Experimental Investigation of the Influence of Moisture on the Bond Behavior of FRP to Concrete Interfaces
Publication: Journal of Composites for Construction
Volume 14, Issue 6
Abstract
The effects of moisture on the initial and long-term bonding behavior of fiber reinforced polymer (FRP) sheets to concrete interfaces have been investigated by means of a two-year experimental exposure program. The research is focused on the effects of (1) moisture at the time of FRP installation, in this paper termed “construction moisture,” consisting of concrete substratum surface moisture and external air moisture; and (2) moisture, in this paper termed “service moisture,” which normally varies throughout the service life of concrete. Concrete beams with FRP bonded to their soffits were prepared. Before bonding, concrete substrates were preconditioned with different moisture contents and treated with different primers. The FRP bonded concrete beams were then cured under different humidity conditions before being subjected to combined wet/dry (WD) and thermal cycling regimes to accelerate the exposure effects. Adhesives with different elastic moduli were used to investigate the long-term durability of each adhesive when subjected to accelerated WD cycling. Pull-off tests and bending tests were conducted at the beginning of the cycling and then again after 8 months, 14 months, and 2 years of exposure so as to evaluate the tensile and shear performance of the FRP-to-concrete interfaces. It was found that the effect of the concrete substrate moisture content on short-term interfacial bond performance could be eliminated if an appropriate primer was used. All FRP-to-concrete bonded joints failed at the interface between the primer and concrete after exposure while those not exposed usually failed within the concrete substrate. After exposure to an environment of accelerated WD cycles, it was also found that the interfacial tensile bond strength degraded asymptotically with the exposure time while the flexural capacity of the FRP sheet bonded plain concrete beams even increased. The mechanism behind the above, which is an apparently contradictory phenomenon, is discussed.
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Acknowledgments
The writers gratefully acknowledge the financial support provided by the Grant-in-Aid for Young Scientists B, MEXT, Japan (Project No. MEXT-JP20760309) and by the General Research Fund (GRF) of Hong Kong SAR Government (Project Code No. UNSPECIFIED516509). The writers would also like to thank the reviewers for their very constructive comments and Professor Jin-Guang Teng and Dr. Lik Lam for their valuable discussion. In addition, the writers would like to appreciate the contribution of Nippon Steel Composite Co., Ltd., Japan for providing experimental materials and thank Mr. Makoto Saito for providing valuable information relating to the properties of adhesive materials.
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Published In
Journal of Composites for Construction
Volume 14 • Issue 6 • December 2010
Pages: 834 - 844
Copyright
© 2010 ASCE.
History
Received: Nov 16, 2009
Accepted: May 7, 2010
Published online: May 12, 2010
Published in print: Dec 2010
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