Early-age moisture loss from the surface of a concrete pavement may induce undesirable effects that play a factor in long-term performance. Early-age detrimental behavior such as slab curling, warping, delamination, and even plastic shrinkage cracking are affected by the amount of evaporation and the effectiveness of the curing medium. The rate of evaporation is a key item in the monitoring of the quality of the curing. However, most approaches for this are largely empirical and are useful only under laboratory conditions. The effective curing thickness concept is introduced as a method to evaluate the effectiveness of a curing method. The surface relative humidity has the biggest influence on both the effective curing thickness and the rate of evaporation. Thus, prediction of the rate of evaporation of the water from concrete depends on the relative humidity of the surface and is important for evaluation of the curing method. Existing evaporation models, including the American Concrete Institute nomograph, were evaluated for their capabilities in predicting evaporation from curing concrete. Data from a series of laboratory experiments with a modified version of Penman's evaporation model are also presented.