Improving the tensile resistance at high strain rates of high-performance fiber-reinforced cementitious composite with twisted fibers by modification of twist ratio

This study aims to examine effects of twist ratio on the tensile resistance at high strain rates and strain rate sensitivity of high-performance fiber-reinforced cementitious composites (HPFRCCs) with a small amount of twisted fibers. Two types of twisted steel fibers with different twist ratios, T3-fibers (3 twists/30 mm) and T9-fibers (9 twists/30 mm), were incorporated at 1% by volume into two matrices with different matrix strengths, M1 (56 MPa) and M2 (84 MPa). The direct tensile test results indicated that HPFRCCs with 1% twisted fibers generated not only high tensile resistance at high strain rates but also great rate sensitivity by maintaining tensile strain hardening accumulated with multiple micro cracks at high strain rates. T9-fibers produced the highest tensile resistance at high strain rates in M1 whereas T3-fibers did in M2. In addition, T9-fibers exhibited lower rate sensitivity than T3-fibers in all matrices. Theoretical models have been used successfully to predict dynamic post cracking strength of HPFRCCs with twisted fibers considering number of twists and the predicted results showed good agreements compared to the experimental results.