Application of X-Ray CT Scanning to Characterize Geomaterials Used in Transportation Construction

Conventional visual evaluation techniques (i.e., microscopy) of geomaterials are limited to the inspection of two dimensional surfaces, leaving internal three-dimensional characteristics ambiguous or resulting in costly slice-by-slice assembly to generate three-dimensional representations. Improved X-ray–computed tomography (X-ray CT) technology now allows a sample to be analyzed nondestructively and viewed in three dimensions. The outcome is the unique ability to obtain quantitative results from volumetrically imaging a sample’s complete structure. Application of this technology is enabling a new area of research in the characterization of geomaterials used in transportation construction (e.g., concrete and soils). Much valuable information can be gathered from CT scanning technology. Cracks can be mapped in soil samples to quantify spatially the planes and angles of failure. Porosity can be determined throughout sand and gravel samples. Air voids and aggregate segregation can be mapped in portland cement concrete. In pervious concrete, void matrixes can be analyzed for clogging, connectivity, and size. A state-of the-art CT scanning chamber was used to develop the images, and post-processing computer programs were implemented to interpret data for evaluation of geomaterials. This paper summarizes research techniques and describes the hardware and procedures required to conduct CT scanning for geomaterial applications. Finally, example images illustrating volumetric files are presented for various geomaterials.