Effect of Combined Metakaolin and Basalt Powder Additions to Laterite-Based Geopolymers Activated by Rice Husk Ash (RHA)/NaOH Solution

The present study deals with the use of locally prepared rice husk ash (RHA)-based sodium silicate for alkaline activation of laterites (uncalcined (LNW) and calcined (LCA)). RHA-based activator (SSR) was prepared by adding as-collected RHA to 6 M NaOH at a solid/liquid mass ratio of 0.56. The various proportions of metakaolin (MK) and basalt powder (BA) influenced the final properties of the geopolymer products. After 28 days of curing at room temperature, XRD, SEM and FT-IR analyses were used to study the evolution phases. Uncalcined laterite-based formulations showed their highest compressive strength at 29.86 MPa with 20 wt.% of MK, whereas calcined ones showed the most elevated strength at 47.02 MPa, with the addition of 25 wt.% MK. Further additions above these thresholds tend to reduce strength and increase setting time. Substitution of calcined laterite with basalt powder permitted to control the porosity of samples at low values with the consequent reduction of strength. In general, the water absorption and apparent porosity decrease with addition of metakaolin in raw laterite-based formulations and relatively decrease with addition of basalt powder in calcined laterite-based formulations, while bulk density remains relatively constant. The locally produced RHA-based alkaline activator is efficient for laterite geopolymerization, resulting in products with robust mechanical and physical properties capable of fostering application in quality housing.