Evaluation of cement composites with heavy metal-contaminated recycled aggregate - toward sustainable utilizationTurk, Tilen (Avtor) Štukovnik, Petra (Avtor) Marinšek, Marjan (Avtor) Bokan-Bosiljkov, Violeta (Avtor) civil engineeringrecycled aggregateconcreteheavy metalstailingssetting timecivil engineering materialsThe 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; however, by day 7, all mixtures except that with 100% recycled aggregate approached the strength of the reference mixtures with natural aggregate. Despite these effects, recycled aggregate can be safely incorporated at replacement levels up to 25 vol.%, which preserves acceptable fresh and hardened properties. Nev-ertheless, the presence of persistent sulfate-bearing phases (e.g., epsomite, anglesite) indicates a potential for long-term sulfate release and associated durability risks, war-ranting further investigation.20252025-12-12 12:37:13Članek v reviji176878UDK: 691ISSN pri članku: 1996-1944DOI: 10.3390/ma18245533COBISS_ID: 261160963sl