International Concrete Abstracts Portal

This paper presents an overview of an experimental study to determine the oxygen barrier characteristics of materials used for infrastructure repair. In the study, a new diffusion cell was developed and a quasi-steady state model used to determine oxygen permeation constants. Results obtained are in broad agreement with the limited published data available. The study found that epoxy was a better oxygen barrier than FRP, with concrete being the poorest. However, bonding FRP to a concrete surface significantly reduced its oxygen permeability. This finding explains why FRP slows down but cannot stop chloride-induced corrosion of steel in concrete. A parametric study was conducted to evaluate the performance of FRP-concrete systems for differing FRP/concrete oxygen permeability combinations. It was found that the greatest reduction in corrosion rate occurred in concretes with the highest oxygen permeability. This result makes it possible to custom design FRP-concrete corrosion repair systems.

This paper presents the development of composite beams using hybrid CFRP/GFRP (HFRP) I-beam and Normal Strength Concrete (NSC) slab and precast Ultra-High Performance fiber reinforced Concrete (UHPFRC) slab. UHPFRC has high strength and high ductility allowing for a reduction in the cross-sectional area and self weight of the beam. A number of full-scale flexural beam tests were conducted using different dimensions of slab and with/without epoxy bonding between the slab and HFRP I-beam. The test results suggested that the flexural stiffness of composite beams with bolted and bonded shear connection is higher than that with bolted-only shear connection. Delamination failure was not observed in the compressive flange of the HFRP I-beam and the high tensile strength of CFRP in the bottom flange was effectively utilized with the addition of the UHPFRC slab on the top flange.

FRP Uwraps have been successfully used for shear strengthening of concrete structures; by contrast, few studies have focused on the use of the Uwrap as an anchorage system for FRP flexure strengthening. This study focuses on exploring the limitations and advantages of using non-contact measuring techniques, such as digital image correlation (DIC) and thermography, to characterize the deformation of FRP Uwrap anchors. Digital and thermo images were used to evaluate the slip profiles and debonding propagation of FRP Uwrap anchors on a pull-out test configuration. Results indicated that the geometry of the Uwrap plays an important factor in controlling the delay or arrest of the debonding propagation of the externally bonded FRP sheet. The DIC technique was capable to accurately measure slip along the bonded FRP sheet whereas the thermography technique was successful at capturing the debonding propagation (in two directions), as well as the locations of stress concentrations and fractured areas.

This paper examines the pre-application of a waterproofing slurry overlay on the performance of bonded CFRP strengthening systems. Overall, the waterproofed specimens experienced an undesirable bond failure between the adhesive and waterproofing coating and/or concrete substrate and less flexural capacity compared to the control specimen with only the CFRP composite. The control performed at a higher strength and resulted with concrete substrate failure. Due to the influence of moisture during the waterproofing slurry system application, further experimentation was performed to isolate the effect of moisture in the concrete specimens and its effects on the adhesive component as a performance factor. The moisture tests resulted in bond failures and lower strength capacities. The waterproofing application was altered relative to the manufacturer’s recommendations to accommodate an on-site construction protocol. Future research will vary curing time, active waterproofing compound, and on-site construction prior to applying the CFRP composite system to further improve performance.

The external confinement of reinforced concrete (RC) columns by means of externally bonded fiber reinforced polymer (FRP) laminates is a well established technique for strengthening and retrofitting purposes. This paper presents a pilot research that includes laboratory testing of full-scale square and rectangular (with side-aspect ratio smaller than 1.5) RC columns externally confined with glass and basalt-glass FRP laminates and subjected to pure axial load. Specimens that are representative of full-scale building columns were designed according to a dated ACI 318 code (i.e., prior to 1970) for gravity loads only. The study was conducted to investigate how the external confinement affects peak axial strength and deformation of a prismatic RC column. The results showed that the FRP confinement increases concrete axial strength, but it is more effective in enhancing concrete strain capacity.