Drying, moisture distribution, and shrinkage of cement-based materials

The aim of this study was to develop a new method to determine hygral diffusion, film, and shrinkage coefficients of cement-based materials. These coefficients are required for the numerical simulation of shrinkage strain and total deformation of concrete elements and structures using the finite element method. Both an experimental approach to determine the time-dependent relative humidity in the pore system of concrete and a numerical method to determine material coefficients on the basis of experimental data are described in this paper. The hygral diffusion coefficient can be expressed as function of moisture content and as function of relative humidity. An experiment is carried out with sliced specimens measuring 150 x 100 x 3 mm. Each specimen is prepared by piling up 11 slices and sealing the outer surfaces with aluminum sheet. The distribution of relative humidity is estimated by measuring the shrinkage strain on each slice at arbitrary drying times. An inverse analysis is then used to obtain the diffusion coefficient from the measured relative humidity distribution. A numerical approach based on the weighted residual method and on a nonlinear least squares method is proposed on the basis of the experimental results.