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Effect of freeze-thaw cycles on mechanical behavior of clay-gravel mixtures

Journal of Mountain Science 2022年第12期19卷 3615-3626页

作者： ZHANG Yong-gan LIU Si-hong DENG Gang FANG Bin-xin ZHANG Yan-yi LU Yang College of Water Conservancy and Hydropower Engineering Hohai UniversityNanjing 210098China Key Laboratory of Construction and Safety of Water Engineering of the Ministry of Water Resources China Institute of Water Resources and Hydropower ResearchBeijing 100048China

The use of clay-gravel mixtures(i.e.,adding excavated or natural gravel particles into clay soil matrix)as the main filling materials is increasing in the anti-seepage system of high Earth Core Rockfill Dams(ECRDs).With the continuous construction of high ECRDs in the Chinese plateaus and cold regions,it is of great urgency and importance to understand the physical and mechanical characteristics of compacted clay-gravel mixtures under freeze-thaw *** this end,laboratory freezing-thawing tests,computed tomography(CT),and triaxial compression tests were conducted to evaluate the effects of freezethaw cycles on moisture loss,pore structure characteristics,stress-strain behavior,failure strength,elastic modulus,cohesion,and internal friction angle of compacted clay-gravel *** results demonstrate that,1)the freeze-thaw cycle significantly changed the mechanical characteristics of the clay-gravel mixture samples,but the shape of the stress-strain curve is less sensitive to it.2)The failure strength of samples exhibits a significant decrease after the first freeze-thaw cycle,but shows a certain increase as the number of freeze-thaw cycles increases from 1 to 2.3)The elastic modulus of samples first decreases and then increases with increasing freeze-thaw cycle,and the most severe deterioration was observed after the first freeze-thaw cycle.4)Regardless of the number of freeze-thaw cycles,there is a linear relationship between failure strength and elastic modulus for a sample that has suffered freeze-thaw weathering.5)The cohesion of samples decreases firstly and then slightly increases with increasing freeze-thaw cycles,while the internal friction angle is hardly affected.

关键词： Earth core rockfill dam Clay-gravel mixtures freeze-thaw cycles Computed tomography Mechanical behavior

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BEHAVIOR OF AIR-ENTRAINED CONCRETE AFTER freeze-thaw cycles

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Acta Mechanica Solida Sinica 2009年第3期22卷 261-266页

作者： Huaishuai Shang Yupu Song Jinping Ou State Key Laboratory of Structural Analysis for Industrial Equipment DaIian University of Technology Dalian 116024 China Shandong Provincial Academy of Building Research Jinan 250031 China State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Dalian 116024 China

The experimental study of air-entrained concrete specimens subjected to different cycles of freeze-thaw was completed. The dynamic modulus of elasticity, weight loss, the cubic compressive strength, compressive strength, tensile strength and cleavage strength of air-entrained concrete were measured after 0, 100, 200, 300, 400 cycles of freeze-thaw. The experimental results showed that the dynamic modulus of elasticity and strength decreased as the freeze-thaw was repeated. The influences of freeze-thaw cycles on the mechanical properties, the dynamic modulus of elasticity and weight loss were analyzed according to the experimental results. It can serve as a reference for the maintenance, design and the life prediction of dams, hydraulic structures, offshore structures, concrete roads and bridges in northern cold regions.

关键词： air-entrained concrete freeze-thaw cycles mechanical properties the dynamic mod-ulus of elasticity weight loss

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Axial Mechanical Properties of Timber Columns Subjected to freeze-thaw cycles

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Journal of Renewable Materials 2020年第8期8卷 969-992页

作者： Kang He Yu Chen Jian Wang College of Civil Engineering Fuzhou UniversityFuzhou350116China School of Urban Construction Yangtze UniversityJingzhou434023China

The behaviour of timber columns subjected to freeze-thaw cycles under axial compression is presented in this paper.A total of forty specimens,including twenty circular timber columns and twenty square timber columns,were tested under axial *** failure modes,ultimate bearing capacity,ductility coefficient,load-displacement curves and load-strain curves were obtained and *** number of freeze-thaw cycles(from 0 to 80)and the specimens’height(from 225 mm to 360 mm)were considered as the main *** freeze-thaw cycles,there was no obvious change on the surface of the timber *** test results showed that freeze-thaw cycles could reduce the ultimate bearing capacity of the timber columns,and the average reduction of the ultimate bearing capacity of the specimen reached 28%.The ductility coefficient of the square specimens subjected to freeze-thaw cycles almost remains constant compared with that of the square timber columns left *** the ductility coefficient of the circular timber columns increases after freeze-thaw *** addition,based on the extensive experimental analysis,a regression formula is derived to predict the ultimate bearing capacity of the timber columns after being subjected to freeze-thaw cycles,which is proved to be reasonable accurate.

关键词： Timber columns freeze-thaw cycles axial mechanical property ductility coefficient regression formula

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Experimental studies on the pore structure and mechanical properties of anhydrite rock under freeze-thaw cycles

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Journal of Rock Mechanics and Geotechnical Engineering 2022年第3期14卷 781-797页

作者： Chao Hou Xiaoguang Jin Jie He Hanlin Li School of Civil Engineering Chongqing UniversityChongqing400045China Key Laboratory of New Technology for Construction of Cities in Mountain Area of the Ministry of Education Chongqing UniversityChongqing400045China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing UniversityChongqing400045China

To study the deterioration mechanisms of anhydrite rock under the freeze-thaw weathering process,the physico-mechanical characteristics and microstructure evolutions of anhydrite samples were determined by a series of laboratory ***,a descriptive-behavioral model was used to measure the integrity loss in anhydrite samples caused by cyclic ***,the freeze-thaw damage mechanisms of anhydrite rock were revealed from the macro and micro *** results show that the pore size of the anhydrite rock is mainly concentrated in the range of 0.001-10μ*** the number of freeze-thaw cycles increases,there is a growth in the proportion of macropores and ***,the proportion of micropores shows a declining *** relations of the uniaxial compressive strength,triaxial compressive strength,cohesion,and elastic modulus versus freeze-thaw cycles can be fitted by a decreasing exponential function,while the internal friction angle is basically unchanged with freezethaw *** the increase of confining pressure,the disintegration rates of the compressive strength and the elastic modulus decrease,and the corresponding half-life values increase,which reveals that the increase of confining pressures could inhibit freeze-thaw damage to ***,it has been proven that the water chemical softening mechanism plays an essential role in the freeze-thaw damage to anhydrite ***,it is concluded that the freeze-thaw weathering process significantly influences the macroscopic and microscopic damages of anhydrite rock.

关键词： Anhydrite rock freeze-thaw cycles Physico-mechanical characteristics Microstructure evolution Deterioration mechanisms

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Effects of freeze-thaw cycles on Physical and Mechanical Properties of Glulam Exposed to Outdoor Environment

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Journal of Renewable Materials 2021年第7期9卷 1293-1307页

作者： Ruyuan Yang Haitao Li Assima Dauletbek Mahmud Ashraf Rodolfo Lorenzo Youfu Sun Yuehong Wu College of Materials Science and Engineering Nanjing Forestry UniversityNanjingChina College of Civil Engineering Nanjing Forestry UniversityNanjingChina University College London LondonWC1E 6BTUK School of Engineering Deakin UniversityGeelongVIC 3216Australia

This paper presents an experimental investigation to identify suitable indices to assess durability of glulam when subjected to freeze-thaw cycles in an exposed *** this study,two types of glulam specimens were tested for their performance when subjected to different levels of aging due to freezing and *** of aging treatment on various parameters including thickness swelling rate,static bending strength,elastic modulus,shear strength,and peeling rate of adhesive layer were *** results showed that freeze-thaw aging treatment did not affect the water-resistance of the specimens as measured by thickness swelling rate and had little effect on the dimensional stability of the ***,the applied aging treatment weakened the bending resistance of the glulam specimens with more pronounced effects on on low-density *** the other hand,bond strength of high-density wood was relatively more affected due to the appliedfreeze-thaw *** highdensity wood,it is suggested that the shear strength of the adhesive layer be taken as an important index to determine the durability of freeze-thaw cycles *** low-density wood,on the other hand,the static bending strength can be used as an index to determine the durability of glulam under freeze-thaw cycles aging.

关键词： freeze-thaw cycles structural glulam durability wood failure percentage accelerated aging

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Dynamic mechanical characteristics of frozen subgrade soil subjected to freeze-thaw cycles

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Journal of Mountain Science 2023年第1期20卷 242-255页

作者： WANG Dan LIU En-long YANG Cheng-song LIU You-qian ZHU Sheng-xian YU Qi-hao Northwest Institute of Eco-Environment and Resources State Key Laboratory of Frozen Soil EngineeringChinese Academy of SciencesLanzhou730000China University of Chinese Academy of Sciences Beijing100049China State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resources and HydropowerSichuan UniversityChengdu610065China Qinghai-Tibet Railway Company Qinghai810000China

As a widely-applied engineering material in cold regions, the frozen subgrade soils are usually subjected to seismic loading, which are also dramatically influenced by the freeze-thaw(F-T)cycles due to the varying temperature. A series of dynamic cyclic triaxial experiments were conducted through a cryogenic triaxial apparatus for exploring the influences of F-T cycles on the dynamic mechanical properties of frozen subgrade *** to the experimental results of frozen clay at the temperature of-10℃, the dynamic responses and microstructure variation at different times of F-T cycles(0, 1, 5, and 20 cycles) were explored in *** is experimentally demonstrated that the dynamic stress-strain curves and dynamic volumetric strain curves of frozen clay are significantly sparse after 20F-T cycles. Meanwhile, the cyclic number at failure(Nf) of the frozen specimen reduces by 89% after 20freeze-thaw cycles at a low ratio of the dynamic stress amplitude. In addition, with the increasing F-T cycles,the axial accumulative strain, residual deformation,and the value of damage variable of frozen clay increase, while the dynamic resilient modulus and dynamic strength decrease. Finally, the influence of the F-T cycles on the failure mechanisms of frozen clay was discussed in terms of the microstructure variation. These studies contribute to a better understanding of the fundamental changes in the dynamic mechanical of frozen soils exposed to F-T cycles in cold and seismic regions.

关键词： freeze-thaw cycles Frozen clay Dynamic triaxial test Dynamic mechanical properties

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Water migration in subgrade soil under seasonal freeze-thaw cycles in an alpine meadow on the Qinghai-Tibet Plateau

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Journal of Mountain Science 2022年第6期19卷 1767-1781页

作者： WU Guan-qing XIE Yong-li WEI Jin YUE Xia-bing School of Highway Chang'an UniversityXi'an 710064China

Highway frost heave and thawing settlement caused by water migration towards the freezing front and ice lens development is widespread in the alpine meadow area of the southeast QinghaiTibet Plateau(QTP). A laboratory experiment on a highway reconstruction and expansion project in the QTP was carried out in this work to analyze the effects of fine particle content, initial water content, and the number of freeze-thaw cycles(FTCs) on frost depth, temperature gradient(Grad T), total water intake, and water intake flux. Based on the results of the laboratory experiment, a modified model of migration potential related to fine particle content, freeze-thaw history, and freezing time was established. The results show that, with the increase of fine particle content, the frost depth of soil decreases, the curve of total water intake over time is transformed from an Sshape to an arch, and the curve of water intake flux over time is transformed from a peak shape to descending shape. The variation trend of migration potential with freezing time and the freeze-thaw history is the same as that of water intake flux with freezing time and freeze-thaw history. The variation trend of soil intake flux can be used as a reference to determine the variation trend of soil migration potential. This study provides a reference for the design and construction of highway subgrade in the alpine meadow area of the QTP.

关键词： Water migration Seasonally frozen ground freeze-thaw cycles Laboratory experiment Migration potential model Qinghai-Tibet Plateau

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Behavior of High Water-cement Ratio Concrete under Biaxial Compression after freeze-thaw cycles

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Journal of Wuhan University of Technology(Materials Science) 2008年第4期23卷 589-594页

作者： SHRUG Huaishuai SONG Yupu OU Jinpin State Key Laboratory of Structural Analysis for Industrial Equipment Dalian University of Technology Dalian 116024 China Shandong Provincial Academy of Building Research Jinan 250031 China State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Dalian 116024 China

The high water-cement ratio concrete specimens under biaxial compression that completed in a triaxial testing machine were experimentally studied. Strength and deformations of plain concrete specimens in two loading direction under biaxial compression with stress ratio of a=0, 0.25, 0.5, 0.75, 1.0 were obtained after 0, 25, 50 cycles of freeze-thaw. Influences of freeze-thaw cycles and stress ratio on the peak stress and deformation of this point were analyzed according to the experimental results, Based on the test data, the failure criterion expressed in terms of principal stress after different cycles of freeze-thaw, and the failure criterion with consideration of the influence of freeze-thaw cycle and stress ratio were proposed respectively.

关键词： concrete freeze-thaw cycles stress ratio strength criteria

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Effect of freeze-thaw cycles on Bond Strength between Steel Bars and Concrete

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Journal of Wuhan University of Technology(Materials Science) 2008年第4期23卷 584-588页

作者： JI Xiaodong SONG Yupu LIU Yuan State Key Lab of Coastal and Offshore Engineering Dalian University of Technology Dalian 116024 China School of Soil and Water Conservation Beijing Forestery University Beijing 100083 China High School Affiliated to Renmin University of China Beijing 100080 China

The effect of freezing and thawing cycles on mechanical properties of concrete （compressive, splitting tensile strength） was experimentally investigated. According to the pullout test data of three kinds of deformed steel bars, the bond stress-slip curves after freezing and thawing were obtained. The empirical equations of peak bond strength were proposed that the damage accounted for effects of freezing and thawing cycle. Meanwhile, the mechanism of bond deterioration between steel bars and concrete after freezing and thawing cycles was discussed. All these conclusions will be useful to the durability design and reliability calculation of RC structures in cold region.

关键词： concrete steel bars bond strength freeze-thaw cycles

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Mechanical and acoustic emission characteristics of anhydrite rock under freeze-thaw cycles

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Journal of Mountain Science 2023年第1期20卷 227-241页

作者： ZHANG Chi JIN Xiao-guang HOU Chao HE Jie School of Civil Engineering Chongqing UniversityChongqing400045China China Railway 14TH Bureau Group Fourth Engineering Corporation Limited Jinan250101China Key Laboratory of New Technology for Construction of Cities in Mountain Area of the Ministry of Education Chongqing UniversityChongqing400045China State Key Laboratory of Coal Mine Disaster Dynamics and Control Chongqing UniversityChongqing400045China

To study the damage mechanisms of anhydrite rock under freeze-thaw cycles, the physicalmechanical properties and the microcracking activities of anhydrite rock were investigated through mass variation, nuclear magnetic resonance, scanning electron microscope tests, and uniaxial compression combined with acoustic emission(AE) tests. Results show that with the increase of freeze-thaw processes,the mass, uniaxial compression strength, and elastic modulus of the anhydrite specimens decrease while the porosity and plasticity characteristics *** example, after 120 cycles, the uniaxial compression strength and elastic modulus decrease by 46.54% and 60.16%, and the porosity increase by 75%. Combined with the evolution trend of stressstrain curves and the detected events, three stages were labeled to investigate the AE characteristics in freeze-thaw weathered anhydrite rock. It is found that with the increase of freeze-thaw cycles, the proportions of AE counts in stage Ⅰ and stage Ⅱ show a decaying exponential trend. Contrarily, the proportion of AE counts in stage Ⅲ displays an exponential ascending trend. Meanwhile, as the freeze-thaw cycles increase, the low-frequency AE signals increase while the intermediate-frequency AE signals decrease. After 120 cycles, the proportion of low-frequency AE signals increases by 168.95%, and the proportion of intermediate-frequency AE signals reduces by 81.14%. It is concluded that the microtensile cracking events occupy a dominant position during the loading process. With the increase of freeze-thaw cycles, the b value of samples *** 120 cycles, b value decreases by 27.2%, which means that the proportion of cracking events in rocks with small amplitude decreases. Finally, it is proposed that the freeze-thaw damage mechanism of anhydrite is also characterized by the water chemical softening effect.

关键词： freeze-thaw cycles Anhydrite rock Physical and mechanical properties AE characteristics Damage mechanism

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