Effect of substitution of blast-furnace slag by fired drinking water sludge on the properties of pozzolanic cement pastes

The effect of fired drinking water sludge (FDWS) as a mineral admixture on the physico-mechanical properties and fire resistance of pozzolanic cement pastes has been investigated. Five blends of ordinary Portland cement, blast-furnace slag (GBFS), and FDWS were prepared, with the Portland cement fixed to 70 mass%, while granulated slag was replaced by 0, 3, 6, 9, and 12 mass% of fired sludge. Phase composition was identified using X-ray diffraction, thermal gravimetric analysis, and differential scanning calorimetry. Results showed an increase in the required water of standard consistency and elongation of setting times with increased FDWS content. Bulk density decreased with higher sludge content, while compressive strength was enhanced at later ages for 3 and 6 mass% FDWS substitution. Moreover, the specimen containing 9 mass% FDWS exhibited the best fire resistance at high temperatures, contrasting with the complete deterioration of the Portland cement paste at 800 °C. These findings suggest that FDWS has significant potential in the formulation of sustainable cementitious materials.