Title: In-Situ Conductivity Method for Monitoring Segregation, Bleeding, and Strength Development in Cement-Based Materials
Author(s): T. V. Pavate, K. H. Khayat, and C. Jolicoeur
Publication: Symposium Paper
Appears on pages(s): 535-560
Keywords: bleeding; segregation; strength
A new conductivity method is proposed to monitor the behavior of fresh cement-based materials during the consolidation, setting, and early hardening periods. The method relies on differences in electrical conductivity measured at different depths, and as function of time, to evaluate variations in the local composition (solids, fluids) of the material. To perform these measurements in a practical and cost-effective way, simple disposable conductivity probes were designed with multiple electrodes, after initial work with similar laboratory-type probes. The approach was tested with several cement-based systems ncluding grouts, mortars, and concrete. During the dormant period, the conductivity readings reflect changes in the homogeneity of the samples as a function of time, which are qualitatively well related to the bleeding-segregation behavior of the cement-based system. From the conductivity data obtained as a function of sample depth, a stability index could be defined using the least-squared deviation from the mean conductivity at a given time. The time-dependence of such a stability index reflects the evolution of the bleeding and segregation phenomena in the material. The multi-electrode conductivity approach also yields other valuable information, namely a determination of the initial setting, and a reasonable estimate of the rate of strength development during the early stages of the hardening period.