Analysis of moisture transport in mortars and concrete using sorption-diffusion approach

Water transport in concretes and mortars is usually described using the sorptivity coefficient. While sorptivity is very useful in capturing the near surface effects, it is believed that the effect of moisture diffusion also has to be included to develop a comprehensive understanding of the long-term moisture transport phenomena. This paper uses a combination of the exponential equation for sorption and a solution of Fick's Second Law for diffusion to predict water transport in mortars and concrete. The transport parameters obtained from the fits of experimental data to the sorption-diffusion equation are useful in explaining specific aspects of moisture transport and also facilitate comparison between mixtures. The term "saturation index" is defined to quantify the influence of saturation levels of concrete in moisture transport. The transport parameters at any saturation level are shown to be equal to the product of the respective parameters at a saturation index of 1.0 and the inverse of the saturation index. The relative contributions of sorption and diffusion to the total moisture intake are also explored. For concretes at any saturation index, sorption contributes to approximately 70% of the overall moisture intake and diffusion to approximately 30%, indicating that it is necessary to consider the effects of both the mechanisms while describing moisture transport.