Optimization of brick waste-based geopolymer binders at ambient temperature and pre-targeted chemical parameters

Abstract

This research focuses on the development of optimized compositions of 100% green red clay brick waste-based (RCBW) geopolymer binders at ambient temperature curing. For this reason, a novel algorithmic mixture design method was used relying on pre-targeted SiO2/Al2O3, Na2O/SiO2 and L/S (liquid/solid) ratios. The relation between SiO2/Al2O3 and Na2O/SiO2 molar ratios and the fresh and mechanical properties of geopolymers was investigated, including flowability, initial and final setting times and compressive strengths. In addition, the effects of high temperature curing of 50 °C, 75 °C and 100 °C and the addition of Class F fly ash (FA-F), Class C fly ash (FA-C), metakaolin (MK), and ground granulated blast furnace slag (GGBS) into RCBW-binders was also studied. A thorough microstructural characterization, including X-ray diffraction, scanning electron microscopy, energy-dispersive X-Ray spectroscopy and Fourier transform infrared spectroscopy, was also completed on high strength geopolymers synthesized at different conditions. The results confirmed that targeting pre-determined chemical ratios is effective to reach RCBW geopolymers with appropriate fresh properties and enhanced strengths at ambient environment. A balanced combination of SiO2/Al2O3 of 7.1 and Na2O/SiO2 of 0.24 was important to achieve greater degree of geopolymerization, compacity and concentration of N-A-S-H and/or C-A-S-H formations, which were further increased in an high-temperature curing of 75 °C and with the addition of calcium-based mineral admixtures.