International Concrete Abstracts Portal

In this study, a procedure for interpreting impact-echo data in an automated, simple manner for detecting defects in concrete bridge decks is presented. Such a procedure is needed because it can be challenging for inexperienced impact-echo users to correctly distinguish between sound and defective concrete. This data interpretation procedure was developed considering the statistical nature of impact-echo data in a manner to allow impact-echo users of all skill levels to understand and implement the procedure. The developed method predominantly relies on conducting segmented linear regression analysis of the cumulative probabilities of an impact-echo data set to identify frequency thresholds distinguishing sound concrete from defective concrete. The accuracy of this method was validated using two case studies of five slab specimens and a full-scale bridge deck, each containing various typical defects. The developed procedure was found to be able to predict the condition of the slab specimens containing shallow delaminations without human assistance within 3.1 percentage points of the maximum attainable accuracy. It was also able to correctly predict the condition of the full-scale bridge deck containing delaminations, voids, corrosion damage, concrete deterioration, and poorly constructed concrete within 3.5 percentage points of the maximum attainable accuracy.

The influence of factors such as cementitious matrix characteristics, fiber inclination, and temperature on the interfacial bond between fiber-reinforced polymer (FRP) fibers and cementitious matrix are studied herein. It was noticed that use of glass fibers in the form of glass FRP (GFRP) composite fiber greatly improved the bonding mechanism over using just constituent glass fibers. With matrix maturity, a steady increase in bond was observed with over 60% bond strength achieved within a day. Densification of the cementitious matrix with the addition of silica fume was found to greatly increase the interfacial bond and changed the failure mode from fiber pullout to fiber rupture and delamination. At inclined loading as well, a different failure mode in the form of fiber rupture after partial pullout was noticed. This change in failure mode from fiber pullout to fiber rupture was also accompanied by a lower apparent tensile strength at large inclination. At lower temperature of –20°C, the bond between FRP fibers and the cement matrix was found to improve, but increased brittleness in fibers was also noted. At higher temperatures, FRP fibers performed satisfactorily up to 80°C, after which a gradual degradation in bond was observed.

The experimental results of a novel ultrasonic monitoring method to identify different types of flaws in reinforced concrete are presented. The authors’ previous work has demonstrated the ability to use the proposed ultrasonic guided wave leakage (UGWL) to identify the onset of mechanical delamination. This paper presents the results from using the UGWL method to identify chemical delamination (corrosion) and cracking in concrete (other than delamination at the steel-concrete interface) in reinforced concrete. The proposed UGWL method monitors the change in amplitude of ultrasonic waves leaked from a guided wave transmitted through an embedded steel reinforcing bar. The energy of UGWL is influenced by the conditions between the steel reinforcing bar, acting as the waveguide, and the surrounding concrete. This experimental study demonstrated that the UGWL monitoring method is sensitive not only to the onset of delaminations, but also to the development of corrosion activity and cracks.

The lack of durability in concrete repairs induces premature repair deterioration. Drying shrinkage of "new" repair material restrained by "old" concrete substrate results in repair layer cracking, and interface delamination between the repair and the concrete substrate. This paper investigates a material solution to these common repair failures. A high-early-strength engineered cementitious composite (HES-ECC) developed for concrete repair is employed for this study. The HES-ECC possesses high early-age strength (over 47 MPa [6885 psi] in 7 days) and high tensile strain capacity several hundred times that of normal concrete or fiberreinforced concrete (FRC). Experimental and numerical studies on a layered repair system were conducted to verify that the high ductility of HES-ECC can relieve shrinkage-induced stresses in the repair layer and at the repair/old concrete interface, thereby simultaneously suppressing large repair surface cracks and interface delamination. Detailed results of these studies are reported in this paper.

Fiber-reinforced polymer (FRP) composite materials have been proposed and used for the upgrade of concrete-based transportation and civil infrastructure. This technology has been proven to be effective, but issues related to bond length, end anchorage, and premature peeling have been a concern when strengthening structures in flexure or shear. This study presents two different types of FRP-based anchor system, namely, a near surface mounted (NSM) end anchor and a spike anchor. Each has been tested in an attempt to prevent or delay the problems listed above. A total of 16 specimens were tested to failure to check the effectiveness of the end anchor system and 19 specimens were tested to check the effectiveness of the spike anchor system. The focus of the study is on the influence of 1) the location, groove size, and anchor bar size for the first system; and 2) the location and embedment of the spike anchors for the second system. Test results show that each of these systems is highly effective in increasing the capacity of the strengthened member by delaying delamination of the FRP material. Bond-dependent coefficients of 0.90 (Km) and 0.25 (Kv) are recommendedwhen using these anchors for flexural and shear strengthening applications, after comparing the experimental results with the design guidelines.