Lightweight artificial aggregates from ornamental rock cutting sludge and aggregate washing sludge: raw material for sustainable construction and agriculture.

Lightweight aggregates (LWAs) were produced exclusively from waste-derived raw materials: aggregate washing sludge, granite cutting sludge, slate cutting sludge and cork dust. The composition and number of mixtures were designed following a protocol based on Mixture Experiments-Design of Experiments (ME-DOE). The produced materials were technologically characterized by determining the bloating index (BI), oven-dry density (ρ), water absorption (WA), strength (S), and additional parameters such as porosity and open porosity volume per specimen. Statistical models developed for BI, ρ, WA and S provided a more accurate understanding of the behavior of the mixture components and their synergistic effects, using response surface and effect plots. A cork dust content of approximately 1.5 % was established as the optimal value for maximizing BI and WA, while minimizing ρ. The resulting models are statistically significant (p-value <0.05) and showed high coefficients of determination (R: 0.80-0.94), suggesting a strong correlation with the experimental data. Moreover, predictive models were developed for the operational variables temperature (T) and optimum water content for extrusion (W) as a function of the mixture composition, supporting process manufacturing. Finally, the use of these residues in the production of LWAs has environmental benefits, with GWP reductions of between 13 and 36 % for SCS and 56-78 % for GCS compared to expanded clay lightweight aggregates, resulting in products with a lower environmental footprint.