Electromagnetic wave-based measurement techniques to study the role of Portland cement hydration in cemented paste backfill materials

Variations in electrical conductivity and real relative permittivity of cemented paste backfill (CPB) at early times of cement hydration are studied using non-destructive, electromagnetic wave-based techniques. The CPB used in this study consists of normal Portland cement (PC), process water and gold mine tailings. The measurements were performed using (i) a broadband network analyser, which operates at frequencies ranging from 20 MHz to 1.3 GHz and (ii) a capacitance probe, which operates at a single frequency of 70 MHz. This study shows that the electromagnetic properties of CPB are sensitive to specimen composition, the stage of binder hydration, binder content and the operating frequency of the instrument, and, as such, are a useful tool to monitor changes in CPB caused by binder hydration. The electromagnetic (EM) data also suggest that, as binder hydration progresses, a portion of free water in CPB becomes bound into the newly formed hydration products or onto the surface of hydrating cement particles. In addition to EM properties, the progress of binder hydration and setting in CPB was also monitored using conventional measurement techniques, such as temperature evolution measurements and penetrative resistance measurements.