Abstract
A non-destructive testing program has been designed to evaluate the integrity of the bond strength of plain concrete beams strengthened by Glass Fiber Reinforced Polymer (GFRP) Laminates. A series of concurrent static load and non-destructive testing experiments were carried out in the materials and testing laboratory at the college of engineering, Mataria, Helwan University, Cairo, Egypt. A total of 90 plain concrete standard beam specimens of dimensions 150 mm x 150 mm x 750 mm were constructed in the laboratory with three different design strength categories (38, 45, and 50) MPa. The beam specimens were strengthened by externally bonded GFRP laminates with various number of layers namely (3, 5 and 7) layers. In addition, the effect of debonding of the GFRP laminates was investigated by simulating it by variation in voids between concrete and laminates namely, (0, 30 and 60%). This study investigates the effectiveness of externally bonded GFRP laminates on the flexural strength of plain concrete beams by using Ultrasonic Pulse Velocity (UPV) device before and during loading until failure and their effect on the p-wave velocities. Four-point flexural tests were performed on the concrete beams, strengthened with different layouts of GFRP laminates and different percentage of voids at the concrete-laminate interface. The capacity of the beams and p-wave velocity were investigated. It was found that as the percentage of voids decreased, the capacity of strengthened concrete beams increased linearly. The reduction in voids enhanced the beam flexural behavior and controlled tension crack propagation. In addition, it was observed that use of GFRP laminates were more effective with higher concrete characteristic strength provided that debonding is not present. Finally, it was evident that the UPV technique was successful in detecting the variation in concrete p-wave velocity with strength and laminate layers variation.
Highlights
Strengthening of reinforced concrete structures by externally bonded FRP systems is a widely accepted technique [1]
This research article presents the results of an assessment of the behavior of concrete beams strengthened by Glass Fiber Reinforced Polymer (GFRP) laminates under four-point load concurrent with a non-destructive test using Ultrasonic Pulse Velocity (UPV)
The discussion will focus on four major parameters which are: Cracking and failure loads Load vs mid-span deflection relationships Strength vs UPV relationships Stiffness improvement index
Summary
Strengthening of reinforced concrete structures by externally bonded FRP systems is a widely accepted technique [1]. Correlations between the UPV and load-test results were established in a form of a family of curves that were useful in tracking the progression of damage due to increase in delamination. The quality of an FRP rehabilitation system is highly affected by its integrity, which includes the composite and the adhesive layer in the case of bonded strip, and the composite and the impregnating polymeric resin in the case of dry sheets and fabrics. Potential defects in FRP composites could affect the quality of the rehabilitated structures. The presence of such defects as voids, improper cure, debonds and delaminations is almost common during the manufacture and installation of the composite systems. The general effects of potential defects on the rehabilitated concrete structures are discussed by Kaiser and Karbhari [4]
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