A model for predicting evaporation from fresh concrete surface during the plastic stage

Abstract

Fresh concrete exposed to hot, dry, or windy conditions is very sensitive to plastic shrinkage cracking. However, there are some challenges in assessing and controlling plastic shrinkage cracking since a number of factors should be considered, of which the evaporation of bleeding water from the surface of concrete is an important one. In this article, the characteristics of evaporation from the surface of fresh concrete were experimentally studied, and the variables include the w/c ratio and the wind velocity. Based on a conventional method for the calculation of evaporation from bulk water surface, a modified model was proposed to predict the rate of evaporation from fresh concrete surface. The initial rate of evaporation was calculated by assuming that the surface of fresh concrete is always covered by bleeding water and that the evaporation rate of the bleeding water is equal to that of the bulk water. The modified model was then verified by experimental data, and applied to analyze the effect of wind velocity and temperature on the surface drying of fresh concretes. This method is capable of predicting the time-dependent variation of evaporation rate of the fresh concrete under different environment conditions. The findings are of significance for assessing the cracking risk of structural concrete during the plastic stage and for consequently taking measures to prevent it from plastic cracking.