Commonly Used Porous Building Materials: Geomorphic Pore Structure and Fluid Transport

Abstract

Knowledge of microscopic geomorphic structures is critical to understanding transport processes in porous building materials. X-ray scans were obtained of a variety of commonly used porous building materials to both qualitatively and quantitatively evaluate their pore structures. The specimens included natural materials (two sandstones and a limestone) and engineered materials (three types of concretes and a brick). Scanned images were processed to reconstruct the geomorphic structures of these materials. Random walk analyses were performed on the reconstructed pore structures to estimate macroscopic transport properties (including tortuosity, specific surface, and permeability). The effective porosity and permeability of these materials were also experimentally determined and compared to computed values. Calibration of the threshold pixel value used in the postprocessing of X-ray images against measured effective porosity appears to be a more appropriate method of selecting this value than the typical approach, which employs selection based solely on observed histograms. The resulting permeabilities computed by using a calibrated threshold pixel value compare better with the measured permeabilities. This study also demonstrates that the relatively homogeneous and heterogeneous pore structures associated with the natural and engineered building materials under investigation can be captured by X-ray tomography.