International Concrete Abstracts Portal

The use of Fiber-reinforced polymer (FRP) composite materials in new construction and repair of concrete structures has been growing rapidly in recent years. FRP provides options and benefits not available using traditional materials. The promise of FRP materials lies in their high-strength, lightweight, noncorrosive, nonconducting, and nonmagnetic properties. ACI Committee 440 has published several guides providing recommendations for the use of FRP materials based on available test data, technical reports, and field applications. The aim of these document is to help practitioners implement FRP technology while providing testimony that design and construction with FRP materials systems is rapidly moving from emerging to mainstream technology.

Lap splices are an easy to implement low cost method of transferring force between reinforcing bars in concrete structures. However, the bond between lap spliced bars is usually the weakest region in a reinforced concrete structure. Fiber reinforced polymer materials (FRP) are widely used to strengthen and repair lap splices because of their high strength, durability and ease of handling. Researchers have found that increased concrete cover provides an increase in bond strength similar to that supplied by wrapping with FRP sheets. Currently the FRP industry produces a new generation of high stiffness FRP sheets that provide a high degree of confinement and large increases in bond strength to lap splices.

This paper compares the effectiveness of wrapping with very high stiffness carbon FRP sheets (CFRP 900), wrapping with low stiffness glass FRP sheets (GFRP 430) and no wrapping on the bond strength of lap splice connections for various concrete covers. The test variables were the amount of concrete cover and the wrapping condition. The results showed that the GFRP wrapped beams had an increased in bond strength of approximately 25% compared to the unwrapped beams for each of the concrete covers. However, the CFRP wrapped beams had a percentage increase in bond strength that decreased as the concrete cover increased. The CFRP wrapped beams had increases in bond strength of 71%, 60% and 44% compared to the unwrapped beams for concrete covers of 20mm, 30mm and 50 mm, respectively.

This study investigates the effect of aggressive regime of 300 freeze-thaw (FT) cycles, at a core temperature range of +5 oC (+41 oF) to -18 oC (-0.4 oF) on the structural behaviour and bond integrity of concrete beams cast onto glass fiber reinforced polymer (GFRP) stay-in-place (SIP) structural forms. The study aims at comparing two configurations of the SIP forms, namely a flat plate with T-shape ribs and a corrugated plate, under the potential ‘frostjacking’ effect arising from FT cycles. The study explored specimens with no surface treatment, wet adhesive bonding to freshly cast concrete, and bonded coarse aggregates to enhance roughness of SIP form. It was clearly shown that flat-ribbed form specimens are superior to the corrugated form ones, as no loss in strength occurred after the FT exposure, whereas the corrugated form specimens lost 18-21%. This is attributed to the anchorage advantage provided by the T-shape rib embedment into concrete. Specimens with untreated corrugated forms showed strengths that are only 21-26% of treated ones. For flat-ribbed form specimens, the one with untreated form had 44% the strength of that with bonded aggregates.

This work presents an experimental investigation of composite girders consisting of precast Ultra-High Performance Fiber-Reinforced Concrete (UHPFRC) slabs placed on pultruded Fiber-Reinforced Polymer (FRP) Igirders. Two control girder specimens and seven large-scale composite girders were tested under static four-point bending. Two series of the FRP-UHPFRC composite girders were examined. H-series girders composed of hybrid carbon/glass FRP (HFRP) I-girders topped with either full-length precast UHPFRC slabs or segmental counterparts. G-series girders included segmental UHPFRC slabs placed on glass-fiber-reinforced polymer (GFRP) I-girders. Twelve precast UHPFRC segments were used in each slab of the segmental composite girders. Either high-strength mortar or epoxy adhesive were used to join the precast UHPFRC segments. The test results revealed that the flexural stiffness of the composite girder with the epoxy-connected segmental precast slabs is almost identical to that of the full-length precast composite girder. The mortar-connected girder exhibited slightly more ductile behavior than the epoxy-connected girder. The G-series girder with thick GFRP plate externally bonded to the soffit of the GFRP Igirder showed pseudo-ductile behavior. All the composite girders demonstrated significant improvements in flexural stiffness and moment-carrying capacity compared with the control FRP I-girders without the UHPFRC slabs.

The bond between external fiber reinforced polymer (FRP) reinforcement and concrete substrate is of critical importance for the effectiveness of this strengthening technology. As a result, the design of reinforced concrete (RC) members strengthened with FRP composites is to account for, among other failure modes, the debonding of the laminate from the substrate. Although analytical and experimental research conducted for over two decades has led to archival publications and guides, no standard test methodology is yet available for shear bond strength evaluation after aggressive environmental conditioning.

This paper aims at studying the durability of the bond strength between carbon FRP (CFRP) laminate and concrete substrate. The set-up consists of a small, plain concrete beam reinforced with an externally-bonded CFRP laminate that is tested under three-point bending. The force that the CFRP laminate can bear before detaching is easily calculated and the effect of accelerated conditioning is thus evaluated. Different environments and times of exposure are considered including 100% relative humidity, saltwater, alkali solution and dry heat. Statistical analysis are carried out to obtain statistical evidence on the effect of both the conditioning environment and the time of exposure on shear bond strength. The test methodology used in this work has the attributes of an effective standard.