Determination of Moisture Diffusion Coefficient of Concrete at Early Age from Interior Humidity Measurements

Abstract The moisture diffusion coefficient of concrete is critical for moisture distribution calculation in concrete members. This article aims at building an experimental model to solve the moisture transfer coefficient of early age concrete and investigating its variation law with age as well. The model is based on experimental measurements on the interior humidity of concrete specimens under fully plastic sealing and environmental drying conditions. The model results show that the moisture diffusion coefficient of concrete at an early age is significantly dependent on age. The coefficient may vary from 10−8 to 10−10 from 3 to 28 days starting from concrete casting. The variation law of the coefficient with age can be described as a rapidly decreasing stage within 7 to 10 days from concrete casting followed by a slow decreasing stage. This obvious two-stage variation law may principally due to the change of the continuity of liquid and/or vapor phases during drying, which reflects the transformation of the moisture removal mechanism from liquid flow to vapor diffusion. High-strength concrete has a lower moisture diffusion coefficient than that of normal strength concrete under the same curing period. Keywords: Diffusion coefficientEarly age concreteRelative humidity ACKNOWLEDGMENT This work has been supported by a grant from the National Science Foundation of China (No. 50978143) and a grant from the National Basic Research Program of China (No. 2009CB623200) to Tsinghua University.