Reduction of fire spalling of concrete with small doses of polypropylene fibres

Abstract

SummaryThe addition of polypropylene (PP) fibres has been shown to reduce the fire spalling propensity of concrete. When including this type of fibres in the concrete, the concrete mix becomes less robust, and small deviations in the constitutes change the workability and properties of the concrete. So, from a manufacturing perspective as small dosages as possible of PP fibres are desirable. Very few large‐scale fire resistance tests of concrete loaded in compression exist showing the function of PP fibres at low dosages on concrete mixes sensitive to spalling if no fibres are added. In this paper, results from 26 fire tests are presented and analysed. The test results are from four different experimental campaigns, but all the mixes have in common that the water‐to‐cement ratio is 0.40. The results show that an amount of only 0.6 kg/m3 PP fibres has a significant effect on the spalling propensity and that even lower amounts reduce the spalling although they do not eliminate it entirely. During one of the fire tests on large slabs loaded in compression, unloaded small cubes of the same mixes were also included in the furnace. None of the small specimens spalled, whereas some of the corresponding large slabs spalled beyond the layer of reinforcement. This illustrates that tests on small, unloaded specimens are not relevant when assessing fire spalling of larger cross‐sections loaded in compression.