Abstract
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 (Na2SiO3) 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.
Highlights
Lateritic soils are formed in tropical and subtropical regions around the world and are mainly composed of aluminum, silicon and iron oxides as major elements [1, 2]
Available laterite soils were used in the production of geopolymer binders as an alternative to the conventional Portland cement
The findings from this study showed that the thermal activation of laterite soils through calcination resulted in the transformation of the phases and an increase in the reactivity of the laterites
Summary
Lateritic soils are formed in tropical and subtropical regions around the world and are mainly composed of aluminum, silicon and iron oxides as major elements [1, 2]. In parts of the world where lateritic soils are widely available, they are usually mixed with Portland cement in certain proportions to produce compressed earth stabilized blocks (CEBs) for building houses or pavements [3,4,5]. These lateritic soils are formed from the alteration of kaolinite by iron minerals in which some aluminum atoms occupying the octahedral site are replaced by iron atoms from iron minerals like ilmenite, goethite and hematite [6, 7]. With varying availability of the conventional precursors (i.e. fly ash and slag) in various parts of the world, the use of locally available laterite soils as precursors would result in more sustainable and economical development of geopolymers
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