Study On Mechanical Properties And Mesoscopic Structure Of CA Mortar Under Temperature Cycle

As an organic-inorganic composite layer material filled in the high-speed railway slab ballastless track,CA mortar can serve to support the track plate,adjust the construction,buffer the train load,block the crack,and provide elasticity.Therefore,CA mortar is required to have sufficient strength and necessary elasticity.The asphalt content of CRTS I type CA mortar is about 30%,and its mechanical properties are greatly affected by temperature.In the past,most scholars focused on the macroscopic study of the influence of temperature on the mechanical properties of CA mortar,but the research from the mesoscopic level is lacking.Based on CT technology,this paper designed the temperature test of CA mortar specimen,pure concrete specimen and emulsified asphalt at-20 °C ~ 80 °C,and explored the temperature stress,cement hydration,aging of emulsified asphalt and softening during temperature cycling.The influence of migration and other factors on the mechanical properties of CA mortar;and the relationship between the microstructure of CA mortar and its mechanical properties.Draw the following conclusions:(1)When the temperature cycle is 0~90 times,the cement continues to hydrate and the asphalt cement aging is the main one,which together cause the CA mortar compressive strength and elastic modulus to increase;at this time,the asphalt cement can provide better toughness,and the low temperature shrinkage and high temperature thermal expansion effect caused by temperature stress do not play a leading role.When the temperature cycle is 90~120 times,the aging effect and temperature stress of the asphalt cement become the dominant factor,which causes the plasticity of the mortar to decrease,the brittleness to increase,the elasticity to decrease,and the damage to occur more easily under normal working conditions.(2)During the temperature cycle,the internal structure and mechanical properties of CA mortar changed: The void volume is increased by about 2.5%;the asphalt cement content is reduced by about 3.15%;the compressive strength and elastic modulus of the CA mortar increase with the number of cycles.This explain that the mechanical properties of the material are not only related to the physical structure,but also related to the chemical properties of the components;during the temperature cycle of 120 times,the void volume increase is limited,which is not the dominant factor affecting the mechanical properties of the mortar;while the continuous hydration of cement,the reduction of asphalt content,the continuous hardening or embrittlement caused by asphalt aging and the temperature stress affect the temperature.The dominant factor in the mechanical properties of the mortar during the cycle.(3)The mechanical properties of CA mortar specimens are not only related to the density,void volume and emulsified asphalt content of the specimen,but also related to the distribution position of each component.Under certain conditions,the compressive strength of CA mortar specimens decreases with the increase of void ratio.The higher the asphalt content,the smaller the compressive strength value,the better the plastic properties of the mortar,and the more obvious the deformation is.However,the density of the CA mortar specimen is large,and the cement mortar content is high,which does not mean that the compressive strength is high.The compressive strength of the test piece is also related to the distribution position of each component.The more uniform the distribution of each component in the test piece,the better the mechanical properties of the test piece.