Influence of Drying Induced Damage on the Hygral Diffusion Coefficient

most hygral analyses the drying process and crack formation due to shrinkage stresses are treated as independent processes. It has often been speculated that crack formation and damage in the highly stressed outer layers of a drying concrete element ought to increase the rate of drying. Comparative tests have been carried out on concrete cylinders with and without hygral damage. Drying induced damage has been prevented half of the samples by using flat cylindrical specimens. these short cylinders, hygral stresses cannot be built up because the curvature of the end faces. The damaged zone in long cylinders has a slightly increased hygral diffusion coefficient. The variation of the hygral diffusion coefficient due to shrinkage damage, however, is small enough so that it can be neglected most practical cases. This result justifies assumption of drying process and crack formation being uncoupled. 1 many engineering applications it is necessary to carry out a rigorous hygral analysis order to prevent uncontrolled cracking. step in such an analysis is realistic prediction of the time- dependent moisture distribution a concrete element or a complete 1519 structure. Pihlajavaara (1965) and B3Zant and Najjar (1971) have shown the drying process can be described by means of the theory of non- diffusion with a concentration dependent diffusion coefficient. moisture dependent diffusion coefficient can be determined drying experiments by inverse analysis (Wittmann et al., 1989). results obtained in this way from experiments on ordinary concrete having three different W/C ratios have been described by Wittmann (1990). Alvaredo (1994) has used the same method to determine diffusion coefficients of different types of concrete. The moisture dependent diffusion coefficient allows us to predict the time-dependent moisture distribution under given boundary conditions.