| In this paper,the abundant aeolian sand and pumice resources in Inner Mongolia are used to develop alternatives to traditional raw materials for concrete,and a new type of green environmental protection concrete is studied,which is aeolian sand lightweight aggregate concrete.Considering the influence of various adverse factors such as freeze-thaw,sulfate erosion and low temperature,this paper explores the mechanism of damage and deterioration of frost resistance of aeolian sand lightweight aggregate concrete in the environment of freeze-thaw and salt erosion from the aspects of macro performance degradation law,pore water ice transformation mechanism,micro pore structure characteristics and pore three-dimensional structure dynamic development,so as to provide a theoretical basis for the application of aeolian sand lightweight aggregate concrete in cold region.The main research contents and results are as follows:1.By testing the compressive strength and pore structure of aeolian sand lightweight aggregate concrete under different curing ages,it can be concluded that the porosity,average pore diameter,pore radius of<1.0?m,1.0-10?m and>10?m of aeolian sand lightweight aggregate concrete increase first and then decrease with the increase of age.The compressive strength of aeolian sand lightweight aggregate concrete can be predicted by the grey model GM(1,4)established by the compressive strength and the fractal dimension of the pore radius of<1.0?m,1.0-10?m and>10?m.2.Through the fast freeze-thaw test with water and sulfate of aeolian sand lightweight aggregate concrete,the rules of pore radius and freeze-thaw damage of aeolian sand lightweight aggregate concrete can be obtained.Under the action of water freeze-thaw,when the porosity of<0.1?m decreases and the porosity of>1.0?m increases,the freeze-thaw damage of aeolian sand lightweight aggregate concrete increases.On the contrary,when the porosity of<0.1 ?m increases and the porosity of>1.0?m decreases,the freeze-thaw damage of aeolian sand lightweight aggregate concrete slows down.Under the action of sulfate freeze-thaw,when the porosity of<0.1?m decreases and the porosity of 1.0-10?m increases,the freeze-thaw damage of aeolian sand lightweight aggregate concrete increases.On the contrary,when the porosity of<0.1?m increases and the porosity of 1.0-10?m decreases,the freeze-thaw damage of aeolian sand lightweight aggregate concrete slows down.3.Low-temperature nuclear magnetic resonance technology are used to explore the changes of nuclear magnetic signal,unfrozen water content,T2 spectrum distribution,pore radius distribution and porosity during freeze-thaw of aeolian sand lightweight aggregate concrete.It is found that the freezing process of pore solution always lags behind the melting process of aeolian sand lightweight aggregate concrete.During the freezing process,the unfrozen water in the pores of aeolian sand lightweight aggregate concrete freezes faster between-5 to-10? and slower between-10 to-40?.During the melting process,aeolian sand lightweight aggregate concrete freezes faster between-10 to-5? and slower between-40 to-10?.The freezing of aeolian sand lightweight aggregate concrete starts with large pores,and the melting starts with small pores.The main reason for the freeze-thaw failure of aeolian sand lightweight aggregate concrete is the hydrostatic pressure caused by the freezing of pore solution above-10?.4.X-ray computed tomography technology is used to study the distribution characteristics and evolution of three-dimensional pore structure of aeolian sand lightweight aggregate concrete under freeze-thaw environment,and the statistical parameters are used to analyze the pore structure parameters of aeolian sand lightweight aggregate concrete before and after freeze-thaw.Before freeze-thaw,the pore volume of aeolian sand lightweight aggregate concrete is concentrated in the range of 0.01-0.1mm3,the pore surface area is concentrated in the range of 0.1-10mm2,and the pore length is concentrated in the range of 0-1.0mm.After freeze-thaw,the pore volume of aeolian sand lightweight aggregate concrete is concentrated in the range of 0.1-10m3,the pore surface area is concentrated in the range of 10-100mm2,and the pore length is concentrated in the range of 2.0-3.0mm.The internal area of aeolian sand lightweight aggregate concrete is affected by freeze-thaw in order from the inside to the outside,and the pore change is mainly reflected in the area near the surface of the sample.5.The pore structure parameters and pore size distribution of aeolian sand lightweight aggregate concrete before and after freeze-thaw are analyzed by nuclear magnetic resonance method and mercury intrusion method.According to NMR test results,the proportion of pores in aeolian sand lightweight aggregate concrete is the largest.After 200 freeze-thaw cycles,the proportion of pores increases.According to the mercury intrusion test results,the proportion of gel pores in aeolian sand lightweight aggregate concrete is the largest.After 200 freeze-they cycles,the proportion of gel pores is higher than before freeze-thaw.The pore structure measured by nuclear magnetic resonance method has dual fractal characteristics,and the pore structure measured by mercury intrusion method has single fractal characteristics. |
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