Civil Engineering Association

Characterization of Aggregates for Sustainable Freight Transportation Infrastructure

A novel method, X-ray computed tomography (CT), has recently emerged as a powerful, nondestructive methodology for material characterization, including geomaterials. This method produces 3D images of the object that can be analyzed in various ways based on the purpose of the scan. The objective of this research is to use X-ray CT technology to investigate the internal structure and porosity of various types of aggregates such as limestone, granite, and quartzite. In addition, this research used X-ray CT technology to investigate the influence of harsh environments such as freezing and thawing on the durability of the aggregate. Virgin and treated aggregate specimens were subjected to X-ray CT to obtain high-resolution 3D images. Aggregate treatments (wetting/drying and freeze-thaw cycles) were conducted using the sodium sulfate soundness test and the actual free-thaw test. The CT scans were carried out using a sector 13-BMD synchrotron microtomography beamline at the Advanced Photon Source of the Argonne National Laboratory, Illinois. Analysis was conducted on the acquired 3D high-resolution images to investigate the pore structure and micro-cracks of these aggregates types. The X-ray CT technology was useful for visualizing the internal structure of aggregate particles with high resolution. This visual inspection provided information on pore space characteristics such as pore shape, connectivity, and distribution. In addition, volumetric quantities such as the volume of aggregate particles and the volume of pore space were identified and measured. These measured quantities were used to calculate porosities of the investigated aggregates, which provided properties of these aggregates using the constructed 3D CT images (non-conventional method). Sodium sulfate soundness test effects on the treated aggregates (degradation, disintegration, and weathering) were significant, as observed in the 3D CT images of treated aggregate particles. Pore space volume increased as the aggregate particles were treated with wetting/drying cycles of sodium sulfate solution. The sodium sulfate soundness test significantly affected the permeable (connected) pore space and induced degradation/disintegration, which increased the volume of connected pore space with the increase of the number of wetting/drying test cycles. Isolated pore space remained unchanged with the number of sodium sulfate test cycles, since the salt could not penetrate these pores to induce internal force of expansion, which degraded and disintegrated the aggregate structure. The freeze-thaw test induced changes to the pore space of the treated aggregates with a noticeable impact on the connected pore space of the aggregate particle.