Comparative study of laterite and metakaolin/hematite-based geopolymers: Effect of iron source and alkalization

The objective of this study is to investigate and characterize geopolymers based on laterite or metakaolin-hematite mixture model. The model has been used to reproduce laterite in areas where laterite is not available. The geopolymers were synthetized using (i) calcined laterite and (ii) a mixture of metakaolin and hematite as solid precursors and two alkaline solutions of SiO2/Na2O and SiO2/K2O equal to 1.3. The obtained results reveal that both laterite and metakaolin/hematite-based geopolymers display efficient mechanical properties, regardless of the alkaline activating solution used. Thermal conductivity and compressive strength vary almost linearly, from 0.7 to 1 W/(m.K) and from 20 to 70 MPa, respectively: Na-activated laterite (NaLc) > Na-activated metakaolin + hematite (NaMF) > K-activated metakaolin + hematite (KMF) > K- activated laterite (KLc). This order can be explained by structural modifications after thermal treatment at 1175 °C. In the case of NaLc and NaMF, the samples display weak porosity due to higher crystallinity of the powder. In contrast, KMF and KLc are more heterogeneous with higher porosity.