International Concrete Abstracts Portal

While completing concrete repairs, is it necessary to remove sound concrete if a nearby reinforcing bar exhibits rust? Can terms like corrosion or rust be used interchangeably? This month’s Q&A provides answers to these questions as well as a discussion on various factors influencing the extent of a repair of corrosion-related damage in concrete structures.

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.

This paper presents an experimental study that investigated the physical and mechanical properties of the helical wrap glass fiber-reinforced polymer (GFRP) bars. The physical tests are conducted to check the feasibility and quality of the production process through the cross-sectional area and evaluation of the fiber content, moisture absorption, and glass transition temperature of the specimens. While the mechanical tests in this study included testing of the GFRP specimens to determine their tensile properties, transverse shear, and bond strength. Four bar sizes (#3, #4, #5, and #6), representing the range of GFRP reinforcing bars used in practice as longitudinal reinforcement in concrete members subjected to bending, are selected in this investigation. The GFRP bars had a helical wrap surface. The tensile failure of the GFRP bars started with rupture of glass fibers followed by interlaminar delamination and bar crushing. The bond strength of the GFRP bars satisfied the limits in ASTM D7957/D7957M. The test results reveal that the helical wrap GFRP bars had physical and mechanical properties within the standard limits.

This month’s Q&A focuses on the issue of delaminations caused by troweling of concrete. It discusses a “hard troweled” expression used by the industry, as well as the influence of concrete’s air content and using various power finishing equipment on blister formation and concrete delaminations.

CFRP reinforcement has become a consolidated technology in the retrofit of existing structures. Extensive experiments have shown that delamination of externally bonded CFRP plies governs their failure mode. To delay delamination, CFRP anchors are particularly attractive due to their wide range of applicability and large increases in strength and deformability. This paper presents a 2D finite element model for single-lap push-pull tests of concrete blocks reinforced with CFRP subject to monotonic loading. A numerical model is implemented to simulate the bond between CFRP anchors and concrete. CFRP anchors present a complex geometry and a combined tensional state of tangential and normal stresses. For these reasons it is difficult to determine a bond-slip law for CFRP anchors; however, with the proposed procedure the necessary parameters are obtained numerically, at a low computational cost. Experiments taken from literature with a single CFRP anchor are replicated and used to capture the parameters of the bond-slip curve for a particular anchor. The procedure is then validated with experiments with two and three anchors. The proposed procedure achieves reasonable results when comparing the obtained maximum strength achieved, the strains along with the CFRP reinforcement, and the anchor stress behavior with the experiments.