Effect of Alkaline Concentration and Solid Liquid Ratio on the Acid Resistance of Fly Ash Based Geopolymer Mortar

Abstract

Ordinary Portland cement (OPC) is one of the most widely used binders in building materials. However, OPC production is related with high CO2 emission and high energy consumption. Currently geopolymer cements are found to be the alternative substitute for OPC. Geopolymers most commonly are covalently bonded alkali-aluminosilicates which are X-ray amorphous at ambient and medium temperatures. The current study focusses on fly ash which is a byproduct of coal combustion process and due to its amorphous nature and chemistry, it is considered an appropriate raw material for geopolymer synthesis. In this study the effect of alkali concentration and solid liquid ratio on the acid resistance of fly ash based geopolymer mortar was studied. The fly ash was obtained from ayka Addis Textile, Addis Ababa, Ethiopia. Samples were prepared with different solid to liquid ratio and NaOH molarity and were tested for mechanical and durability properties. It was found that as the molarity of NaOH solution and solid to liquid ratio increase the initial and final setting time become shorter. Compressive and flexural strength show that after 28 days of curing sample with high Liquid to solid ratio and higher molarity show higher strength and smaller water absorption percentage. Sample were immersed in a 2% H2SO4 solution for 25 days and the sample with higher strength with smaller water absorption percentage show higher resistance.