Effects of palm oil fuel ash and metakaolin blend on properties of geopolymer mortar

Abstract

Geopolymer, an inorganic polymeric binder material synthesized from materials containing alumina and silica compounds, has evolved to become an alternative to Portland cement. The drawbacks of using Portland cement are its carbon dioxide emission, high energy consumption during production, and inadequate durability performance of its concrete. The valorization of wastes such as fly ash and blast furnace slag is an important feature of geopolymer that in a broad sense contributes to its environmental friendliness. In the same manner, palm oil fuel ash (POFA) waste generated from industrial production of palm oil for construction purposes is also beneficial and contributes towards a more sustainable environment since it aids in the disposal of waste and leads to economic gains. POFA has been successfully developed as supplementary material for Portland cement. Its emerging use in geopolymer production is made possible by blending it with alumina rich material like Metakaolin, which addresses its deficient alumina content. The maximization of POFA and the minimization of metakaolin use in geopolymer preparation underscore the need to study the behavior of high volume POFA blends with metakaolin geopolymers with specific objectives of determining the effect of high volume blend on the strength, durability performance and microstructure characteristics. The ratio of blends studied range from 0:100 to 80:20 POFA: Metakaolin. The geopolymer specimens were prepared with sodium hydroxide and sodium silicate and were cured in both ambient and oven conditions. The analysis of formulations revealed the extent of influence of the synthesis factors on the geopolymer. The evaluation of strength and durability properties of geopolymer specimens was accomplished with mortar for various mixes at varying ages. High volume POFA was found to improve the strength and durability properties as well the microstructure characteristics, which were mainly due to the participation of Si-O-Si and Si-O-Al bonds in the reaction products. Test results show that all mixes developed appreciable mechanical strength under the studied curing conditions. The aspects of durability studied are permeability properties, resistance to acid, resistance to sulfate, and effects of elevated temperature. The test results showed that the geopolymer specimen was highly resistant to water penetration and aggressive conditions. Microstructure tests in the form of FESEM, XRD, EDX, FTIR and TGA were performed on selected specimens to study the interactions of the geopolymerization products. It is therefore concluded that geopolymer mortar produced with up to 80% POFA could give adequate strength and durability properties.