Dynamic mechanical properties of steel fiber-reinforced reactive powder concrete after the exposure to high-temperatures

The mechanical properties of steel fiber-reinforced reactive-powder concrete (SF-RPC) are examined in this research project under dynamic loading after the exposure to high temperatures (residual conditions). Three mixes with similar compressive strength (143, 156 and 159 MPa on cylinders) and different fiber content by volume (vf = 1, 2 and 3%) have been investigated, by casting short concrete cylinders (diameter = height = 50 mm), that were tested in compression as such (reference specimens, no thermal treatment) or after being exposed to 200, 400, 600 and 800 degrees C. All tests were performed by means of a split Hopkinson pressure bar (SHPB) with a diameter of 50 mm in order to derive the stress-strain curves in dynamic conditions and to measure other mechanical properties. The Zhu-Wang-Tang's (ZWT) damage-based constitutive model was improved and extended to take care of the temperature and of the fiber. The stress-strain curves in compression provided by the proposed model fit quite well the experimental curves. Steel fiber is shown to significantly improve the ductility and the energy-absorption capacity of RPC. The compressive strength is markedly strain-rate dependent, as it increases roughly linearly with the strain rate. As expected, high temperature markedly impacts on RPC properties, with an increase of such parameters as compressive strength, toughness and elastic modulus between 200 and 400 degrees C, followed by a steep decrease. At and above 800 degrees C the positive effect of the fiber is practically lost. The test results and the proposed constitutive model may contribute to the design codes by improving their provisions on FRC exposed to high temperatures.