Effect of Various Recycled Construction and Demolition Fines on Cementitious Mortars Rheological and Mechanical Performance

This study presents an extensive investigation on the rheological and mechanical performance of cementitious mortars incorporating fines derived from recycled construction and demolition waste (CDW), including masonry units (bricks and ceiling blocks), autoclaved aerated concrete (AAC) units, and mixed demolition residues obtained during the renovation of a pre-war tenement house located in Warsaw, Poland. The CDW fines were assessed for their potential as secondary cementitious materials, SCMs. The proposed material concept aimed to integrate CDW into sustainable binder systems and reduce Portland clinker consumption, thereby lowering CO2 emissions of the concrete industry. Binder blends were produced by replacing 25 wt%. of Portland cement with recycled fines, achieving a 33–36% fines/clinker mass ratio. Recycled fines obtained by grinding CDW materials were characterized in terms of morphology, specific gravity, PSD, specific surface area, pozzolanic activity, pH and—in the case of recycled AAC—also carbonation. Mortars mixes were tested for consistency directly after mix preparation, while hardened composites were tested for density, compressive strength and flexural strength after 28 and 90 days of water curing. Statistical analysis showed that the origin of recycled fines affected mortar performance, with pozzolanic activity identified as the key factor. However, all analyzed composites were characterized with good mechanical strength. Overall, the performed investigation confirmed the suitability of analyzed CDW fines for clinker-reduced, low-carbon binders and highlighted their potential (especially in the case of ceramic fines) to support circularity in construction.