Early Concrete Thermal Stress And Crack Control

This paper studied thermal stress of concrete and control of concrete crack at early ages; Using finite element program,the thermal stress of an externally restrained concrete slab and the concrete cushion cap at early ages are simulated firstly. And then the results are analyzed.The heat production induced by the cement hydration and the evolving environmental variation are considered in the thermal model. The heat production changes with time and it is the key factor of concrete temperatures; the boundary conditions, which is the key parameter which effects temperature gradient, is expressed by convection-radiation coefficient according to conditions such as curing and weather. Finite element model is a simplified model of construction phase because the situ case is very complex.The variable Young`s modulus which changes with time and reproduced objective stress of concrete are considered in the mechanical mode. This paper considered influence of concrete early-age creep and reinforcement to concrete stress: General creep models which are for long-term concrete creep, are not fit for concrete at early ages, Relaxation factor is get from long-term concrete creep, which is not fit for early concrete too, This paper used the most widely used function, the Double Power Law (DPL), for describing the early-age creep, providing good predictions. The result indicates that early-age creep reduces stress of early-age concrete very much. According test result of some documentation, the effect of reinforcement on the thermal stress and the risk of cracking are calculated in this paper. After considering the active action of reinforcement, the ultimate strain of concrete could be increased and the crack of concrete could be prevented.In one word, if the effect of creep and reinforcement of early concrete is considered properly, the crack of concrete at early ages will be controlled effectively.