Mechanical and Microstructural Properties of Geopolymeric Fly Ash Based Mortar Cured in Ambient Conditions

Abstract

This experimental study aims to improve the IST and FST, flowability, and compressive strength of FA-based geopolymer mix samples for pastes, mortars, and mortars with steel fibre additions by substituting GGBS with various alkaline to binder ratios. GGBS substitution in geopolymeric mixtures is essential for achieving quicker setting in the resultant geopolymeric samples and also to accomplish the practical viability without any heat curing. SEM-EDS and FTIR were used to perform microstructural characterization and chemical identification of structural growth in the resulting geopolymers. According to the obtained findings, GGBS addition increased geopolymeric samples compressive strength while decreasing their setting time. The IST attained for geopolymeric paste samples is 20 minutes for F50:G50 samples with an alkaline to binder ratio of 0.5. However, the FST attained is 485 minutes for F100:G0 samples with an alkaline to binder ratio of 0.8. The highest 28 days compressive strength attained for geopolymeric paste samples is 85 MPa for F50:G50 samples with an alkaline to binder ratio of 0.5. Furthermore, for geopolymeric mortars, the IST attained is 22 minutes for F50:G50 samples with an alkaline to binder ratio of 0.5, whereas the FST attained is 668 minutes for F100:G0 samples with an alkaline to binder ratio of 0.8. A highest compressive strength of 56 MPa at 28 days is attained for F50:G50 geopolymeric mortar samples with an alkaline to binder ratio of 0.6. Additionally, for geopolymeric samples with steel fibres, after a curing period of 28 days, the compressive strength obtained is 69.5 MPa. This was observed in specimens containing 1% steel fibre content, an alkaline to binder ratio of 0.6, and binder proportions of 50%:50%. SEM microphotographs of geopolymeric pastes and mortar samples revealed the presence of a dense matrix with the GGBS substitution. Furthermore, the presence of rough steel fibre surfaces and hydration reaction products on the steel surface implies a rather good link between the geopolymer matrix and steel fibre, which boosts compressive strength values, as observed in SEM images of steel fibre-containing mortar samples. The FTIR analysis of geopolymeric paste samples reveals a notable downward shift in wavenumbers of distinctive bands, corresponding to varying levels of GGBS substitution. This shift signifies a heightened degree of geopolymerization within the paste samples.