The effect of fiber reinforcement on the corrosion controlled degradation of reinforced concrete flexure elements

This study explores the impacts of a hybrid fiber reinforced concrete (HyFRC) mix design on the corrosion behavior of embedded rebar. The hybrid fiber gradation was chosen to meet flexural deflection hardening performance goals in order to promote a tougher crack resisting mechanism. When combined with conventional steel reinforcement (rebar) in flexural elements, the use of fiber hybridization increased both the element flexural stiffness and flexural strength when compared to a normal strength concrete matrix.;The corrosion behavior of embedded rebar was examined in terms of corrosion initiation and propagation. Flexural beam specimens containing rebar were prepared with plain concrete and HyFRC matrices and tested under equivalent, cyclic load based demands. This resulted in visible flexural surface cracks for the plain concrete specimens, while the HyFRC specimens showed no signs of cracking. A 3% sodium chloride solution was ponded on the tensile flexure surfaces and the corrosion rate of the tensile rebar was measured through time. Longer times to corrosion initiation and lower active corrosion rates were observed in the HyFRC beam specimens when compared to the reinforced specimens containing plain concrete matrices. Lollipop style specimens were also prepared to explore the relative impacts of the proposed HyFRC on corrosion propagation rates of embedded rebar. No difference in corrosion rate of the rebar was observed between the plain concrete and the HyFRC specimens when cracking was not apparent.;In addition to the experimental observations concerning the influence of the proposed HyFRC mix on corrosion rate, the impact of the enhanced tensile toughness provided by the fibers on flexural performance was explored within a theoretical framework. A model is proposed that utilizes fictitious crack propagation to explore the impacts of uniform rebar corrosion on the confining pressure (and resulting bond) provided by the surrounding matrix. The bond model was incorporated into a deterministic, time dependent, theoretical framework that predicts flexural strength degradation associated with rebar section loss and bond loss/cover spalling. The proposed modeling method demonstrates that reductions in the rate of strength degradation for the beam elements tested in this study can be realized in the presence of the proposed HyFRC mix.