Table of Content

15 May 2021, Volume 40 Issue 5

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Cement and Concrete

Influencing Factors and Enhancement Methods of Early Strength of Supersulfated Cement

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

2021, 40(5):  1413-1419. 

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As an environmentally friendly material, supersulfated cement has many advantages, such as low hydration heat, good corrosion resistance, and high strength in the later stage, but there are some deficiencies such as low strength in the early stage. The research progress of influencing factors and improving ways of early strength of supersulfated cement is summarized, and the future research direction has been prospected in this paper. Slag activity, alkalinity and sulfate concentration are the key factors affecting the early strength, especially alkalinity. There are some technical approaches to improve the early strength, such as selecting the slag with high activity and the gypsum with suitable dissolution characteristics, and using the additives with the function of controlling alkalinity and promoting the dissolution of slag. How to control the alkalinity, and then control the formation rate, morphology and proportion of hydration products, is worthy of being studied in the future.

Research Progress on Relationship Between Pore Structure and Water Absorption Performance of Cement-Based Materials

WANG Dongli, YANG Ce, PAN Huimin, LI Tong, CHI Yaao, XU Zehua

2021, 40(5):  1420-1428. 

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Water molecules are transported inside the cement-based materials through all levels of pores, bringing corroding ions into the material, which have an adverse impact on the properties of the materials. In order to deeply understand the pore structure and water absorption performance of cement-based materials, the relevant literature reviews on mechanical theory research were conducted in this paper. The classification methods of the pore of cement-based materials were compared and the multiple technologies on characterization of pore structure were analyzed, as well as their applications were presented. In addition, it emphasized the permeability theory of cement-based materials and the relationship between capillary water absorption mechanics with pore structure parameters. Meanwhile, the paper reviewed the present scholars’ studies in terms of nano-scale pore simulation of cement-based materials based on molecular dynamics theory. Finally, it summarized the relationship between pore structure and water absorption performance and looked forward the prospect of research in this field.

Research Progress on Preparation of Nano Calcium Silicate Hydrate and Its Influence on Cement Hydration

CHEN Jiao, YU Cheng, MU Ru, YU Xin

2021, 40(5):  1429-1140. 

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With the continuous development of nanotechnology, nanomaterials are gradually used in traditional concrete materials to improve the various performance of concrete. Nano calcium silicate hydrate (nano C-S-H) is a new type of early strength nanocomposites, it can accelerate the early hydration rate of cement through the seeding effect, and significantly improve the early mechanical properties of cement-based materials, so as to improve the construction efficiency and meet the special construction requirements. In this paper, the preparation methods of nano C-S-H and the influence of nano C-S-H on the early and long-term properties of cement-sbased materials are systematically summarized, the influence mechanism of nano C-S-H on the hydration process and hydration products of cement is discussed, especially the C-S-H/PCE (polycarboxylic acid type water reducer, called PCE) nanocomposites prepared by polymer dispersed nanoparticles are introduced.

Research Progress on Influence of High Rock Temperature on Performance of Shotcrete

CHEN Junsong, WANG Wei, QIAO Min, ZHAO Shuang, ZENG Luping

2021, 40(5):  1441-1452. 

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In some major tunnel projects, the phenomenon of high rock temperature often occurs. High temperature will lead to the deterioration of the workability, mechanical properties and durability of shotcrete, which will affect the stability and safety of tunnel structure. Therefore, it is vital to study the influence of high rock temperature on the performance of shotcrete. This paper summarizes the research progress on the effect of high rock temperature on the mechanical properties, durability and microstructure of shotcrete in recent years, introduces the modification measures of shotcrete under high rock temperature, and prospects the prevention and control measures for thermal damage of high temperature tunnel in the future.

Effect of Co-Existence of FeS and TiO₂ on Solidification and Migration of Ti and Mineral Composition in Cement Clinker

FENG Qingge, LIANG Siliang, YANG Yi, BAI Xiukui, WANG Dongbo, ZHAO Zhengshu, HUANG Lilin

2021, 40(5):  1453-1461. 

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To investigate the effect of co-existence of FeS and TiO₂ on the solidification and migration of Ti and mineral composition in cement clinker, the content and distribution of Ti in cement clinker and the mineral composition of clinker were measured by inductively coupled plasma emission spectrum (ICP-OES), energy dispersive spectrum (EDS), X-ray diffraction (XRD) and Rietveld full spectrum fitting. The existence forms of S and Ti in cement clinker were investigated by X-ray photoelectron spectroscopy (XPS), structural difference factor D and Hume-Rothery empirical formula. The results show that the incorporation of FeS has little influence on the curing capacity of cement clinker to solidify Ti, but it makes Ti migrate from intermediate phase to silicate phase. With the increase of FeS content, the content of Ti in C₂S increases by 46.9%. The incorporation of FeS promotes the formation of α-C₂S, thus enhancing the curing ability of silicate phase to solidify Ti. Meanwhile, with the increase of FeS content, the increase of Fe²⁺/Fe³⁺ mole ratio and the generation of CaSO₄ in clinker are the main reasons for the decrease of C₃S and C₄AF content and the increase of C₂S and C₃A content.

Hydration Characteristics of Composite Cementitious System Driven by Chemistry and Thermodynamics

ZHANG Xiuzhen, LIU Zhichao, HE Yongjia, HU Shuguang, ZENG Bo

2021, 40(5):  1462-1469. 

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In order to understand the hydration heat release characteristics of the composite cementitious material system, and the influence of chemical and thermodynamic driving on the hydration heat release of the composite cementitious material system, the development ofhydration heat of the binary composite cementitious system of fly ash- or slag-cement with different content was studied. At the same time, the influence of different harden accelerator content and different temperatures on the hydration heat release of the fly ash-cement binary composite cementitious system was explored. The results show that both fly ash and slag can reduce the hydration heat release rate of the binary composite cementitious system, but the activity of slag is higher than that of fly ash, which has little effect on the hydration heat release rate and the final cumulative heat release. Chemical driving can significantly increase the rate of hydration heat release of the system and promote the development of early hydration, but it does not change the final cumulative heat release. The thermodynamic driving effect is more significant, which greatly increases the heat release curvature of the system and the cumulative heat release. Using the chemical reaction rate as the criterion to establish a connection between the two driving forces can effectively design the hybrid driving mode.

Synergistic Effect of Tricalcium Aluminate and Calcium Carbonate on Early Mechanical Strength and Setting Time of Portland Cement

YAN Ziwei, LIU Li, SUN Jinfeng, LU Bao, ZU Qinghe, ZANG Jun, LI Debiao, HOU Guihua

2021, 40(5):  1470-1476. 

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In this paper, the synergistic effect of tricalcium aluminate (C₃A) and calcium carbonate (CaCO₃) on the early hydration and hardening properties of Portland cement was studied. Then a series of methods including X-ray diffraction (XRD), thermogravimetric analysis (TG) and scanning electron microscopy (SEM) were adopted to analyze the hydrates and microstructures. Results indicate that the simultaneous addition of C₃A and CaCO₃ effectively boosts the mechanical strength of the Portland cement mortar and the content of C₃A and CaCO₃ are 15% (mass fraction, the same below) and 5.6% respectively presented the best mechanical performance. Compared to the reference mortar, this combination increases the compressive strength by 28.8%, 55.7%, 26.8% at 3 d, 7 d and 14 d, respectively. It is inferred that the simultaneous addition of C₃A and CaCO₃ stimulates the formation of calcium carboaluminate, which benefits the early mechanical strength development.

Effect of Few-Layer Graphene on Properties of Ordinary Concrete

HE Wei, XU Jihang

2021, 40(5):  1477-1488. 

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To further study graphene/concrete composites, the effect of few-layer graphene (FLGR) on the slump, mechanical properties, impermeability and electrical properties of ordinary concrete was systematically studied, and SEM was used to analyze the microstructure of FLGR/concrete composites. Meanwhile, AFM, Raman and SEM were used to characterize FLGR. The results show that the layer number of FLGR is between 3 layers and 6 layers, and the D and G peaks of FLGR are red-shifted compared with that of monolayer graphene. FLGR is an ultra-thin lamellar structure with wrinkles on the surface and it has a very tight microstructure. The addition of FLGR reduces the slump of concrete, and 28 d compressive strength of concrete increases by 15.08%, 28 d flexural strength increases by 35.03%, the height of penetration decreases by 57%. FLGR has the function of increasing the conductivity of concrete, and FLGR/concrete composites present negative temperature coefficient effect. FLGR can better promote the connection between hydration products, act the part of bridging ettringite and C-S-H gel to fill cracks and pores in cement matrix.

Workability and Mechanical Properties of Polymer Modified Self-Compacting Concrete

HOU Shengjun, JIANG Chenchen, TANG Weiyu, TAO Wenjiang, AN Xuehui, MA Jiajun

2021, 40(5):  1489-1496. 

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The polymer modified cement concrete has good tensile properties and durability, and it is widely used, while the polymer modified self-compacting concrete is rarely used. The basic mechanical properties and workability of epoxy resin modified self-compacting concrete were studied. Four kinds of epoxy resin content (0%, 5%, 10%, 15%, mass fraction) were used in the experiment, and the effect of different epoxy resin content on the basic mechanical properties and workability of modified self-compacting concrete were obtained. The results show that: compared with ordinary self-compacting concrete, when the mass fraction of epoxy resin is 5%, the compressive strength is improved to a certain extent; when the mass fraction of epoxy resin is 10%, the flexural strength is the best; when the mass fraction of epoxy resin is 10% or more than 10%, the macropores in concrete turn into micropores; when the mass fraction of epoxy resin reaches 15%, the epoxy resin solidifies into clusters and destroys the internal structure of concrete. The flexural toughness of self-compacting concrete is improved with the increase of epoxy resin content. When the content of epoxy resin is high, the fluidity of self-compacting concrete decreases, but the fluidity can be improved by appropriately blending a water reducing agent.

Deformation Performance of Steel Tube Self-Compacting Lightweight Aggregate Concrete

LI Shuming, ZHENG Xinguo, LIU Jing, XIE Yongjiang, HU Jialin, ZHANG Xu

2021, 40(5):  1497-1502. 

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Using shale ceramsite with bulk density of 500 kg/m³ and 800 kg/m³ and gravel with bulk density of 1 600 kg/m³ as coarse aggregates to prepare self-compacting lightweight aggregate concrete and ordinary concrete, forming steel tube lightweight aggregate concreteand ordinary concrete-filled steel tube. Compared with ordinary concrete-filled steel tube, the shrinkage strain, axial compression stress-strain change rule and temperature-strain change rule of the two are contrasted. The results show that as the bulk density of coarse aggregate decreases, the density, strength and elastic modulus of the same proportion of lightweight aggregate concrete gradually decrease. At the same age, the shrinkage strain of steel tube lightweight aggregate concrete is smaller than that of steel tube ordinary concrete, and the shrinkage strain of core lightweight aggregate concrete is also smaller than that of core ordinary concrete, better adhesion between steel tube and core lightweight aggregate concrete. The axial compression stress-strain change law of lightweight aggregate concrete-filled steel tube is basically the same as that of ordinary concrete-filled steel tube. Compared with ordinary steel tube concrete, the elastic modulus of steel tube lightweight aggregate concrete is reduced, but it is smaller than the reduction amplitude of lightweight aggregate concrete under non-steel tube confinement state. The temperature-strain of lightweight aggregate steel tube concrete and ordinary steel tube concrete are equivalent, both are about 4.0 με/℃.

Influences of Saturated Surface-Dry Recycled Fine Aggregate on Fluidity and Strength of Ultra-High Performance Concrete

CHEN Zhiwu

2021, 40(5):  1503-1509. 

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In order to investigate the influence of the content of saturated surface-dry recycled fine aggregate on the fluidity and strength of ultra-high performance concrete (UHPC), the UHPC with various recycled fine aggregate contents (0%, 25%, 50%, 75%, and 100%, by mass fraction) in the saturated surface-dry state were designed under the same net water-binder ratio, and the fluidity and strength under standard curing at various ages of the UHPC were tested. The mechanism was revealed by SEM and MIP et al. The study results show that, with the increase of the recycled fine aggregate content, the friction between particles increases, and more cement slurry are needed to wrap and fill the surface of recycled fine aggregate, resulting in the decrease of the fluidity of UHPC. With the increase of the content of recycled fine aggregate, the total water-binder ratio increases, and the length of ITZ₂ (the interfacial transition zone between the old fine aggregate and the old cement matrix) and ITZ₃ (the interfacial transition zone between the old cement matrix and the UHPC matrix) increase, the amount of micro-cracks increase, and the harmful hole and multi-harmful hole content increase, and the compactness of UHPC decreases, and therefore the flexural strength and compressive strength of UHPC decrease.

Calculation Method of Effective Thermal Conductivity of Steel Fiber Reinforced Concrete after High Temperature

ZHU De, HAN Yang, DUAN Junfeng, SHEN Lei, YAO Xiupeng, CAO Maosen

2021, 40(5):  1510-1519. 

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The thermal conductivity of steel fiber reinforced concrete (SFRC) is a primary property for structure fire resistance performance analysis. It is of great significance to estimate the thermal conductivity at/after high temperature quickly and accurately. For this demand, a multi-scale method for thermal conductivity of SFRC was proposed, featuring with the thermal cracking behavior at high temperature, namely the interfacial thermal resistance (ITR), rather than the temperature-dependent decreasing law of components thermal conductivity. Afterward, the experiments on the thermal conductivity and porosity of mortar, high strength concrete, and SFRC with 1% and 2% (volume fraction) fiber heated up to various temperatures (20 ℃, 60 ℃, 150 ℃, 300 ℃, 450 ℃, 600 ℃) were performed to validate the proposed model. The results show that the numerical predictions satisfy the experimental data very well when the ITR coefficient is assumed to linearly increases with heating temperatures.When the temperature reaches 600 ℃, the decreases of thermal conductivity of mortar, high strength concrete and SFRC with fiber (volume fraction 1% to 2%) caused by ITR effect are about 50%, 36%, 7% and 12%, respectively. When the ITR coefficient of high strength concrete is 0.4 and the ITR coefficient of SFRC is 1.0, the addition of particles with good thermal conductivity has no help to increase the effective thermal conductivity of composite materials.

Solid Waste and Eco-Materials

Research Progress on Synthesis of Municipal Sludge-Derived Functional Carbon Materials and Pollution Control During Pyrolysis

YUAN Zhihang, LOU Ziyang

2021, 40(5):  1520-1528. 

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As the process by-product generated from the wastewater treatment plant, excess municipal sludge has turned into a special challenge in the global environment, due to its huge output and potential biochemical contamination. Utilizing sludge as carbon rich precursor and converting it into functional carbon materials by thermochemical method may be a promising way for the disposal and re-utilization of sludge. Through the systematic investigation of the synthesis and modification of sludge-derived carbon functional materials and the in-situ pollution control during the pyrolysis, it was found that the postchemical activation method has a stronger pore-forming ability compared with other methods, and the potassium compounds possess superior activation effect. The physical and chemical adsorption and specific catalytic properties of the sludge carbon materials can be strengthened by surface oxidation, ammoniation or sulfonation process, thus being favorable to expand the material application scope. Sludge carbon-nanostructure composite can endow the material multiple characteristics and improve the stability and dispersion of the nanostructure. Based on the discussion of thermochemical transformation of typical elements in sludge, the production path of sulfur oxide and nitrogen oxide is clarified, and meanwhile it is found that the metal oxide blending pyrolysis and heat source optimization can significantly inhibit the emission of pollutants.

Removal of Chromate(VI) from Water Using Kaolinite Enhanced by Nano-Zero-Valent Iron and Its Mechanism

LIU Liu, HU Peiwei, GAO Runqin, CHENG Gangli, YAO Yao

2021, 40(5):  1529-1535. 

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Nano-zero-valent iron (nZVI) has received widely attention as an environmental protection material for the treatment of heavy metal and nuclide pollutants. Clay mineral, as a common heavy metal adsorption material, has low cost and wide sources, but its removal performance is generally limited. nZVI/Kao(nZVI/kaolinite) was prepared by liquid phase reduction method for the efficient removal of Cr(VI) from water. XRD, SEM and TEM were used to characterize the phase and structure of the composite. The effects of Cr(VI) initial concentration, nZVI/Kao dosage and temperature on the removal rate of Cr(VI) by the composite were studied. Meanwhile, the removal ability and mechanism of Cr(VI) from water were also discussed. The results show that nZVI has the low crystallinity and its particle size is between 50 nm and 100 nm. The Cr(VI) removal rate of the nZVI/Kao is 91.7% in 60 min, which is 2.7 times and 18.5 times than that of the single nZVI and kaolinite, respectively. The removal kinetics fits well with the pseudo-second order kinetic model and the apparent activation energy is 27.97 kJ/mol. The removal process is the result of common action of adsorption, reduction and co-precipitation. The application prospect of kaolin in water treatment and environmental remediation can be strengthened by loading nZVI.

Reuse of Stone Waste Powder Based on Uniform Design Test Method

TIAN Jiandong, LU Longyuan

2021, 40(5):  1536-1544. 

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In order to solve the problem of stone waste pollution, the preparation of economical, practical, and excellent performance fiber cement boards were studied. The raw materials of this board were granite waste powder and marble waste powder, combined with Portland cement, natural quartz sand, fly ash, and wood pulp fiber. The uniform design test method and regression analysis method were used to reveal the influences of granite waste powder and marble waste powder on the flexural strength, impact strength, and thermal conductivity of fiber cement boards. Through comparative experiments, the influences of granite waste powder and marble waste powder on the physical properties, hydration products, and microstructure of fiber cement boards were analyzed. The test results show that mixing granite waste powder and marble waste powder effectively improve the mechanical properties of fiber cement boards. When the mass ratio of granite waste powder, marble waste powder and cement is 0.625 and 0.417, it does not have a significant impact on the internal hydration products and internal microstructure morphology of the fiber cement boards. And the cement fiber boards can be prepared, which meet the requirements and are economical and applicable.

Freeze-Thaw Resistance of Granite Waste Recycled Concrete Pavement Brick

KONG Liang, MENG Yanyu, GU Yuanyuan, WANG Weiqi

2021, 40(5):  1545-1553. 

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50 freeze-thaw cycles of recycled concrete pavement brick with granite waste were carried out by the slow freezing method. Based on the mass loss and compressive strength, the change rule of freeze-thaw resistance of recycled concrete pavement brick was studied. Based on the theory of volume expansion and osmotic pressure and combined with scanning electron microscope analysis, the microstructure, and hydration product composition of recycled concrete pavement brick before and after freeze-thaw were compared. The freeze-thaw damage mechanism was revealed from the perspective of microcrack accumulation and expansive stress. The slurry pore structure change model and the osmotic pressure model caused by slurry concentration difference were established. The results show that the mass loss rate and compressive strength loss rate of recycled concrete pavement brick with the optimal replacement rate of micro, fine and coarse aggregates of 20%, 30% and 50% (mass fraction) are 1.5% and 10.0% respectively, which is lower than reference group. But the utilization rate of granite waste is improved to a great extent and meets the basic requirements of experimental standards and road performance. The microscopic analysis results show that higher content of ettringite in the hydration products of slurry makes the microcracks of concrete enriched, and finally leads to the formation of macrocracks causing frost heave failure. The model reveals that the invasion of external water, resulting in volume expansion, and the expansive stress caused by osmotic pressure in the pores and gel pores are the real reasons for freeze-thaw damage.

Experimental Study on Groutability of Low Calcium Fly Ash-Cement Slurry

ZHOU Shengquan, CHEN Wei, LI Jianwei, LI Dongwei

2021, 40(5):  1554-1563. 

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In order to explore the application of low calcium fly ash in the grouting method, based on the engineering background of strengthening low strength broken roof, the corresponding laboratory tests were carried out. The variation law of bleeding rate, concretion rate, viscosity, setting time, and grouting stone body strength of slurry were investigated under the influence of different water-solid ratios and fly ash content. The microstructure of the grouting body was analyzed by the scanning electron microscope (SEM) and the X-ray diffraction (XRD). The results show that when the water-solid ratio of the slurry is 0.7:1 (mass ratio) and fly ash content is 70% (mass fraction), the performance parameters of the slurry are optimal. At this time, the viscosity of the slurry is 55.50 s, the bleeding rate is 3.89% (volume fraction), and the concretion rate is 94.16% (volume fraction). The compressive strength of the slurry stone at three curing age stages of 3 d, 7 d, and 28 d are 0.67 MPa, 1.77 MPa, and 3.10 MPa, respectively. XRD qualitative phase analysis shows that the addition of alkaline activator increases the diffraction peak of Ca(OH)₂ in the system. And with the increase of curing age, the diffraction peak of Ca(OH)₂, quartz, and mullite phase decrease significantly, which promote the release of the potential activity of fly ash. SEM microstructure and morphology analysis reveal that the microstructure of slurry is loose in the early stage, with thin-plate crystal Ca(OH)₂ and a small amount of acicular AFt (ettringite). At the later stage, the thin-plate crystal Ca(OH)₂ and the flocculated C-S-H gel intertwine together to form a dense network structure.

Influence of Fly ash Content on Physical and Mechanical Properties of Magnesium Oxychloride Cement Concrete

LIU Pan, CHANG Chenggong, LIU Xiuquan, DONG Jinmei, ZHENG Weixin, XIAO Xueying, WEN Jing

2021, 40(5):  1564-1572. 

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In order to expand the application fields of magnesium oxychloride cement (MOC) materials, magnesium oxychloride cement concrete (MOCC) with different fly ash content was prepared by using bischofite, light burned magnesia and fly ash as cementitious materials, in which bischofite is a by-product of potassium fertilizer extracted from salt lake. The influence of fly ash content on compressive strength, phase composition, micromorphology and pore structure of MOCC were studied. The results show that with the increase of fly ash content, the compressive strength of MOCC gradually decreases. When the content of fly ash is 40% (mass fraction), its 300 d compressive strength decreases to 39.99 MPa, which is a decrease of 22.52%. The main hydration products of MOCC are 5Mg(OH)₂·MgCl₂·8H₂O(5·1·8) and Mg(OH)₂. The addition of fly ash does not produce a new crystal phase. The addition of fly ash increases the porosity and harmful pore volume of MOCC, thereby reducing its compressive strength. Ordinary Portland cement concrete was prepared with the same water-cement ratio. The comparative test results of compressive strength show that although the compressive strength of MOCC with 40% fly ash is lower than that of MOCC without fly ash, it is still 19.66% higher than that of ordinary Portland cement concrete at 300 d age, indicating that MOCC has higher compressive strength than that of ordinary Portland cement concrete.

Influence of Fly Ash Content on Compressive Strength Development of High Performance Self-Compacting Concrete

WANG Hui, LIU Xuhui, CAI Shengyu, ZHANG Wu

2021, 40(5):  1573-1578. 

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Fly ash has a significant impact on the workability, strength, and durability of self-compacting concrete. In order to explore the influence of fly ash content on the compressive strength of self-compacting concrete, self-compacting concrete with 30%, 45%, and 60% (volume fraction) fly ash content and water-cement ratio of 1.05, 1.15, and 1.25 (volume ratio) was prepared, and the cube compressive strength tests of 3 d, 7 d, 28 d, and 90 d were carried out. The results show that with the increase of fly ash content, the compressive strength of concrete gradually decreases. And then the strength ratio of 3 d/28 d, 7 d/28 d, and 90 d/28 d were analyzed. The results show that fly ash has little influence on the early strength of concrete, but has a greater influence on the later strength. Finally, referring to the European standard CEB-FIP, the influence coefficient of the composite powder mixed with fly ash and cement on compressive strength of self-compacting concrete is explored, which provides a theoretical basis for related engineering applications.

Dissolution Characteristics of Coal Gasification Slag and Its Effect on Cement-Based Materials

GU Yue, WANG Dongmin, FANG Kuizhen, YAO Guang, WANG Qibao, ZHANG Ming, SUN Rui, LYU Nan

2021, 40(5):  1579-1585. 

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The continuous development of clean coal technology in our country has brought a large amount of industrial by-product gasification slag. From the point of view that gasification slag was used as cement mineral admixture, the dissolution characteristics of the gasification slag in different environments were determined by ICP, and its hydration activity was observed. Then the effect of gasification slag on the workability and mechanical properties of the binary composite system was studied. It is concluded that the dissolution rate of Ca²⁺ is low and the gasification slag has no self-hardening property. The dissolution rate of Si⁴⁺ and Al³⁺ increases with time, and the gasification slag has hydration activity. Alkaline and high temperature environments promote the dissolution of Si⁴⁺ and Al³⁺, indicating that the gasification slag is more likely to break chemical bonds and increases hydration activity under appropriate excitation. The morphological effect of the gasification slag improves the workability of the binary system, and the fluidity of the system with 30% and 50% (mass fraction) gasification slag increases by approximately 8.8% and 19.4%, respectively. The binary system conforms to the fluid model described by Herschel-Bulkey, and shear thinning is found. The pozzolanic reaction of low content gasification slag improves the mechanical properties of the composite cementitious system, and the 90 d compressive strength reaches 90 MPa. The high content gasification slag replaces too much cement, reduces hydration products and environmental alkalinity, the activity of the gasification slag cannot be fully excited, resulting in the increase of porosity, loose structure, and decrease of mechanical properties.

Effects of Ultrafine Ground Granulated Blast Furnace Slag and Metakaolin on Hydration and Strength of Calcium Sulfoaluminate Cement

LI Yagang, LIAO Yishun, LIU Yanling, HUANG Haoran

2021, 40(5):  1586-1593. 

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The addition of mineral admixtures is one of the main technical methods to improve the setting and hardening properties of calcium sulfoaluminate cement (CSA) concrete and to reduce the cost of concrete production. The influences of ultrafine ground granulated blast furnace slag (UFS) and metakaolin (MK) on setting time, fluidity, electrical resistivity, and compressive strength of calcium sulfoaluminate cement paste with water-binder ratio of 0.4 were investigated. The hydration products cured at 1 d and 28 d were analyzed by XRD semi-quantitative analysis. The results show that both single and multiple admixtures accelerate the setting of cement paste, but the effect of MK is significant, and the fluidity of cement paste decreases with the increase of UFS and MK. The time for the peak value of electrical resistivity rate changing curve is shortened by adding UFS and MK, and the peak value decreases with the increase of UFS and MK. When the content increases from 0% (mass fraction, the same follows) to 20%, the 28 d compressive strength of the sample with UFS decreases by 24.7%, the 28 d compressive strength of the sample with MK decreases by 17.7%, and the 28 d compressive strength of the sample with both decreases by 17.3%. UFS and MK have no obvious effect on hydration products, but accelerate the early hydration of β-C₂S.

Effect of Nano-SiO₂ on Steel Slag/Cement-Based Cementitious Materials

WU Siyao, DAI Shaobin, MA Baoguo, ZHANG Ting, YANG Hang, SHANG Lishi

2021, 40(5):  1594-1600. 

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Steel slag has similar mineral composition with cement, which can be used as a potential cementitious material. However, the high content of steel slag is not conducive to the development of early properties of concrete. Steel slag/cement-based cementitious materials with 30%(by weight) steel slag as the research object were used to discuss the influence of nano-SiO₂ on its early properties. Physical and mechanical properties were evaluated by measuring fluidity, setting time, and compressive strength. The hydration process and hydration products of steel slag/cement-based cementitious materials with nano-SiO₂ were analyzed by micro-thermal analysis, X-ray diffraction (XRD), and differential scanning calorimetry (DCS-TG). Results show that when the mass fraction of nano-SiO₂ is 3%, nano-SiO₂ consumes large amounts of Ca(OH)₂ due to its high pozzolanic activity. Meanwhile, due to the crystallization nucleation and micro-aggregate filling effect of nano-SiO₂ particles, the hydration of steel slag and cement is promoted, and the heat release rate at the initial stage of hydration is improved, thus improving the mechanical properties of steel slag/cement-based cementitious materials, and the 28 d compressive strength increases by 14.0%.

Efficient Synergistic Stabilization/Solidification of Phosphogypsum and Copper Smelter Slag

WANG Wei, XU Xiangqun, LI Jie, GUO Li, CHEN Rongsheng, DU Dongyun

2021, 40(5):  1601-1609. 

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Phosphogypsum (PG) and copper smelter slag (CSS) are solid wastes produced from phosphorus chemical industries and nonferrous metal smelting industries. PG mainly consists of CaSO₄·2H₂O with harmful impurities such as residual acids, phosphate, fluorides, and trace metals (e.g., Cr, As and Cd). CSS contains large amounts of heavy metals such as lead and zinc. The soluble portions of the harmful substances in PG and CSS may enter the environment and cause serious pollution problems. In this study, NaOH and CaO were added as activators and additional calcium sources in mixed slag of PG and CSS with water to produce cemented blocks (named PG-S). Unconfined compressive strength (UCS) test and leaching test show that the compressive strength of PG-S reaches 14.8 MPa, and the stabilization efficiency of $PO^{3-}_{4}$ and F^- in PG are 99.87% and 92.13%, respectively. The concentrations of heavy metal zinc, lead and other harmful substances in the leaching solution meet the requirements of "integrated wastewater discharge standard" (GB 8978—1996) of China. The stabilization/solidification (S/S) of PG and CSS using the proposed method shows high efficiency and feasibility. Through XRD and SEM analysis, the stabilized wastes show structures similar to C-S-H, ettringite, Zn₃(PO₄)₂(H₂O)₄, Pb₁₀(PO₄)₆(OH)₂ and CaF₂. On this basis, the possible mechanism of the stabilization/solidification process is: the harmful substances in PG and CSS may be stabilized/solidified by formation of insoluble substances and adsorption of cementitious substances.

Preparation and Characterization of Composite Cementitious Material Based on Electrolytic Manganese Residue-Phosphogypsum

ZHANG Xin, LIU Fang, ZHU Jian, CHEN Zuyong

2021, 40(5):  1610-1619. 

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In order to effectively improve the resource utilization level of electrolytic manganese residue, according to the chemical composition and mineral composition characteristics of electrolytic manganese residue, the electrolytic manganese residue was used as the main raw material, and the cementitious material was prepared by supplementing phosphogypsum, cement and slag powder. On the basis of fixing the slag and cement content, by changing the content of phosphogypsum, the effect of different sulfate content on the mechanical properties of composite cementitious materials was studied. The research results show that the best quality ratio of electrolytic manganese residue, phosphogypsum, slag powder and cement in the prepared composite cementitious material is 50:20:20:10, and the 14 d compressive strength of the hardened body reaches 20.62 MPa, and the softening coefficient is 0.80. The hydration products of electrolytic manganese residue-phosphogypsum composite cementitious material are mainly ettringite, C-S-H and C-A-S-H. The concentration of pollutants in the leachate of the hardened body after hydration for 14 d is within the limits of the standard of Class V water in the "Surface water environmental quality standard" (GB 3838—2002). The concentration of Cr, Cu, Zn, As, Pb, Cd and other heavy metals can reach the standard of Class I water, and the hardened body has good environmental stability.

Effect of Preparation Process of Pressurized Aqueous Solution Method on Properties of α-High Strength Gypsum

HAN Kang, GUAN Xuemao, WANG Yanfeng, LIU Songhui, LI Yifan

2021, 40(5):  1620-1630. 

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The high strength gypsum is prepared from desulfurization gypsum by pressurized aqueous solution method, and its process parameters are the key to determine the preparation quality of the high strength gypsum. The effects of hydrothermal temperature, hydrothermal time, stirring speed and slurry concentration on the properties of α-high strength gypsum were studied. The crystal morphology and gypsum phase composition of the samples prepared under different process parameters were qualitatively and quantitatively analyzed, and the optimal preparation process of α-high strength gypsum by pressurized aqueous solution method was optimized. The results show that the hydrothermal temperature has a great influence on the size and aspect ratio of the generated crystals, while the hydrothermal time mainly affects the size of the crystals and has little influence on the aspect ratio. While the hydrothermal temperature and hydrothermal time are important factors affecting the phase composition of α-high strength gypsum. The stirring speed and slurry concentration mainly affect the size and the aspect ratio of the high strength gypsum and have little influence on the composition of the gypsum phase. Under the optimum process conditions: the hydrothermal temperature of 130 ℃, the hydrothermal time of 4 h, the stirring speed of 250 r/min and the slurry concentration of 30% (mass fraction), the 2 h flexural strength of α-high strength gypsum is 5.4 MPa and the drying compressive strength of 41.9 MPa.

Effect of Cement Kiln Collaborative Disposal of Refuse Derived Fuel on Generation and Transformation of NO_x and SO₂

YI Zhengming, SHI Lichen, CHEN Xiaolin

2021, 40(5):  1631-1637. 

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It is one of the developing trends to utilize cement kiln to co-dispose refuse derived fuel (short for RDF). But in the process of actual disposal, there exists the problem of unstable pollutant discharge. Hence, five kinds of RDF treated by a cement plant in Hubei province were taken as the research objects. The high-temperature tubular furnace was used to carry out experiments to study the generation and transformation of NO_x and SO₂ at 500~900 ℃. The experimental results show that in the process of RDF combustion the peak concentration of NO_x is more affected by temperature at low temperatures (500~600 ℃), which increases multiply with temperature; the peak concentration of NO_x is less affected at high temperatures (700~900 ℃). At 900 ℃, the NO_x conversion rate is low and the combustion rate is fast, so it’s the suggested temperature to dispose of RDF. In the combustion process of different RDF, the conversion rate of NO_x shows an “inverted V shape” with the changing of combustion temperature, while the conversion rate of SO₂ shows a “positive V shape” with the change of combustion temperature. The NO_x and SO₂ play a mutual inhibition role in the formation process.

Mechanical and Fatigue Properties of Lime-Fly Ash Stabilized Recycled Concrete Aggregate Mixture

BIAN Wei, LI Yalong, GAO Xuekai, RONG Yapeng

2021, 40(5):  1638-1645. 

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The compaction properties of lime-fly ash stabilized recycled concrete aggregate (LFSRCA) mixture were analyzed, and the growth law of mechanical properties of the LFSRCA mixture such as unconfined compressive strength, splitting strength, flexural tensile strength, and compressive resilient modulus of resilience were studied. The fatigue life prediction method of the LFSRCA mixture was established, and the fatigue properties of the LFSRCA mixture were analyzed. The results show that with the increase of recycled concrete aggregate (RCA) content, the maximum dry density of the LFSRCA mixture decreases, and the optimum water content increases. With the increase of curing period, the mechanical properties of the LFSRCA mixture have the same growth law. The strength of the mixture increases slowly during the curing period from 0 d to 28 d, rapidly increases within 28 d to 60 d, and then the growth rate slows down within 60 d to 90 d, and finally, the strength growth tended to be flat when the curing period exceeded 90 d. The mechanical properties and fatigue life of the LFSRCA mixture decrease with the increase of RCA content. Effect of RCA content on fatigue life of the LFSRCA mixture at low stress level is higher than that at high stress level.

Ceramics

Research Progress and Perspective on Synthesis of TiC Powder

WANG Zhen, LING Yongyi, YIN Yicheng, WANG Zihao, ZHANG Jing, JIA Quanli, LIU Xinhong

2021, 40(5):  1646-1656. 

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TiC has excellent properties like high melting point, super hardness, high chemical stability and good wear resistance. It can be used to manufacture tools, grinding wheels, etc., or composite with other ceramic materials (alumina, silicon nitride, silicon carbide) to manufacture structural components with high temperature resistance or corrosion resistance. At the same time TiC powder has good application prospect in the fields of biomedicine, environmental purification and new composite materials. Presently, there are many methods to synthesize TiC powder. The main synthesis methods including carbon/metal thermal reduction method, molten salt-assisted synthesis method, mechanical alloying synthesis method are summarized in this review paper. And the advantages and disadvantages of each method are also briefly described. The prospects for the synthesis of TiC powder in future research are discussed.

Review on Preparation of Spherical Alumina Powder

JIA Rui, LIU Hongyu, SUN Xuemiao, JIANG Su, SHEN Huiling, XIE Kaixin

2021, 40(5):  1657-1665. 

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Spherical alumina powder is an indispensable part of alumina products and has attracted much attention due to its special physical and chemical properties. Compared with irregular alumina powder, the performance of products made of spherical alumina powder is greatly improved due to its morphology and size. At present, there is a large amount of literature discussing the method of preparing spherical alumina powder, but there is a lack of literature to systematically compare the suitable preparation methods and advantages and disadvantages of different raw materials. This paper summarizes and analyzes the existing literature from different alumina materials, and finds that different alumina materials determine different preparation methods and thereby determining the difficulty of industrialization. Among them, irregular alumina is the best raw material for industrial mass production of spherical alumina powder.

Research on Interface of Diamond Reinforced Na₂O-B₂O₃-Al₂O₃-SiO₂ Ceramic Matrix Composite Materials

ZHANG Aiju, LI Zicheng, FENG Jing, LI Zhihong

2021, 40(5):  1666-1671. 

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The diamond reinforced ceramic matrix composite with Na₂O-B₂O₃-Al₂O₃-SiO₂ low-temperature glass as basic binder was fired. The interface bonding strength, interface element distribution and interface chemical bonds were characterized by scanning electron microscopy, X-ray energy spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy and mechanical property testing. The result indicates that the interface of Na₂O-B₂O₃-Al₂O₃-SiO₂ vitrified bond and diamond particle has high bonding strength. The flexural strength of sample fired at 790 ℃ reaches 77.82 MPa. The elements of Si, B, Na and Zn diffuses at the interface position, but the element of Al does not diffuse significantly. The holding force of vitrified bond on diamond is improved by element diffusion. The C-O, C=O and C-B chemical bonds are formed at the interface between vitrified bond and diamond, the interface bonding is further enhanced by chemical bonds formation. In addition, the diamond particles in composite fired at 790 ℃ are well preserved, however, the signs of graphitization are shown while the diamond in composite fired at 850 ℃.

Experimental Study on Iron Removal Purification of Potassium Bearing Sand Shale and Its Application of Ceramics

HE Ruiming, ZHAO Yulian, WANG Yong, SHI Wei, LI Cheng, LI Aimin

2021, 40(5):  1672-1678. 

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Based on the analysis of the occurrence state of iron in potassium bearing rock, the experiment of iron removal purification of potassium bearing sand shale was carried out, and the application of iron removal powder in ceramic raw materials was studied. The results show that, under the optimum conditions that the grinding fineness (-74 μm) is 50% (mass fraction), the magnetic field strength is 190 mT, the hydrochloric acid concentration is 20% (mass fraction), the leaching temperature is 90 ℃, the total iron content in iron removal powder can be reduced to 0.13% (mass fraction), and the total content of K₂O and Na₂O increases to 11.00% (mass fraction) which meets the requirements of grade I potassium feldspar for ceramics. The iron removal powder is easy to be formed in the forming test of ceramic embryo, with wide firing temperature range and high yield, It can be used as ceramic raw material instead of feldspar. A new direction of using potassium bearing sand shale as raw materials of ceramics has been developed.

Properties of Mullite Whisker Precursor In-Situ Reinforced Urchin-Like Mullite Materials

HU Qiguo, LIU Ying, SHAO Qing, LI Ji

2021, 40(5):  1679-1684. 

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In order to improve the high value-added utilization of fly ash, mullite whisker precursor reinforced urchin-like mullite ceramic materials were in-situ prepared by the solid-phase method by using aluminum hydroxide and fly ash hollow sphere as aluminum and silicon source of urchin-like mullite precursor, aluminum hydroxide and fly ash as the aluminum and silicon source of mullite whisker precursor reinforcing agent, AlF₃ and V₂O₅ as the whisker accelerator and sintering aid severally. The effects of the ratio of reinforcing agent to the urchin-like mullite precursor (the mass ratio were 3:7, 4:6, 5:5, 6:4, and 7:3 respectively) on the properties, phase composition, and microstructure of the prepared mullite ceramic materials were studied. The results show that when the ratio of reinforcing agent to the urchin-like mullite precursor change from 3:7 to 7:3, the crystal phase formed in the sample is mullite, and the interior of the material is denser, the bulk density and compressive strength gradually increase, total porosity gradually decrease. The introduction of the reinforcing agent improves the linear change rate and thermal shock resistance, but reduces the reheating linear change rate of materials, and the residual compressive strength and residual strength ratio first increase and then decrease. The prepared mullite materials with better comprehensive properties can be obtained when the mass ratio of the reinforcing agent to urchin-like mullite precursor is 6:4.

Glass

Effect of B₂O₃ on Structure and Properties of Low Expansion Borosilicate Glass

ZHANG Pan, ZHANG Qinyu, JIANG Hong, MA Yanping

2021, 40(5):  1685-1691. 

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The low expansion borosilicate glass was prepared by using Na₂O-B₂O₃-SiO₂ low expansion glass system and gradually replacing SiO₂ with B₂O₃ by high temperature melting method. The microstructure of borosilicate glass was analyzed by infrared spectrum and scanning electron microscopy. The content of bridged oxygen and non-bridged oxygen was analyzed by X-ray photoelectron spectroscopy. The effects of the content of B₂O₃ on the mechanical properties, thermal expansion properties and UV-Vis transmittance of borosilicate glass were studied. The results show that [BO₃] in glass structure increases with the increase of B₂O₃ content, and the phase separation of glass becomes more and more serious. The glass system has good mechanical properties, with microhardness up to 802 kg/mm² and flexural strength up to 147 MPa. The transition temperature and softening temperature decreased gradually, and the thermal expansion coefficient increased gradually. The visible light transmittance of the glass sample is about 90% without an obvious rule. The increase of [BO₃] increases the content of non-bridged oxygen in the glass structure, and the UV-vis transmittance of the glass decreases gradually.

Structural Origin of Change Rate in Viscosity for Several Chalcogenide Glasses

ZHOU Peng, ZHAO Hua, ZU Chengkui, TAO Haizheng, LIU Yonghua, ZHANG Rui, CHEN Wei

2021, 40(5):  1692-1697. 

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Ge₃₃As₁₂Se₅₅, Ge₂₂As₂₀Se₅₈, Ge₁₀As₄₀Se₅₀, As₄₀Se₆₀, and Se chalcogenide glasses were prepared by the melt-quenching technique. The viscosities of these chalcogenide glasses were measured by a rheometer. Based on these data, the corresponding Vogel-Fulcher-Tammann equationsand change rate in viscosity were obtained. Based on the Raman spectra, the structural characteristics of these glasses were analyzed systematically. With the increase of Ge and As content in Ge_xAs_ySe_100-x-y chalcogenide glasses, the change rate in viscosity upon temperature decreases first and then increases. When the average coordination number <r> is 2 to 2.6, with the increase of the average coordination number, the average chemical bonding energy and network structure stability of the glass gradually increase, and the change rate in viscosity upon temperature decreases. When <r> is 2.6 to 2.78, with the appearance of As-As/Ge-Ge chemical bonds in the structure, the stability of the glass network is deteriorated, and the glass viscosity changes faster upon temperature. The change rate of glass viscosity is consistent with the structural constraint theory, and the change rate of glass viscosity reaches its minimum value at <r>=2.6.

New Functional Materials

Research Progress of CHA Molecular Sieve Membrane

HUA Shaoqiang, ZHOU Zhihui, WU Hongdan, DU Yijin, ZHANG Jian

2021, 40(5):  1698-1706. 

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CHA molecular sieve membranes have been favored by people because of their higher acid stability and better pore structure. The main systhesis methods include the liquid phase deposition, the vapor phase transfer, the microwave synthesis, the secondary growth, and the two-step variable temperature crystallization. Based on the synthesis mechanism, preparation of CHA membrane has there two means: synthesis gel containing structure directing agent (SDA) and SDA-free. The synthesis trend of SDA-free is the future development direction of CHA molecular sieve membranes due to shorter reaction time and better environmental benefits, which is generally to use Sr²⁺, Cs⁺, F^- or K⁺ instead of SDA to prepare CHA molecular sieve membranes. This article mainly discusses its synthesis mechanism. Synthetic CHA membranes with SDA are also introduced. At the same time, the flux, selectivity and stability of CHA molecular sieve membranes are reviewed. The application and research status of CHA molecular are discussed, and the future research development of CHA membrane has prospected.

Preparation and Photocatalytic Properties of Composite Catalyst ZnFe₂O₄/FeVO₄

LIU Shuai, XIE Yinde, YAN Shuo, HOU Baosen, LIU Ruijie

2021, 40(5):  1707-1713. 

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In order to degrade organic dyes in wastewater, the photocatalytic degradation of organic dyes by composite catalyst ZnFe₂O₄/FeVO₄ was studied to promote the healthy growth of aquatic organisms and the balance of the entire ecosystem. ZnFe₂O₄ was prepared by PVP assisted hydrothermal method, FeVO₄ was prepared by hydrothermal method and the composite catalyst ZnFe₂O₄/FeVO₄ was synthesized according to the different mass ratios of ZnFe₂O₄ and FeVO₄. The activities of ZnFe₂O₄, FeVO₄ and composite catalyst ZnFe₂O₄/FeVO₄ were tested under the same conditions with the methyl orange as the degradation dye. The experimental results indicate that composite catalyst ZnFe₂O₄/FeVO₄ is a high efficiency catalyst. Through SEM analysis, it is seen that the ZnFe₂O₄ and FeVO₄ are combined together. With the condition of adding H₂O₂, after 20 min of reaction, the dye degradation rates of ZnFe₂O₄ and FeVO₄ are only 15% and 25% respectively, and the dye degradation rate of ZnFe₂O₄/FeVO₄ reaches 75%. The effects of catalyst dosage, H₂O₂ concentration and pH value on the catalytic activity ZnFe₂O₄/FeVO₄ were investigated. The results show that ZnFe₂O₄/FeVO₄ samples have the best photocatalytic efficiency when pH value of the solution is 5.0, H₂O₂ concentration is 0.044 mol/L and the catalyst dosage is 1.0 g/L.

Synthesis of Ru Cs/Mo₂C Nanorods and Its Electrocatalytic Hydrogen Evolution

QIN Weiyan

2021, 40(5):  1714-1719. 

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Mo₂C is known as the most promising electrocatalytic hydrogen evolution catalyst, but its high overpotential and low efficiency restrict its large-scale production. In this paper, Ru nanoclusters (Ru Cs/Mo₂C) supported Mo₂C nanorod composites were prepared by a simple solvothermal method. The results show that Ru Cs/Mo₂C (Ru, mass fraction 7.79%) exhibits superior electrocatalytic hydrogen evolution performance, with a current density of 104 mV at the overpotential of 10 mA·cm^-2, and a Tafel slope of 96.30 mV·dec^-1. Meanwhile, Ru Cs/Mo₂C catalyst has excellent stability and broad application prospects in industrial electrolysis systems.

Synthesis of P-Type Zeolite from Oil Shale Ashand Its Adsorption to Co²⁺

ZHAO Wen, LI Hanfei, WU Wei

2021, 40(5):  1720-1727. 

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The thesis takes oil shale ash as the research object, adopts alkali fusion-hydrothermal synthesis method to synthesize P-type zeolite, and studies the influence of ash-alkali ratio, alkali fusion temperature, hydrothermal temperature, NaCl addition amount, and other conditions on the synthesis of P-type zeolite. And using the prepared P-type zeolite to carry out the Co²⁺ adsorption experiment. The results show that the addition of NaCl is beneficial to the synthesis of zeolite, while the increase in the ash-alkali ratio, alkali fusion temperature, and hydrothermal temperature is not conducive to the synthesis of zeolite. The removal rate of Co²⁺ in wastewater by oil shale ash and P-type zeolite shows an upward trend with the increase of adsorbent dosage. The adsorption performance of P-type zeolite for Co²⁺ is better than that of oil shale ash. And with the increase of the initial concentration of Co²⁺ solution, the removal rate of Co²⁺ by P-type zeolite gradually decreases.

Preparation of Modified Zeolite Ammonia Nitrogen Adsorbent and Its Application in Domestic Sewage Treatment

FU Jinxiang, ZHANG Yanping, LI Sen, YOU Kun, FAN Donghan, LI Xin

2021, 40(5):  1728-1734. 

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In order to solve the problem of excessive ammonia nitrogen in the drainage of conventional sewage treatment process in some areas, through the preparation of modified zeolite ammonia nitrogen adsorbent, combined with adsorption experiment, characterization analysis and pilot test, the performance of the modified zeolite ammonia nitrogen adsorbent for the removal of ammonia nitrogen from municipal domestic sewage was deeply studied and the optimum preparation process and removal characteristics of the modified zeolite ammonia nitrogen adsorbent were investigated. The results show that the modified zeolite ammonia nitrogen adsorbent has more sodium zeolite and pore channels, and the removal rate and adsorption amount of ammonia nitrogen reach 83.51% and 0.840 mg/g respectively at NaCl concentration of 1.5 mol/L, stirring time of 3 h and heating temperature of 75 ℃. The pilot test results show that the content of ammonia nitrogen in the water filtered by modified zeolite ammonia nitrogen adsorbent is stable below 2.0 mg/L, and the adsorbent can be recycled and reused. This study can provide theoretical basis for ammonia nitrogen treatment of municipal domestic sewage.

Effect of Surface Modified Zirconia Inorganic Filler on Properties of Dental Self-Etching Adhesive

TU Baoli, ZHANG Qinghong, WANG Haifeng, LIU Mei

2021, 40(5):  1735-1742. 

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By silica coating the surface of zirconia powder with sol-gel method and subsequently modifying the surface with silane coupling agent γ-methacryloxypropyltrimethoxysilane (γ-MPS), an inorganic filler for dental adhesive was prepared. Using bisphenol A-glycidyl methacrylate (Bis-GMA) monomer, triethylene glycol dimethacrylate (TEGDMA) diluent, 2-hydroxyethyl methacrylate (HEMA) amphoteric monomer, and 10-(2-methacryloyloxy)monodecyl phosphate (10-MDP) etching agent as main components, and the modified zirconium oxide is filled with a mass fraction of 1% to 10%, the bonding strength and other properties of self-etching adhesive were tested. The results show that the mechanical properties of the adhesive are significantly improved when the filler mass fraction is 2%, and the bonding strength is (31.63±1.53) MPa. However, when the mass fraction of ZrO₂ increases to 5%, the bond strength begins to decrease. Scanning electron microscope analysis of the bonding section shows that with the increase of ZrO₂ filling amount, the infiltration effect of self-etching adhesive on dentin tubules and composite resin is somewhat weakened, resulting in the decrease of bonding performance. The sample sections under the ultra-depth-of-field microscope shows that the presence of adhesive significantly reduces the gap between teeth and composite resin.

Road Materials

Effect of Salt Concentration on CR-WMA Cracking Characteristics under Freeze-Thaw Cycles

FENG Lei, CHEN Zheng, WANG Lan, LUO Xin

2021, 40(5):  1743-1750. 

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In order to scientifically analyze the effect of deicing salt erosion on the cracking characteristics of warm rubber powder modified asphalt mixture (CR-WMA) and hot rubber powder modified asphalt mixture (CR-HMA) under the action of freeze-thaw cycles, application of digital image (DIC) technique for three-point bending test repeated loading levels of the two semi-circular pieces under the test strain generated analysis were used for quantitative description damage cracking of asphalt mixture. The semicircular bending tensile test (SCB) was used to analyze the creep strain energy (DCSE) of the two specimens, and the correlation analysis with the damage and cracking index based on DIC technology was carried out. The test results show that the point with a larger value in the horizontal strain field is closely related to the evolution of damage and cracking of the specimen. The damage and cracking resistance of CR-WMA and CR-HMA first decreases and then increases with the increase of salt concentration at worst concentration of 8%. Whether it is frozen or salt water freezing conditions, D_E value and the value CR-WMA D_CSE relatively high CR-HMA, described CR-WMA cracking resistance and were superior erosion salt CR-HMA: it is found that D_E and D_CSE have a good correlation, which verifies the rationality of the DIC technology to evaluate the cracking characteristics of asphalt mixtures.

Effect of Internal Parameters of Activator on Performance of Alkali-Activated Grouting Material

CHI Fengxia, HAN Bo, CHENG Qinling, ZHOU Wenjing

2021, 40(5):  1751-1759. 

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Preparation of alkali activator by sodium silicate and sodium hydroxide, and the influence of the molar concentration of SiO₂ and module in activator on the performance of alkali-activated slag grouting material were studied. The results show that the fluidity of alkali-activated grouting material is mainly controlled by the molar concentration of SiO₂ in the activator, and the influence of module on the fluidity of grouting material is only reflected when the molar concentration of SiO₂ is high. The molar concentration of SiO₂ and module in activator are the key parameters affecting the autogenous shrinkage of alkali-activated grouting material, and jointly control the autogenous shrinkage of alkali-activated grouting material. When the molar concentration of SiO₂ in the activator is greater than 2 mol/L, in order to ensure that the alkali-activated grouting material has sufficient compressive strength at the later stage, the module should not be less than 1.2. The molar concentration of SiO₂ in the activator should be controlled below 4 mol/L to reduce the impact on toughness and durability.

Road Performance of Cement Stabilized Recycled Materials with Different Strength Waste Concrete

GUO Licheng, REN Huang, ZENG Guodong, HE Yuzhong, WU Chaofan, FANG Yang, HAN Qingkui, JIANG Yuelou

2021, 40(5):  1760-1766. 

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In order to study the influence law among the strength of waste concrete, the performance of recycled aggregate and the mechanical and durability performance of cement stabilized recycled base material, the compressive strength of different parts of the waste bridge T-beam concrete, waste bridge column concrete, and waste pavement cement concrete was tested. The estimated strength values of these three kinds of waste concrete were 25.8 MPa, 37.4 MPa, and 58.1 MPa. The effects of three kinds of waste concrete with different strength on the properties of recycled aggregate and mechanical and durability of cement stabilized recycled materials were analyzed. The results show that with the increase of the strength of waste concrete, the crushing value, the content of needle and flake particles, water absorption, liquid limit and plastic limit of recycled aggregate are decreased, but the plastic limit index and the relative apparent density is increased. With the increase of the strength of waste concrete, the best content of cement stabilized recycled mixture is obtained. The water absorption and relative apparent density of recycled aggregate are not affected by the strength.Besides, the best water ratio and the maximum dry density are approximately linear decreasing and increasing respectively. When the strength of waste concrete is increasing, the unconfined compressive strength at 7 d, 28 d, 90 d, and 180 d, the splitting strength at 7 d,28 d, and 90 d, and the compressive resilience modulus at 28 d and 90 d are increased about the waste bridge T-beam concrete, waste bridge column concrete, and waste pavement cement concrete. Moreover, the dry shrinkage water loss rate of the mixture and the dry shrinkage performance is also decreased. And the mass loss rate of the erosion test is reduced and the anti-erosion performance is enhanced. Overall, increasing the strength of waste concrete can effectively improve the road performance of cement stabilized recycled materials.