In this paper, we investigate the influence of cementitious matrix cracking on the electrochemical polarization and impedance behaviors of corroding reinforced concrete and crack-resistant reinforced hybrid fiber-reinforced concrete (HyFRC). Samples were exposed to a chloride environment for 2.5 years while in either a continuous tensile stress state or in a nonloaded condition, and were periodically monitored for Tafel polarization responses. Electrochemical impedance spectroscopy (EIS) was additionally performed at the conclusion of the test program. Greater severity of corrosion-induced matrix splitting cracks along the length of embedded steel reinforcing bars and subsequent formation of anodic surfaces were found to affect several electrochemical parameters, including increase of the corrosion current and decrease of the ohmic resistance of concrete. Cathodic and anodic Tafel coefficients and Stern-Geary coefficients for passive and active samples are also reported, highlighted by a Stern-Geary coefficient of B ¼ 28.1 mV for active corrosion.
Many reinforced concrete structures susceptible to corrosion damage are subjected to externally applied loads, causing cracking. These cracks increase the permeability of the material, accelerating the ingress of corrosion-inducing deleterious agents. In this paper, the effect of multiple microcracking and macrocrack formation on corrosion initiation was investigated. A hybrid fiber-reinforced concrete (HyFRC), which forms ductile, distributed microcracking prior to dominant crack localization due to multiple tiers of fiber reinforcement, is being studied for its performance against corrosion damage. The effect of matrix cracking on corrosion initiation was studied with beam specimens preloaded in flexure prior to long-term corrosion exposure. Reinforced HyFRC composites were found to have a delayed corrosion initiation response due to reductions in crack widths and suppression of splitting cracks, compared to conventional reinforced concrete. The influence of microcracks on corrosion is studied using X-ray micro-computed tomography (μCT) on reinforced fiber-reinforced cementitious composites and reinforced mortar preloaded in tension.
The corrosion of steel reinforcing bars in concrete structures is a primary durability concern in aging infrastructure. Cracks caused by the internal growth of corrosion products increase the permeability of the matrix and degrade the designed capacity of structural elements. In this longterm study, two types of hybrid fiber-reinforced concrete (HyFRC)a baseline HyFRC and a selfconsolidating HyFRC (SC-HyFRC)are investigated for serviceability enhancement under a twostage corrosion model (time to corrosion initiation and damage during corrosion propagation). HyFRC, which contains a synergistic blend of microfibers and macrofibers, utilizes a multi-scale approach towards crack control and is extended to durability-related applications. Reinforced HyFRC and reinforced concrete beams were exposed to chloride penetration and monitored for corrosion activity for up to two years. Because concrete structures are subjected to various crack-inducing loads while in service, beam specimens in this study were placed under a cyclic, flexural preloading protocol prior to induced corrosion to account for such service conditions. The time to corrosion initiation was found to increase with reduced maximum flexural crack widths and suppression of surface splitting cracks during preloading, both of which were improved by HyFRC compared to concrete. Crack resistance provided by hybrid fiber reinforcement was evident during the corrosion propagation stage, as additional surface cracking was not detected with reinforced HyFRC and residual flexural testing revealed no significant degradation in flexural performance. In contrast, damage to reinforced concrete beams resulted in nearly complete loss of rebar-matrix bond due to extensive splitting crack formation and widening. The results suggest hybrid fiber reinforcement was effective in resisting tensile stresses from mechanical loading and from the internal growth of corrosion products, ultimately limiting the damage to reinforcing steel and maintaining the service capacity of beam elements.
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