Journal of Materials Research and Technology (Mar 2023)
Investigation of autoclave curing impact on the mechanical properties, heavy metal stabilization and anti-microbial activity of the green geopolymeric composite based on received/thermally-treated glass polishing sludge
Abstract
Recycling Pb-containing-sludge, as industrial hazardous waste, in the fabrication of eco-friendly construction material with high mechanical characteristics and antimicrobial activity is the nominal target behind this investigation. The received sludge (RS) has been thermally treated at 500 °C to weed out the entire organic content to benefit from received (RS) and treated (TS) sludges in preparation for geopolymer pastes as an alternative to commercial Portland cement. OPC paste cured up to 28-days at normal conditions was used as a reference, and two other geopolymer pastes were prepared by 5%NaOH-activation; slag containing 50%RS (AAS-RS) and 50%TS (AAS-TS). Two curing regimes treated geopolymer pastes: high humidity at 25 °C for 28-days and hydrothermal treatment at different steam pressures (2, 5, 8 bars) and different time intervals (2, 4, 8 h). The formed binding phases are detected by XRD, TGA/DTG and SEM techniques. A microbial resistivity test was conducted using two different fungi (Aspergillus-terreus and Mucor-circinelloide) and two different bacteria (K.pneumonia-ATCC13883 and Bacillus-subtilis-ATCC6633). The overall outcomes of this study confirmed that the AAS-TS composite possessed higher compressive strength than AAS-RS. Moreover, autoclaving at 5 bars/4hrs for AAS-TS paste was the best condition to reach high strength (72 MPa) compared to OPC (68 MPa). The inhibition zone data confirmed that OPC pastes have no resistance against mentioned microbes, while the composite AAS-RS (cured under humidity for 28-days) possessed the highest antimicrobial action among all geopolymer pastes. Successful immobilization of toxic lead in all geopolymeric pastes, whatever the curing conditions, was achieved according to the toxicity characteristics leaching procedure (TCLP).
