Table of Content

15 February 2021, Volume 40 Issue 2

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Cement and Concrete

Simulation and Emission Reduction Optimization of NO_x Generation in Cement Kiln Based on Aspen Plus

LIU Dingping, ZHOU Youkun

2021, 40(2):  351-358. 

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Aiming at the whole process of NO_x generation in the calciner and rotary kiln in the production process of cement kilns, the Aspen Plus software was used to establish a simulation model of the system, and the reliability of the model was verified by field test data. Then the model simulation was used to study the influences of temperature and combustion atmosphere in the calciner on NO_x. It is concluded that the temperature in the calciner changes from 804 ℃ to 1 050 ℃, and the NO_x concentration changes from 242 mg/m³ to 800 mg/m³. After the calciner temperature exceeds 900 ℃, the NO_x concentration rises sharply. The CO concentration in the calciner changes from 26 mg/m³ to 990 mg/m³, and the NO_x concentration drops from 585 mg/m³ to 154 mg/m³. The NO_x concentration in the calciner is greatly affected by the flue gas temperature in the rotary kiln. When the flue gas temperature of the rotary kiln rises from 900 ℃ to 1 400 ℃, the NO_x concentration in the calciner changes from 260 mg/m³ to 430 mg/m³. It is feasible to use Aspen Plus to simulate the NO_x changes of cement kilns, and the model setting is flexible, which can provide parameter optimization and data support for the NO_x control of cement kilns.

Effects of Antifreeze and Early-Strength Agent on Hydration of Sulphoaluminate Cement under Sub-Zero Temperature

LIU Yunpeng, LI Junhao, YANG Chao, LIU Zhichao

2021, 40(2):  359-367. 

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The effects of different antifreeze and early-strength agent on strength, microstructure and hydration products of sulphoaluminate cement (SAC) mortar curing at -20 ℃ for 7 d and 28 d without pre-curing were investigated. Mechanical property test, ultrasonic wave velocity test, mercury intrusion porosimetry (MIP) test, thermogravimetric (TG) analysis, X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) analysis were used. The results show that, the combination of inorganic antifreeze calcium nitrate with early-strength agents aluminum sulfate and triethanolamine promote the SAC hydration and microstructure development, which improve the mortar strength. The combination of organic antifreeze urea and calcium nitrate delays the SAC hydration and microstructure development, which reduce the mortar strength. Mortar with lower water-cement ratio show denser microstructure and higher strength. Ultrasonic wave velocity can characterize the microstructure development of mortar during heating process, which has a certain correlation with mortar strength.

Effect of Superfine CaCO₃ on Properties of Sulphoaluminate Cement-Based Double Fluid Grouting Material

WANG Yanfeng, LIU Songhui, HAN Kang, ZHANG Li, GUAN Xuemao

2021, 40(2):  368-376. 

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In order to further improve the mechanical properties and carbonation resistance performance of sulphoaluminate cement-based double fluid grouting material (SCGM), superfine calcium carbonate (SC) was synthesized by gas-liquid carbonation method, and the effect of SC content on the setting time, hydration and hardening performance, carbonation resistance performance and microstructure of SCGM was studied. The results show that SC promotes the hydration of SCGM, improves mechanical strength and carbonation resistance performance. When the SC mass fraction is 3%, the compressive strength of 6 h and 28 d increases by 29.40% and 26.43%, respectively. After 5 d of carbonation, the depth of carbonation was reduced by 24.12%, and after 7 d of carbonation, the carbonation shrinkage was reduced by 19.05%.The research results provide a new method for improving the mechanical properties and the carbonation resistance performance of SCGM.

Effect of Lithium Salt on Function of Borax in Sulphoaluminate Cement

SHEN Yan, ZHU Hangyu, WANG Peifang, ZHANG Wei

2021, 40(2):  377-383. 

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In the practical engineering application of sulphoaluminate cement, borax is commonly used as a retarder. However, borax can cause excessive retardation of sulphoaluminate cement. In order to control the setting time of sulphoaluminate cement, lithium salt was added to sulphoaluminate cement to control the effect of borax. The setting time, compressive strength and hydration products were analyzed. The results show that lithium hydroxide significantly shorten the setting time of the sulfoaluminate cement with 0.1% borax. The addition of lithium hydroxide reduces the compressive strength. In the case of 0.5% borax, the setting time of cement is greatly shortened due to the addition of more than 0.07% lithium hydroxide. The early compressive strength increases slightly with the increase of lithium hydroxide content, and the later compressive strength decreases slightly. The addition of lithium salt does not change the type of hydration products of sulphoaluminate cement with borax. In the case of 0.5% borax, the intensities of ettringite peaks decrease significantly after 1 d of hydration, while the intensities is not influenced at 28 d.

Property and Pore Structure of Nano-SiO₂ Modified High Volume Slag Powder-Cement Cementitious System

LIN Peitong, ZENG Yu, ZHAO Yonggang, LIU Jinhong, WANG Junfeng, LU Liulei

2021, 40(2):  384-391. 

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Using the strong pozzolanic activity of precipitation method nano-silica (PNS) to improve the early compressive strength and loose internal structure of the high volume slag powder-cement cementitious system. The influence of PNS on the compressive strength and the resistance to chloride ion permeability of high volume slag powder-cement cementing system were studied. The hydration products and pore structure of the system were analysed by XRD, TG-DSC and MIP. Research shows that with the increase of PNS content, the compressive strength of the specimens increases, especially the 7 d compressive strength. The strength of specimens with 5% (mass fraction, the same blow) PNS increases by 20%. The resistance to chlcride ion penetration capacity first increases and then decreaces. When PNS content is 3%, it reaches the optimal level, and its 28 d chloride ion diffusion coefficient is 44.8% lower than that without PNS. PNS can consume a large amount of Ca(OH)₂ in the early stage and generate more hydration products such as C-S-H gel, which makes the pore structure more compact and reduces the porosity. Incorporating PNS within the range also refines the pore size.

Effect of Heat Treatment on Physical and Mechanical Properties of Polymer Modified Fiber Reinforced Cementitious Composites

ZHOU Jianwei, YU Baoying, KONG Yaning, YANG Wen, CHENG Baojun

2021, 40(2):  392-400. 

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Polymer modified fiber reinforced cementitious composites were prepared by epoxy emulsion and emulsion powder. The effects of heat treatment at 200 ℃, 400 ℃, 600 ℃ and 800 ℃ on the physical and mechanical properties of the composites were studied. Results show that high temperature volume stability of specimen is improved by adding polymer. There is no cracking of specimens with polymer during heat treatment at 800 ℃. The temperature corresponding to the peak value of residual strength decreases from 400 ℃ to 200 ℃ under the condition of air cooling. The residual strength of specimens decreases continuouslyas the temperature of the heat treatment increases under water cooling. The polymer modified fiber reinforced cementitious composites collapses during water cooling after heat treatment at 800 ℃. The cross-linking channels formed by polymer decomposition in the specimen improve the pore structure of heat-treated specimen, which delays the degradation rate of high temperature heat treatment on the properties of the sample.

Research on Flowability of Cement Powder and Its Adhesion with Different Wall Materials

ZHAN Jiayu, LI Wanmin, FANG Guiming, LIANG Wenxue, YANG Feihua, ZHOU Yulun

2021, 40(2):  401-406. 

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The flowability of cement powders is closely related to the storage, transportation, feeding, mixing and other operations. The effect of moisture content on the flowability of cement powders was investigated by the repose angle, inner friction angle, adhesion and unconfined compressive strength. The wall friction angle and adhesion of cement powder with mortar, steel, coating and anticorrosive coiled material were compared. The results show that as the moisture content of cement powder increases, the repose angle, cohesion and unconfined compressive strength increase, and the flowability of cement powder decreases. With the increase of storage time, the flowability of cement powder becomes better with the increase in particle size caused by the hydration of cement. The unconfined compressive strength increases obviously with the increase in consolidation stress, resulting in the poor flowability of cement powder. The adhesion of cement powder on different wall materials increases with the increase of moisture content. The friction force and adhesion between cement powder and wall reduce by covering the inner surface of cement silo with coating or anticorrosive coiled material.

Different Methods for Measuring Hydraulic Conductivity of Cement-Soil

TONG Yuxiao, WEI Song, CHEN Qing, DENG Jiemei

2021, 40(2):  407-414. 

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Because of excellent physical and mechanical properties, cement-soil has been widely used in engineering construction. Compared with ordinary soil, the addition of cement makes cement-soil have lower permeability and better anti-seepage performance. The hydraulic conductivity of cement-soil is a principal indicator indicating the engineering properties of cement-soil, which can directly reflect the permeability of cement-soil. However, the current test methods for the hydraulic conductivity of cement-soil are unified, which may cause differences and deviations in actual work, so it needs to be studied. Based on the actual project, the onsite borehole water injection permeability test on the cut-off wall was conducted, and the indoor variable head permeability test and triaxial permeability test on the cement-soil sample made by core drilling were conducted at the same time.The results of the indoor test with the results of the field test were compared and the suitable indoor test method for detecting the cement-soil core sample were discussed.The influence of confining pressure on the hydraulic conductivity of cement-soil in the triaxial permeability test was analyzed. At the same time, the cement-soil samples were newly prepared indoors, the variable head permeability test, the triaxial permeability test and the cement-soil permeability test were carried out to study the difference of different methods to determine the cement-soil hydraulic conductivity. The study found that the original cement soil (core drilling) measured by the indoor triaxial permeability test is close to the result of the on site bore hole water injection permeability test. The hydraulic conductivity of original cement-soil (core drilling) measured by the indoor variable head test is too large. In the triaxial permeability test, the hydraulic conductivity of the undisturbed cement-soil sample will increase with the increase of pore water pressure when the confining pressure is 0, and the hydraulic conductivity will decrease with the increase of confining pressure when it changes. After the confining pressure is 20 kPa higher than the pore water pressure, the hydraulic conductivity becomes stable. The test results of indoor variable head permeability test, the triaxial permeability test and cement-soil permeability test are basically similar to each other. It can be concluded that the indoor triaxial permeability test is more suitable for measuring the hydraulic conductivity of undisturbed cement soil (core drilling) than the indoor variable head test. The Nan 55 type infiltration meter, the stress-strain controlled triaxial shear permeability test and cement soil permeability tester can be used to identify the hydraulic conductivity of cement soil (indoor preparation). The research results have important reference significance for the method of measuring the permeability coefficient of cement soil.

Research Progress on Application of Sea Sand Concrete under Strong Dynamic Load

YANG Chenglin, XU Ying, HONG Jian, KONG Xinli

2021, 40(2):  415-422. 

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Constructions of islands and reefs are of great significance to safeguard rights and interests of our country. However, it is time-consuming, laborious and uneconomical to transport concrete raw materials from the mainland to islands and reefs. Therefore, sea sand concrete made from the existing resources on islands and reefs has become an important building material in the construction of islands and reefs. In this paper, the research on static and dynamic mechanical properties of sea sand concrete materials are summarized and the mechanical properties of fiber reinforced polymer (FRP) bar-sea sand concrete structure are systematically introduced. Meanwhile, it is pointed out that the dynamic mechanical properties of sea sand concrete should be further studied. The recent researches show that sea sand concrete has higher early strength and the final strength is equivalent to ordinary concrete. Reasonable fiber addition significantly improve the mechanical properties of sea sand concrete. Strain rate effect of sea sand concrete is obvious. FRP bar-sea sand concrete structure with its great corrosion resistance can be better used in a wide range of marine environment and it is an important choice for protective structures. The current international situation is more complex, and the reef construction projects may be subject to explosion, penetration and other extreme loads. It can be concluded that the researches on dynamic mechanical properties of sea sand concrete need to be further strengthened. Therefore, the further researches on the impact resistance and anti-explosion performance of FRP bar-sea sand concrete composite structure are of great significance.

Effects of Curing Regimes on Tunnel Fire Resistance of Self-Compacting Concrete Coated with Aerogel Cement Paste

XU Donghang, ZHU Pinghua, CHEN Chunhong, LIU Hui, LIU Shaofeng

2021, 40(2):  423-430. 

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To further strengthen the protective effect of aerogel cement paste (ACP) coating for self-compacting concrete (SCC) in a simulated tunnel fire (1 100 ℃, 2.5 h), the influence of wet curing time (7 d to 28 d, based on site construction curing regimes) on tunnel fire resistance of SCC coated with ACP was investigated. The experiment results show that the non-composite C40 SCC burst after simulated tunnel fire, with 116 times of burst and 0 residual compressive strength. In contrast, SCC coated with ACP under different curing regimes have no burst. The more loose microstructure of ACP, the more microcracks are generated under fire. Microcracks accelerate the damage of cement paste and reduce fire resistance of ACP. Under all curing regimes, the thermal conductivity of ACP under 14 d wet curing is the lowest (0.179 W/(m·K)), and the residual compressive strength of SCC coated with ACP under this curing regime is the highest (13.5 MPa). 14 d wet curing is the optimal curing regime.

Effect of Curing Temperature on Hydration and Mechanical Properties of UHPC

LUO Yaoling, YANG Wen, XIE Yuhao, YAN Xinyi, BI Yao

2021, 40(2):  431-438. 

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The mechanical property and hydration of ultra-high performance concrete (UHPC) are enhanced by heat curing. However, the long-term performance of UHPC has not been studied systematically. The mechanical performance testing, scanning electron microscope (SEM), and X-ray diffraction (XRD) were used to research the long-term mechanical performance and hydration of UHPC after 5 different curing temperatures (20 ℃ standard curing, 90 ℃ steam curing, 120 ℃ dry heat curing, 200 ℃ dry heat curing and 250 ℃ dry heat curing). The test results indicate that the early compressive strength of UHPC is significantly improved by accelerating the hydration, especially the curing temperature exceeding 200 ℃ due to the generation of xonotlite. The influences of different curing temperatures on the long-term strength of UHPC are different. The long-termcompressive strength of UHPC still continues to grow after 90 ℃ steam curing and 120 ℃ dry heat curing, while the long-term compressive strength of UHPC has a significant decrease after 200 ℃ dry heat curing and 250 ℃ dry heat curing. The change of long-term compressive strength mainly depends on the content of remaining unhydrated particles in UHPC after early hydration.

Influences of Active Admixtures on Anti-Carbonization Performance of Concrete

WANG Yilin, WANG Shunyao, LIU Qiaoling

2021, 40(2):  439-446. 

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The influence of strength grade (C30 and C45), age (28 d and 120 d) and mineral admixture (mineral powder and fly ash) mass content on the anti-carbonization performance of concrete mixed with high efficiency aliphatic superplasticizer(SAF) was studied. A regression model between the carbonization depth of C30/C45 concrete at 28 d/120 d age and the proportion of mineral powder/fly ash was established. The results show that the reduction of water-binder ratio and the extension of curing age improve the compactness of cement stone, which improve the compressive strength and carbonization resistance. The anti-carbonization performance of concrete increases with the increase in the amount of mineral powder and the decrease in the amount of fly ash. When the mass fraction of mineral powder in the cementing material is 37.5%, the carbonization resistance of C30 concrete is the best. When the mass fraction of mineral powder in the cementing material is 31.9%, the carbonization resistance of C45 concrete is the best. When the age increases, the greater the proportion of fly ash, the greater the decrease in carbonization depth. When the relative proportion of mineral powder and fly ash content changes, the degree of influence on low-strength concrete is greater than that of high-strength concrete.

Mechanical Properties and Acoustic Emission Response of Steel Fiber Reinforced Concrete under Real Time High Temperature

LIU Xin, HOU Xinyu, LIN Jun, JING Jingjing, LIU Weiping, SHE Junwen, ZHU Hao

2021, 40(2):  447-454. 

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The uniaxial compression tests of the reference concrete and steel fiber reinforced concrete under the thermo-mechanical coupling were tested, the acoustic emission technology was used to monitor the concrete under the action of thermo-mechanical coupling. The results show that compared with the reference concrete at the same temperature, in mechanical properties, the compressive strength of steel fiber reinforced concrete with four temperature ranges from 20 ℃ to 600 ℃ increases by 12.07%, 4.15%, 11.25% and 3.24%, the residual strength increases by 2.67 MPa, 3.51 MPa, 0.98 MPa and 2.74 MPa, and the stress curve of steel fiber reinforced concrete has better ductility. In acoustic emission, compared with the same temperature of the reference concrete, the steel fiber reinforced concrete releases more energy during the process of compression. The acoustic emission signal has higher activity and intensity, and the signal is longer in dense bands, and the maximum ringing cumulative count is greater, the macroscopic mechanical properties of concrete and its acoustic emission response have a good corresponding relationship. The steel fiber can delay the deterioration and damage of concrete at high temperature in real time.

Strength Prediction of Mechanical Properties of Polypropylene Fiber Reinforced Concrete after High Temperature Based on Machine Learning

LIANG Ninghui, YOU Xiufei, CAO Guojun, LIU Xinrong, ZHONG Zuliang

2021, 40(2):  455-464. 

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There are many factors affecting the mechanical properties of polypropylene fiber reinforced concrete (PFRC) after high temperature. Therefore, the relevant experimental period is long and experimental volume is large. How to use the existing experimental data to predict the strength of PFRC after high temperature effectively improves the test efficiency and provide reference for practical projects. By studying the influences of fiber scale, fiber content and temperature on concrete strength, three models, namely regression tree (RT), support vector regression (SVR) and BP artificial neural network, were established. The experimental values of splitting tensile strength and compressive strength of PFRC at different heating temperatures (20 ℃, 200 ℃, 400 ℃, 600 ℃, 800 ℃) were compared with the predicted values. The results show that three models predict the splitting tensile strength and compressive strength of PFRC at high temperature with high precision. Compared with the measured value, the relative error between the predicted value and the measured value of three models are basically controlled within 15%, except for individual data. By comparing the mean absolute error (U_MAE) and average correlation coefficient R² of three models, the prediction results of artificial neural network (ANN) model are better, which verifies the reliability of machine learning in predicting the mechanical properties of PFRC after high temperature.

Thermal Expansion Coefficient of Carbon Nanotubes Reinforced Face Slab Concrete of Rockfill Dam at Early Age

ZHAO Zhifang, WU Xu, ZHANG Zhenyu, QI Jieyi, ZHANG Guangbo, XU Jiaming

2021, 40(2):  465-472. 

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Thermal stress is the main cause of non-structural cracking of rockfill dam face slab concrete. The coefficient of thermal expansion (CTE) is directly related to the thermal deformation and thermal stress of concrete. Carbon nanotubes (CNTs) have good mechanical properties and unique nano-effects of one-dimensional nanomaterials. CNTs also have great potential in improving the CTE of face slab concrete. The construction mix concrete (JC) and the face slab concrete (NC) with 0.1% (mass fraction) CNTs were prepared, and the temperature stress testing machine (TSTM) was used to measure the free strain of the early age concrete under temperature matching curing (TMC) mode and the constant temperature mode. The CTE value of early age concrete was calculated and a time-varying CTE model of face slab concrete was proposed. The results show that the CTE of two kinds of face slab concretes quickly decrease to a minimum value after final setting, and finally slowly increase to a stable value. The incorporation of CNTs increases the CTE of the face slab concrete near the final setting, but reduces the stable value of the concrete CTE.

Deterioration Law of Recycled Concrete under the Coupling of Chloride and Freeze-Thaw

XIE Guoliang, SHEN Xiangdong, LIU Jinyun, ZHANG Bin

2021, 40(2):  473-479. 

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In order to study the damage and deterioration law of recycled concrete in severe cold and saline environment, the recycled coarse aggregate mass replacement rate of 0%, 50%, and 100% of recycled concrete were prepared to carry out the experimental study under the coupling of chloride and freeze-thaw. And its damage and deterioration law was discussed from the aspects of appearance, mass loss rate, relative dynamic elastic modulus and compressive strength. The results show that the damage to recycled aggregate concrete caused by chloride and freeze-thaw increases with the increase in the replacement rate of recycled aggregate.Compared with 200 freeze-thaw cycles and 0 freeze-thaw cycles, the mass loss rate, relative dynamic elastic modulus and relative compressive strength of the recycled concrete with 100% replacement rate decrease by 6.8%, 54.2% and 50.5%, respectively. The mass loss rate used to evaluate the durability of recycled concrete against salt and freezing has certain limitations. The loss rate of compressive strength is more suitable to characterize the degree of durability damage of recycled concrete than the relative dynamic modulus. A linear evolution model based on the loss of compressive strength as the damage variable is established. The model characterizes well the damage and deterioration of recycled concrete under the action of chloride and freeze-thaw, and provides a theoretical basis for the use of recycled concrete in severe cold and saline areas.

Coupled Multiphase Numerical Analysis of the Effect of Drying-Wetting Cycles on Chloride Ion Distribution in Concrete

LI Rongtao, TUAN Christopher Y.

2021, 40(2):  480-484. 

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Due to corrosion of steel by chloride ions, the durability of reinforced concrete structure is influenced strongly by chloride ingress. In order to study the effect of environmental humidity on chloride ion distribution in concrete, a coupled multiphase model of chloride ions penetration was developed. The variation of chloride ion erosion process with environmental humidity was studied by numerical simulation. The numerical simulation results show that the change of environmental humidity not only drives moisture transfer within the concrete, but also has significant effect on the chloride ion distribution in concrete, particularly induces formation reactions of salt crystals inside the concrete pores, which is recognized to be a major factor of degradation of concrete. The numerical simulation results will provide important reference for the anticorrosion design of concrete structures.

Solid Waste and Eco-Materials

Research Progress on Purification and Application of High-Silicon Magnesite

QI Xin, LUO Xudong, LI Zhen, ZHOU Yuanpeng, PAN Zhenzhong

2021, 40(2):  485-492. 

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Magnesite is one of superior mineral resources in China. It has been widely used in metallurgy, building industry, chemical industry etc. High-silicon magnesite (SiO₂＞3%, mass fraction) is one of low-grade and difficult-to-select magnesite with high content of SiO₂. High-quality magnesia products are prepared from high-silicon magnesite by flotation. By direct calcination of high-silicon magnesite with reasonable ingredients, high value-added refractory materials such as magnesia-silica, forsterite and composite powder materials are prepared. Important raw materials such as building materials and chemical materials are also prepared from high-silicon magnesite. Hence high-silicon magnesite has high economic and scientific research value. In the paper, the purification processes of high-silicon magnesite at home and abroad were reviewed. The purification principles and technical indicators were expounded. Finally the comprehensive utilization of high-silicon magnesite were introduced.

Research Progress on Layered Silicate Clay/Silicone Rubber Nanocomposites

ZHAO Huahua, SONG Huanling, TAO Xinyao, CHEN Gexin, WANG Aiqin, CHOU Lingjun

2021, 40(2):  493-504. 

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Layered silicate clay has attracted great attention in improving the properties of silicone rubber due to its unique nano-layered structure, resourceful, low-cost and pollution-free characteristics. Recent advances in the mechanism and properties of silicone rubber nanocomposite materials modified with layered silicate clay including 2∶1 structure such as montmorillonite, attapulgite and 1∶1 structure such as kaolinite and halloysite are reviewed. In this article, the emphasis of the recent studies is pointed out to be the improvement of the performance of silicone rubber. And uniform dispersion of the layered silicate clay particles into silicone rubber matrix is crucial and challenging due to the disparity in hydrophilic and hydrophobic character of the layered silicate clay and the rubber matrix. The development of layered silicate clay/silicone rubber nanocomposites is prospected in order to provide reference for the deep-digging of the modified layered silicate clay and silicone rubber nanocomposites with high performance.

Main Influencing Factors of Ammonium Sulfate Crystallization in Ammonia Desulfurization Process

DAI Meng, HUANG Bangfu, LI Lu, WANG Defu, YANG Zhengyu, LUO Feng, YE Fuyin, LI Ming

2021, 40(2):  505-512. 

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Ammonia desulfurization technology has many advantages compared with other desulfurization technologies. This technology can effectively control SO₂ and also obtain by-product fertilizer ammonium sulfate, but it has the problems of small by-product ammonium sulfate crystal particles and low crystal formation rate. Therefore, the effects of seed crystals, Fe³⁺, additives and suspended solids on the crystallization of ammonium sulfate were reviewed. The mechanism of various factors on the nucleation of ammonium sulfate was analyzed. The current research deficiencies were summarized, and the key research direction of ammonium sulfate crystallization in the future was prospected.

Composition Design and Multi-Scene Application of Grouting Material for Sandstone Stone Cultural Relics

WANG Xiaofei, WEI Xiaohong, ZHU Jianfeng, LUO Hongjie, WANG Fen, SHI Pei, ZHANG Biao

2021, 40(2):  513-520. 

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In order to prepare a sandstone stone cultural relic grouting material with adjustable properties and meet the requirements of multi-scene application, the four-angle experiment method was adopted. The hydraulic lime (NHL2), sulphoaluminate cement (SAC), metakaolin (MK) and water-based epoxy resin (WER) were used as raw materials to prepared grouting materials with different formulations. Furthermore, the mechanical properties, setting time, fluidity and abonding strength of the grouting material were tested and analyzed. The results indicate that the grouting material with higher content of NHL2 and MK is suitable for repairing murals or mosaic patterns because of its low compressive strength and bonding strength. The grouting material with higher content of SAC and WER has higher compressive strength and bonding strength, which is suitable for repairing cliff and overhanging sandstone stone relics. Besides, the grouting material with higher content of WER and MK has good toughness and deformation ability, and it is suitable for repairing sandstone cultural relics susceptible to external stress.

Simulation Analysis of Mechanical Properties of Marble Containing Hole with Weak Intercalation

LUO Xulin, WANG Guozhu, HAO Yaxun

2021, 40(2):  521-526. 

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To study the failure mode and mechanical properties of marble with one weak intercalation and central hole under uniaxial compression, the fracture process of the sample is simulated by the numerical simulation software RFPA2D. The results show that the existence of the weak intercalation changes the failure mode of the marble sample. When the strength of the weak intercalation is lower and the thickness is larger, the marble under the weak intercalation basically does not appear failure. When the strength of the weak intercalation is unchanged, the peak stress of the marble sample decreases with the increase of the thickness of the weak intercalation, and the strain corresponding to the peak stress increases with the increase of the thickness of the weak intercalation. When the thickness of the weak intercalation is constant, the peak stress of marble sample increases with the increase of the strength of the weak intercalation, and the strain corresponding to the peak stress decreases with the increase of the strength of the weak intercalation. The results reveal the failure mode and mechanical characteristics of marble containing holes with different thickness and strength weak intercalation, which provides some reference for the instability failure of the rock mass engineering in the upper part of the weak intercalation.

Microwave Irradiated Coal Series Kaolin and Its Oil Absorption Performance

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

2021, 40(2):  527-533. 

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As a raw material, Shanxi coal series kaolin (3 g) was processed under the microwave of 1800 W to increase the oil absorption value of coal series kaolin. The morphology and structure of kaolin before and after treatment were analyzed by means of scanning electron microscopy, X-ray diffractometer, infrared spectrum analyzer, and specific surface area analyzer. The results show that the oil absorption value of coal series kaolin increases first and then decreases with the increase of microwave treatment time. The oil absorption value reaches the highest (74.4 g/100 g) when the treatment time is 17.5 min (the highest temperature is 1 100 ℃), which is higher than the original kaolin by 61%. At this time, the adsorption average pore diameter of calcined kaolin is the largest and a small amount of mullite is produced. As the microwave process time increasing, the calcined kaolin sinters, which causes the closure of internal pores and the decrease of the oil absorption value. The oil absorption value of calcined kaolin is related to its adsorption average pore diameter and pore size distribution, and the production of a small amount of mullite can promote the increase of the oil absorption value.

Preparation and Hydration Characteristics of Antimony Tailings Powder-Based Composite Cementitious Material

WANG Hao, DENG Hang, LIU Shuhua

2021, 40(2):  534-541. 

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Antimony tailings fine powder was used as the main raw material, supplemented with cement clinker, activator and accelerator to prepare antimony tailings powder-based composite cementitious material. Hydration characteristics of composite cementitious materials in terms of mechanical properties and microstructure were investigated. The results show that compressive strength of specimen slurry decreases with the increase of the amount of antimony tailings fine powder. When the mass fraction of admixture is 70%, it still meets the requirements of tailings solidification and damming. Effects of different activators on the strength of composite cementitious materials are significantly different. When phosphogypsum and quicklime are mixed and the mass ratio is 2∶1, the activition effect of specimen is the best, and compressive strength reaches 10.42 MPa in 7 d. The final hydration products of specimen slurry are mainly C-S-H gel, calcium hydroxide, and a small amount of ettringite. When aluminate cement is selected as the accelerator and the mass fraction is 3%, it effectively shortens the setting time of specimen and meets the requirements of rapid solidification. The use of antimony tailings powder-based composite cementitious material achieves rapid in-situ solidification of fine-grain antimony tailings.

Desilication Reaction and Kinetics of Aluminum-Extracting Silicon Slag in NaOH Solution

XIAO Yongfeng, CHEN Aiguo, ZHANG Yuwei, JIANG Xiaolin, LIU Huidong

2021, 40(2):  542-547. 

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The desilication behavior of amorphous SiO₂ in NaOH solution was studied by taking aluminum silicon slag extracted from an acid method fly ash in Inner Mongolia as the object. Through the change of desilication rate with time in the desilication reaction, the effects of stirring speed, reaction temperature and NaOH solution concentration on the desilication rate of SiO₂ were studied. By fitting the experimental data, the kinetic law and macroscopic kinetic equation of desilication reaction were determined, and the corresponding apparent activation energy was calculated. The results show that the stirring speed has little effect on the desilication rate, and the desilication rate greatly increases by increasing the reaction temperature and concentration of NaOH. The desilication reaction of aluminum-extracting silicon slag in NaOH solution is controlled by chemical reaction and conforms to Avrami equation. The apparent activation energy of desilication reaction is 82.086 kJ/mol.

Durability of Geopolymers under Different Erosion Environments

QIU Xiumei, LIU Yadong, YAN Chunjie

2021, 40(2):  548-556. 

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Geopolymer is a kind of new green cementitious material with network structures and amorphous phase, which has the characteristics of mineral and polymer materials. Fly ash and metakaolin were respectively used as raw materials to prepare geopolymer through alkali excitation. The durability of geopolymers (curing 28 d) under 5%HCl, 10%NaOH, 5%MgCl₂+5%NaCl, and 5%H₂SO₄ (all were mass fraction) erosion environment for 1 d to 84 d were researched. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), mass change and compressive strength reveal that geopolymers show different responses under different erosion environments. Fly ash based geopolymer exhibits excellent durability in low concentration of H₂SO₄, NaOH and salt solution, shows stability in microstructure, appearance, mass and compressive strength. Metakaolin based geopolymer has stable structure and property in salt solution. But under HCl erosion environment, the loss of mass and compressive strength for two geopolymers are significant, indicating obvious corrosion. The durability of fly ash based geopolymer in low concentration acid and base solution is more excellent than that of metakaolin based geopolymer. The potential application of these geopolymers is marine construction.

Mix Design and Performance Research of Environment-Friendly Sleeve Grouting Material

HU Xing, CHEN Dongping, YU Linwen, WANG Wenwen, WU Wenjie

2021, 40(2):  557-564. 

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Alkali activated slag cement is selected as the binding material, combined with the tightly packed theory of Dinger-Funk equation, fly ash float beads are used as mineral admixture and copper tailings are used to replace natural sand to improve the bulk density of powder, so as to prepare sleeve grouting material. This experiment studied the effects of plastic expansion agent dosage, fly ash float beads dosage, copper tailings dosage, and the sand-binder ratio on the performance of sleeve grouting material. The closest packing design mix ratio was verified. The results show that with the increase of plastic expansion agent content, the vertical expansion rate of the sleeve grouting material increases continuously, the fluidity increases, and the early compressive strength decreases. With the increase of fly ash float beads content, the fluidity of the sleeve grouting material continues to increase, while the compressive strength continues to decrease. With the increase of copper tailings content, the fluidity of the sleeve grouting material continues to decrease, and the compressive strength first increases and then decreases. When the mass ratio of sand-binder increases, the fluidity of the sleeve grout material continues to decrease, and the compressive strength first increases and then decreases. When the plastic expansion agent is 0.2%, the sand-binder ratio is 1.1, the fly ash float beads content is 12%, and the copper tailings content is 13% (the above are all mass fraction), the sleeve grouting material prepared with the mix design has excellent performance. The initial fluidity is 340 mm, 30 min fluidity is 280 mm, 1 d compressive strength is 37.2 MPa, 3 d compressive strength is 63.0 MPa, 28 d compressive strength is 86.4 MPa, 3 h vertical expansion rate is 0.20%, 24 h vertical expansion rate is 0.36%.

Performance Influence Mechanism of Lightweight Plastering Phosphorus Building Gypsum

WU Chao, YANG Lin, LI Wei, WANG Jiacai, CAO Jianxin, LI Jianqiu

2021, 40(2):  565-572. 

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Light gypsum plaster was prepared by using phosphorus building gypsum (PBG), sodium citrate (SC), methyl cellulose (MC) and vitrified microsphere as raw materials. The influence mechanism of admixtures and lightweight aggregates on mortar properties was systematically analyzed. The results show that sodium citrate improves the fluidity of mortar, and the compressive strength of the sample reaches 16.3 MPa when the content of sodium citrate is 0.8% (all the content are mass fraction). However, the fluidity of the mortar is reduced by methylcellulose, and the compressive strength of the sample is only 11.3 MPa when the content is 0.40%. The density of the mortar added with vitrified microsphere decreases, and the fluidity and setting time of the mortar also decrease. The water retention rate and tensile adhesive strength of hardened body increase. When 95% phosphorus building gypsum, 5.0% vitrified misrosphere are used and 1.0%SC and 0.20%MC are added by according to the quality of PBG, the properties of the mortar samples can meet the requirements of lightweight plaster gypsum properties in GB/T 28627—2012 “gypsum plaster”. With the increase of SC content, the morphology of dihydrate gypsum, which is the hydration product of lightweight plastering gypsum, changes to long strip and needle shape. The crystal crystallinity decreases and the overlapping degree increases, which makes the flexural strength increase, the compressive strength and tensile adhesive strength decrease. With the increase of MC content, the morphology of dihydrate gypsum, which is the hydration product of lightweight plastering gypsum, becomes thick plate, the degree of overlapping between crystals and crystallinity increases, which makes the hardening strength increase.

Characteristics of Interface Transition Zone of Waste Tire Rubber Concrete

ZHU Xingtong, GENG Ou, ZHU Siyuan

2021, 40(2):  573-578. 

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SEM, EDS and other equipments were used to study the micro morphology, hydration product distribution and the width of interface transition zone (ITZ) in 1 mm to 3 mm waste tire rubber concrete. The results show that the interface bond between rubber and cement stone in rubber concrete is weaker than that between coarse aggregate and cement stone, that means rubber concrete has looser structure and higher porosity of ITZ than ordinary concrete.The content of hydrated calcium silicate (C-S-H) in hydrated products of ITZ of rubber concrete is less than that of ordinary concrete, while the content of calcium hydroxide (CH) and ettringite (AFt) crystals is higher than that of ordinary concrete. The width of ITZ of 1 mm to 3 mm waster tire rubber concrete is about 50 μm, while that of ordinary concrete is only 40 μm, so rubber concrete have more unstable interface transition zone.

Influence of Municipal Sludge Dosage on Performance of Coal Gasification Slag Ceramsite

GAO Yuxin, LI Kunjie, MA Jianfeng, GAO Da, YANG Wen, BI Yao, LUO Yaoling

2021, 40(2):  579-586. 

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The coal gasification slag was used as the main material to sinter ceramsite, and the sintering system of ceramsite was studied. In addition, the influence of municipal sludge dosage on the basic properties, pore structure and microscopic mechanism of ceramsite were studied. The results show that the strength of coal gasification slag ceramsite is reached to 11.3 MPa when the preheating temperature 500 ℃ for 30 min and sintering temperature 1 100 ℃ for 15 min. The compressive strength of ceramsite is greater than 6.5 MPa when the municipal mass content is 20% in this sintering system. Besides, the porosity and average pore diameter of ceramsite increase with the increase of sludge content, and the internal structure of ceramsite became loose, which increases the water absorption rate, reduces the apparent density, and adversely affects the strength of the ceramsite.

Ceramics

Investigation on Phase Transition of Al₂O₃ Doped with TiO₂ and SiO₂

LIN Congyi, SUN Xiaoman, LI Wei

2021, 40(2):  587-590. 

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TiO₂, SiO₂ and TiO₂ + SiO₂ doped Al₂O₃ powders were prepared by ball milling. After calcination at different temperatures, X-ray diffraction (XRD) tests were carried out, and the effects of these three kinds of doping on the phase transition temperature of Al₂O₃ powder were compared. The results show that TiO₂ and SiO₂ doping promote the phase transition from γ-Al₂O₃ to α-Al₂O₃ effectively. In the case of doping mass fraction of 0.5%, temperatures of γ-Al₂O₃ to α-Al₂O₃ are reduced by 100 ℃ and 125 ℃ respectively. The effect of TiO₂+ SiO₂ co-doping on the phase transition of Al₂O₃ is better than that of TiO₂ and SiO₂ alone. The doping of 0.3% (mass fraction) TiO₂ and 0.3% (mass fraction) SiO₂ reduces the temperature of γ-Al₂O₃ to α-Al₂O₃ by 150 ℃. In addition, the mechanism of TiO₂, SiO₂ and TiO₂+SiO₂ doping to promote the phase transformation of Al₂O₃ powder was analyzed.

Subcritical Hydrothermal Removal of Si Impurity in β-SiC Powder

WANG Bo, DUAN Xiaobo, DENG Lirong, LU Shuhe, WANG Xiaogang, BAI Xiao

2021, 40(2):  591-596. 

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The β-SiC powder synthesized by the multi-heat source method was selected as the raw material, and the Si impurity in the β-SiC powder were removed by the subcritical hydrothermal method. The phase composition, microstructure and Si impurity content of β-SiC powder were characterized by XRD, SEM, EDS and visible spectrophotometer, and focused on the optimization of subcritical hydrothermal removal process parameters for Si impurity in β-SiC powder. The results show that the Si impurities in β-SiC powder are mainly SiO₂ and free silicon (F·Si), while the F·Si mainly existe in the form of large particles. The increase of reaction concentration, reaction time and reaction temperature have beneficial to improve the removal rate of Si impurities. The best hydrothermal treatment process is as follows: the liquid-solid ratio is 5∶2, the NaOH concentration is 4 mol·L^-1, the best reaction temperature is 180 ℃, and the best reaction time is 4 h. Under this process, the removal rate of SiO₂ in β-SiC powder reaches 100%, and the removal rate of F·Si is 96.4%.

Preparation and Properties of Foamed Ceramicsfrom Turmeric Residue

TAN Hongbo, LYU Zhouling, MA Baoguo, JI Xiaoli, LIU Xiaohai, JIAN Shouwei

2021, 40(2):  597-604. 

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As a new type of building wall material, foamed ceramics have the excellent characteristics of lightweight and heat preservation, which is conducive to building energy saving. A new type of closed-cell foamed ceramics was prepared by mixing, tableting, sintering and other processes with turmeric slag as the main billet, adding proper amount of Macheng stone powder to optimize the billet composition, and SiC as the foaming agent. The effects of firing system, molding pressure, foaming agent content, and stone powder content on the macroscopic properties and microscopic characterization of turmeric residue foamed ceramics were studied. The test results show that when the firing temperature is 1 130 ℃, the heating rate is 5 ℃/min, the molding pressure is 1 MPa, the SiC content is 0.5%, and the Macheng stone powder content is 40% (both are mass fraction), the turmeric waste slag foamed ceramics has the best preparation effect and the best overall performance.

Preparation and Properties of Foamed Ceramics from Fly Ash

ZHOU Mingkai, LIU Jianfeng, GE Xuexiang, LI Zhenyu

2021, 40(2):  605-609. 

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In the face of increasingly scarce ceramic raw materials, the use of solid waste to prepare foamed ceramics has become an inevitable trend. The fly ash was used as the main raw material to study the effects of chromium slag content, cullet content and grinding process on fly ash foamed ceramics. The results show that the properties of fly ash foamed ceramics are improved by adding appropriate amount of chromium slag, and small amount of cullet has little effect on the properties of fly ash foamed ceramics. When the ratio of raw materials is m(fly ash)∶m(chromium slag)∶m(feldspar)∶m(cullet)=60∶10∶20∶10, the foamed ceramics with average pore diameter of 0.64 mm, bulk density of 368.54 kg/m³ and compressive strength of 8.11 MPa is prepared by wet grinding for 3 h.

Effect of Fumed Silica on Properties of Glazed Coating in Restoration of Porcelain Relics

JIA Hanhui, WEN Jianhua, ZHOU Hua

2021, 40(2):  610-615. 

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The colorless and transparent organic coating used in the restoration of porcelain relics is called glazed coating. Currently, the traditional glazed coating products have two common shortcomings: the lack of hardness and poor ageing resistant performance.In order to make the glaze coatings better meet the needs of restoration, three kinds of imitated glaze coatings (nitrocellulose lacquer, acrylic gloss and waterborne polyurethane lacquer), which are commonly used in ceramic restoration, were modified by using fumed silica powder. And conducted a series of performance tests on the hardness, gloss, contact angle, adhesion and aging resistance of the coating before and after modification. The results of performance test show that when the volume proportion of fumed silica powder is 5%, the pencil hardness of the nitrocellulose lacquer film is increased to 3H, the pencil hardness of the acrylic gloss and polyurethane lacquer is increased to H. The performance in adhesion, light aging resistance, environmental weather resistance and pollution resistance of these three coatings have also be improved while the glossiness is reduced.

Unification of Abrasion Resistance Standard for Unglazed Tiles and Glazed Tiles

SU Huazhi, YU Yougen, LIU Yijun, WU Jianqing

2021, 40(2):  616-621. 

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Abrasion resistance is a key performance of ceramic tiles. At present, GB/T 4100—2015 "Ceramic tiles" requires that different test methods are used for unglazed tiles and glazed tiles. Abrasion resistance of unglazed tiles and glazed tiles were determined by deep abrasion equipment, surface abrasion apparatus and Taber abraser respectively. Whether the same test method can make accurate judgment on ceramic tiles was discussed. The results show that unglazed tiles can be determined by the method of resistance to deep abrasion for unglazed tiles and the method of relative resistance to wear of unglazed ceramic tiles by the Taber abraser. But neither of them is suitable for glazed tiles. Replacing visual evaluation with the loss in mass can get more objective and accurate results in the test method of resistance to surface abrasion for glazed tiles, and applicable to the determination of abrasion resistance for both unglazed tiles and glazed tiles.

Glass

Study on t-ZrO₂ Phase Transition to ImproveTensile Strength of Enamel

LI Zhiheng, XU Kunshan, XU Wenyou, XUE Hongxi, LIU Jie

2021, 40(2):  622-629. 

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The mechanical properties of the enamel coating were enhanced by adding tetragonal zirconium oxide (t-ZrO₂). The changes in the surface strain of the enamel were researched through a three-point bending experiment, and the fracture section is analyzed by XRD, SEM, and Raman. The results show that adding a proper amount of t-ZrO₂ improves the surface morphology of the enamel and reduces the number of pores. In the three-point bending experiment, the maximum force of the enamel with 2%t-ZrO₂ mass content increases by 7 kN. Cracks appear under the action of 11 kN three-point bending pressure, and the strain value increases by about 37%. The t-ZrO₂ enamel sample has a phase transition from t-ZrO₂ to m-ZrO₂ before and after the fracture. The crack deflection occurs at the boundary between the t-ZrO₂ phase and the original enamel phase, which restricts the crack propagate.

Theory and Analysis of Sound Insulation Performance of Composite Tempered Vacuum Glass

WANG Lu, YUE Gaowei, LIN Haixiao, LI Yanbing

2021, 40(2):  630-637. 

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Tempered vacuum glass, as a new generation of energy saving and environmental protection glass, not only has the characteristics of safety and high strength, but also has heat insulation, sound insulation and other superior performance. In this paper, the acoustic wave transfer model of composite tempered vacuum glass was established, and the formula of sound insulation was deduced by using wave transfer method (WTM), and the sound insulation loss of composite tempered vacuum glass under the influence of different factors was analyzed theoretically. The results show that the sound insulation performance of composite vacuum glass is significantly higher than that of single glass, i.e. the thicker the glass, the higher the sound insulation loss, at the same time reducing pillars also increases the property of sound insulation. The thickness of vacuum layer has different sound insulation loss in a different frequency, and the sound insulation performance of tempered vacuum glass is relatively best when the thickness of vacuum layer is about 0.25 mm. This research has an important guiding significance for the analysis of sound insulation performance of other similar structures and the selection of sound insulation structure of buildings.

New Functional Materials

Development of Thermal Protective Materials for Aircraft

HUANG Hongxiang, WANG Feng, HE Zhiyong, WANG Xiaobo

2021, 40(2):  638-644. 

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Thermal protective materials are the important guarantee of aircraft which avoid burning out during flight for overheating. The working environment of thermal protective materials becomes worse for the high speed of aircraft, which sets a higher demand for the properties of thermal protective materials. In addition to ablative energy, mechanical properties are also the focus of research. Since the 1950s, further research on thermal protective materials has been carried out at home and abroad. According to different aerodynamic conditions, a variety of thermal protective materials have been developed. At present, thermal protective materials include metal, ceramics, and resin matrix composites. In this paper, the types, properties, and application status of thermal protective materials are reviewed, and the development prospect is also proposed.

Preparation Technology of Enamel Coating of Metal/Fly Ash-Based Spherical Composite Fixed Phase Change Materials

ZHAO Yu, ZHU Guihua, LYU Shuo, ZHANG Pan, WU Meiling

2021, 40(2):  645-652. 

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Using fly ash as the matrix material and aluminum powder as the phase change medium, the spherical high temperature composite fixed phase change material with diameter of 15 mm was prepared by the mixed sintering method. The surface coating of low temperature black glaze was prepared by dipping glaze method and four sintering systems, and its waterproof property was evaluated by water permeability and microscopic characterization. Researches show that the sintering temperature of glaze layer and glaze concentration have significant influence on glaze layer properties. When the sintering temperature of glaze layer is 950 ℃, the glaze volume concentration is higher than 90%, the glaze layer cracks and coking are caused by the large difference in expansion coefficient between the blank glazes and the incomplete release of organic decomposition products before the glaze power melting; the volume concentration is more than 80% and less than 90%, the surface density of glaze layer increases and the waterproof property is enhanced, but there is the flow phenomenon of glaze. When the sintering temperature is 870 ℃ and 810 ℃, and the glaze volume concentration is 85% to 95%, the glaze gloss is good, the flow glaze is reduced, and the waterproof property is enhanced. When the sintering temperature of glaze layer is 750 ℃, because the temperature is too low, the gas between glaze layers cannot be discharged in time, it leads to the increase of pinholes in glaze surface and the decline of waterproof property. Compared the properties of glaze layer under four sintering systems, when the highest sintering temperature of glaze layer is 810 ℃ and slurry volume concentration is 88% to 92%, the coating has high density, good tightness with the surface of spherical phase change material, outstanding waterproof property, and good experiment repeatability.

Preparation of NaP Zeolite Doped with Cobalt and Its Adsorption Performance for Pb(II)

CHEN Yanguang, SUN Jie, WU Xiaohui, ZHANG Yanan, DENG Jitong, HAN Hongjing, ZHANG Mei, GUAN Jinshuang

2021, 40(2):  653-657. 

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A series of NaP zeolites doped with cobalt were synthesized by hydrothermal synthesis method using the sodium silicate and the sodium meta-aluminate as raw material. The crystal phase, morphology and pore structures of NaP zeolite samples were characterized by X-ray diffraction spectroscopy (XRD), scanning electron microscope (SEM), and N₂ adsorption-desorption methods. Moreover, the adsorption performance of NaP zeolite doped with cobalt for Pb(II) was evaluated. The results show that the NaP zeolite doped with cobalt at n(Al₂O₃)∶n(Co(NO₃)₂)=8∶1 has a specific surface area of 162.490 m²/g, which is 5 times more than the undoped NaP zeolite (from 26.767 m²/g to 162.49 m²/g), and a pore volume of 0.104 cm³/g, which is 2.5 times more than the undoped NaP zeolite (from 0.029 cm³/g to 0.104 cm³/g). When the adsorption time is 120 min, the adsorption temperature is 25 ℃, and the initial concentration of Pb(II) is 100 mg/L, Co-NaP zeolite has a removal rate of 98.8% for Pb(II). Employing the EDTA-2Na as the regeneration regent, the adsorbed NaP zeolite is regenerated completely at 30 ℃ for 30 min. After three adsorption-regeneration cycles, Co-NaP zeolite has a better adsorption property for Pb(II), and the removal rate of Pb(II) keeps over for 97%.

Research on Electrocatalytic Hydrogen Evolution Reaction Performance of Pt-P25 Prepared by Critical Point Drier

ZOU Hanjun, CHANG Qiuxiang, YANG Wenda, ZHANG Bin, GONG Xiangnan, WANG Guiwen, ZHOU Kai

2021, 40(2):  658-663. 

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Among various hydrogen production processes, electrochemical water splitting is an important way to obtain hydrogen energy, and Pt is the most ideal catalyst for the hydrogen evolution reaction (HER). Nevertheless, large-scale application of Pt-based materials in HER are limited due to their scarcity and high cost, there is an urgent need to develop a low content and efficient platinum catalyst. P25 is a kind of hybrid titanium dioxide with high lattice defect density and high current carrier concentration, which has good catalytic effect. Commercially available mixed crystal TiO₂ (P25) as catalysts supported Pt (Pt-P25) were prepared by a critical point drier, the structure and morphology of catalysts were analyzed by XRD、TEM and XPS, and the electro-catalytic HER performance of Pt-P25 were explored in different critical point drying conditions. The results show that TiO₂ supported Pt atom cluster is successfully prepared by the critical point drying method. Under certain conditions, electro-catalytic HER of Pt-P25 is the best when carbon dioxide intake rate is slow, exchange rate is 7, and outlet gas heating rate is med.

Refractory Materials

Research and Prospect of Alumina-Carbon Refractories

XU Zhiqiang, ZUO Haibin, LIU Lincheng

2021, 40(2):  664-675. 

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Alumina-carbon refractory is a kind of carbon composite refractory made from alumina and carbon, adding additives such as Al, Si and SiC, and bonded with binders such as asphalt or resin. It is widely used in blast furnace ironmaking, hot metal pretreatment, steelmaking, continuous casting and other metallurgical processes. The composition of refractories is the basis for obtaining high quality properties. Sorting out and analyzing the effects of various components in refractories on properties can provide theoretical support and research guidance for the development of lowcost and high quality refractories. In this paper, the functions of carbon sources, binders and additives in alumina-carbon refractories and their effects on the properties of alumina-carbon refractories were summarized, and the potential research directions were prospected.

Road Materials

Shrinkage and Mechanical Properties of Internal Curing Pavement Concrete with SAP

LAO Jiarong, HUANG Zhongcai, GUO Yinchuan, CHEN Lin, SHEN Aiqin, YANG Jingyu

2021, 40(2):  676-682. 

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Super-absorbent polymer (SAP), as a kind of internal curing material, has very important value when applied to highway concrete pavement, and it significantly improves the mechanical properties and shrinkage properties of concrete. In this paper, the mechanical properties, shrinkage deformation and internal relative humidity of concrete were studied, and the internal micro morphology and crack characteristics of SAP curing concrete were analyzed by SEM. The results show that the addition of SAP significantly reduces the shrinkage strain of concrete, and limits the volume expansion of concrete that gradually increases with age. And it timely compensates the concrete moisture when the internal humidity of the concrete drops, so that the relative humidity within 28 d can be kept above 90%. SAP parameters (mesh and content) have a greater influence on the flexural tensile strength of concrete, among which 100 mesh to 120 mesh (150 μm to 120 μm) SAP has the best effect on the improvement of flexural tensile strength. The incorporation of SAP increases the degree of cement hydration, generates more hydration products, improves the internal structure of concrete, increases the compactness of concrete, and reduces the length and width of micro-cracks inside the concrete, so SAP improves the mechanics strength, shrinkage performance and durability of concrete to a certain extent.

Research and Application on Road Performance of Asphalt Mixture Reinforcing Agent

LIU Hefeng, TIAN Zhouyi, XU Hui, KOU Xiaozhou, HAN Sen

2021, 40(2):  683-691. 

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In order to comprehensively analyze the road performance of the reinforcing agent, the rutting test, low temperature bending test, submerged Marshall test, freeze-thaw splitting test and Hamburg rutting test (HWTD) were carried out on the AC-13 asphalt mixture with different mass fraction of reinforcing agent (0%, 0.2%, 0.35%, 0.5%), to test its high-temperature anti-rutting performance, low-temperature anti-cracking performance and water stability performance, and then compare it with the currently commonly used domestic anti-rutting agent A and SBS modifier from the perspectives of road performance, construction method and cost, and finally pass the test road supplementary verification. The test results show that the road performance of AC-13 asphalt mixture increases non-linearly with the increase of the dosage of reinforcing agent, and the recommended mass fraction is 0.35%. Compared with the SBS modifier,the asphalt mixture with reinforcing agent has a higher high-temperature anti-rutting performance. Although low-temperature anti-cracking performance is slightly lower, its cost is lower and the construction method is simpler. Compared with anti-rutting agent A, although the cost of asphalt mixture is slightly higher, its high temperature, low temperature and water stability are better. The use of test rode shows that the reinforcing agent has the advantages of simple construction method, convenient use and significant effect.