Influence of steel fiber type, content, and dimensions on compressive strength and ultrasonic pulse velocity of high-performance concrete

Fiber-reinforced high-performance concrete (HPC) has attracted significant research interest because of its enhanced mechanical performance, yet the reliability of ultrasonic pulse velocity (UPV) for its evaluation remains unclear due to material heterogeneity. This study investigates how UPV and compressive strength of HPC are affected by steel fiber type, geometry, and volume fraction (1–3%). UPV and compressive strength techniques were used to test 180 cylindrical specimens with straight-end and hooked-end fibers. The findings showed that, for straight steel fibers, raising the fiber volume fraction from 1 to 2% led to improvements in compressive strength of up to 24–36% and UPV increases of about 2.0–3.3%; however, increasing the fiber content to 3% only slightly increased the results. Steel fiber length, on the other hand, had a greater impact: extending the fiber length from 13 to 35 mm resulted in gains in compressive strength of up to 46% and UPV increases of up to 4.4%, suggesting a near-linear relationship. In comparison to straight fibers, hooked-end fibers showed a lesser sensitivity to fiber content, as seen by more gradual UPV increases of roughly 1.1–2.0% and compressive strength gains of roughly 6–17% when the fiber percent was increased from 1 to 3%. But the advantages were more noticeable when the fiber length was increased from 13 to 45 mm, with UPV gains of about 2–3% and compressive strength improvements of up to 19%. For both fiber types, the relationship between fiber length and compressive strength and UPV appeared to be almost linear within the ranges under study, and it was discovered that fiber length had a greater impact than fiber diameter. Compressive strength and UPV showed a substantial correlation, with coefficients of determination for straight-end and hooked-end fibers being 0.982 and 0.977, respectively, confirming UPV as a reliable predictor of strength in fiber-reinforced HPC. In both laboratory and field settings, these results demonstrate the potential of UPV as a useful, non-destructive method for assessing the mechanical performance of fiber-reinforced HPC.