Effect of confining pressure and microcracks on mass transport properties of concrete (original) (raw)

Investigation of moisture transport properties of cementitious materials

Cement and Concrete Research, 2016

Moisture transport in cementitious materials is directly related to the durability of concrete structures. When the material loses moisture, the drying shrinkage induces cracks which are harmful to the solid body. When liquid moves into the material, it can carry aggressive ions. Hence, moisture transport properties are important to cope with durability issues. The present paper is focused on two ways to enhance our understanding of moisture transport properties of cementitious materials. They are based on the indirect determination of the liquid water permeability and water vapour diffusion coefficient. The first one is known as the " inverse analysis " method. In a moisture transport model, the liquid permeability and diffusion coefficient can be adjusted in order to fit the measured mass loss curves and water content profiles. In the second way, measured apparent diffusion coefficient (also called moisture diffusivity) curves are fitted over a large range of relative humidity (RH) by a general expression which includes both liquid transport and vapour diffusion. Due to different RH ranges of predominance of liquid and vapour transport, the liquid water perme-ability and vapour diffusion coefficient can be determined separately. Input experimental data on cement pastes are collected from the literature. Discussions on relative permeability and Knudsen diffusion show a significant influence on modelling of moisture transport. A further comparison with measured permeability data is able to provide a better understanding of moisture transport properties. Keywords: cement paste (E), moisture transport (C), diffusion coefficient (C), liquid water permeability (A), inverse analysis (B), Knudsen effect (A)

Characterisation of microcracks and influence on transport properties

Microcracks are known to form in concrete when subjected to drying and it has long been suspected that they could impact transport properties and durability of concrete structures. However, very few studies have been carried out to thoroughly characterise the microcracks or correlate their characteristics to transport. More crucially, no attempts have been made to isolate the influence of microcracks from other factors (e.g., water content, pore structure). Thus, it has not been conclusively shown whether microcracks impact transport properties and to what extent. This project aims to enhance our understanding of microcracks by: a) developing 2D & 3D imaging techniques to characterise microcracks; b) quantifying the effect of microcracks on transport; c) investigating factors influencing microcrack formation; and d) providing experimental data for modelling of transport processes in microcracked concrete. This paper presents some of the findings to date from on-going experiments and...