Application of synchrotron microtomography for pore structure characterization of deteriorated cementitious materials due to leaching

Deteriorated mortars and cement pastes (w/c = 0.50) were prepared by an accelerated leaching test using electrochemical migration technique. This technique enabled the reduction of the CaO/SiO2 molar ratio to less than 2.0. Non-destructive three-dimensional imaging of the internal microstructure of the deteriorated cement matrix in hardened cement paste and mortar was performed using synchrotron X-ray computed microtomography at SPring-8, Japan. After image analysis at a spatial resolution of 0.5 μm/voxel the microtomographic images successfully visualized increased pore spaces in the deteriorated cement matrix with the effective porosity ranging from 0.31 to 0.38. In addition the diffusion tortuosity in the pore space derived from random walk simulation was also evaluated as a pore structure-transport parameter. Indications suggest that the deterioration of the cement matrix due primarily to the dissolution of portlandite decreases the diffusion tortuosity to a single digit as the degree of pore connectivity becomes larger at the submicron scale.