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

Abstract

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.

Keywords:

• cemented paste backfill
• non-destructive electromagnetic wave-based measurement techniques
• electrical conductivity
• real relative permittivity
• cement hydration

Acknowledgements

This work was carried out under the Geomechanical Design of Cemented Paste Backfill Systems research project led by Professor M.W. Grabinsky and W.F. Bawden and Dr Ben Thompson at the University of Toronto, and involving researchers at the University of Toronto, University of Waterloo and Carleton University. The project is supported financially by the Barrick-Teck Cominco Joint Venture, Xstrata Copper Canada, Inmet Mining Corporation, and the Natural Sciences and Engineering Research Council Canada (NSERC). Field work has been supported through Williams Operating Corporation, Kidd Mine and Çayeli Mine. The authors would also like to thank Dr Colin Campbell from Decagon Devices for useful comments and summer students Brady Lee, Jeannot Ouellette, David Laserson and Emilie Schnarr for helping with the laboratory experimental work in this study.