Experimental Study On The Tensile Creep At Early Ages Of High Strength Concrete Containing Mineral Admixture

Investigation on tensile creep behavior at early ages of high strength concrete can provide important parameters for high-precision stress analysis and crack prediction.The early-age tensile basic creep testing apparatus which was designed by our research team was applied to the experimental study.In this program,firstly,the basic mechanical property and autogenous shrinkage of high strength concrete containing mineral admixture were evaluated.Then,the effects of loading age,stress/strength ratio and mineral admixture on the behavior of basic tensile creep at early ages were discussed systematically under the constant stress.The basic tensile creep behavior at early ages of high strength concrete was studied furtherly under varying stress.The conclusions can be drawn as follows:(1)The development rate of elastic modulus of high strength concrete containing mineral admixture at early ages were obviously faster than that of splitting tensile strength and compressive strength.(2)The fly ash played a role in restraining the autogenous shrinkage of concrete.However,it was obvious that the blast furnace slag promoted the autogenous shrinkage.The composite group had the characteristics of fly ash group and blast furnace slag group,so the development of autogenous shrinkage strain which was close to the reference group was between the fly ash group and the blast furnace slag group.(3)Under the constant stress,the effect of loading age on the tensile creep of high strength concrete containing mineral admixture was mainly centralized in first three days,and a particularly high magnitude of specific creep was observed when concrete was loaded at 1 and 2 days.In the case of concrete containing mineral admixture,the characteristic of nonlinear creep under different stress/strength ratios gradually became linear creep with the loading age going by.The fly ash group had an obvious promotion function on the tensile basic creep when the loading age was 1 day with each stress/strength ratio.The blast furnace slag group played a role in restraining the tensile basic creep when the loading age was 1 day with each stress/strength ratio or the situation of the loading age was 2 days and the stress/strength ratio was 0.2.The composite group had a bit promotion function on the tensile basic creep in general when the loading age was 2 days before.(4)The fly ash group and the blast furnace slag group under the varying stress respectively promoted and restrained the tensile creep.The tensile basic creep of the composite group was consistent with the reference group.The differences of the basic creep of composite group,fly ash group,blast furnace slag group and reference group decreased in turn when the varying stress and the constant stress were compared.(5)Whether the high strength concrete at early ages had a linear creep can also be determined by the tensile creep experiment under the varying stress,and the conclusion was consistent with the constant stress.