Valorization of Washing Sludge for Enhanced Mechanical Performance and Durability of Pressed Earth–Calcined Mixtures via Pozzolanic Activation

AIn the framework of the transition towards a circular economy, the valorization of industrial by-products as reactive precursors represents one of the most significant challenges for contemporary civil engineering. This Master's thesis investigates the technical feasibility of transforming industrial washing sludges into active components for stabilizing pressed earth mixtures through a thermally induced pozzolanic activation process. The primary objective is to verify whether calcination actually leads to performance improvement or not. The research involved an extensive experimental campaign structured in three phases. Initially, a multi-scale characterization was conducted on five materials (three washing sludges A, B, C, a general soil and a processed earth) using mineralogical (XRD), chemical (XRF), and thermal (TGA) analyses, complemented by the determination of specific surface area (BET-BJH/DH) and Atterberg limits. Based on the thermogravimetric behavior, a calcination temperature of 800°C was defined to optimize phase transition and the reactivity of clay minerals. In the second phase, "7-7-2" dosage mixtures (soil, aggregates, cement) were formulated, comparing standard matrices with mixtures incorporating calcined fractions. Uniaxial compression tests on cubic specimens (3 and 7 days) allowed for the evaluation of the treatment's effectiveness, showing that calcination led to an increase in mechanical performance only for Sludges A and B, while no significant benefits were observed for the other materials. Based on these findings, the study was subsequently extended to a durability assessment for the reactive materials only (Sludge A and B) through water erosion tests (IRA, immersion, brush test) and mechanical testing under wet conditions.