Fire resistance of VHPFRC thin plates

VHPFRC thin-walled elements used for structural components were proved to be very efficient and can be also sustainable, if the performance increase, in relation to ordinary concrete, allows a significant volume reduction and an improved durability. Even if they can also achieve a noticeable resistance when subjected to high temperature, their weakest point remains the possibility to be subjected to explosive spalling even if the high-carbon steel fibre amount used is over 1% by volume. Major explosive spalling was observed in a full-scale test carried out on a thin-walled roofing panel made of a VHPFRC matrix with 1.2% high-carbon straight fibres. In this study, high temperature behaviour of the same mixture is compared with another mixture which, in addition to steel fibres, has 2 kg/m3 of micro-polypropylene fibres. To this end, three circular elements, 20 mm thick with a diameter of 560 mm, were cast for each mix design. One specimen was tested in bending with a continuous support and a central point load. The remaining two panels were exposed to high temperature following the Hydrocarbon fire curve for a given fire duration. The response of the mix designs in exposure to fire is observed and residual bearing capacity of the mix designs are examined on the circular panels. Furthermore, prismatic unnotched thin beam elements were tested without exposure to fire, to determine the post-cracking behaviour of the mix designs. The results confirm the effect of high temperatures on the mechanical response and highlight that spalling phenomena observed at the real scale may not be effectively identified on small-scale specimens.