Strength and rheology of cement mortars incorporating quarry and commercial limestone filler

Clarifying the contrasting effects of limestone fillers in cement-based materials is crucial for the sustainable valorisation of quarry by-products. This study investigates the influence of three limestone fillers – quarry limestone dust (2985 cm²/g), commercial limestone filler (4690 cm²/g), and laboratory-ground limestone powder (4073 cm²/g) – on the rheological and mechanical properties of cement mortar. Two substitution strategies were considered: replacing sand (0–20%) with quarry limestone dust and laboratory-ground powder, and replacing cement (0–30%) with commercial filler. Quarry dust substitution reduces workability with little effect on strength, but washing and superplasticiser restore consistency. In contrast, cement replacement with commercial filler improves workability but decreases strength. Laboratory-ground limestone powder from washed sand, with finer particles and higher purity confirmed by XRD and FTIR, exhibited a nucleation effect and increased strength by 32.7% at 7 days. These results demonstrate that the impact of limestone fillers is governed by their origin, fineness, and substitution route, offering insights for optimising mortar formulation and enabling efficient utilisation of quarry by-products without compromising performance.