VCCTL results have shown that in low w/c ratio systems, the coarser cement particles can be replaced by limestone filler with little reduction in long term compressive strength. A w/c ratio of 0.3 may allow a 15% replacement by volume, and a w/c ratio of 0.25 may allow a 20% replacement.
Further simulation results suggest that replacing the finest 15% by volume cement particles by limestone (as would be expected when the two materials are interground) will result in a substantial decrease in both early-age and longer-term compressive strengths.
To experimentally check model results, a high purity limestone and a reference CCRL cement (Pielert, 2002) were classified, separating both materials at a cutoff size of 30 µm, and the PSD was evaluated via laser diffraction. The coarse limestone particles were then blended with the fine cement particles using a V-blender. High performance mortars (w/s=0.3) with and without 15% limestone replacement of the coarse cement particles were prepared. The compressive strengths of the mortar cubes were evaluated after 7 days and 56 days of curing in limewater. After 7 days of curing, the system with 15% limestone had a 10% lower compressive strength than the "control" system. But after 56 day of curing, both systems achieved compressive strengths of 99 MPa, demonstrating the viability of replacing coarser cement particles by limestone in low w/c ratio mortars and concretes without detracting from the eventual compressive strength (see Figure 10.3.7).
Figure 10.3.7. Effects of replacement of either "fine" or "coarse" cement particles by limetone filler on degree of hydration and strength development.