Investigating the Suitability of Nigerian Calcined Kaolins as Raw Materials for Geopolymer Binders

Abstract

Clay minerals constitute large deposits of natural resources in Nigeria which may exhibit the pozzolanic properties of geopolymer materials. Therefore, this study investigated the suitability of Ikare and Ikere kaolins from two different geological locations in Nigeria as raw materials to synthesis geopolymer binders. In order to ascertain optimal geopolymerization conditions, the effects of calcining temperature, activator concentration and particle size on the compressive strength (engineering) and water absorption (durability) properties of the geopolymers produced were measured at 7 and 28 days at room temperature. The two kaolins with particle sizes 600, 425, 212 µm were calcined at 600°, 700° and 750°C and activated with sodium silicate at SiO₂/Na₂O mole ratios 2.1, 2.5 and 2.8. The best compressive strength and water absorption were obtained at 700°C calcination temperature, SiO₂/Na₂O mole ratio 2.1, 212 µm clay particle size and at 28 days curing time. The obtained CS for Ikare and Ikere kaolins at the optimal conditions were 23.2 and 26.1 MPa while water absorption values were 1.62 and 0.12% respectively. Calcined Nigerian kaolins are proposed as cost-effective and sustainable binders which may be applied to substitute or augment ordinary Portland cement in construction applications.

Keywords:

• Calcined kaolin
• Nigerian kaolin
• Geopolymers
• Compressive strength
• Water absorption