Permeability measurement on high strength concrete without and with polypropylene fibers at elevated temperatures using a new test setup

•A new test setup for permeability measurements of concrete at high temperatures.•Permeability measurements on high strength concrete at high temperatures.•Plain concrete exhibits a steady permeability increase with rising temperature.•Concrete with PP fibers shows a jump in permeability between 80 °C and 130 °C.•The results confirm the role of permeability on explosive spalling of concrete.

A new test setup for permeability measurement at room and high temperature is presented. The experimental results obtained by employing the new setup are reported and validated. The experiments are performed on high performance concrete, without and with addition of polypropylene fibers under temperatures ranging from 20 °C to 300 °C as well as after cooling of previously heated specimens to the room temperature. The results show that plain concrete exhibits steady increase in permeability with increasing temperature, whereas concrete with fibers exhibit a sudden increase of permeability at temperatures between 80 °C and 130 °C. The results confirm the governing role of permeability on explosive spalling and suggest the existence of mechanisms of pressure relief other than just melting of fibers. The microstructure of concrete with fibers is investigated using SEM before and after exposure to high temperature. It is observed that the melted polypropylene flows only into the micro-cracks and does not penetrate into cement paste.