Time-dependent behavior of pre-coated crimped, 4-Dimensional and 5-Dimensional steel fiber pull-out in normal and rubber concrete

Abstract

Bond mechanism of various types of steel fiber embedded in normal and high strength concrete prepared without and with rubber particles are typically evaluated using single fiber pull-out test. Three distinct types of steel fiber, i.e., crimped (aspect ratio, l/d = 50 and 100), 4D (Double Hooked) and 5D (Triple Hooked) (l/d = 65) fibers embedded in different matrix strengths (M30, M30RC, M60 and M60RC), (RC-rubber concrete) were utilised. The fibers were pre-coated with Zinc Phosphate (ZnPh) in order to enhance the frictional resistance and bond strength between fiber and concrete which portrayed higher peak load than the un-treated fibers. Two different loading rates were adopted such as 1 mm/min (static loading) and 10 mm/min (dynamic loading) for single fiber pull-out test to examine the rate sensitivity on fiber pull-out for various conditions. Crimped fibers failed due to fiber rupture without attaining complete potential in most of the cases, at both loading rates. The pull-out load of 5D fiber was 1.37 times higher than that of 4D fiber at static loading rate. The dynamic increase factor of 4D and 5D fiber was found to be 1.31 and 1.23 respectively at dynamic loading for normal strength concrete, 1.21 and 1.15 respectively for high strength concrete on considering the effect of treatment of fiber. In the case of lesser embedment length, the fiber pulled off from the concrete matrix easily, especially at higher loading rates and in concrete prepared with addition of rubber particles. Performance of 5D steel fiber was found to be better in terms of Pmax and average shear stress.