Model for Early-Age Rate of Evaporation of Cement-Based Materials

Early-age cracking affects the structural integrity of concrete structures and, if not inhibited, would lead to a reduction in service life. Plastic cracks are observed in the first few hours after placing the concrete, a time period well within the initial stages when the drying process is controlled by the rate of evaporation of concrete surfaces, which is roughly constant and similar to the rate of evaporation from water surfaces. In the absence of a theoretical method, this rate is commonly estimated using a nomograph based on Dalton's law. In this paper, a fluid mechanics-based approach for water evaporation based on the boundary-layer theory, mass transfer, diffusion, and convection is described. A parametric study is conducted on the effect of boundary-layer temperature, wind speed, relative humidity, and evaporation characteristic length on the calculated evaporation rates. Predicted evaporation rates are verified by recent experiments. Results show that given appropriate environmental parameters, evaporation rates can be predicted with a good degree of accuracy. DOI: 10.1061/(ASCE)EM.1943-7889.0000435. (C) 2012 American Society of Civil Engineers.