Water Washing: An Efficient Solution for the Total Recovery of Construction and Demolition Wastes

The reuse of the finest fraction derived from recycled aggregate washing has been investigated for the manufacture of mortars. This practice contributes to the circular economy and lowers CO2 emissions in the manufacturing of construction materials. A distinction was made between concrete-rich residues (RH) and mixed concrete–ceramic wastes (RHM). Chemical and mineralogical analyses of samples collected over a two-year period revealed consistent homogeneity over time. The RH residues are richer in CaO, primarily as calcite. Conversely, higher ceramic content in the waste correlates with increased SiO2, Al2O3, and K2O concentrations, predominantly as phyllosilicates and feldspars. Ettringite and portlandite occur in trace amounts. DTA-TG analysis reveals the presence of minor contents of portlandite and C-S-H gel. Mortars were prepared by replacing 10%, 20%, and 30% of Portland cement (OPC) with concrete-derived (RH) and mixed concrete–ceramic (RHM) wastes. At 10% and 20% substitution, both wastes yielded similar strengths, confirming their high potential for masonry mortars without prior treatment. However, at 30% replacement, RH provided markedly higher compressive and flexural strengths than RHM, likely due to a greater presence of the C-S-H gel phase in concrete waste. While 10% and 20% replacements successfully meet the 70% Strength Activity Index (SAI) threshold, a 30% limit severely reduces strength. Consequently, substitutions of 30% or higher require mechanical or thermal activation to enhance CDW reactivity. Given the minimal performance gap between RH and RHM, processing mixed CDW streams uniformly is recommended to maximize economic viability and ensure batch homogeneity in industrial washing plants.