Ovrednotenje cementnih kompozitov z recikliranim agregatom, onesnaženim s težkimi kovinami - v smeri trajnostne uporabe

The use of recycled aggregate provides clear environmental advantages but may in-troduce chemical interactions that influence cement hydration, particularly when the material originates from mining by-products containing heavy metals. This study ex-amines cementitious composites containing different volume fractions of recycled ag-gregate derived from Pb–Zn mine tailings and identifies the mechanisms responsible for the observed early-age hydration delay. The recycled aggregate was characterized using XRD, hydration was monitored through ultrasonic pulse velocity (UPV) and temperature evolution, mechanical performance was assessed at 1, 3, and 7 days, and phase evolution was interpreted using SEM-EDS and thermodynamic equilibrium modeling (GEMS/Cemdata18). The results show that heavy-metal-bearing phases (Zn-, Pb-, and Fe-sulfides/sulfates) promote the formation of metastable metal–silicate complexes, temporarily lowering the oxidation potential and d elaying setting by up to 28 h in mixtures containing 100% recycled aggregate. Early-age strength was substantially reduced