Influence of carbonate coarse aggregate properties on surface resistivity of high performance concrete

Abstract Surface resistivity (SR) test measures the extent of ionic transport in cementitious systems. The present study sought to understand the influence of coarse aggregate type (limestone, dolostone), their chemical composition, and pore structure on the SR of high-performance concrete (HPC). In this study, water absorption and pore structure of five different coarse aggregates were measured. Concrete specimens were made with identical materials, mix proportions, and preparation methods, except for the difference in the sources of the coarse aggregates. Pore structure and SR of the concrete and the corresponding mortar were evaluated. The microstructures, especially the aggregate-paste interfaces, of the concrete were examined using scanning electron microscopy (SEM). The micromorphology of the specimens was also observed using thin section petrographic analysis. The results indicate that the SR of the concrete mixes decreased linearly (R2 >0.91) with the total porosity of all five coarse aggregate until 28 days. After 28 days, this trend no longer held likely due to the chemical interaction of dolostone aggregates with paste, while limestone aggregates did not react. SEM-backscatter (BSE) and SEM-secondary electron (SE) imaging coupled with energy dispersive X-ray spectroscopy (EDS) and thin section petrography suggested that dolostone aggregate-paste reactions resulted in precipitation of newer calcite deposits at aggregate-paste interfaces. This densified the interface and probably reduced the concentration of mobile ions in the pore solution within the concrete pore network resulting in higher SR after 28 days. Due to less stable nature of dolostone aggregates in highly alkaline conditions, HPC with dolostone aggregate also provided a conducive environment for the mineralization of secondary ettringite (calcium sulfoaluminate) within paste pore spaces. We contend that the greater SR gain by dolostone concrete mixes than that by limestone concrete mixes in later ages is explained by the combination of the aggregate-paste interface densification, reduction in ionic concentration of the concrete pore solution, and secondary ettringite mineralization.