Experimental and Statistical Analysis of Repeated Impact Records of Hybrid Fiber-Reinforced High-Performance Concrete

The effect of fiber type and fiber hybridization on the repeated impact strength was investigated experimentally using six high-performance concrete mixtures reinforced with a 2.5% fiber volume fraction. The fiber types considered in this study included short steel fibers (SF) with 6 mm length, long SF with 15 mm length, and polypropylene (PP) fibers. The repeated impact test was conducted using a specially made automatic testing machine following the test setup recommendations of the ACI 544-2R test, where cracking (Ncr) and failure (Nf) impact numbers were recorded and the failure mode and crack pattern were observed. The results were statistically analyzed using the normality test and variations were discussed. The test results showed that specimens with pure long SF (S15) obtained the highest Ncr and Nf values, which were 20% and 327% higher than those of the mixture with pure short SF (S6) owing to the better bond between fibers and the cementitious matrix in S15. Replacing 0.5% of the mixture’s SF with PP decreased the cracking resistance by 7% to 15%, while its effect on Nf was dependent on the length of SF. In most cases, the Ncr and Nf records did not exhibit a significant departure from normal distribution, according to the Anderson-darling test.