Prediction of setting time of fly ash concrete

A model for predicting the initial setting time of concrete with and without fly ash is presented. Based on a theoretical initial spacing between the particles of unhydrated cementitious material and the rate of growth of hydration products, the model is developed in terms of parameters that are usually known. The rate coefficient is shown to be very sensitive to temperature and also dependent on chemical composition. Generally, initial setting times of all previous investigators' data, as determined by the ASTM C 403 method, are estimated to within 16%. The input data required for the model are water-cementitious material ratio, fineness, specific gravity, temperature, and the blended oxide ratio: CaO/(SiO2 + Al2O3 + Fe2O3). Final setting time can be estimated to within 13% by simply increasing the initial setting tithe by a factor of 1.35.