Research On Moisture Transport Under Wetting And Drying Conditions

Moisture transport in concrete plays an important role in durability research basis as well as vital status. The capillary absorption is one of the most common ways of nature concrete get moist, and the capillary absorption coefficient has been an important and significance guide for the evaluation of material durability. The main goal of researching the moisture transport is to get the moisture distribution inner concrete, and in present work through numerical calculation to research the moisture distribution in the concrete during wetting and drying process.In this paper, main research work is as follows:(1) Studying the influence of mineral admixtures and curing system on the concrete capillary absorption coefficient, and through conducting mercury intrusion test of concrete during different curing system, analysis of the relationship between the capillary water absorption coefficient and the pore structure; it is found that in the standard curing conditions, capillary absorption coefficient of concretes with mineral admixtures were a little higher than those without mineral admixtures; curing system has a significant influence on the concrete capillary absorption coefficient, during the pore structure analysis, the critical pore size and the change of the number of multi-harm pores play the main impact on the concrete capillary absorption coefficient.(2) During solving the concrete moisture distribution in the process of capillary absorption, the accuracy of the moisture diffusion coefficient is essential, in present work, based on genetic algorithm, the analysis was conducted about the moisture diffusion coefficient during the phase of capillary absorption water, and the optimal solution was calculated, and numerical analysis of moisture distribution during capillary absorption was done using the optimal solution.(3) In present work, both considering the wetting and drying two phases in calculation using the same diffusion equation, the different diffusion coefficients, treating the wetting phase end of the drying phase start point, and wetting phase of the final moisture distribution is the initial conditions of drying phase, regarding the saturation as the variable, computing the necessary moisture diffusion coefficient and surface diffusion coefficient obtained by inverse analysis, the adsorption isotherm (primary desorption curve) will combine the calculating results of the saturation with the experimental results, it shows good agreement between the computing result and the experiment results, which indicts that the calculation mean is feasible.The research was financially supported by National Natural Science Foundation of China (Grant No.50838008.51008272and51178413), High Technology Research and Development Program of China(863Program,2012AA050903),and National Basic Research Program of China(973Program,Grant No.2009CB623200).