Influence of alumina on the compressive strengths and microstructural properties of the acid-based geopolymers from calcined indurated laterite and metakaolin

Abstract The main objective of this work is to investigate the influence of alumina on the compressive strengths and microstructural properties of the acid-based geopolymers using calcined indurated laterite and metakaolin. These raw materials have been replaced by 0, 5, 10, 15 and 20 mass% of calcined bauxite. Phosphoric acid with molarity 10 M was used as a chemical reagent. The compressive strengths of the acid-based geopolymers increase with increasing the calcined bauxite content. Those from the substitution of calcined laterite by calcined bauxite are ranging from 21.45 to 47.95 MPa and higher compared to those from metakaolin (12.55 and 21.97 MPa). TG and DSC curves of all acid-based geopolymers indicate the decomposition of AlPO4.H2O at between 230 and 248 °C to an amorphous phase. In addition to this mineral, those from calcined laterite show the transformation of amorphous FePO4·2H2O at in the range 451–788 °C to the crystalline FePO4. The micrography images of the acid-based geopolymers indicate the formation of dense amorphous geopolymer matrices. It was found that the alumina incorporated in the acid-based geopolymers increases the compressive strengths. The presence of hematite in the calcined laterite leads to the formation of amorphous FePO4·2H2O which could contribute to enhancing exponentially the compressive strengths of the acid-based geopolymers.