Evaluation of cement composites with heavy metal-contaminated recycled aggregate - toward sustainable utilization

Turk, Tilen (author), Štukovnik, Petra (author), Marinšek, Marjan (author), Bokan-Bosiljkov, Violeta (author)

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.

• Language: English
• Keywords: civil engineering, recycled aggregate, concrete, heavy metals, tailings, setting time, civil engineering materials
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Publication status: Published
• Publication version: Author Accepted Manuscript
• Year: 2025
• Number of pages: Str. 1-19
• Numbering: Vol. 18, iss.,dec. [article no.] 5533
• PID: 20.500.12556/RUL-176878
• UDC: 691
• ISSN on article: 1996-1944
• DOI: 10.3390/ma18245533
• COBISS.SI-ID: 261160963
• Publication date in RUL: 12.12.2025

Record is a part of a journal

• Title: Materials
• Shortened title: Materials
• Publisher: MDPI
• ISSN: 1996-1944
• COBISS.SI-ID: 33588485

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Title: Ovrednotenje cementnih kompozitov z recikliranim agregatom, onesnaženim s težkimi kovinami - v smeri trajnostne uporabe

Abstract

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.

• Keywords: gradbeništvo, recikliran agregat, beton, težke kovine, jalovina, čas vezanja, gradbeni materiali