Microstructural Characterization of Portland Cement Concrete Containing Reclaimed Asphalt Pavement Aggregates Using Conventional and Advanced Petrographic Techniques

摘要

Potential issues associated with depletion of good aggregate sources and management of excess reclaimed asphalt pavement (RAP) stockpiles increasingly motivate the use of RAP in Portland cement concrete (PCC) as an aggregate replacement. Although the mechanical properties of the PCC containing RAP (RAP-PCC) have been extensively studied, detailed microstructural characterization and understanding crack propagation in RAP-PCC is yet to be established. Although thin-section-based petrographic study (ASTM C856, Standard Practice for Petrographic Examination of Hardened Concrete) combined with scanning electron microscope-energy dispersive x-ray spectroscopy (SEM-EDS) provides useful information on this aspect, both methods introduce artifacts associated with destructive sample preparation techniques. High-resolution X-ray computed tomography (X-ray CT) testing has the merits to provide three-dimensional (3D) dispositions of the microstructural features nondestructively and can be used effectively to validate the observation based on conventional techniques. This paper presents a comprehensive microstructural characterization and crack propagation of RAP-PCC through a combined approach of thin section based petrographic observation, SEM-EDS, and X-ray CT. Thin-section study was useful to (1) identify agglomerated RAP particles, (2) characterize air void distribution and quantify air voids content, and (3) perform overall characterization of interfacial transition zone (ITZ). The SEM-EDS was used for a detailed characterization of ITZ and calcium hydroxide distribution. Based on thin-section and SEM studies, a cohesive failure through the asphalt layer was identified as the primary mechanism for strength reductions in RAP-PCC. X-ray CT was used to scan the RAP-PCC samples with high resolution followed by image reconstruction to generate 3D images of the specimens, which was effective not only to validate the cohesive failure mechanism but also to provide an extensive analysis of multiple features, including air void distribution and quantification and crack propagation.