Influence of Thermal Activation and Silica Modulus on the Properties of Clayey-Lateritic Based Geopolymer Binders Cured at Room Temperature

In this study, a laterite soil which is a locally available material in many parts of the world was used as the aluminosilicate precursor. The main objective of this study is to investigate the effect of calcination temperature on physicochemical properties of the resulting geopolymers synthesized from calcined laterite soils. In order to produce the geopolymer binders, the laterite soil was activated thermally through calcination (from 550 to 750 °C) and the resulting calcined laterite was activated with an alkali activator composed of 8 and 10 M of sodium hydroxide (NaOH) and sodium silicate (Na 2 SiO 3 ) in mass of 0.5. Then, the calcined laterite soils and synthesized geopolymer products were analyzed using X-ray diffraction (XRD), Brunner-Emmet-Teller (BET), Fourier Transform Infra-Red (FTIR), X-Ray Fluorescence (XRF), thermogravimetry (TG), scanning electron microscopy (SEM/EDX), and differential scanning calorimetry (DSC). The results from this study indicate that increasing the calcination temperature from 550 to 750 °C resulted in the transformation of phases and an increase in the reactivity of the laterites, resulting in material with improved properties. The use of laterite calcined at 750 °C and activated with 8 M NaOH solution resulted to an increase in the 28 days compressive strength by 35.3 MPa when compared to laterite calcined at 550 °C. Increasing the concentration of the NaOH solution was also found to yield higher material performance. Microstructural investigations showed a heterogeneous compact and dense structure resulting from high polycondensation much pronounced with the rise of calcination temperature from 550 to 750 °C.