International Concrete Abstracts Portal

This paper presents the prediction of bond strength between ultra-high performance concrete (UHPC) and fiber reinforced polymer (FRP) reinforcing bars using an artificial neuronal network (ANN) approach. A large amount of datasets, consisting of 183 test specimens, are collected from literature and an ANN model is trained and validated. The ANN model includes six variable inputs (bar diameter, concrete cover, embedment length, fiber content, concrete strength, and rebar strength) and one output parameter (bond strength). The model performs better than other models excerpted from existing design guidelines and previously published papers. Follow-up studies are expected to examine the individual effects of the predefined input parameters on the bond strength of UHPC interfaced with FRP rebars.

Corrosion of steel reinforcement is one of the primary contributing factors to bridge deck deterioration. Based on the extent of corrosion, different corrosion mitigation strategies can be used to extend the service life of a bridge deck. Bridge deck overlays are efficient tools in reducing active corrosion. While there are multiple overlay solutions that are commonly deployed, including concrete-based and polymer-based systems, ultra-high performance concrete (UHPC) overlays have gained interest from bridge owners in recent years. Another corrosion mitigation strategy is the application of corrosion-inhibiting chemicals and sealers to a concrete surface to reduce the ingress of deleterious ions. The purpose of this paper is to compare different corrosion mitigation strategies and study the effects of such techniques on the bond between the UHPC overlay and the substrate concrete. UHPC overlays were found to be effective in reducing corrosion rates by more than 50 percent. Sealers and corrosion inhibitors applied to the concrete substrate in combination with placing a UHPC overlay reduced the corrosion rates even further. However, sealers and corrosion inhibitors appeared to negatively affect bond strength, potentially increasing the likelihood of overlay delamination.

As a result of the limited data available when the current ACI 440.11-22 development length equation was developed, certain parameters were disregarded. Additionally, the equation was based on bars that are no longer in use today, and significant advancements have been made in FRP material properties and production methods since its calibration. Conflicting research findings have led to differing perspectives on its reliability, with some suggesting it yields overly conservative results, while others argue it may overestimate bond strength. To address this concern, an experimental study was conducted to assess the bond stresses between GFRP bars and conventional concrete in under-reinforced concrete beams. The beams were reinforced using a single M16 (No.5) Glass/Vinyl-ester FRP sand-coated bar. Three different lap splice lengths (i.e., 40-, 60-, and 80-times bar diameter) were selected based on available literature. The results indicate that the bond is primarily governed by surface friction, with negligible impact from relative slippage. The lap-spliced specimens exhibited slippage failure but exceeded design moments based on ACI provisions, indicating efficient performance. Stiffness remained comparable to that of the un-spliced beam, suggesting intact bond capacity despite some slippage. Average bond stress calculations closely aligned with ACI maximum bond stress values. Overall, the study offers valuable insights into GFRP bar behavior and bond capacity.

This paper presents the crack monitoring of reinforced concrete beams strengthened with fiber reinforced polymer (FRP) sheets. Emphasis is placed on the development of a smart FRP bonded material that can measure the crack opening of a reinforced concrete beam strengthened by FRP. The reliability measured by a conventional digital image correlation (DIC) and by the proposed smart FRP is employed to assess the contribution of the FRP to control the crack. The monitoring process is based on a large set of experimental database consisting of 19 test beams. The effect of FRP to control the crack opening is studied depending on the steel ratio, FRP ratio and the level of damaged of RC beams when FRP is applied. The results were compared with the theoretical values of crack width and spacing predicted using the Eurocode 2 (EC2) formula, calibrated for non-strengthened RC elements. The corresponding results were compared in order to clarify the effect of external bonded FRP on the cracking behaviour of RC beams.

The first phase of this work uses experimental evidence to critique some shortcomings of the so-called improved double-lap bond shear tests regarding their limited application to wet layup fiber-reinforced polymer (FRP) and their inapplicability to pultruded FRP laminates. Even in the case of the wet layup FRP, the study provides some evidence of high chances of obtaining undesirable fiber rupture that preclude the use of the results as reliable means for interpreting the FRP-concrete bond-slip models. Further proposed modifications to overcome these challenges are provided by designing a convertible bond tester applicable to both wet layup and pultruded FRP laminates. Apart from the application of the apparatus to FRP-concrete bond assessment under pure double shear, it proved to be applicable to conducting mixed-mode bond tests. The second phase of the work upgrades the so-designed test apparatus to make it convertible to bond testing of other variants (near-surface mounted [NSM] FRP bars/strips, fiber-reinforced cementitious mortar [FRCM], etc.) of strengthening systems without developing a different apparatus for each. The apparatus allows testing the NSM FRP-concrete bond in a novel manner compared to the traditional practice. Also, given the absence of mixed-mode studies for FRCM, the apparatus provides a pioneer means of conducting the same.