Residual behaviour of fibre reinforced geopolymer concrete following exposure to a standard fire

Recent years have seen a very significant increase in the development of cement-replacement products, owing to the environmental challenges associated with ordinary Portland cement (OPC). Geopolymer concrete replaces cement with alternative binders such as fly ash and ground granular blast furnace slag (GGBS), and the behaviour in terms of the workability, fresh and hardened properties, and durability has been studied by researchers and practitioners. However, there is a shortage of available performance data on structural members, such as beams, both at ambient temperature and also following exposure to fire conditions. Accordingly, this paper presents a detailed experimental investigation into the residual flexural behaviour, load carrying capacity and failure patterns of geopolymer concrete with and without fibre reinforcement. A total of six concrete mixes were examined, including unreinforced geopolymer concrete, as well as mixes with steel, polypropylene or basalt fibres, as well as combinations of steel/basalt fibres, and steel/polypropylene fibres. The tests focussed on the compressive strength, concrete quality and flexural behaviour following exposure to a standard fire for 30, 60, 90 or 120 mins. A series of microstructural analyses were also conducted to further understand the behaviour. The results show that with the addition of fibres, the compressive strength and flexural properties of geopolymer concrete is excellent following a fire, compared with unreinforced geopolymer concrete. In particular, the basalt fibres provided excellent behaviour in terms of strength, failure and concrete quality.