Synthesis of geopolymer binders and mortars from Ijero-Ekiti calcined clay, blast furnace slag and river sand

Abstract

Geopolymer, an inorganic polymer is a greener alternative to Portland cement because of less CO₂ emissions generated during its synthesis. Main precursors needed for its formation is silica and alumina. Geopolymer source materials are primarily fly ash, blast furnace slag, calcined kaolin clays. Ijero-Ekiti kaolin clay that is rich in silica and alumina is relatively abundant in Nigeria. Hence, the aim of this study was to develop geopolymer binder and mortars using Ijero-Ekiti calcined clay, blast furnace slag and river sand. Chemical and structural characterisation of source materials was determined. Geopolymer binders were synthesised at varying proportions of clay and BFS. The binder that gave the optimum compressive strength was used to prepare geopolymer mortars with sand at varying mix ratios with 8M NaOH/NaSi₂O₃ solution at ambient temperature. Mechanical, structural and durability properties of the geopolymer products were investigated. FTIR spectrum of Ijero-Ekiti calcined clay showed a disappearance of surface OH groups when compared to its raw clay, confirming the transformation of kaolinite to metakaolinite. The calcined clay was composed mainly of silicon oxide and aluminium oxide. Si-O stretching vibration decreased as the BFS content increased in the binders. The water absorption values substantiated the low porosity of the binders. The geopolymer mortars compressive strength was in accordance with ASTM standard. The results confirmed the suitability of Ijero-Ekiti calcined clay as a geopolymer precursor and its combination with blast furnace slag can be used as a greener alternative to Portland cement.