Comparative study of metakaolin-based geopolymer characteristics utilizing different dosages of water glass in the activator solution

Abstract

Geopolymers gained attention from researchers due to their durability and potential to replace materials based on Portland cement. They offer a promising and eco-friendly alternative as binders in the construction industry. This study goal is to investigate the effects of varying dosages of sodium silicate (water glass) and sodium hydroxide in activator solutions, as well as the impact of different curing temperatures, on metakaolin-based geopolymer binder. Kaolin was heated to 750 °C for 3hr to produce metakaolin, and activator solutions were prepared with various amounts of water glass (0, 25, 50, 75, and 100) wt%. The fresh geopolymer binder was cured at two temperatures: 60 °C and 75 °C for one day. After a curing period of 28 days, various properties such as microstructural characteristics (examined through SEM), chemical bonding (analyzed using FTIR), chemical compositions (analyzed XRD), thermal conductivity and bulk density, volumetric shrinkage, and efflorescence were determined. Compressive measurements were conducted at early stages (7, 14, and 28 days) to assess mechanical properties, revealing a significant increase in mechanical strength. The geopolymer sample with 50 wt% of water glass cured at 60 °C exhibited optimal characteristics, including a higher compressive strength of 16.3 MPa and minimal efflorescence. This composition achieved an appropriate Si/Al ratio of 1.85, resulting from the formation of gel products through the reaction of compact structures. When the water glass content exceeded 50 wt%, the higher Si/Al ratio led to the deposition of the Al–Si phase, slowing down the interaction between the metakaolin powder and the alkaline activator. Regarding the influence of curing temperature, the average compressive strength of the geopolymer binder cured at 60 °C was greater as compared to the binder cured at 75 °C. Moisture loss and porosity increased with higher curing temperatures. The geopolymer binders exhibit a thermal conductivity value range (0.09–0.39)W/m.k.