Effects of various fibres on high-temperature spalling in high-performance concrete

• The jute, WSPVA, and PP specimens did not explosively spall.
• The straw-like structure of jute prevents high vapour pressure.
• WSPVA prevents vapour pressure, because it becomes flexible over 50–90 °C in water.

We elucidated how polypropylene, jute, and water-soluble polyvinyl alcohol fibres mitigated the increase in pressure in fibre-reinforced high-performance concrete (HPC) heated to elevated temperatures. The vapour pressures of the water inside the HPC specimens reinforced with the three types of fibres were compared with the saturated vapour pressure of water in the specimens. Permeability tests were also performed on specimens of the fibre-reinforced HPC at 100, 200, 300, and 400 °C. The heated control, jute, and WSPVA specimens exhibited increased permeabilities. Although the permeabilities of the three specimens heated below 200 °C did not significantly change, the permeability of the control specimen heated above 200 °C was four times higher than its permeability prior to heating. The permeability of the jute specimen heated higher than about 200 °C was four to nine times higher than its permeability prior to heating. The jute specimen exhibited the highest permeability of all the heated specimens. The permeability of the WSPVA specimen heated above 200 °C was three to six times higher than its permeability prior to heating. The normalised permeabilities of the WSPVA and jute specimens were smaller than those of the PP specimen.The WSPVA fibres also resulted in the development of pressure-induced tangential spaces (PITS) at the fibre-concrete interface at temperatures of 50–90 °C, which is the temperature range at which WSPVA fibres dissolve in water and above which solid WSPVA becomes increasingly flexible. The straw-like structure of the jute fibres prevented the vapour pressure within the concrete from increasing.