X-ray microtomographic studies of pore structure and permeability in Portland cement concrete

The pore structure of concrete has long been recognized as the key to a wide range of different mechanical, physical and chemical properties. However, the finite range of the different interrogation techniques for measuring pore structure has always limited our overall picture. In order to add to that picture, a high resolution, three-dimensional imaging technique called x-ray microtomography was employed as a way to link measurable microstructural features with alternate measurements of permeability in different concrete systems. Four different concretes were imaged at spatial resolutions between 1 and 4 microns. Using 3D image analysis techniques, the pore system was characterized by size distribution and connectivity. A parameter we termed "disconnected pore distance" correlated well with standard measures of chloride permeability.