Comparative experimental investigations on the compressive impact behavior of fiber-reinforced ultra high-performance concretes using split Hopkinson pressure bar

In this paper the compressive impact behavior of steel fiber reinforced ultra-high performance concrete (UHPC) with compressive strengths in excess of 210 MPa was investigated. Different steel fiber volume fractions were used ranging from 0% to 4%. The tested strain rate ranged from 22 to 110 s−1. Based on the obtained results a general equation was developed expressing the dynamic impact factor (DIF) in dependency of the fiber volume fraction. The impact resistance of all UHPC specimens was investigated using a split Hopkinson pressure bar complemented with pulse shaping disks or a shaped striker bar. All analyzed test results were found to satisfy the requirements of dynamic testing such as stress equilibrium, constant strain rate, and reduced friction to minimize inertial effects. A complementary finite element model was developed to simulate the behavior of UHPC specimens under high strain rates. From the results of the finite element analysis it was concluded that the contribution of friction between a greased specimen and the impact bars on the DIF can be neglected. Additionally, UHPC specimens reinforced with 0.5% volume fraction of steel, basalt, or polyvinyl alcohol fibers were tested under dynamic compressive loading at a strain rate of about 40 s−1. The results showed that the slope of the DIF versus strain rate increased with increasing fiber volume fraction. Moreover, UHPC with polyvinyl alcohol fibers was more strain rate sensitive than UHPC with steel and basalt fibers of the same length and volume fraction.