Integrated Interpretation of Electrical Conductivity Changes, Heat Generation, and Strength Development in the First Week in Cemented Paste Backfill

Underground mining operations need nondestructive test methods to assess placed backfill strength development at early age (especially up to 1 week of curing time) so that they can continue proximate mining quickly. Recent developments in electrical conductivity (EC) transducers for field applications offer this possibility, but the EC measurements must be correlated to backfill strength. To determine the feasibility of this approach, a laboratory test program used a mine’s backfill materials mixed with varying water and binder contents and tested these over a 7-day period. Strength was characterized using unconfined compressive strength (UCS) tests and correlated to EC. Comparisons were also made to complementary test results using Vicat and heat generation measurement techniques. Strong and consistent correlations were determined between EC and UCS for a given binder content and water content. But moreover, a lower-bound correlation was determined and could also be used in the field if as-placed properties vary to an unknown extent within the limits of parameters considered in the study. This provides the basis to use EC measurements in the field and confidently assess the backfill’s minimum attained strength in real time.