Influence Of Different Replacement Methods Of Grade ? Fly Ash On Pavement Concrete Frost Resistance

Concrete is widely used because of its many advantages.Natural river sand is an important raw material for concrete,which consumes a lot of resources.Fly ash is fly ash produced in the process of coal-fired power generation.Ecological pollution.As natural river sand resources are increasingly depleted,the productivity of fly ash in Ningxia is increasing year by year.Replacing river sand in concrete with grade III fly ash with low utilization rate has significant economic and environmental benefits.This subject is aimed at rural roads in Ningxia region,using fly ash admixture technology,trying to explore the frost resistance of ordinary concrete,fly ash instead of part of fine aggregate concrete,and the same amount of fly ash instead of cement concrete.The effect of different replacement methods of grade III fly ash on the frost resistance of rural highway concrete.This paper first puts forward the technical requirements of raw materials for the preparation of pavement concrete mixed with fly ash,and then puts forward the design plan of the mix ratio of pavement concrete and the production and maintenance of the test pieces,and studies the ordinary concrete,fly ash concrete,fly ash fine aggregate concrete The compressive and frost resistance performance of the concrete is determined by testing the concrete quality,dynamic elastic modulus and flexural strength after the test,and analyzing the relationship between it and the number of freeze-thaw cycles.Frost resistance of rural pavement concrete under different ash replacement methods.The results show that the equivalent volume of grade ? fly ash with good physical and chemical indexes instead of 25%fine aggregate can significantly improve the mechanical properties and frost resistance of concrete.Compared with concrete with the same amount of fly ash instead of cement,it can improve the early strength Obvious advantages.On the basis of experimental research and theoretical analysis,the following research results have been achieved in this paper:(1)For the concrete applied to rural roads,raw material requirements and technical indicators that meet the requirements of coarse aggregate,fine aggregate,cement and other raw materials that meet fly ash pavement concrete are proposed.(2)Through the measurement of the compressive strength of concrete,the compressive strength of concrete with different replacement methods of grade III fly ash is obtained.At 56 days of age,the compressive strength of fly ash fine aggregate concrete is better than that of ordinary concrete and fly ash Gray concrete increased by 18.42%and 43.05%respectively.(3)The rapid freeze-thaw test method was used to study the effect of different replacement methods of grade ? fly ash on the frost resistance of concrete.When the freeze-thaw cycle reaches 200 times,the relative dynamic elastic modulus of the fly ash fine aggregate concrete is increased by 20.11%compared with ordinary concrete.At this time,the relative dynamic elastic modulus of the fly ash concrete has dropped to below 60%.(4)After studying the microscopic morphology of the concrete through scanning electron microscopy experiments,it was found that after incorporating fly ash,the active components contained in the fly ash reacted with Ca(OH)2 produced by cement water to form C-S-H gel and water Calcium aluminate(CaH)and other cementitious materials fill the pores to make the structure more dense.From the mechanism,the reason why fly ash improves the mechanical properties and freezing resistance of concrete is analyzed.(5)Calculate the concrete damage value after freezing and thawing cycles,establish a second-order mathematical damage model and exponential damage model,and obtain it by substituting the test data for fitting.The second-order mathematical model can better show the number of concrete freeze-thaw cycles Under the macroscopic damage law,the value of R2 ranges from 0.964 to 0.996,and the fitting result is good.