Influence of bonded mortar of recycled concrete aggregates on interfacial characteristics – Porosity assessment based on pore segmentation from backscattered electron image analysis

Abstract

Abstract In this study, the porosity assessment of bonded mortar of recycled aggregates (RA) is done by backscattered electron (BSE) image analysis, for the first time. The resulting effect on concrete mechanical properties was determined as well. Different mixes of recycled aggregate concrete (RAC) were formulated. The concrete specimens were cast to determine the compressive strength at various ages. Later, after 28 – day age, the hardened concrete specimens were used to extract samples for BSE image analysis. The BSE analysis was done by using the pore segmentation method previously developed to ascertain the microstructural features of hydrated cement pastes. From the image analysis, plots of segmented area versus grey value and brightness histograms at different threshold levels were obtained. The BSE image analysis was used to determine the pore area and total area in each frame for porosity assessment. The results indicated that RA affect the resulting mechanical strength of hardened concrete due to the lower specific gravity and higher water absorption as compared to the natural aggregates (NA). Recycled coarse aggregate (RCA) has about 28% higher bonded mortar content (BMC) with porosity of bonded mortar (BM) almost double as that of recycled fine aggregate (RFA). This leads to inferior interface between aggregate and cement paste thereby affecting the overall concrete properties. It is suggested to use pre-treatment methods for surface modification of RA for efficient use in eco-friendly and sustainable construction.