20.500.12556/RUL-176878 Evaluation of cement composites with heavy metal-contaminated recycled aggregate - toward sustainable utilization 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; 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. Uporaba recikliranega agregata prinaša jasne okoljske prednosti, vendar lahko povzroči kemične interakcije, ki vplivajo na hidracijo cementa, zlasti kadar material izvira iz rudarskih stranskih produktov, ki vsebujejo težke kovine. Ta študija preučuje cementne kompozite z različnimi prostorninskimi deleži recikliranega agregata, pridobljenega iz jalovine rudnika Pb–Zn, ter opredeljuje mehanizme, odgovorne za opaženo zakasnitev hidracijskih procesov v zgodnji fazi. Reciklirani agregat je bil okarakteriziran z rentgensko difrakcijo (XRD), hidracija je bila spremljana z ultrazvokom (UPV) in razvojem temperature; mehanske lastnosti so bile določene po 1, 3 in 7 dneh, razvoj faz pa interpretiran z uporabo SEM-EDS in termodinamičnega ravnotežnega modeliranja (GEMS/Cemdata18). Rezultati kažejo, da faze, ki vsebujejo težke kovine (sulfidi/sulfati Zn, Pb in Fe), pospešujejo nastanek metastabilnih kovinsko-silikatnih kompleksov, kar začasno znižuje oksidacijski potencial in zakasni vezanje tudi do 28 ur pri mešanicah s 100 % recikliranim agregatom. Trdnost v zgodnji fazi je bila izrazito zmanjšana; vendar pa so se do 7. dne vse mešanice, razen tiste s 100 % recikliranim agregatom, približale trdnosti referenčne mešanice z naravnim agregatom. Kljub tem vplivom je reciklirani agregat mogoče varno uporabiti pri nadomestitvah do 25 vol. %, pri čemer se ohranijo sprejemljive lastnosti v svežem in strjenem stanju. Vendar pa prisotnost obstojnih sulfatnih faz (npr. epsomit, anglesit) nakazuje možnost dolgoročnega sproščanja sulfata in s tem povezanih tveganj za trajnost, kar zahteva nadaljnje raziskave. civil engineering recycled aggregate concrete heavy metals tailings setting time civil engineering materials gradbeništvo recikliran agregat beton težke kovine jalovina čas vezanja gradbeni materiali true false true Angleški jezik Slovenski jezik Članek v reviji 2025-12-12 12:37:13 2025-12-12 12:37:24 2025-12-25 03:37:10 0000-00-00 00:00:00 2025 0 0 Str. 1-19 iss.,dec. [article no.] 5533 Vol. 18 2025 0000-00-00 PostprintKoncna Objavljeno apc 0000-00-00 0000-00-00 0000-00-00 691 1996-1944 10.3390/ma18245533 261160963 materials-18-05533_(1)_(1).pdf materials-18-05533_(1)_(1).pdf 1 9CF6B9F6F1B64C589B9CB7F31A40B296 4821298d8168b5f9aede48a1d866464e9c2b0802d414369cd57e7bc63ae469ca bbe84c96-d74e-11f0-9328-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=223520 https://www.mdpi.com/1996-1944/18/24/5533 1 81e8aa5d-d74e-11f0-9328-0050569b8976 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=223519 Fakulteta za gradbeništvo in geodezijo 0 0 0