Reactive powder concrete (RPC) with dense microstructure are found to perform poorly at elevated temperatures due to a build-up of pore pressure that causes explosive spalling. This paper presents the results of an experimental investigation of the behaviour of six RPC mixes containing hybrid steel and polyvinyl alcohol (PVA) fibres, following exposure to high temperatures up to 700°C. Residual compressive strength, static elastic modulus and ultrasonic pulse velocity measurements were carried out for all the RPC mixes. A mix containing hybrid steel-PVA fibre is proposed as suitable for hightemperature applications based on these results. Further tests were conducted for the mix at a hot state using a specially designed furnace-loading frame assembly. The hot-state elastic modulus, free thermal strains (FTS) and transitional thermal creep (TTC) were measured at the hot state. Residual compressive strength results for all the mixes indicated an initial increase in strength up to 300°C, followed by a drastic drop. No apparent changes in elastic modulus and ultrasonic pulse measurements were observed till 300°C, after which both dropped sharply. RPC containing only either steel fibres or only PVA fibres showed some form of instability, which was explosive in some cases. RPC with no fibres was also susceptible to explosive behaviour; however, the addition of hybrid fibres seemed to have beneficial effects. A mix containing equal volumes of steel and PVA fibres occupying a total fraction of 2 % by volume was found to give the best results. The FTS of that mix was similar to that of siliceous aggregate concretes, and the TTC was significant above 250°C.

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