Computational investigation on mass diffusivity in Portland cement paste based on X-ray computed microtomography (μCT) image

The mass diffusivity in Portland cement paste plays an important role in the durability design and assessment of cement-based materials. This paper presents a link between mass diffusivity in cement paste and its microstructure. X-ray computed microtomography (mu CT) was applied to derive the three-dimensional (3D) images of cement paste specimens with water-to-cement (w/c) ratio 0.50 at curing ages of 1, 3, 7, 28 and 120 days at a resolution of 0.485 mu m/voxel. By choosing the image threshold value based on the gray level histogram, the phases, i.e., capillary pores, hydration products and unhydrated cement grains in the microtomography images of each specimen were segmented and the 3D microstructure and pore structure were obtained. The degree of pore connectivity and percolation of each specimen were analyzed in detail on the basis of cluster-labeling algorithm. In addition, the finite element method (FEM) was applied to simulate the diffusion process of tritiated water through the extracted microstructure and quantify the diffusivity of tritiated water by associating with Fick's law. The simulated diffusivity was compared with the measured value and seemed consistent with the experimental investigation. The results suggest that X-ray mu CT is a reliable non-destructive technique and suitable tool to investigate the 3D microstructure. The obtained microstructure can be considered as an input to predict the transport properties of cement-based materials. (C) 2011 Elsevier Ltd. All rights reserved.