Decarbonizing cementitious materials with reactive pozzolans derived from water treatment sludge

The growing demand for sustainable practices in the construction industry has driven the search for solutions that promote the reuse of waste and reduce the consumption of natural resources. In this context, sludge generated at water treatment plants (WTPs) emerges as a promising material for use in cementitious matrices, due to its predominantly inorganic composition and its potential reactivity. This study evaluated the pozzolanic potential of calcined WTP sludge and its application as a cement replacement in mortars. Chemical, mineralogical, and thermal characterization showed that calcination at 600 °C transforms the predominantly kaolinitic raw sludge into a highly reactive amorphous metakaolin rich in of SiO₂, Al₂O₃, and Fe₂O₃. Pozzolanic reactivity was confirmed through Luxán electrical conductivity and R3 tests, both indicating high reactivity. The results demonstrated that up to 12.5% of Portland cement can be replaced with calcined WTP sludge without compromising mechanical properties. Overall, 600 °C-calcined WTP sludge is a waste product considered a highly reactive pozzolanic additive, representing a technically and environmentally viable alternative for reducing cement consumption, mitigating environmental impacts, and promoting the expansion of sustainable innovation potential in the construction industry.