Impact response of the fiber-matrix bond in concrete

Fiber reinforced concrete (FRC) is a heterogeneous material comprising of distinct components: fiber, matrix, and fiber-matrix interface. Many applications require an enhanced resistance to impact loading from FRC. While designing for impact, the fiber-matrix interaction is by far the most critical. In the study reported here, three polymeric fibers and one steel fiber were investigated to examine the influence of fiber material, geometry, orientation, and the matrix strength under static and impact loading. Results show bond stiffening under impact loading. This was evident through higher peak loads, lower corresponding values of crack opening and a transition in the failure mode of some polymeric fibers from pull-out to fracture. Higher matrix strength resulted in a stiffer bond for all fiber types. Inclined loading produced better results for steel fibers. Under high crack opening rates, the bond stiffening in deformed polymeric fibers brought it closer in performance to the steel fiber.Key words: bond-COD response, impact loading, steel fiber, polymeric fiber, pull-out test, rate effects.