Pore pressure and spalling in fire-exposed high-strength self-consolidating concrete reinforced with hybrid fibres

This work investigates the influence of different fibres (steel fibre, micro polypropylene (PP) fibre and macro PP fibre) on the build-ups of pore pressure of fibre reinforced high-strength self-consolidating concrete (FRHSSCC). The results showed that the introduction of fibres prolongs the occurrence time of maximum pore pressure. Micro PP fibre plays a dominant role in reducing pore pressure of HSSCC. The active zone of steel fibre is the deeper regions, while the macro PP fibre exerts a better effect in shallow regions for the tested HSSCC specimen. The combination of steel and micro or macro PP fibres further mitigate the maximum pore pressure of HSSCC. However, the pronounced positive hybrid effect is only found in the shallow regions near the fire. Compared to the combination of steel fibre and micro PP fibre, the use of steel fibre and macro PP fibre has a better positive hybrid effect on reducing the pore pressure of HSSCC. Prediction for the pore pressure of HSSCC and FRHSSCC using a thermo-hygral method was carried out. The prediction results are acceptable, thus the thermo-hygral method used in this paper can be simply employed to analyse the pore pressure build-ups and spalling of HSSCC and FRHSSCC.