Experimental research on dynamic impact mechanical properties of ultra-high performance concrete after high temperature

An experimental research is performed on the impact mechanical properties of UHPC after exposure to 25 degrees C, 200 degrees C, 400 degrees C, 600 degrees C and 800 degrees C. Four sets of UHPC specimens with various polypropylene fiber volume contents of 0, 0.1 %, 0.2 % and 0.3 % were tested. A Phi 50mm split Hopkinson pressure bar (SHPB) was adopted to conduct impact experiments at different strain rates ranging from 10-30s-1 to 70-90s-1. The dynamic stress-strain curves and various dynamic mechanical properties of UHPC are obtained. The test results indicate that the dynamic compressive strength, elastic modulus, and toughness increase at first and then decrease with the increasing temperature. With the increase of strain rate, the dynamic increase factor (DIF) of hybrid fiber UHPC increases approximately linearly. By comparison, after endured temperature exceeding 600 degrees C, with rise in the polypropylene fiber content, the toughness increases accordingly. The adjusted Holmquist-Johnson-Cook (HJC) model was used for finite element (FE) simulation of SHPB test and fit the experiment results well. Based on the Zhu-Wang-Tang (Z-W-T) constitutive model, an improved hybrid fiber UHPC dynamic damage constitutive model incorporates temperature and fiber content was derived, the theoretical values of the model are in good agreement with the experimental data. The test results and the proposed constitutive model may contribute to the design codes by improving their provisions on fiber-reinforced concrete exposed to high temperatures.