Assessment of the pozzolanic reactivity of aggregate washing fines for use in Cement-Based Materials

This study focuses on the valorization of fines from aggregate washing ( AWF) , an industrial residue with a high clay mineral content, as a pozzolanic alternative to additions in cementitious binders. The Fines, were subjected to thermal activation at 750°C to induce a change in their crystalline structure towards reactive amorphous phases. Chemical and mineralogical analyses revealed a composition rich in silica, alumina and clay minerals such as smectite, illite and kaolinite, indicating strong pozzolanic potential. The suitability of this heat treatment was supported by thermogravimetric criteria, including a loss on ignition of 9.38% and a dehydroxylation peak observed at 477°C. Following calcination, the samples showed a reduction in specific surface area and changes in particle size, reflecting the effects of internal thermal transformations. Pozzolanic activity was evaluated through mechanical tests in compliance with NF EN 450-1 and EN 196-1 standards revealing encouraging results, particularly for cement substitution rates of between 10% and 20%. Compressive strength measurements and thermogravimetric analysis confirmed effective portlandite consumption in formulations containing calcined, confirming their reactivity. Finally, their incorporation into concrete formulations using the Dreux-Gorisse method has enabled a partial reduction in cement without significantly altering mechanical performance, thus supporting a sustainable approach combining waste recycling and a reduction in concrete's carbon footprint. • Aggregate washing fines (AWF), rich in clay minerals, were thermally activated at 750 °C to enhance pozzolanic activity. • Mineralogical and thermal analyses confirmed the formation of reactive amorphous phases with strong pozzolanic potential. • Mechanical tests showed promising strength performance for 10–20% cement replacement. • Incorporation of calcined AWF in concrete enabled partial cement reduction without compromising mechanical properties.