Investigation and Prediction of Pullout Behavior of Twisted Fibers from Ultra High Strength Concrete

This research demonstrates the pullout response of twisted steel fibers from various matrices. The high strength twisted steel fibers, characterized by three twists along their length and a high aspect ratio of 100, were embedded in two types of matrix: high strength concrete (HSC) matrix with a compressive strength of 81 MPa and ultra high strength concrete (UHSC) matrix with a compressive strength of 152 MPa. Moreover, a theoretical model was established to estimate the pullout response of twisted fibers. The experiment results revealed that twisted fibers embedded in the HSC matrix exhibited slip-hardening behavior by maintaining pullout mode during the fiber pullout from matrix, whereas those in the UHSC matrix exhibited brittle failure due to fiber rupture. The HSC matrix produced a 41% lower maximum pullout load but a 1217% higher pullout energy than the UHSC matrix. The theoretical model was able to accurately capture the pullout behavior of twisted fibers from different matrices.