life and Physicochemical Properties of Enamel

XUE Hongxi, CUI Yongfeng, XU Kunshan, LIU Jie, LI Zhiheng

2020, 39(12):  3991-3997. 

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Enameled equipment has the advantages of metal strength and high-temperature resistance, corrosion resistance, and easy cleaning of enamel. It is widely used in the pharmaceutical and chemical industries and has become a piece of irreplaceable equipment in the current chemical industry. However, the short service life of enamel and its various properties are far from the expected value. Therefore, it is of great significance to improve the physicochemical properties of enamel and extend its service life by introducing additives. By improving the integrity of the network structure, the chemical stability of enamel is significantly improved. The addition of abrasive additives and hard particles reduces the porosity and friction coefficient, and improves the wear resistance of enamel. The increase of anchor points and dendrites at the interface significantly enhances the adhesion of enamel. The addition of ceramic particles reduces the difference in thermal expansion coefficient, enhances toughness and oxygen resistance, thereby improving the high temperature protection performance of enamel. This paper summarized the research on the influence of additives on corrosion resistance, abrasion resistance, adherence and high temperature protection performance of enamel, and made a summary analysis, which had certain reference value for the subsequent experimental research.

Preparation and Properties of Graphene/Glass Bulk Composites

ZHOU Wentao, LI Jianlin

2020, 39(12):  3998-4002. 

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An in-situ strategy for the preparation of reduced graphene oxide/sodium calcium silicon (rGO/SLS) glass bulk composites using 3-aminopropyltriethoxysilane as a surfactant was reported. GO nanosheets that were negatively charged in an aqueous solution were combined with positively charged glass particles modified by amino groups through electrostatic self-assembly to generate composite particles. Through high temperature vacuum hot press sintering, GO was reduced to rGO, and rGO/SLS bulk composites were in situ produced. Results show that rGO is evenly distributed in the glass matrix and greatly enhances the mechanical properties of rGO/SLS bulk composites. With a 0.5% (mass fraction), addition of rGO in the rGO/SLS bulk composite, the flexural strength of the composite is about double that of pure SLS glass.

Development of High-Purity Dense Zircon for Melting Low-Loss Special Glasses

QIAN Min, ZOU Zhaosong, TANG Jingping, JIANG Yasi, XU Yongchun, HU Lili

2020, 39(12):  4003-4009. 

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High-purity zircon (ZrSiO₄) powders were synthesized by high-temperature solid-phase reaction method, using 99.9% (mass fraction) high purity ZrO₂ and SiO₂ powders as raw materials and small amount of TiO₂ as additive. The effects of temperature and reaction time on the synthesis efficiency of high-purity zircon powders were studied. It is found that the fraction of the ZrSiO₄ phase reaches 95.77% (mass fraction) after the solid-phase reaction is carried out at 1 500 ℃ for 48 h using raw material powders with particle size less than 50 μm. The prepared high-purity zircon powders were used as a raw material, and sintered at a high temperature above 1 550 ℃ after ball milling cold isostatic pressing to form a high-purity dense zircon brick. The concentrations of Fe and Cu impurities in high-purity dense zircon are 29 μg/g and less than 1 μg/g, respectively, which are only 1/10 of those in the commercial high dense zircon samples. The static optical loss of phosphate glass caused by the high-purity dense zircon samples is only 1/3 of that of the commercial high dense zircon samples. Using this high-purity dense zircon material for laser glass furnaces can reduce the optical loss at 1 053 nm and improve the laser performance of laser glasses.

Effect of ZrO₂ on Structure and Properties of Lead Silicon Glass for Microchannel Plate

ZHU Jiaqi, MAO Hanqi, ZHANG Zhengjun, SUN Jianning, LI Jingwen, LIN Yanjian, QIAO Fangjian, ZHANG Huan

2020, 39(12):  4010-4015. 

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The effects of ZrO₂ on the structure and performance of the microchannel plate lead silicon glass were investigated by X-ray diffraction (XRD), Raman spectroscopy (Raman), thermal expansion coefficient and Vickers hardness. The results show that the lead silicon glass for nondevitrification microchannel plate is prepared by adding ZrO₂ within 8% (mass fraction, the same below). With the increase of ZrO₂ content, the vibration intensity of bridging oxygen bonds in glass increases first and then decreases, and the corresponding thermal expansion coefficient decreases first and then increases. When the content of ZrO₂ is 2%, the content of bridge oxygen in the glass reaches the maximum, and the thermal expansion coefficient of the corresponding glass is 80.5×10^-7 ℃^-1. At this time, the ion bombardment resistance of the microchannel plate is 33% higher than that of the normal microchannel plate. Vickers hardness of glass increases with the increase of ZrO₂ content. When the content of ZrO₂ is lower than 5%, the change of Vickers hardness is more obvious. When the content of ZrO₂ is 8%, the maximum Vickers hardness of glass is 5.1 GPa.

Effect of Zircon on Corrosion Resistance of Al₂O₃-Cr₂O₃-ZrO₂ Bricks and Hexavalent Chromium Formation

XU Tengteng, XU Yibiao, NATH Mithun, LI Yawei, ZHANG Wenhui, ZHANG Weixing, ZHANG Sheng

2020, 39(12):  4016-4021. 

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Al₂O₃-Cr₂O₃-ZrO₂ bricks are widely used as lining material in hazardous waste incinerators because of their excellent slag corrosion resistance. However, toxic water-soluble Cr(VI) may be formed during the preparation and service of Al₂O₃-Cr₂O₃-ZrO₂ bricks, and the related research work has not been reported. In present study, two kinds of Al₂O₃-Cr₂O₃-ZrO₂ bricks were prepared using monoclinic zirconia and zircon as zirconia sources. The corrosion behavior of the bricks in four kinds of hazardous waste incinerator slags and the content of Cr(VI) in the bricks before and after slag corrosion were studied. The results show that zircon decomposes into monoclinic zirconia and amorphous silica at high temperatures, which promotes the formation of highly chemical stable (Al,Cr)₂O₃ solid solution and improves the densification as well as corrosion resistance of the Al₂O₃-Cr₂O₃-ZrO₂ bricks. Furthermore, the formed silica can reduce Cr(VI) compound, which lowers the content of Cr(VI) in Al₂O₃-Cr₂O₃-ZrO₂ bricks. The content of Cr(VI) in the penetration layer of Al₂O₃-Cr₂O₃-ZrO₂ bricks is closely related to the composition of slag. There is higher Cr(VI) content in the penetration layer after being corroded by the slag with high alkaline oxide content, while Cr(VI) content in the origin and penetration layer of Al₂O₃-Cr₂O₃-ZrO₂ bricks with zircon is lower than the EU limit standard in the four kinds of slag.

Research Progress of MXenes-Based Materials for Electrocatalytic Hydrogen Evolution

WANG Jiapei, JIANG Song, CONG Ye, LI Xuanke, DONG Zhijun, YUAN Guanming, LI Yanjun, ZHANG Jiang

2020, 39(12):  4022-4033. 

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MXenes with unique layered structure are a new family of two-dimensional nanomaterials, including two-dimensional transition metal carbides, nitrides and carbonitrides. The materials have high specific surface area, abundant surface chemical properties, good hydrophilicity and conductivity. Thanks to these excellent chemical and physical properties, more and more scholars around the world are interested in the research of MXenes in the fields of energy storage, electromagnetic shielding and electrocatalysis. Especially, electrocatalytic hydrogen evolution (HER) is one of the effective strategies to solve the problem of energy shortage. In this paper, the structure and properties of MXenes were introduced, and the research progress of MXenes-based materials in the field of electrocatalytic hydrogen evolution in recent years was reviewed. Finally, the challenges and future development of MXenes-based electrocatalysts were summarized and prospected.

Characteristic Analysis of Layered Double Hydroxides Functional Materials and Its Flame Retardant Application

ZOU Yu

2020, 39(12):  4034-4042. 

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Hydrotalcite-like compounds,also known as layered double hydroxides (LDHs),are a new type of layered materials with special structure and function. Chemical composition, structure and properties of LDHs were introduced, and the thermal decomposition behavior and flame retardant mechanism of typical LDHs (Mg₆Al₂(OH)₁₆CO₃·4H₂O) were analyzed. Finally, the application of LDHs in the field of flame retardant was reviewed from the three aspects of main layer regulation, functional guest intercalation, and synergistic effects.

Effects of Pavement Structure and Material on Fatigue Performance of Double-Deck One-Time Paving Pavement

JIANG Yingjun, LI Qilong, SHANGGUAN Yuhao

2020, 39(12):  4043-4053. 

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The effects of paving technology, mixture type and structural layer thickness on fatigue performance of asphalt pavement were studied. The results show that compared with traditional paving technology, the fatigue life of asphalt pavement with double-deck one-time paving technology is increased by 54% under the same stress. The combination of 3 cm thickness of upper layer and 7 cm thickness of lower layer of double-deck one-time paving pavement and mixture type of upper layer AC-13 and lower layer AC-20 have the best fatigue performance. And the fatigue life is increased by 113%, compared with the traditional stratified paving typical pavement. For asphalt mixture under high stress, the anti-fatigue performance and stress change sensitivity of double-deck one-time paving technology are the best. Paving technology is superior to traditional paving technology, which is mainly reflected in the fact that the fatigue equation intercept a value of asphalt mixture in double-deck one-time paving technology is larger than that of Marshall method, while the slope value b is just the opposite. In order to improve the fatigue performance of pavement effectively, it is suggested that the structure of double-deck one-time paving pavement should be composed of upper layer 3 cm AC-13 and lower layer 7 cm AC-20.

Shear Performance of Different Types of High Modulus Asphalt Mixtures

HAO Peiwen, WANG Junbiao, ZENG Zhiwu, ZHAO Chaozhi, WU Tao, LI Dewen

2020, 39(12):  4054-4060. 

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In order to study the shear performance of different types of high modulus asphalt mixtures, the complex shear modulus and phase angle of EME2 asphalt mixture and AC-20 asphalt mixture were measured by Superpave shear testing machine according to frequency sweep test at constant height (FSCH) method. According to the time-temperature equivalent principle, the complex shear modulus master curves at reference temperature were obtained through non-linear least square regression analysis, and the master curves were used to predict the high and low temperature performance of the two types of asphalt mixtures. Through the repeated shear test at constant height (RSCH), the end load strain and shear slope of two high modulus asphalt mixtures were obtained. The FSCH results show that the complex shear modulus of the two asphalt mixtures decreases with the increase of temperature and increases with the increase of load frequency. The high temperature shear performance of AC-20 asphalt mixture is better than that of EME2 asphalt mixture, and the normal temperature deformation resistance of EME2 asphalt mixture is better than that of AC-20 asphalt mixture. The RSCH results show that the shear performance of AC-20 asphalt mixture is better than that of EME2 asphalt mixture at 60 ℃.

Research on Visco-Elastoplastic Constitutive Model for AC-13 Graded Asphalt Mixture with Steel Slag

ZENG Guowei, LIU Haoxuan, BAI Fan, WU Liang, ZHOU Peng

2020, 39(12):  4061-4067. 

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Based on the coupling of Schapery viscoelastic model and modified Swchartz viscoplastic model, an integral constitutive model was proposed to study the characterization of nonlinear visco-elastoplastic deformation of asphalt mixture with steel slag. The specimens of AC-13 gradation were fabricated, while the limestone coarse aggregate sizes larger than 2.36 mm were replaced by steel slag. A series of uniaxial compressive creep tests were designed and conducted. The elastic, viscoelastic and viscoplastic strains under different stresses were decomposed from multiple-stress repeated creep-recovery test. And then the parameters in the model were fitted and determined. The capability of the constitutive models was verified by the creep recovery tests under 0.4 MPa and 1.0 MPa. The result shows that the proposed model not only accurately describes the deformation of elastic, viscoelastic and viscoplastic behavior of steel slag asphalt mixture during the creep recovery behaviour, but also be able to predict the creep recovery deformation rule of asphalt mixture with steel slag with different stress levels.