Abstract: Characterization of surface gas permeability measurements on a variety of natural and engineered building materials using two relatively new, non-destructive surface permeameters is presented. Surface gas permeability measurements were consistent for both laboratory and field applications and correlated well with bulk gas permeability measurements. This research indicates that surface permeability measurements could provide reliable estimates of bulk gas permeability; and due to the non-destructive nature and relative sampling ease of both surface gas permeability tools, it is possible to quantify the range of the spatial autocorrelation, heterogeneity, and anisotropy in porous building materials and their degree of degradation from weathering.
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. (C) 2013 American Society of Civil Engineers.
Abstract: Microscopic geomorphic structure is critical to the process of transport in porous building materials. X-ray scans were obtained on a variety of building materials to both qualitatively and quantitatively evaluate their pore structures. Scanned images were subsequently processed using a random walk analysis to estimate the macroscopic transport properties that are useful for numerical simulation of transport phenomena. 3D image reconstruction was also performed to provide better visualization of the pore structures and a basis for 3D simulation.
Abstract: Understanding permeability of building materials is important for problems involving studies of contaminant transport. Examples include contamination from fire, acid rain, and chemical and biological weapons. Our research investigates the gas permeability of porous building substrates such as concretes, limestones, sandstones, and bricks. Each sample was cored to produce 70 mm (2.75'') diameter cores approximately 75-130 mm (3-5'') tall. The surface gas permeability was measured on the top surface of these specimens using the AutoScan II device manufactured by New England Research, Inc. The measurements were taken along a 3 mm grid producing a map of surface gas permeability. An example map is shown in Figure 1. The macroscopic measurements were performed along the entire cored specimen. A second set of measurements were made on a 5 mm thick slice cut from the top of each specimen to examine whether these measurements compare better with the surface measurements. The macroscopic gas permeability was measured for all specimens using ASTM D 4525. The results are summarized in Table 1. In general, the surface and macroscopic gas permeability measurements (Table 1) compare reasonably well (within one order of magnitude). The permeability of the 5 mm slices is not significantly different from the entire core for the specimens tested. Figure 1. Results of surface permeability mappingof Ohio Sandstone using the AutoScan II device. a) Map of gas permeability b) Range of gas permeability c) Density function of permeability. Table 1. Gas permeability values (mD)