Design and characterization of Cameroonian pegmatite-calcined clay binary mortars via geopolymerization

In this work, geopolymer binders obtained from a mixture of Cameroonian pegmatite and type 1/1 calcined clays (metakaolin and metahalloysite) at different proportions (10–30 wt%) were used for the formulation of mortars. The kinetic parameters of the reactivity of the pegmatite mixed with different calcined clays in alkaline medium were evaluated via heat of reaction data measured at isothermal conduction calorimeter (ICC) at 27 °C for the first 24 h. As feedstock precursors, the different products obtained were characterized by means of mechanical flexural and compressive resistances (dry and wet), physical properties, Fourier Transform infrared spectroscopy and Scanning Electron Microscope. The results showed that the compressive strength values vary with the type and percentage of calcined clays. The highest values were achieved with mortars containing 30 wt% of the different calcined clays, ranging from approximate 25–35 MPa in dry conditions. The flexural strength values of the mortars increase also with the incorporation of calcined clay and vary from 1.0 to 4.5 MPa. After 72 h of immersion of these samples in water, they lost less than 60% of their mechanical performance. The water absorption rate of the mortars decreases with the incorporation of calcined clays and ranges from 7.5 to 13.8%. FT-IR indicated the reactivity of pegmatite during the geopolymerization process while SEM micrographs exhibited a better cohesion between the aggregates (river sand, 200 μm ≤ ɸ ≤ 2000 μm) and the binder. The above-mentioned pegmatite-calcined clay mortars appear to be a suitable candidate for engineering applications (civil engineering). •The alteration of finely ground feldspar by 15–30 wt% of calcined clays contribute to enhance the properties of geopolymer mortars.•The flexural and compressive strengths values of mortars increase from ∼3 to 6 MPa and ∼11–36 MPa, respectively with addition of calcined clay.•SEM micrographs exhibit a better cohesion between the aggregates and the binder.