Explosive spalling of concrete in fire: novel testing to mitigate design risk

Heat-induced explosive spalling in fire poses a credible risk to concrete structures, and has received considerable research attention in recent decades. However, no validated guidance to enable the design of concrete mixes to prevent spalling, nor any established, widely verified, repeatable test methods are yet available to confidently quantify or demonstrate spalling resistance for a particular mix in a given application. As a result, no models yet exist that can predict spalling with sufficient confidence to be used in design. This paper summarises contemporary research on heat-induced concrete spalling, with particular emphasis on design for fire of concrete-lined tunnels. The topic is also relevant for modern concrete buildings. A novel, repeatable and economical testing method to reduce project risk by quantifying the propensity of concrete mixes for spalling under a range of different thermal and mechanical conditions is described. The intent of this paper is to present the limitations of knowledge to enable design for heat-induced spalling, and to highlight research currently under way to overcome some of the issues faced in practice.