Synergistic bond properties of new steel fibers with rounded rounded-end from carbon nanotubes reinforced ultra ultra-high performance concrete matrix

A novel type of steel fiber with a rounded rounded-end shape is presented to improve the bonding behavior of fibers with Carbon Nanotubes ( CNT)-reinforced Ultra Ultra-High Performance Concrete (UHPC) matrix matrix. For this purpose purpose, by performing a parametric study and using the nonlinear finite element method method, the impact of geometric characteristics of the fiber end on its bonding behavior with UHPC has been studied studied. The cohesive zone model investigates the interface between the fibers and the cement matrix matrix. The mechanical properties of the cohesive zone model are determined by calibrating the finite element results and the experimental fiber pull pull-out te test. AlsoAlso, the results are evaluated with the straight steel fibers outcomes outcomes. Using the novel presented fibers fibers, the bond strength has significantly improved compared to the straight steel fibers fibers. The new proposed fibers increase bond strength by 1 1.1 times f or the same diameter of fibers fibers. By creating fillet at the contact area between the rounded end and the fiber fiber, bond strength is significantly improved improved, the maximum fiber capacity is reachable reachable, and the pull pull-out occurs in the form of fracture and tearing of t he fibers fibers, which is the most desirable bonding mode for fibers fibers. This also improves the energy absorbed by the fibers and is 4 4.4 times more than the corresponding straight fibers fibers.