International Concrete Abstracts Portal

SP-188 This volume presents 24 papers from the Fourth International Symposium and represents a significant expansion in the state of knowledge that has occurred since the First Symposium in 1993.

Upgrading often becomes a necessity due to changes in usage of buildings due to factors such as deterioration and aging, change in occupancy, or the need for installation of facilities such as air-conditioning, heating, escalators, elevators, additional skylights, or new façade structures. In a number of cases upgrading is related to changes which affect the load bearing components of the structure. Fiber reinforced polymer matrix composites provide an efficient means of both strengthening slabs for enhanced load carrying capacity and for strengthening slabs after installation of cut-outs. This paper reports on a series of tests conducted to assess the comparative efficiencies of a commercially available strip form and a fabric form of material vis-à-vis strengthening ability and ductility. It is shown that material tailoring can result in significant changes in efficiencies. The extension of this to the rehabilitation of cut-outs is also detailed and aspects of an on-going full-scale test program in that area are elucidated.

Fiber reinforced polymer (FRP) is proving to be increasingly cost-effective as a solution for the repair and rehabilitation of substandard concrete structures. As the integrity of the repair is dependent on the FRP/concrete bond, its evaluation for both acceptance and long-term maintenance purposes is of obvious importance. FRP/concrete adhesion is currently evaluated from the more common tension test or the less used shear test. In either test, a metal disk called a dolly is bonded to the FRP surface. The force needed to separate the dolly under tensile or shear loads is used to determine the FRP-concrete interface adhesion. The similarity of the procedures for the two tests suggests it would be logical to develop a single device that could be used to conduct both in-situ tension and shear tests. This paper describes the basis and development of a new device that allows both tension and shear tests to be carried out in-situ. The device is simple to use and only requires an instrumented socket wrench to apply the separation load. Preliminary results from tests carried out to assess the role of different surface finishes on the FRP/concrete bond are presented to demonstrate the application of the device.

The use of non-metallic bridge deck reinforcement is of interest in regions where corrosion is a problem. A number of manufacturers have developed GFRP rebar for this application. Because the production of the material is relatively new, there is a great deal of variability among the products from different manufacturers. In addition, as the manufacturers continue to develop their own product, variations in GFRP from single manufacturers have been observed. The objective of this study was to investigate the bond between GFRP reinforcement and concrete using inverted half-beam specimen. The inverted half-beam specimen were designed to simulate the conditions likely to be found in a bridge deck (no transverse reinforcement and small concrete cover). Products from two different manufacturers were chosen for the study because of the widely varying characteristics of the product. One manufacturer produced reinforcement with surface deformations created by a helical wrap of glass fibers around the GFRP bar; the other manufacturer developed a ceramic coating that emulated the surface texture of a deformed steel bar. The two different bar types exhibited different bond behaviors. The bond for the bars with the ceramic deformations relied most heavily on mechanical interlock, as was evident from cracking patterns. The bond for the bars with the helical wrap deformations relied most heavily on friction. Both bar types demonstrated large variability for the bond specimen that failed in bar fracture, with some bar failure loads more than two standard deviations below the average bar tensile strength.

An experimental study on bond strength of Continuous Fiber Sheet (CFS) was conducted. Based on the experimental results the bond strength and various factors are clarified. Bond strength does not increase with bond length for bond length longer than 100 mm. As CFS stiffness increases, the maximum local and average bond stresses at delamination increase and CFS strain gradient decreases. CFS with a narrower width has a bond strength greater than that with a wider width. Non-uniform loading decreases the bond strength, however anchor steel plate with tensioned bolt increases it due to the bond between steel plate and CFS and confinement from the bolt. From the observed bond stress in CFS, the equation to predict the maximum local bond stress was proposed.