Assessment of fire-induced spalling in stainless steel reinforced concrete with recycled steel tyre microfibres

Fire-induced spalling of concrete poses a significant threat to concrete structures, given its potential to trigger structural failures and lead to substantial negative economic and societal impacts. To address this concern, and to improve the sustainability of concrete structures, this study explores the efficacy of including Recycled Steel Tyre Microfibres (RSTM) into concrete as a sustainable means of mitigating fire spalling. In addition, the study focusses on reinforced concrete which employs inherently durable stainless steel, in place of carbon steel bars. The motivation to use this solution is to extend the service life of concrete structures and to develop more durable and sustainable infrastructure; nevertheless, there is no information available on how stainless steel reinforced concrete behaves in fire, especially in terms of fire-induced spalling. The paper presents a series of tests on concrete elements exposed to elevated temperature using a radiant panel loading and heating system. Different test variables were considered, including the fibre type, reinforcement details and concrete cover depth. The results show that both virgin steel fibres and RSTM are effective in mitigating the explosive spalling of stainless steel reinforced concrete. The severity of fire spalling increases as the specimen size increases. The type of the stainless steel rebar and concrete cover depth are also influential to the spalling behaviour. The microstructural damage resulting from differential thermal expansions between the fibres, reinforcement and concrete, as well as their different thermo-hydral behaviours, are discussed as the reason for the test observations and results. • Recycled steel tyre microfibres (RSTM) reinforced concrete showed much less fire-induced spalling than plain concrete. • Duplex stainless steel rebars delayed the fire spalling more effectively than austenitic stainless steel rebars. • Austenitic stainless steel reinforcement combined with thin cover thickness may help mitigate fire spalling. • The fire spalling mitigation mechanism for stainless steel-reinforced concrete with steel fibres is illustrated.