Assessing behaviour of fresh and hardened geopolymer concrete mixed with class-F fly ash

Geopolymer binders have been shown to be a potential green replacement for Ordinary Portland Cement (OPC) in concrete manufacture. This paper presents an experimental study into the behaviour of geopolymer concrete in both its wet and hardened states using Class F fly ash. The experimental program included 15 mix designs to investigate the influence of water-to-binder and superplasticiser-to-binder ratios on the workability and strength of fly ash-based geopolymer concrete. The results show that the addition of naphthalene sulphonate polymer-based superplasticiser has little to no influence on workability and a detrimental effect on strength. Furthermore, the indirect tensile strength, flexural tensile strength and elastic modulus of fly ash-based geopolymer concrete were recorded in this experimental program and have been added to a database of available tests in the open literature. The experimentally determined results are subsequently compared with prediction models developed for OPC-based concrete. The comparison suggests that existing OPC models provide reasonably accurate predictions of the elastic moduli and stress-strain relationships, whereas they slightly underestimate flexural and splitting tensile strengths.