Characterization and performance evaluation of laterite based geopolymer binder cured at different temperatures

This paper presents the results of experimental evaluation of curing conditions on the microstructure and performance of geopolymer binders developed from iron-rich laterite soils. Two calcined iron-rich laterites namely LB600 and LY600 were used as solid precursors in the preparation of geopolymer binders. The geopolymer samples were cured at 20, 60 and 80 °C. FTIR, XRD, EDS and DTA/TG were used to evaluate the microstructural properties of the prepared products. The performance of the binder was evaluated in terms of the compressive strengths, water absorption, porosity, bulk density and thermal conductivity. The findings from this study showed that the dissolution of the calcined laterites in 8 M NaOH increased the dissolution of Al, Si and Fe elements with increasing temperature from 20 to 80 °C. This higher dissolution of the monomers further resulted to an increase in the compressive strength of the binders at 7 and 28 days. It was also found out that curing the geopolymer in the dry state resulted in higher compressive strength at all ages compared to those cured in the wet and wet-dry state. Drying shrinkage evaluation of the geopolymer samples cured between 60 and 80 °C exhibited a lower linear shrinkage due to a high degree of geopolymerization. Microstructural investigation of the geopolymer samples cured at 80 °C showed a heterogeneous compact and dense structure resulting from high polycondensation. This densified microstructure also induced an increase in the thermal conductivity from 0.65 to 0.90 W/mK and 0.75 to 0.91 W/mK for LB600 and LY600, respectively. Nonetheless, both geopolymer binders made of LB600 and LY600 laterite powders performed well in dry, wet and wet-dry conditions, and can be used for various construction applications especially in the precast industry.