Table of Content

Volume 43 Issue 9
15 September 2024

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Cement and Concrete

Effect of Cement Paste Mix Sequestration Carbon Dioxide on Cement Properties

WANG Yali, ZHAO Xinyu, MENG Wanyou, WANG Menglu, ZHANG Meng

2024, 43(9):  3109-3117. 

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In order to study effect of cement paste mix sequestration carbon dioxide on cement properties, different states and dosages of carbon dioxide were added to fresh cement paste. The carbon sequestration effect and mechanical properties of fresh cement paste were tested, and characterization methods such as TG-DTG, MIP, SEM were used to explore the effect of carbon dioxide on strength and microstructure of cement. The results show that when the water-cement ratio is 0.50, gas state carbon dioxide dosage is 1.5% (mass fraction), the compressive strength and carbon sequestration effect of cement are optimal. The compressive strength increases by 100% at 3 and 7 d, and by 139.6% at 28 d. After adding carbon dioxide, pores with diameters between 100~600 nm almost disappear while pores below 100 nm significantly increase, effectively reducing harmful pores inside cement matrix and enhancing pore structure in hardened cement paste. Carbon dioxide is directly accelerating cement early hydration. The growth state and bonding mode of hydration products are optimized to achieve carbon sequestration and strengthening of cement-based materials.

Effects of Polyacrylamide and Water Reducer on Hydration of Cement

YIN Jun, QIAN Xiong, HU Chuanlin

2024, 43(9):  3118-3127. 

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The effect of polyacrylamide (PAM) on cement hydration and performance limits the large-scale application of manufactured sand. In this paper, the effects of the interaction of three typical polyacrylamides (PAM) with polycarboxylate superplasticizer (PCE) and naphthalene superplasticizer (FDN) on the early performance of cement pastes were investigated. The study finds that the interaction of PAM with PCE and FDN significantly enhances the shear stress of cement paste, and negatively affects its fluidity. The bridging effect of PAM attenuates the electrostatic repulsive effect of PCE and FDN, and binds some of the reactive free water, which reduces the hydration release heat and hydration product generation of cement paste. With the increase of PAM doping, the PAM-PCE system mainly increases nanopores, but the effect on strength is small, while the increase in pores of the PAM-FDN system is concentrated in micrometer pores, and the strength decreases significantly. Among the three PAM, the interaction of cationic PAM (APAM) with PCE and FDN significantly inhibits the generation of cement hydration products.

Effect of Dosage of Polycarboxylate Copolymer Used in Synthesis Process on Nucleation and Early Strength of Nano C-S-H Seeds

TANG Ruifeng, CUI Suping, YANG Feihua, WANG Zhaojia, WANG Ziming

2024, 43(9):  3128-3136. 

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Nano hydrated calcium silicate/polycarboxylate copolymer (C-S-H/PCE) crystal nucleus suspension is a new type of early strength agent for cement concrete. It can shorten the cement hydration induction period and promote the development of early strength of cement through crystal seed nucleation. This article investigated the effect of PCE dosage on the grain size, morphology, and PCE actual combined dosage of nano C-S-H/PCE using dynamic light scattering (DLS), electron transmission microscopy (TEM), organic carbon analyzer (TOC), and thermogravimetric analysis (TGA) during the synthesis process. The effects of different dosages of PCE on the hydration heat release rate, flowability, and early strength of cement with nano C-S-H/PCE seeds were also investigated. The results show that when the PCE dosage accounted for less than 5.0% of the mass fraction of nano C-S-H/PCE seeds suspension, the average particle size of nano C-S-H/PCE seeds gradually decreases with the increase of PCE dosage, and the agglomeration situation improves, gradually presenting a clear tin foil like morphology. When the amount of PCE increases to 10.0%, there is little change in the particle size and morphology of the nano C-S-H/PCE seeds. TOC and TGA tests show that when the PCE dosage is 5.0%, it basically reaches saturation adsorption capacity on C-S-H. Therefore, excessive PCE will reduce the promoting effect of nano C-S-H/PCE seeds on the hydration heat release and early strength of cement.

Uniaxial Tensile and Compressive Mechanical Properties of Shrinkage-Resistant ECC and Damage Constitutive Model

CHEN Yu, SONG Xuewei, WU Jialiang

2024, 43(9):  3137-3148. 

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Engineering cementitious composite (ECC) is a new type of fiber-reinforced material with good ductility and microcrack control capability. Because ECC does not contain coarse aggregate, shrinkage cracks are easy to appear in the early stage of molding, and its molding shrinkage can be effectively suppressed by adding an expansion agent. In this paper, shrinkage-resistatant ECC was prepared by adding high-performance calcium sulfoaluminate (HCSA) expansion agent, and the effects of HCSA on the tensile and compressive mechanical properties of ECC were investigated. The results show that when HCSA doping is 4% (mass fraction), the uniaxial tensile and compressive strength of ECC can be increased. In order to describe the mechanical properties of ECC, the uniaxial tensile and compressive behaviors of ECC were simulated based on the damage variables from the perspective of the effective stress, and the tensile damage evolution equation for ECC was proposed. The uniaxial tensile and compressive damage constitutive model of ECC was developed and implanted into the ABAQUS finite element program to simulate the tests. The results show that the proposed uniaxial damage constitutive model of ECC can better describe the mechanical behavior and damage evolution of ECC during monotonic tension and monotonic compression, and its parameters are simple and easy to calibrate.

Restricted Expansion Rate of Cement Mortar Containing MgO Expansive Agent under Constant and Variable Temperature Curing Conditions

DUAN Jinsong, CUI Yong, FU Yongpan, SONG Qida, YU Xiao, WANG Tao, LING Yanfang, FANG Kuizhen

2024, 43(9):  3149-3156. 

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The influence of temperature on the compensation effect of MgO expansive agent in cement-based materials is crucial. This article reveals the temperature sensitivity of MgO expansive agent in cement-based materials by testing the restricted expansion rate, mineral composition, morphology and distribution of hydration products, and hydration degree of MgO expansive agent of cement mortar under different curing conditions. The results show that with the increase of curing temperature, the restricted expansion rate of medium speed MgO cement mortar containing 8% (mass fraction) significantly increases, especially under the curing condition of 50 ℃, and 28 d restricted expansion rate is 1.7 times that of 25 ℃. There are differences in the impact of different curing conditions on the expansion of MgO. In the high-temperature rise slow cooling variable temperature curing condition, the cement mortar containing rapid MgO has the highest restricted expansion rate, and the expansion rate decreases significantly during the cooling process. However, in the low-temperature rise fast cooling variable temperature curing condition, the hydration of the system continues, and the MgO expansive effect can be sustained. In addition, the reaction degree of MgO in cement paste also increases with the increase of curing temperature, which is 25%~65%. The hydration product Mg(OH)₂ mainly exists in the gel state, but with the temperature rising to 50 ℃, some gel like Mg(OH)₂ is transformed into lamellar crystals, further optimizing the microstructure and expansion performance of cement-based materials. This study provides a reference for understanding and optimizing the application of MgO expansive agent in cement-based materials.

Preparation of SiO₂ Composite Materials Loaded with Different Air-Entraining Agents and Their Application in Cement-Based Materials

SHEN Fei, QIAO Min, SHAN Guangcheng, WU Qingyong

2024, 43(9):  3157-3163. 

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SiO₂ nanoparticles loaded with air-entraining agents were prepared with four different anionic air-entraining agents as the templating agent. The introduction of (3-aminopropyl) triethoxysilane during the hydrolysis of silicon sources can attract more anionic air-entraining agents to SiO₂ through electrostatic interaction. The feasibility of preparation method for loading various anionic air-entraining agents was verified. Meanwhile, the influences of structure of air-entraining agents on structure and application of products were investigated. The results show that all SiO₂ composite materials loaded with air-entraining agents present a release of air-entraining agents in solution and improve the bubble stability in mortars. The addition of SiO₂ composite materials to cement mortar results in a low loss of air content within 2 h, also optimizing the air-void parameters of hardened mortars. The volume of surfactant molecules and micelles significantly affects the particle size and the load of surfactants in products, which in turn influences the air content of SiO₂ composite materials in solutions and the enhancement of bubble stability in mortars.

Mechanism of Aggregate Type Influence on Properties of Ultra-High Performance Concrete

WU Xiaogang, YANG Jianhui, YUAN Dongdong, TIAN Daopo, LI Zhichao, WANG Tinghui

2024, 43(9):  3164-3172. 

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Aggregate optimization can compensate for the high cost and shrinkage of ultra-high performance concrete (UHPC). In this paper, different volume ratios of river sand and pottery sand were used as aggregates to produce UHPC, and it was determined through testing that the performance of UHPC was excellent when the volume ratio of pottery sand replacing river sand was in the range of 12.5% to 25.0%. Then UHPC was prepared by quartz sand, river sand and pottery sand, as well as mixing of pottery sand and river sand. The mechanism of aggregate influence on the physical and mechanical properties of UHPC was analyzed using macroscopic and microscopic testing methods. The results show that the internal curing effect of lightweight aggregate not only reduce the shrinkage of UHPC, but also significantly improve the pore structure in the interfacial zone and enhance the splitting tensile and compressive strength of concrete. Compared with quartz sand aggregate, river sand aggregate has a rougher and irregular surface, from which UHPC is prepared with relatively poor workability but better pore structure in the interfacial zone. Taking slump, compressive strength, splitting tensile strength and 56 d shrinkage as the comprehensive evaluation indexes, although the compressive strength of river sand aggregate UHPC is not lower than that of quartz sand aggregate UHPC, there is no advantage in other indexes. The combined performance of mixed aggregate UHPC is higher than that of quartz sand aggregate UHPC when the volume ratio of pottery sand replacing river sand is in the range of 12.5% to 50.0%.

Molecular Dynamics of NaCl Evaporation Crystallization in C-S-H Gel Amorphous Nanopores

ZHAO Guoqing, YANG Jinbo, YIN Hang

2024, 43(9):  3173-3181. 

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The dry and wet cyclic crystallization of sodium chloride (NaCl) can damage cement concrete materials, and the limitations of the existing experimental methods make it difficult to study the salt crystallization damage mechanism from the nanoscale. Therefore, this paper adopted the molecular dynamics method for the main microscopic product of cement hydration, calcium silicate hydrate (C-S-H) gel, to study the evaporation crystallization process of NaCl in the amorphous pores of C-S-H gel and the crystallization damage mechanism. The results show that the C-S-H gel amorphous model constructed in this paper is closer to the C-S-H gel with low density, and the evaporation crystallization of NaCl in the pores of this model follows a two-step nucleation mechanism, and the filling of C-S-H gel nanopores by evaporated crystallized NaCl crystals significantly reduces the overall tensile deformation capacity of C-S-H gel, and makes C-S-H gel brittle, which is a conclusion to this conclusion provides a basis for explaining the phenomenon of C-S-H gel destruction under the action of evaporation crystallization.

Experimental Study on Mechanical Properties and Microstructure of Aeolian Sand Concrete after High Temperature

ZHAO Yanru, LONG Sirui, BAI Jianwen, LIU Ming

2024, 43(9):  3182-3191. 

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In this paper, 0%, 10%, 30% and 50% of aeolian sand were used to replace ordinary river sand to prepare aeolian sand concrete. The appearance change, mass loss, compressive strength and flexural strength of aeolian sand concrete at 20, 200, 400, 600 and 800 ℃ were studied. The evolution of mechanical properties of aeolian sand concrete at different temperatures and different aeolian sand content was analyzed by flexural-compressive ratio. The evolution process of the internal microstructure of aeolian sand concrete under different temperatures was studied by scanning electron microscope (SEM), and the microstructure mechanism was analyzed. The results show that the appropriate amount of aeolian sand can increase the hydration products, optimize the pore structure of concrete, reduce the thickness of interfacial transition zone in concrete, make the internal structure of concrete more compact, improve the mechanical properties, and delay the formation of cracks and pores in concrete after high temperature. However, too much aeolian sand will have the opposite effect, which will reduce the mechanical properties of concrete after high temperature. This study can provide a basis for the application of aeolian sand concrete and the evaluation of aeolian sand concrete structure after high temperature.

Mechanical Properties of Geopolymer Concrete Based on Response Surface Method

ZHANG Zhenyang, ZHANG Lu, YI Haihe, ZHENG Run, MA Keshun, ZHANG Lin, REN Mengqi, WANG Chunguang

2024, 43(9):  3192-3202. 

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In order to obtain the optimal mixture ratio of geopolymer concrete with the best mechanical properties, the optimization method of mix ratio of geopolymer concrete with fly ash and slag as precursors was systematically. The water/binder ratio, alkali activator modulus (the ratio of SiO₂ and Na₂O molecules in alkali activator) and slag content (the mass fraction of slag in precursor) were selected as variables to design the response surface scheme for compressive test of geopolymer concrete. The response surface model of compressive strength was established by statistical method, and the fit between model and test results was verified. The results show that the water/binder ratio has a significant effect on the compressive strength of geopolymer concrete, and the best choice of water/binder ratio is 0.376. The effect of slag content on the compressive strength of geopolymer concrete is extremely significant. The higher the proportion of slag instead of fly ash is, the higher the compressive strength of geopolymer concrete is. The optimum content of slag is 48.2%. The modulus of activator has no significant effect on the compressive strength of geopolymer concrete. The water/binder ratio affects the pore structure of matrix, and the slag affects the macroscopic mechanical properties of matrix by changing the compactness of matrix structure.

Mechanical Properties of Steel Fiber Geopolymer Concrete under Low Temperature

WANG Xiaoxiao, DONG Peisen, YANG Xinrui, ZHANG Ju, YAN Changwang, DONG Yufei

2024, 43(9):  3203-3213. 

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In order to study the variation of mechanical properties of steel fiber geopolymer concrete (SFGPC) under low temperature, a self-made low temperature environment test device was used to study the failure characteristics and compressive strength and flexural strength of geopolymer concrete at different temperatures (-30, -20, -10, 0, 20 ℃) and different steel fiber volume content (0%, 0.5%, 1.0%, 1.5%). The microstructure of SFGPC was analyzed by scanning electron microscope (SEM). At the same time, the response surface method (RSM) was used to construct the mechanical property relationship model of SFGPC, which provided a feasible prediction method of compressive strength and flexural strength. The results show that when steel fiber content is 1.5%, the compressive strength and flexural strength of SFGPC at -30 ℃ are 59.8 and 6.6 MPa, respectively, which are 75% and 65% higher than those when steel fiber content is 0% at -30 ℃, and 41% and 144% higher than those when steel fiber content is 1.5% at 20 ℃, respectively. With the increase of steel fiber content, the internal adhesion and adsorption capacity of SFGPC enhance, and the mechanical properties are improved. The prediction models of compressive strength and flexural strength of SFGPC are obtained by RSM, and the relative errors between the predicted values and the tested values are less than 5.7% and 8.0%, respectively.

Influences of Water Reducing Agent and Steel Fiber on Rheological and Mechanical Properties of Ultra-High Performance Concrete

HUANG Bin, GONG Mingzi, PAN Axin, RAO Xianpeng, WANG Tao, CHEN Chen, HUANG Wei

2024, 43(9):  3214-3223. 

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The workability and mechanical strength of ultra-high performance concrete (UHPC) are the key to its popularization and application. Therefore, this paper used workability test, rheological test, compressive strength test and flexural strength test to explore the variation of UHPC fluidity, time loss, yield strength, plastic viscosity, compressive strength, and flexural strength under different water reducing agent content and fiber physical parameters. The results show that the fluidity of UHPC increases first and then decreases with the increase of water reducing agent content and fiber content. The time loss of UHPC is mainly related to standing time. The longer the standing time of UHPC is, the greater the time loss is. The rheological curve of UHPC shows a trend of shear thickening. With the increase of water reducing agent, the yield stress and plastic viscosity of UHPC decrease first and then increase, and the minimum value is obtained when the content of water reducing agent is 1.00% (mass fraction). The effect of water reducing agent on strength is not obvious. The compressive strength of UHPC increases with the increase of fiber content, and the flexural strength increases first and then decreases with the increase of fiber content. When the fiber length is 13.0 mm, the compressive performance of UHPC is the best, and the flexural performance is the best when the fiber length is 20.0 mm.

Impermeability of Reinforced Concrete Tank Wall with Horizontal Construction Joints

LI Xiaofan, ZHANG Shuang, ZHOU Zhongyu, ZHOU Zhi, HUANG Wei

2024, 43(9):  3224-3234. 

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In reinforced concrete (RC) tank walls, a horizontal construction joint exists because of the interruption of concrete casting, resulting in the old and new concrete not forming a reliable connection. The tank walls are prone to experiencing seepage under high hydrostatic pressure. In this paper, the permeability test of concrete with different mix proportion and simulated horizontal construction joints was first conducted. Their seepage behavior was investigated. The test results show that the addition of polypropylene fibers and cementitious capillary crystalline waterproofing materials (CCCW) can improve the impermeability of concrete. The impermeability at the construction joint is much lower than that of single-casting concrete. Moreover, applying CCCW to the water-facing surface of the construction joint can significantly enhance its impermeability. Then, two 1∶2 scaled RC tank wall specimens were tested for local permeability performance of single-casting and double-layer casting considering construction joints. The experimental results show that the RC tank wall with construction joint is prone to generate initial defects and seepage due to inadequate pouring, vibration, and curing of the concrete at the construction joints, making it difficult to achieve the design watertight requirements. The use of modified concrete materials and surface treatment in the relevant part can effectively improve the impermeability of the local construction joint, and further enhance the impermeability of RC tank walls. Finally, the BP neural network was used to establish a nonlinear prediction model between the impermeability of concrete and its material parameters and construction technology.


Effect of Chloride Erosion on Durability of Concrete Bridges in Saline Alkali Environments

LIN Pengzhen, REN Jinbo

2024, 43(9):  3235-3243. 

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In order to solve the problem of erosion and durability of reinforced concrete bridges in saline alkali environment in Northwest China, through field investigation of bridge diseases in saline alkali environment in Northwest China and the distribution of chloride ion in soil and bridges, the chloride ion diffusion law of each part of bridge was analyzed by modified Fick’s second law and finite element simulation, and the durability life of a proposed bridge was predicted. The improvement effects of measures such as improving concrete strength and protective layer thickness on the durability life of bridge were discussed. The results show that the chloride ion content in the surface soil is the highest in saline alkali environment. There are many diseases in the service bridge, and the substructure is the most vulnerable to chloride ion erosion. The durability life of substructure bearing platform, pier and pile foundation of service bridge is 55.3, 63.1 and 91.5 a respectively. The durability of bridge can meet the requirements by reasonably improving concrete strength and protective layer thickness.

Solid Waste and Eco-Materials

Influences of Igneous Rock Mineral Materials on Properties of Concrete

WANG Hao, TAN Yanbin, LIU Xing, YANG Lu, YUAN Qiang, XIE Binfu, LIU Bo

2024, 43(9):  3244-3251. 

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The mineral admixture resources of fly ash-based concrete in southwest China are scarce, and it is urgent to develop alternative materials. In this paper, the effects of four kinds of igneous rock mineral materials on the working performance, mechanical properties and durability of concrete were studied, and the cracking risk of concrete was evaluated. The results show that the compressive strength and chloride ion penetration resistance of hardened concrete meet the standard requirements after replacing fly ash with igneous rock mineral materials by equal quality. The dosage of water reducing agent, early compressive strength, electric flux and shrinkage rate are higher than those of fly ash concrete. The performance of hardened concrete mixed with tuff micropowder is basically the same as that of fly ash concrete. Basalt micropowder concrete has the largest demand for water reducing agent and the lowest compressive strength. The crack resistance of concrete mixed with igneous rock mineral materials is reduced. The cracking risk of concrete mixed with tuff micropowder and fly ash is low level, and the cracking risk of concrete mixed with andesite micropowder, basalt micropowder and rhyolite micropowder is medium-low level. Among the four kinds of igneous rock mineral materials, tuff micropowder concrete has the best performance and can replace fly ash into concrete.

Study on Accelerated Weathering System of Coal Gangue Aggregate

GONG Tiantian, CHEN Xiao, ZHANG Yanjun, CHEN Zhijun, WANG Wenjun, ZHOU Mingkai

2024, 43(9):  3252-3261. 

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Three kinds of original coal gangue from different emission places were taken as the research object, and the dry-wet cycle, freeze-thaw cycle and disintegration resistance test were used to accelerate the weathering of coal gangue aggregate, aiming to study the weathering characteristics of coal gangue. The weathering characteristics of coal gangue aggregate were characterized by the mass loss rate and crushing value index after accelerated weathering. The effects of accelerated weathering system, particle size and service state on the weathering characteristics of coal gangue aggregate were studied. At the same time, the weathering mechanism of coal gangue was revealed by XRD, SEM and EDS. The results show that the mass loss rate and crushing value index of coal gangue aggregate obtained by accelerated weathering of dry-wet cycle are closest to coal gangue aggregate weathered for 180 d under natural state. Moreover, the larger the particle size of coal gangue aggregate, the more likely it is to be weathered, and the weathering of coal gangue aggregate is not obvious under service state. The microscopic test results show that the weathering mechanism of coal gangue is that the mineral composition and structure inside the coal gangue are destroyed during the weathering process, resulting in disintegration and shedding, while the coal gangue in the service state can effectively reduce its weathering due to the encapsulation of cementitious materials.

Evolution of Pore Structure in Silica Fume Modified Coal Gangue Concrete under Low Temperature Environment

LI Shaoping, SHAN Junwei, LIU Xiaoqin, GUO Meirong, ZHANG Xuening, JING Hongjun, GAO Meng, CHEN Shaojie

2024, 43(9):  3262-3272. 

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To solve the problem of short service life of coal gangue concrete at low temperature, the freeze-thaw cycle test, and nuclear magnetic resonance test were carried out on the coal gangue concrete specimens with different water-binder ratios (0.45,0.35,0.25), and silica fume (SF) content (0%, 5%, 10%, 15%, mass fraction) by adding SF. The mass loss rate, relative dynamic elastic modulus, and pore structure distribution of each group of specimens were tested, and the influence of pore structure evolution on the frost resistance durability of coal gangue concrete under freeze-thaw cycle was analyzed. The results show that after 50 times freeze-thaw cycles, the mass loss rate of coal gangue concrete changes from negative to positive, and the specimen with water-binder ratio of 0.25 gradually produces alkali-aggregate reaction. After 75 times freeze-thaw cycles, SF increases the relative dynamic elastic modulus by 13.60%~62.98%. The addition of SF can improve the mass loss rate and relative dynamic elastic modulus, and inhibit alkali-aggregate failure of coal gangue concrete. During the freeze-thaw process, gel pores (r≤0.01 μm) and fine capillary pores (0.01 μm＜r≤0.05 μm) are gradually transformed into large capillary pores (0.1 μm＜r≤10 μm). The number of large capillary pores is the main factor that determines the occurrence of freeze-thaw damage. The addition of SF slows down the increase rate of large capillary pores and improves the anti-freezing durability of coal gangue coarse aggregate. The freeze-thaw damage model based on macro-scale (relative dynamic elastic modulus) and micro-scale (different pore size integral area) is established. The micro-scale freeze-thaw damage model considering different pore size is also suitable for coal gangue concrete. When the water cement ratio is 0.35 and the SF content is 10%, the coal gangue concrete can serve for 4 714 d in low temperature environment in the northwest region.

Influence of Silica Fume on Compressive Strength and Impermeability of Cement Mortar with Alkali-Free Accelerator at Low Temperatures

LIU Yawei, HU Yang, LUO Qi, LU Liulei, PEI Datian, LI Binbin, MA Jun, WANG Junfeng

2024, 43(9):  3273-3281. 

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Low temperature environment affects the development of early performance of tunnel shotcrete. This study investigated the effects of silica fume on the fluidity, compressive strength, and impermeability of alkali-free accelerator-modified cement mortars at low temperatures. XRD, TG-DTG and MIP were used to analyze the changes in hydration products and pore structure. The results show that using silica fume significantly improves the 1 d compressive strength of mortar at low temperatures with an increase of over 300.0%. At 28 d, incorporating 5% (mass fraction) silica fume also increased the compressive strength by 4.7%. Moreover, the impermeability of mortar increases with the increase of the silica fume content. Especially, the impermeability is remarkably improved when the content of silica fume exceeded 10%. Silica fume modification can exert the pozzolanic effect and micro-filling effect at low temperatures, which transformes more-harmful pores towards less-harmful ones, refining the pore structure and making the paste structure denser, thereby improving the compressive strength and impermeability of mortars.

Solid Waste and Eco-Materials

Damage Characteristics of Highland Barley Straw Ash Modified Magnesium Oxychloride Cement Mortar Protected Reinforced Concrete

CUI Lijun, QIAO Hongxia, CAO Feng, SHU Xiuyuan, SHENG Chenghui

2024, 43(9):  3282-3293. 

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In order to investigate the durability damage characteristics and degradation law of highland barley straw ash modified magnesium oxychloride cement mortar protected concrete, reinforced concrete specimens with different thicknesses of protective layers were prepared. The corrosion degradation of steel bars was tested and analyzed by constant current accelerated corrosion test under salt brine erosion environment. The cracking situation of concrete during the erosion process was monitored by concrete crack defect detection instrument, and the electrochemical parameters obtained based on AC impedance analysis and polarization curve fitting were used to characterize the corrosion degradation of internal steel bars. A numerical model of durability damage degradation of magnesium oxychloride cement mortar protected concrete was established using Weibull distribution function. The results show that under salt brine erosion environment, the corrosion current density of steel bars in magnesium oxychloride cement mortar protected concrete with highland barley straw ash added is still less than 0.2 μA·cm^-2 after 648 h of current passing, indicating a low corrosion state and a slow corrosion development. The Weibull distribution function can effectively predict the degree of corrosion degradation of steel bars in highland barley straw ash modified magnesium oxychloride cement mortar protected concrete.

Preparation and Performance of Calcium Silicate Board Based on Titanium Tailing Slag

AN Xinyu, LI Lin, ZHANG Lan, JIANG Tao

2024, 43(9):  3294-3302. 

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Titanium tailing slag, a chlorinated waste resulting from titanium extraction processes from high-titanium blast furnace slag, has historically lacked viable technologies for large-scale utilization, posing potential environmental risks. This study leveraged titanium tailing slag as the main ingredient in the development of thermal insulation materials, specifically calcium silicate boards, and evaluated the influences of various parameters such as calcium to silicate ratio, diatomite content, water-to-binder ratio, and mix proportion of raw to dechlorinated slag on the material’s performance metrics, phase composition, and microscopic morphology. Findings indicate that the flexural strength of calcium silicate boards exhibits a pattern of initial increase followed by a decrease as the proportion of dechlorinated slag is raised. Excess diatomite, high calcium to silicon ratio, and elevated water-to-binder ratio adversely affect the enhancement of sample attributes. Optimal material properties are observed when the composition included 46% (mass fraction) titanium tailing slag (with an equal ratio of raw to dechlorinated slag), 15% (mass fraction) silicate cement, 17% (mass fraction) diatomite, a calcium to silicon ratio of 0.84, and a water-to-binder ratio of 0.75. Under these conditions, the calcium silicate board demonstrates superior characteristics: a bulk density of 1.25 g/cm³, a flexural strength of 10.4 MPa, a thermal conductivity of 0.297 W/(m·K), and a sample-contained chloride ion mass fraction of 0.36%, achieving a 56% chloride fixation ratio.

Effect of Soluble Phosphorus on Hydration Process of High Content Phosphogypsum Cementitious Materials

KANG Xueer, HUANG Yun, LIU Gang, HE Minghao, WAN Huiwen

2024, 43(9):  3303-3312. 

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Impurities such as residual acid and soluble phosphorus content in phosphogypsum have a great impact on the ratio and strength development of phosphogypsum cementitious material. Two different qualities of phosphogypsum were used to composite with slag and cement to prepare cementitious materials with phosphogypsum content of 60%, 70%, and 80% (mass fraction), and wet grinding modification was carried out on phosphogypsum. By testing the pH value of the pore solution of the cementitious material, the degree of slag hydration, and compressive strength, and combining XRD, SEM-EDS and other testing methods, the influence of soluble phosphorus impurities on the hydration process of high dosage phosphogypsum cementitious materials was explored. The results show that the optimal dosage of Portland cement in high dosage phosphogypsum cementitious material is related to the soluble phosphorus impurities contained in phosphogypsum. The higher the content of impurities, the higher the content of cement. After wet grinding pretreatment, 7 d strength of the cementitious material can be improved, but cannot increase the 28 d strength. The strength of the composite cementitious material depends on the degree of slag hydration. During the hydration process, the soluble phosphorus in phosphogypsum and the Ca(OH)₂ hydrated by cement form calcium phosphate precipitates on the surface of the slag, which hinders the hydration of the slag and is the main reason affecting the development of its strength.

Analysis of Influencing Factors on Mechanical Properties of Alkali- Activated Slag-Fly Ash Binder Materials

SUN Kaiqiang, LIU Lin, ZHENG Hongchen

2024, 43(9):  3313-3319. 

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To address the significant impact of a single control factor on the mechanical properties of alkali-activated slag-fly ash binder materials under the combined action of multiple factors, the effects of fly ash content, water cement ratio, alkali content and sodium carbonate content on the compressive strength of alkali-activated slag-fly ash binder materials were investigated. Grey relational factors and univariate analysis of variance and range analysis based on orthogonal experimental design were used to evaluate the degree of influence of these factors on mechanical properties. The results show that in NaOH/Na₂SiO₃ alkali-activated slag-fly ash binder material system, fly ash content has a major impact on compressive strength. A prediction formula has been established to accurately predict the relationship between fly ash content, water cement ratio, alkali content, sodium carbonate content, compressive strength. The relative error between the predicted results and experimental results is basically controlled within ±10%.


Dynamic and Static Mechanical Properties of Silica Fume-Polypropylene Fiber Double Doped Concrete

LI Yanyan, DU Xiaoli, WANG Haowei, XU Kai

2024, 43(9):  3320-3329. 

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In order to research the effects of silica fume substitution rate and polypropylene fiber content on the mechanical properties of concrete, WAW-1000 microcomputer-controlled electro-hydraulic servo universal testing machine and split Hopkinson pressure bar (SHPB) were used to analyze the dynamic and static compressive strength, material toughness, energy change and fragmentation degree of concrete specimens, and the mechanical properties of silica fume-polypropylene fiber double doped concrete under different mix ratios were obtained. The results show that with the increase of silica fume substitution rate (0%~9%, mass fraction), the dynamic and static compressive strength and toughness of double doped concrete increase first and then decrease. The dynamic and static compressive strength and toughness increase slowly with the increase of polypropylene fiber content (0~4 kg·m^-3). The incorporation of silica fume and polypropylene fiber is conducive to improving the energy consumption effect of concrete and the mass ratio of fragmentation degree, and the transmission energy and mass ratio of fragmentation degree increase first and then decrease with the increase of silica fume substitution rate, and increase with the increase of polypropylene fiber content. The silica fume strengthens the interface bond between mortar and coarse aggregate, the messy distribution of polypropylene fiber restricts the development of cracks, and the combined effect of the two significantly improves the dynamic and static compressive strength, toughness, impact resistance and damage resistance of concrete.

Investigation of Glass-Forming Ability of High-Fe Ash Based on CART Model

WANG Wei, FANG Guang, CHEN Yi, ZHANG Qiansheng, XU Kai

2024, 43(9):  3330-3336. 

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Vitrification technology is a promising method for hardless and resourceful treatment of hazardous waste. However, the vitrification of high-Fe hazardous waste ash is difficult due to its high-Fe content, which can lead to the crystallization or phase separation of glass. In this paper, based on the composition of high-Fe hazardous waste ash, 385 glass formulations with SiO₂-Al₂O₃-CaO-Na₂O-TiO₂-Fe₂O₃ systems were designed using extreme vertices design method. Optical microscopy, X-ray diffraction and acid dissolution test were employed to identify 136 formulations to form glass samples exhibiting excellent chemical durability. Based on CART model analysis, the study determines the range of glass formulation for high-Fe hazardous waste ash with optimal glass-forming ability, in mass fraction (w): 40.0%≤w(SiO₂)≤55.0%, 10.0%≤w(CaO)<14.0%, 14.0%≤w(Na₂O)≤18.0%, 5.0%≤w(Other)<9.5% or 35.0%≤w(SiO₂)<40.0%, 9.0%≤w(TiO₂)≤10.0%, 5.0%≤w(Other)<9.5%. The research in this paper provides design and computation for glass vitrification of high-Fe hazardous waste ash.

Effects of Glass Powder and Biochar on Plastic Shrinkage and Cracking Behavior of Mortar

LUO Haoran, LIU Hui, ZHOU Yiyi, AMARDEEP Singh, LIU Qiong

2024, 43(9):  3337-3347. 

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To investigate the effect of renewable materials on the plastic shrinkage and cracking behavior of mortar, this study selected two renewable materials, glass powder and biochar. Digital image correlation (DIC) technique was employed to quantitatively assess the influence of different dosages (2%, 4%, 6% by cement mass fraction) of glass powder and biochar on the plastic shrinkage and cracking behavior of mortar. The results indicate that the maximum crack width of mortar with glass powder and biochar is smaller than that of the control group without glass powder and biochar. Therefore, adding 2%~6% of glass powder or biochar has a positive effect on the plastic shrinkage and cracking of mortar. Glass powder, due to its smooth surface and hydrophobic nature, enhances the flowability of mortar, but the filling effect and pozzolanic activity of volcanic ash slow down the plastic shrinkage. Biochar, with its porous structure and water absorption capacity, reduces the flowability of mortar, effectively mitigating plastic shrinkage.

Performance of Belite Cement Clinker from Completely Recyclable Cement Mortars

CUI Yingying, HE Jianhui, LYU Minwang, YANG Lu, LIU Yunpeng

2024, 43(9):  3348-3358. 

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Completely recyclable concrete refers to concrete that can be directly used as raw cement materials for calcination and preparation of clinkers after being demolished. In current studies, the target clinker is ordinary Portland cement clinker. In this study, the completely recyclable mortar (CRM) with high belite cement clinker (HBC) and high ferrite-belite cement clinker (HFBC) as target regenerated clinker was prepared. A comparative study was conducted on the effects of the some rate value and calcination temperature on the burnability of cement raw materials, clinkers’ compositions, and performance using fully CRM and chemical analysis pure reagents (as a control group) as raw materials. The results indicate that the clinker obtained from CRM has a higher rate of later strength growth than the control group. Raw materials with CRM have better burnability and lower CO₂ emissions. However, the strength of clinker is sensitive to temperature, and the range of calcination temperature is narrow. The generation of C₃S in HBC prepared with CRM is significantly inhibited, and the early hydration activity and strength decrease, but the later hydration ability is improved. Due to the presence of impurity ions, here is α′-C₂S mineral phase in clinker. For HFBC group, the hydration activity of experimental group with CRM significantly improves compared to the control group. The research can provide support for the design of completely recyclable concrete.

Mechanical Properties and Frost Resistance Durability of Recycled Coarse Aggregate Concrete Dual Doping Graphene and Oxide-Graphene

LIU Hongbo, JIA Xiaojing, ZHANG Boyang, SUN Yan, LI Yong, CHANG Pu, SUN Jing

2024, 43(9):  3359-3367. 

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In order to solve the problem of poor mechanical properties and the frost resistance durability of recycled coarse aggregate concrete (RAC) from construction waste, graphene oxide (GO) and graphene (G) were added as nano modifiers. The effects of dual doping of GO and G with different ratios on the mechanical properties, frost resistance durability, and microstructure of RAC have been thoroughly studied. The results show that compared with RAC without any modifiers, dual doping of 0.03% G and 0.06% GO (calculated by mass percentage of cement) has the most significant improvement effect on the mechanical properties of RAC. The compressive and splitting tensile strength increases by 29.14% and 30.60% respectively after 7 d. The results of frost resistance durability show that dual doping of 0.03%G and 0.06%GO can effectively reduce the mass loss rate and strength loss rate of RAC after freeze-thaw cycles, thereby improving the frost resistance durability of RAC. Microstructure analysis shows that dual doping of 0.03% G and 0.06% GO can improve the regularity of hydration products, significantly reduce the cumulative pore volume of RAC, and increase the compactness of RAC structure. Therefore, dual doping of GO and G dual have a synergistic effect in improving RAC performance.

Effects of Synergistic Action of Pre-Wetting Recycled Sand and Expansion Agents on Shrinkage Properties of Recycled Sand Concrete

LI Beixing, GUO Yuxin, YI Hao, JIN Dechuan

2024, 43(9):  3368-3377. 

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In order to reduce the shrinkage of recycled sand concrete, the effects of pre-wetting recycled sand on working performance, compressive strength, autogenous shrinkage, dry shrinkage and internal relative humidity of concrete were studied. On this basis, three kinds of expansion agents were mixed into the concrete, and the effects of the synergistic action of pre-wetting recycled sand and expansion agents on the autogenous shrinkage and dry shrinkage of concrete were studied. The results show that under the condition of the same additional water consumption, compared with concrete prepared with recycled sand in absolute dry condition, the working performance of the concrete prepared by using pre-wetting recycled sand is reduced, the strength is increased, and the internal relative humidity can be maintained at a higher level, which effectively reduces its autogenous shrinkage and dry shrinkage. Among the three kinds of expansion agents mixed into the concrete, calcium expansive has the best inhibition effect on the autogenous shrinkage of concrete, and calcium magnesium complex expansion agents have the best inhibition effect on the dry shrinkage of concrete. At 100% pre-wetting degree, compared with concrete without expansion agents, the autogenous shrinkage of the 10% calcium specimen of the fully recycled sand concrete is reduced by 83.2%, and the dry shrinkage of the 6% calcium magnesium complex specimen of the fully recycled sand concrete is reduced by 36.1%.

Ceramics

Preparation and Properties of Mg_0.27Al_2.58O_3.73N_0.27 Transparent Ceramics by Hot Pressing and Hot Isostatic Pressing Sintering

CHEN Hao, YANG Jingxiao, XU Yong, JING Zhengyang, TU Bingtian, WANG Hao

2024, 43(9):  3378-3385. 

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MgAlON transparent ceramics have excellent optical and mechanical properties, and have potential applications in both military and civilian fields. In this study, the hot pressing and hot isostatic pressing techniques have been introduced into the fabrication and processing of MgAlON transparent ceramics. The BN material was used to solve the problem of carbon contamination during hot pressing sintering. Mg_0.27Al_2.58O_3.73N_0.27 transparent ceramics with good optical properties were obtained. The in-line transmittance, Vickers hardness, fracture toughness and room temperature flexural strength were also characterized. Using BN to wrap the sample effectively eliminates the carbon contamination during high-temperature sintering, and the in-line transmittance of Mg_0.27Al_2.58O_3.73N_0.27 transparent ceramics at 650 nm increases from 36.51% to 73.74%. Compared with pressureless sintering, hot pressing combined with hot isostatic pressing sintered Mg_0.27Al_2.58O_3.73N_0.27 transparent ceramics have better mechanical properties, with flexural strength of 387.12 MPa, fracture toughness of (3.31±0.20) MPa·m^1/2 and hardness of (15.3±0.7) GPa. The research can provide an important reference for improving the performance and technical preparation of MgAlON transparent ceramics.

Ceramic Slabs Prepared Using Different Flux System and Its Properties

ZHAO Cunhe, NIE Guanglin, LIU Yijun, ZUO Fei, PANG Weike, WANG Qinggang,BAO Yiwang

2024, 43(9):  3386-3398. 

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In this work, the K-Na and Ca-Mg based raw materials were used to prepare SiO₂-Al₂O₃-K₂O(Na₂O)(K₂O-Na₂O) and SiO₂-Al₂O₃-CaO-MgO(CaO-MgO) system ceramics, respectively. The impacts of flux systems (CaO-MgO, K₂O-Na₂O) on sintering characteristic and mechanical properties of ceramic slabs prepared at different firing temperatures (1 110～1 210 ℃) were investigated systematically, and the evolution rule of phase composition and microstructure was studied by XRD and SEM. The results show that the optimal firing temperatures for CaO-MgO and K₂O-Na₂O system ceramics are 1 170 and 1 150 ℃, respectively. The introduction of Ca-Mg based raw materials would lead to the lower firing shrinkage and bulk density of CaO-MgO system ceramics compared to K₂O-Na₂O system ceramics, meanwhile the pore size and content in CaO-MgO system ceramics are larger than those in K₂O-Na₂O system. The formation of anorthite and α-cordierite in CaO-MgO system ceramics is promoted by the introduction of Ca-Mg based raw materials, and the crystalline phase content of CaO-MgO system ceramics is significantly increased to be 75.66%(mass fraction), which is 56% higher than that of K₂O-Na₂O system. The dispersion strengthening effect caused by high crystalline phase content is greater than degradation effect of pore on mechanical strength. The flexural strength of CaO-MgO system ceramics is (56.9±2.6) MPa, fracture energy is (183.2±9.5) J/m², failure strain is (7.4±0.1)×10^-4 and specific strength is (24.9±1.1) kN·m·kg^-1, which are 15%, 25%, 11%, and 23% higher than those of K₂O-Na₂O system ceramics, respectively, indicating that the CaO-MgO flux system is more suitable for the manufacturing of high strength, toughness, and flexibility ceramic slabs compared with the traditional K₂O-Na₂O system.

Structure and Chemical Durability of Actinide Nuclides Solidified by High-Entropy Pyrochlore (La_1/6Pr_1/6Nd_1/6Sm_1/6Eu_1/6Gd_1/6)₂Zr₂O₇

DU Zhanyuan, ZHU Yongchang, CUI Zhu, JIAO Yunjie, DONG Xuanjiang, WANG Dongyu, YANG Debo, WANG Hua

2024, 43(9):  3399-3406. 

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High-entropy ceramics(HECs) are a potential target for high-level waste curing due to their excellent phase and chemical stability. In this work, a high-entropy rare-earth zirconate pyrochlore (La_1/6Pr_1/6Nd_1/6Sm_1/6Eu_1/6Gd_1/6)₂Zr₂O₇ was designed. And the lanthanide element Ce was used as simulated radioactive actinide nuclides. A series of ceramic solidifications (La_1/6Pr_1/6Nd_1/6Sm_1/6Eu_1/6Gd_1/6)₂(Zr_1-XCe_X)₂O₇(0≤X≤0.5) were prepared using a high temperature solid phase method to solidify Ce. The solidifying performances were evaluated by analyzing the physical phase composition, microstructure, microscopic morphology, and anti-leaching. The results show that all the nuclides are uniformly solidly dissolved into crystal structure. As the CeO₂ content increases, the crystal structure changes from an ordered pyrochlore phase to a defective fluorite phase. The normalized leaching rates of Ce range from 10^-7 g·m^-2·d^-1 to 10^-6 g·m^-2·d^-1, showing excellent chemical stability.

Lead-Free Reproduction and Color Regulation of Green Glazes From Jizhou Kiln

WEN Mengtao, ZHANG Xiaohua, YUE Zhenxing

2024, 43(9):  3407-3416. 

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Jizhou kiln, one of the eight southern folk kilns of the Song Dynasty, is famous for its brilliant glaze colors. The traditional ceramic raw materials in Jingdezhen area were used to successfully realize the lead-free preparation of green glaze from Jizhou kiln with CuO as colorant, and the effect of CuO content on the color characteristics of copper glaze was also investigated. The results indicate that with the increase of CuO content, the viscosity of glaze layer gradually decreases, and the glaze surface shows light blue, green, dark green, and blue colors in sequence. Cu²⁺ is mainly green color, but the high concentration of Cu²⁺ as a glass modifier destroys the SiO₂ network, increasing the amount of non-bridging oxygen and the density of oxygen ions around Cu²⁺, and the color of Cu²⁺ is mainly blue. After the addition of CuO, the samples exhibite circular and worm-like phase-separated structure. When the CuO content is higher, the smaller size of circular phase separation structure meets Rayleigh scattering, producing blue opalescence and deepening the glaze color. When the CuO content is lower, the larger size of circular phase separation structure satisfies Mie scattering and produces white milky light. The coloration mechanism of lead-free green glaze from Jizhou kiln results from the synergistic coupling effect of copper ion valence state and phase-separated structure.

One-Step Sintering Preparation of Lithium Lanthanum Titanium Oxide Straight-Hole Ceramics and Solid-State Battery Performance

XIN Wenkai, MA Xiaojun, YANG Shangyun, MAO Dongxu, LI Jiajie

2024, 43(9):  3417-3423. 

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Lithium lanthanum titanium oxide (LLTO) ceramic electrolyte possesses high ion conductivity and thermal stability, rendering it an ideal candidate for solid-state batteries. However, conventional methods of electrolyte preparation suffer from drawbacks such as poor interface contact, cumbersome procedures, and significant lithium loss during high-temperature sintering. To address these issues, a one-step sintering method to synthesize LLTO ceramic electrolytes with a straight-hole structure was developed. The micromorphology and electrochemical properties of one-step sintering prepared LLTO ceramic electrolytes were thoroughly investigated. The results reveal that this method enables the synthesis and sintering of LLTO ceramics with straight-hole structure in one step, thereby efficiently circumventing lithium loss during multiple sintering processes, enhancing the densification of LLTO ceramics, and reducing grain boundary resistance. Notably, LLTO ceramic electrolytes synthesized via one-step sintering method exhibit a high conductivity of 2.31×10^-4 S/cm at room temperature. Moreover, Li/Li symmetric batteries assembled using this electrolytes demonstrate excellent Li⁺ deposition and stripping performance, which can be stable cycling for over 350 h at a current density of 0.1 mA/cm². Furthermore, the all-solid-state lithium battery assembled with this electrolytes maintains a capacity retention rate of 94% after 200 cycles at a rate of 0.2 C, demonstrating the exceptional stability of straight-hole LLTO ceramics prepared via one-step sintering.


Simulation Studies on Silicon Infiltration Process in Porous Silicon Carbide Media

ZHANG Xuxi, ZHANG Ge, BAO Jianxun, CUI Congcong, GUO Conghui, LI Wei, ZHANG Wei, ZHU Wanli, XU Chuanxiang, CAO Qi, DONG Binchao, ZHOU Lixun, LI Yilin

2024, 43(9):  3424-3437. 

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The in-depth study of infiltration process of simulated molten silicon in the porous preform of silicon carbide not only helps to understand the causes of defects in the reaction infiltration process, but also is of great significance to reveal the causes of special infiltration phenomena. In this paper, based on level set method, N-S equation and Young’s equation, the simulation of capillary infiltration process of molten silicon was carried out in the two-dimensional channel extracted and reconstructed by optical microscope image. The infiltration process of preform composed of 40 μm particles by molding and the preform based on particle gradation process was simulated. The results show that the larger inlet in infiltration process is conducive to rapid infiltration. The infiltration process gradually evolves from unsaturated infiltration to saturated infiltration in the same area. The pore structure of large cavity, sharp corner area and blind hole in preform will have a greater probability to evolve pore type defects. The boundary conditions of exhaust outlet of preform has a strong correlation with skin-forming phenomenon of infiltration.

Glass

Research Progress on High Refractive Index Optical Glass

WANG Yanhang, LIU Jiayu, LI Xianzi, YANG Penghui, ZHU Hanzhen, HAN Tao

2024, 43(9):  3438-3445. 

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As an important part of the optical system, high refractive index optical glass has excellent comprehensive performance such as high refractive index, high transmittance and high chemical stability, and can expand the field of view angle (FOV) of devices such as digital cameras, microscopes and virtual reality (VR glasses). At present, the research of high refractive index optical glass mainly involves, 1) the preparation of high refractive index glass without traditional glass forming oxide, which cannot be prepared in large size. 2) By adding heavy metal oxide to lanthanide glass high refractive index, enhanced internal transmittance, and improved glass-forming ability are achieved, and this has now been successfully realized through engineering-scale production. This paper summarizes the research progress of high refractive index optical glass, and discusses the development trend and application.

Effect of ZnO on Crystallization and Properties of Spinel Glass-Ceramics

CHEN Kaoxiang, WANG Mingzhong, RAO Yu, CUI Jialin, TAO Haizheng, LU Ping

2024, 43(9):  3446-3454. 

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Spinel glass-ceramics exhibit excellent mechanical properties and high permeability, making it highly suitable for various applications such as cover glass, aerospace, military, dental and optical devices. The effect of ZnO content on the crystallization behavior and properties of MgO-Al₂O₃-SiO₂ (MAS) glass was investigated. The results show that the increase of ZnO content leads to a gradual decrease in the glass transition temperature. Additionally, the crystallization peak temperature shifts to lower temperatures, accompanied by an increase in the crystallization peak magnitude, which indicates that the addition of ZnO promotes crystallization. The structure of glasses was analyzed by Raman spectroscopy. With the increase of ZnO content, the Q³, Q³(Zr) and Q⁴units in the glass network gradually decrease, and the Q² units gradually increase, indicating that the structure of glass network become loose and conducive to the growth of crystals. The addition of ZnO improves the hardness of sample after heat treatment, and the maximum hardness of sample with 7.5% (mole fraction) ZnO content at 920 ℃ for 2 h is 8.13 GPa. Moreover, the addition of ZnO enhances the transmittance of high-temperature heat-treated samples. The average transmittance of samples is greater than 80% in the visible light range, which has excellent optical transparency.

Deformation and Fatigue Behavior of Flexible Glass under Two-Point Bending

WEI Shaoshan, RAO Meijuan, LIU Xiaogen, CAO Dake,WAN Detian, ZHENG Dezhi

2024, 43(9):  3455-3461. 

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Based on the two-point bending loading method and principles, the bending deformation and fatigue behavior of flexible glass were analyzed. The quantitative relationship between the bending curvature radius, bending stress, and plate spacing was derived. Employing the high-cycle fatigue theory, a stress-life (S-N_f) model for flexible glass was established. The results indicate that under two-point bending, the thickness of flexible glass specimen does not alter its bending trajectory. By adjusting the plate spacing, the desired bending curvature radius for experiment can be achieved. Neglecting the influence of flexible glass thickness, the bending curvature radius of specimen shows a linear relationship with the plate spacing, and the maximum tensile stress during bending is inversely proportional to the bending curvature radius. As the selected minimum bending curvature radius R_min increases, the fatigue life also increases, and an increase in the maximum bending curvature radius R_max does not significantly affect the bending fatigue cycles of specimen. The Basquin model can effectively predict the bending fatigue life of flexible glass under different alternating stresses or different bending curvature radii.

Effect of Methane to Flue Gas Flow Ratio on Thermochemical Reforming Process of Oxy-Fuel Combustion Glass Furnaces

ZENG Hongjie, ZHOU Wencai, GUAN Min, SHEN Zhongjie, HE Guinan, CHEN Shuyong, CHEN Jiarui, LI Hongqiang, ZUO Zefang

2024, 43(9):  3462-3471. 

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The methane to flue gas flow ratio significantly affects the progress of thermochemical reforming reaction in oxy-fuel combustion glass furnaces. An experimental study was conducted on the methane and flue gas thermochemical reforming reaction under different methane to flue gas flow ratios using atmospheric pressure tube furnace, and the influences of different methane to flue gas flow ratios on thermochemical reforming reaction performance were analyzed. The results indicate that the methane to flue gas flow ratio significantly affects the effective gas yield of thermochemical reforming reaction and the proportion of each accompanying reaction in reforming process. Under the same reaction time and total gas flow rate conditions, the effective gas yield and main reaction proportion of thermochemical reforming reaction within the test temperature range of 1 000 ℃ to 1 400 ℃ are the highest when the methane to flue gas flow ratio is 2∶1. The exorbitant methane to flue gas flow ratio can easily lead to a decrease in the proportion of methane dry reforming and methane steam reforming reactions during the methane to flue gas reforming process, while an increase in the proportion of methane cracking reaction. The methane reaction rate increases with the increase of methane to flue gas flow ratio and decreases with the increase of flue gas flow rate.

New Functional Materials

Composite Slurry for Room-Temperature Extrusion 3D Printing HA/β-TCP/DCPA Bone Scaffold

HAN Zheng, WANG Tao, LIU Zhiwei, NIE Yunpeng, WANG Xueting

2024, 43(9):  3472-3478. 

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Bone tissue engineering based on 3D printing bone scaffolds is a potential bone repair strategy. The composite powders of phytic acid chelating modified hydroxyapatite (IP6-HA), β-tricalcium phosphate (β-TCP) and anhydrous calcium dihydrogen phosphate (MCPA) with different molar ratios were used as solid phase, and the aqueous solution with different propylene glycol (glycerine) content was used as liquid phase. By adjusting IP6-HA powder content in composite powders and glycerine content in the curing solution, the calcium phosphate composite slurries of brushite system that can be applied to the room-temperature extrusion 3D printing bone scaffolds were prepared. The results show that hydration products of the composite slurries are mainly hydroxyapatite (HA), β-TCP and anhydrous calcium hydrogen phosphate (DCPA). When the glycerine content in the curing solution is 50% (mass fraction), the composite slurries exhibit excellent printability and mechanical properties, and the compressive strength can reach up to 19.8 MPa. The presence of residual IP6-HA changes the mineralization structure of apatite on surface of the solidified samples and improves the mineralization ability. The prepared scaffolds have a complete structure and uniform pores, and the compressive strength can reach 5.8 MPa. The composite slurries prepared in this study can be used to prepare bone scaffolds by room-temperature extrusion 3D printing technology, and has a good application prospect in the field of 3D printing bone scaffolds.

Road Materials

Research Progress of Fiber Modified Cement-Based Materials: Cement Stabilized Base

CHEN Feng, YI Ke, WANG Chaohui, DANG Wujuan, QU Xifeng

2024, 43(9):  3479-3493. 

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To improve the crack resistance of pavement semi-rigid base, and promote the application and development of fiber cement stabilized base materials, the fiber types, physical and chemical properties were systematically combed, and the suitable length and content of fiber for cement stabilized base were determined. The mechanical properties and deformation characteristics of different types of fiber cement stabilized base were compared and evaluated, and the toughening and crack resistance mechanism of fiber cement stabilized base was further analyzed. The results show that, in terms of length and content, polyester fiber data is concentrated in 15~50 mm and 0.06%~0.08% (mass fraction), which are higher than other fibers. The mechanical properties and deformation characteristics of cement stabilized base modified by fibers have significantly improved. Among them, the 28 d unconfined compressive strength of the polyvinyl alcohol (PVA) fiber cement stabilized base has been improved by 6%~34%, and the average improvement in the 28 d splitting strength of the polypropylene fiber cement stabilized base and PVA fiber cement stabilized base is 30% and 18%, respectively. In addition, polypropylene fiber has the best effect on improving the dry shrinkage coefficient of cement stabilized base at 28 d, which can be reduced by about 18%~37%. The average reduction in the 28 d temperature shrinkage coefficient of PVA fiber cement stabilized base is 23%, and the data of 90 d temperature shrinkage coefficient is concentrated in 6%~22%, both at a high level. By analyzing the toughening principle of fiber cement stabilized base material, it can be seen that the fiber mainly weakens the internal stress concentration of the base through bridging effect and delays the development of cracks.