Study On Tensile Creep Of High Performance Concrete With Fly Ash At Early Ages

The research on tensile creep and its behavior of concrete at early ages can provide reliable technology for supporting the prevention of concrete cracking at the early age. In this study, a testing apparatus and method for early-age tensile basic creep was improved and used to investigate the influence of the age at loading(1, 3, 5and 7 days) and stress/strength ratio(0.4 and0.5) on the behavior of tensile basic creep of high performance concrete with fly ash.The main conclusions of this study include:(1) In order to reduce the test error effectively caused by eccentric and stress concentration, the prism specimen is improved to be the dumbbell specimen, and the length of the specimens is also increased.(2) Compared mechanical properties of fly ash concrete at the early ages, with the mechanical properties of reference concrete at the same age, it is found that the effect of the fly ash on compressive strength is greater than on splitting tensile strength, and the development rate of the elastic modulus at the early ages are also improved due to fly ash being added.(3) The autogenous shrinkage of concrete with fly ash at the age of 1 day is accounted for 40% of that at 28 days, the rate of autogenous shrinkage deformation at28 days fell sharply, and autogenous shrinkage became convergence.(4) The tensile creep of concrete which the loading age is 1 day is greater than other loading ages, as the loading age delaied, the value of creep decreases. The performance of creep rate is great during the early loading period, with loading continuous, creep rate decreases obviously, the earlier of loading age, the creep changes obvious.(5) The creep of concrete with fly ash showed nonlinear obviously at the early ages, in the case of same loading age, the greater of stress/strength ratio, the greater of specific creep. As the loading age delaied, the linear behavior of creep of concrete containing fly ash appeared gradually, and became more obvious after loading age of5 days..(6) Although the model of ZC and BP- 2 cannot be used to predict directly the early tensile creep of concrete with fly ash directly, but the ZC model showed a better adaptation. Prediction value obtained by model ZC present a great deviation at the beginning of the loading time; the later the loading time, the greater the deviation.