Effect of varying molarity and curing conditions on the mechanical and microstructural characteristics of alkali activated GGBS binder

Abstract

Geopolymer binder offers a more sustainable choice for producing concrete in comparison to traditional ordinary Portland cement (OPC). The substitution of geopolymer binder for construction practices can decrease carbon dioxide emissions by decreasing OPC usage and repurposing industrial waste materials like ground granulated blast furnace slag (GGBS), fly ash, red mud, silica fume. In order to assess the suitability of GGBS as a binding material, it is essential to conduct conventional tests like consistency, setting times, and compressive strength, which are widely employed in cement testing. This study produced alkali activated paste (AAP) from GGBS and an alkaline activator comprising sodium hydroxide at various molarities from 1 M to 8 M. This investigation focused on the compressive strength of alkali-activated GGBS-based AAP under varying alkali activation molarities and curing conditions, including ambient, hot air oven, and humidity chamber curing. Additionally, the end reaction products of AAP showing higher compressive strength were examined for scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analysis. The experimental outcomes indicated that GGBS reduced the final setting time of AAP while increasing its compressive strength. Additionally, increasing the quantity of NaOH in the AAP increased its compressive strength. Furthermore, the research findings indicated that the mechanical properties of the alkali-activated GGBS-based material were notably influenced by the chosen curing conditions. Specifically, ambient curing demonstrated superior compressive strength, measuring at 47.06 MPa after 28 days, surpassing the results obtained from hot air oven curing and humidity curing.