Experimental Study On Shrinkage Performance Of Fly Ash Concrete With Equal Strength

Fly ash concrete has been widely applied in all kinds of infrastructure constructions,thanks to its technological,economic and social benefits.In actual projects,concrete materials are mostly designed based on the requirements on compressive strength,so the research on strength development and volume deformation of fly ash concretes with equal strength conditions is of significance,and the outcome of the studies will be more conducive to guide the engineering practice.In this thesis,the mix design method for fly ash concretes with equal strength was proposed;with the content of fly ash(0,30%,40%,50%,60%,70%),water-binder ratio(0.36,0.42,0.46,0.50,0.54,0.60)and the initial drying age(1d,3d,7d,28d)as the basic parameters,the strength development and shrinkage properties of fly ash concretes with equal strength were studied,and the prediction formulas for autogenous shrinkage and total shrinkage with different initial drying ages of fly ash concretes with equal strength were proposed.The main conclusions of this thesis are as follows:(1)Under standard curing,the compressive strength of fly ash concretes with equal strength grew faster at early ages,and then the growth trend gradually slowed down at late ages;with more fly ash,the compressive strength of concrete developed more slowly at early ages,but when the age getting late,the compressive strength of fly concrete was close to that of pure cement concrete;under drying curing,the compressive strength of fly ash concretes with equal strength grew faster at early ages,and then the growth trend gradually slowed down at late ages.Under different curing conditions,the early-age compressive strength of fly ash concrete was relatively close;as the age getting late,the compressive strength of concretes was gradually becoming lower than that under standard curing.(2)Under standard curing,the splitting tensile strength of fly ash concrete increased rapidly at early ages,and then the growth rate gradually slowed down;the growth rate of splitting tensile strength of fly ash concrete was lower than that of pure cement concrete at early ages,but when the age getting late,the splitting tensile strength of fly ash concrete gradually approached that of pure cement concrete.At the age of 60 days,the splitting tensile strengths of some fly ash concretes were higher than that of pure cement concrete;under dry curing conditions,the development trend of splitting tensile strength of fly ash concrete was consistent with the compressive strength,and the splitting tensile strengths at different ages were all lower than that of pure cement concrete.Under different curing conditions,the splitting tensile strengths under dry curing at different ages were lower than that under standard curing.(3)The autogenous shrinkage of fly ash concretes with equal strength was influenced by the coupled effect of the two factors,i.e.water-binder ratio and fly ash content.Within the scope of this study,the autogenous shrinkage of fly ash concretes with equal strength increased with the increase of fly ash content at early ages.When fly ash contents were 50% and 60%,the autogenous shrinkage of fly ash concrete at 1d could be higher than 60% of autogenous shrinkage at 60d;the late-age autogenous shrinkage of fly ash concrete with equal strength increased first then decreased,with the increase of fly ash content.(4)The total shrinkage and drying shrinkage of fly ash concretes with equal strength were affected by the amount of fly ash,water-binder ratio,and initial drying age.Generally,they decreased with the later initial drying age;Within the scope of this study,the drying shrinkage of fly ash concrete decreased first and then increased with the increase of fly ash content.There is an optimal fly ash content to make fly ash concrete exhibit the lowest drying shrinkage.(5)The autogenous shrinkage of fly ash concretes with equal strength and the compressive strength under standard curing,and the total shrinkage of fly ash concretes with equal strength and the compressive strength under drying curing were approximately in a linear relationship.The quantitative prediction formulas were proposed for the autogenous shrinkage and total shrinkage with different initial drying ages of fly ash concretes with equal strength,using fly ash content,water-binder ratio and curing age as variables.The formulas have a certain accuracy.