Abrasion Resistance And Frost Resistance Of Calcium Carbonate Whisker Cement-based Composites

Based on the multi-scale physical characteristics of cement-based composites,multi-stage cracking characteristics,abrasion,and freeze-thaw cycles performance degradation theory,micron-scale calcium carbonate whiskers(CW)are introduced to construct CWRC.The aim is to study its physical and mechanical properties under abrasion and freeze-thaw cycles,as well as micro structure.In addition,the steel fiber-polyvinyl alcohol(PVA)fiber-CW(MSFRC)is also constructed.The physical and mechanical properties under the action of freeze-thaw cycles are studied,and the microstructure is analyzed.The specific contents are as follows:(1)The abrasion resistance and compression performance of CWRC are studied.It can be found that with the increase of CW volume fraction,the abrasion resistance and compressive strength of cement mortar also increase.The bridging effect,filling effect,dilution effect and CH orientation improvement effect of CW limit the growth of CH hydration products,reduce the total amount of non-evaporated water and CH,and make the matrix denser.Meanswhile,the synergy effect of CW and fly ash is more effective in improving abrasion resistance.And there is a good linear relationship between abrasion resistance parameters and compressive strength.(2)The semi-circular bending test is used to clarify the mechanism of CW by analyzing the variety in the physical and mechanical properties and microstructure of CWRC before and after freeze-thaw cycles.The study find that after different freeze-thaw cycles,the impermeability of CWRC increase with the increase of the volume fraction of CW;under the action of three-point bending load,after different freeze-thaw cycles,the deterioration of the physical and mechanical properties of cement mortar is effectively alleviated with the increase of the volume fraction of CW;the physical and mechanical parameters of the volume fraction of 3.0% CW are the highest;CW bridging,CW breakage,CW pull-out and crack deflection and other microscopic crack resistance mechanisms become more effective with the increase of CW volume fraction;based on the theory of material mechanics,established three different constitutive models(two-parameter rational fraction model,rational fraction equation model,single parameter rational power function model)to explain the influence of CW on the stress-strain behavior of cement mortar after different freeze-thaw cycles.The results show that only model ? fully meets its boundary conditions and fits the test results best.(3)Analyze the uniaxial compression performance and microstructure of MSFRC before and after freeze-thaw cycles.The study find that the introduction of CW improves the frost resistance of MSFRC,and this trend become more obvious with the increase of CW volume fraction.Specifically: After the introduction of CW,the uniaxial compressive strength,elastic modulus,and strain energy of MSFRC are improved;however,these mechanical parameters decrease with the increase of the number of freeze-thaw cycles.A damage constitutive model of MSFRC considering the number of freeze-thaw cycles and CW volume fraction is established.This model can explain the effect of the number of freeze-thaw cycles and CW volume fraction on the initial damage of MSFRC.In addition,the micro-morphology and pore structure of MSFRC before and after the freeze-thaw cycles are analyzed.The introduction of CW can increase the density of the transition zone between the surface of steel fiber and PVA fiber,and effectively improve the micro-morphology and pore structure of cement-based materials before and after freeze-thaw cycles.Altimately,improve the frost resistance.(4)Through the study of the physical and mechanical properties and microstructure of MSFRC before and after different freeze-thaw cycles,it can be found that the synergistic effect of steel fiber,PVA fiber and CW hybrid fiber system on the macro-,mecro-and microscales can refine and restrict pores and cracks caused by pore interconnection;and enhance the bending performance and compression performance of the specimen;improve the failure form of the matrix,from brittleness to ductility;after 150 freeze-thaw cycles,the control prismatic specimen has been completely destroyed,and the cube specimens still maintain good integrity after 600 freeze-thaw cycles.Based on the theory of damage mechanics,the damage constitutive model of MSFRC is establish.It can be found that the prediction model fits well with the test results.