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

Funmilayo I Adeniyi,Mary B Ogundiran

doi:10.34198/ejcs.4120.1534

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.

Highlights

Binders and mortars are important ingredients in building and construction works
The results showed that compressive strength increased when the geopolymers binders were cured at 20°C
The chemical composition of river sand indicates its high silica content compared to calcined clay

Summary

Introduction

Binders and mortars are important ingredients in building and construction works. The most common binder/cement used worldwide is Ordinary Portland cement. Common Cement mortars are paste made from Portland cement, sand and water. Environmental issues of Ordinary Portland Cement (OPC) production are a major concern to the 21st century world. OPC manufacturing process emits a total of 80% carbon dioxide per 1kg of OPC [1]. Carbon dioxide (CO2) and a host of other green house gases such as nitrous oxide (NOx), sulphur dioxide (SO2) are responsible for changes in the world climate through global warming [1, 2]. Efforts to reduce the use of OPC led to the utilisation of geopolymers, a greener alternative in the construction industry

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