Abstract
Effectiveness and durability of interventions on deficient concrete structures remain a major concern, comprising the challenge of old-to-new concrete compatibility and bonding, as stress concentrations and microstructural flaws at the old-to-new concrete interface compromise structural integrity and create migration paths for harmful contaminants. Fiber reinforcement can be beneficial, but proper quantification and mastering of fundamental mechanisms is required before these are fully utilized. A study is presented on Mode-I crack growth resistance at the interface between two concretes (substrate and repair). Countered Double Cantilever Beam tests are performed, crack growth resistance curves calculated (Modified Linear Elastic Fracture Mechanics), and complemented with analysis of interfacial roughness and failure planes. Polyvinyl alcohol (8 and 12 mm length) and steel fibers (13 mm) are introduced in the repairs at 0.5% and 1% volume fractions. Results indicate that fibers improve fracture behavior of both the repair material and substrate-repair interface; correlations with interfacial roughness, crack deviation, and fracture parameters are discussed.
Highlights
In order to extend the service life of deteriorating reinforced concrete structures, and to grant safety in the case of increased loading demand, interventions of repair and rehabilitation have become of frequent practice worldwide
Experimental Splitting Load (SL) compared to crack mouth opening displacement (CMOD) curves obtained with 8 mm PVA fibers are shown in Figure 5a, where the curve of the plain repair material is plotted for comparison
According to American Concrete Institute (ACI) 224R the maximum crack width at the tensile face of reinforced concrete structures is specified as 150 μm for exposure conditions of seawater, seawater spray, wetting, and drying, and 180 μm for deicing chemical exposure
Summary
In order to extend the service life of deteriorating reinforced concrete structures, and to grant safety in the case of increased loading demand, interventions of repair and rehabilitation have become of frequent practice worldwide. The interface between the concrete substrate and the new repair layer is typically weaker than the materials on either side. Due to such weakness, combined to stress concentrations (emphasized in case of poor substrate-repair compatibility), the interface is much more vulnerable to cracking and failure. Fiber reinforced concrete (FRC) is recognized as a promising option for improving concrete durability [6,7,8,9] These benefits become even more relevant in repaired structures, where fibers can help improve compatibility to the substrate or, at least, reduce the extent of damage arising from poor compatibility [8,10]
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