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.

Flexural strengthening of Reinforced Concrete (RC) beams using fiber reinforced polymer (FRP) has become a common practice in the construction industry. Such strengthening is typically performed by attaching FRP laminates to the tension side of RC beams. In many occasions reaching the tension side of the beam can be a major challenge due to existing ducts as in buildings or the need of large scaffolds underneath the beam as in bridges. This challenge makes FRP strengthening an expensive alternative. In this paper, we suggest an alternative flexural strengthening method using a composite system made of Ultra High-Performance Concrete (UHPC) and Carbon Fiber Reinforced Polymer (CFRP) laminates for RC beams without reaching the tension side of the beam. In this technique, the accessible cover of the RC T-beam is removed, the CFRP laminates are attached to top side of the beam then a thin UHPC overlay is cast over the FRP. We show that the combination of UHPC and FRP allows the FRP to act as additional tensile reinforcement and increase the flexural capacity of the RC T-beams. The proposed method might be effective for shallow to medium RC T-beams specifically T-beams with very wide flange.

This paper presents the results of an experimental study conducted to investigate the effectiveness of a glass fabric reinforced cementitious matrix (GFRCM) composite system to strengthen reinforced concrete (RC) beams. A total of fifteen beams were tested in two groups: Group A was designed to investigate the use of GFRCM to rehabilitate corrosion damaged tension lap splices in RC beams. Group B was designed to investigate the use of GFRCM to strengthen shear critical RC beams. The test results demonstrated that GFRCM is a promising system to enhance the load carrying capacity of RC beams.