Replacement of “coarse” cement particles by inert fillers in low w/c ratio concretes

It has been suggested that in low water-to-cement ratio (w/c) concretes, the “coarser” cement particles could be replaced by an “inert” filler with little loss in performance in terms of hydration and strength development. This communication presents the results of an experimental study conducted to validate this hypothesis, using a coarse limestone filler and a classified cement. The cement and limestone powders were both classified with a cutoff diameter of about 30 μm. The coarse limestone was then blended with the fine cement, and water-to-solids ratio=0.3 pastes and mortars were prepared to compare to reference (original cement powder) systems. The results for chemical shrinkage for the pastes were consistent with a simple dilution of the cement by the limestone and also with the results predicted by the CEMHYD3D hydration model. In mortars, the predicted compressive strength loss in the filled system at 7 days was consistent with model predictions, and furthermore, at 56 days, no detectable difference in strength was measured. Thus, this study further supports the idea that coarse limestones could be used to replace equivalent size cement particles in low w/c concretes with little loss in hydration and strength performance.