Synthesis and optimization of binary systems of brick and concrete wastes geopolymers at ambient environment

Abstract

This study investigates the use of binary system of concrete waste (CW) and red clay brick waste (BW) to develop geopolymer binders with appropriate fresh properties and high mechanical strengths at ambient curing. Binary waste geopolymers were adjusted based on the contents of BW and CW precursors between 20% and 80% and predetermined liquid/solid (L/S) and oxide ratios of SiO2/Al2O3 and Na2O/SiO2. The effect of oxide ratios on the fresh and mechanical properties were considered by assessing the flow spread diameter, initial and final setting time and compressive strengths of BW + CW binders. Further optimization of the optimal binary BW + CW mixture was also explored by partial replacement of BW + CW precursors with 15%, 30% and 45% wt.% of ground granulated blast furnace slag (GGBS), metakaolin (MK), class C fly ash (FA-C), class F fly ash (FA-F) at room temperature curing and by applying 24 h initial high temperatures of 50 °C, 75 °C, and 100 °C. Extensive microstructural study with X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and Fourier transformed infrared spectroscopy was performed to characterize the optimized compositions at various conditions. The results indicate that 40% CW + 60% BW, at SiO2/Al2O3 of 8.4 and Na2O/SiO2 of 0.18, was the optimal binary mix, which reached high mechanical properties at ambient curing. The addition of SCMs with elevated alumina or calcium contents permitted the geopolymer mixture to attain significant strength enhancements with very high mechanical strengths of more than 100 MPa at 28 days at room temperature. An advanced degree of geopolymerization and enhanced formation of intermixed C-A-S-H/C-S-H and N-A-S-H products was confirmed in relation to the well-adjusted SiO2/Al2O3 and Na2O/SiO2 ratios and optimized strength geopolymers.