Study On The Evolution Of Freeze-thaw Microstructure Of Aeolian Sand Concrete Under Multi-factor Action

In this paper,the aeolian sand in the Kubuqi Desert in Inner Mongolia was used to replace some natural river sands with aeolian sand as fine aggregate to develop aeolian sand concrete.Five working conditions were designed:fresh water freeze-thaw cycle test,3%MgSO₄ freezing thaw cycle test,6%MgSO₄ freeze-thaw cycle test,freezing and thawing-cycle test carbonation,carbonation-freeze-thaw cycle test,mainly for the experimental study of the following items:1.Through testing the mass loss and relative dynamic elastic modulus of the test specimens under different working conditions,it is found that using the relative dynamic elastic modulus as an indicator for evaluating the durability of concrete is more accurate;the higher the amount of wind and sand deposits,the higher its quality loss rate.The smaller the relative dynamic elastic modulus change,the more aeolian sand can play a“filling”effect,which can effectively reduce the concrete porosity and make the concrete structure more compact.The incorporation of aeolian sand can significantly increase the frost resistance of the concrete.2.Based on nuclear magnetic resonance technology,pore structure test of concrete:The durability degradation of concrete is not accurate with the change of porosity.The freeze-thaw cycles of wind-sand-concrete concrete have three characteristic peaks in the NMR T2 spectrum curve,under the action of freezing and thawing cycles.The internal pores develop,and the T2 spectrum curve evolves from three peaks to two peaks.At the same time,the T2 spectrum curve shifts to the right,that is,the small pores in the pore distribution curve move toward the large pores.3.Before the test,the proportion of gel pores in the concrete is the largest.Freeze-thaw cycles significantly reduce the proportion of gel pores,increase the proportion of capillary pores and proportion of multi-harmonic pores,and negatively correlate porosity with the proportion of gel pores.The correlation coefficient was-0.88,and the porosity was positively related to the ratio of capillary pores.The correlation coefficient was 0.89.4.Freeze-thaw cycle will have a"polarization"effect on pore distribution,carbonization will have a"homogenization"effect on pore distribution,and definition w is the ratio of the proportion of gel pores to the proportion of capillary pores,w value and test piece Porosity is an exponential function.5.Using field emission scanning electron microscopy and X-ray diffractometry to analyze the meso-features of concrete:The mesostructure of aeolian sand concrete is significantly denser than ordinary concrete,and the incorporation of aeolian sand can improve the antifreeze and anti-carbonation ability of concrete.6.Using hydraulic conductivity to evaluate the impermeability of concrete,the addition of aeolian sand can optimize the pore structure of concrete and significantly improve the impermeability of concrete.The permeability of concrete is negatively related to the value of w.