Impact of inherent characteristics of raw laterite and its calcination on properties of geopolymers

Laterite is a sustainable solid precursor for synthesising geopolymers with interesting properties. However, the intrinsic characteristics of raw laterite and their impact on the reactivity of calcined laterite in an alkaline medium are poorly understood. This research aims to investigate the chemical, mineralogy and physical characteristics of eight (8) raw lateritic soils from three regions of Cameroon and their calcination products to lay down the knowledge base for mainstreaming this material as a solid precursor in geopolymer synthesis. The mineralogy and chemistry of raw laterites are correlated with those calcined laterites along with their reactivity and reaction kinetic in an alkaline solution, and the 28-day compressive strength of resulting geopolymers. The results show that the degree of laterization influences the mineralogy and chemistry of raw laterites. The partial transformation of goethite or gibbsite into hematite or γ-Al₂O₃ respectively during calcination impairs the evolution of the amorphous phase content of calcined laterite. This hinders the reaction kinetics and compressive strength development. The 28-day compressive strength of the geopolymer strongly depends on the composition of the amorphous phase of calcined laterite with the highest strength achieved for samples with higher amounts of reactive Si, Al and Fe. The 1:1 clay minerals content of the raw laterite induces higher reactivity of the calcined laterite and higher compressive strength of the resulting geopolymer.