Cement hydration based model to predict the mechanical properties of precast concrete

An adiabatic temperature rise (ATR) test was used to determine the degree of cement hydration in concrete. In the experiments, emphasis was placed on the influences of water to cementitious material ratio (w/b) and aggregate content on the ATR and the development of degree of cement hydration. A total of nine concrete mixtures with three w/b ratios (0·30, 0·43, 0·62) and three aggregate contents (50%, 60%, 70% by volume) were used in the tests. The experimental results show that, for a given aggregate content, the lower the w/b ratio, the higher the temperature rise. For a given w/b ratio, the higher the aggregate content, the lower the temperature rise. The effects of temperature and age on the hydration process of cement may be taken into consideration by the equivalent age concept. For the same equivalent age, the degree of cement hydration is a function of w/b ratio only, regardless of the aggregate content. The advance of degree of cement hydration with equivalent age can be described as an initially slow developing stage, followed by a fast increasing stage and then a nearly steady-state stage. With an increase in w/b ratio, both the length of the initial stage and the ultimate degree of cement hydration at steady state increase. The higher the w/b, the longer the equivalent age needed to achieve the steady state. In addition, a model for predicting concrete elastic modulus and compressive strength, based on the degree of cement hydration in which the effect of environmental drying can be taken into account, was developed; good agreement was found between the test and model results. The model may be used for the prediction of mechanical properties of precast concrete under different curing conditions.