Static and Fatigue Bond Characteristics of Interfaces between CFRP Sheets and Frost Damage Experienced Concrete

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Title: Static and Fatigue Bond Characteristics of Interfaces between CFRP Sheets and Frost Damage Experienced Concrete

Author(s): J.G. Dai, Y. Saito, T. Ueda, and Y. Sato

Publication: Special Publication

Volume: 230

Issue:

Appears on pages(s): 1515-1530

Keywords: concrete; external bonding; fatigue; frost damage; FRP;relative dynamic elastic modulus

Date: 10/1/2005

Abstract:
Both short and long-term performances of repaired or strengthenedconcrete structures using external FRP bonding are greatly affected by states ofbonding substrates, which are covercrete and may have experienced various damages.One of them is frost damage in cold regions. This paper intends to investigate how theinitial frost damages in concrete influence the static and fatigue bond performances ofCFRP/concrete interfaces. Concrete specimens were exposed to freeze and thaw cyclesbefore being bonded with CFRP sheets. The initial frost damage of concrete wascontrolled approximately at three different levels in terms of its relative dynamicmodulus of elasticity, which was 100% (non frost damage), 85% and 70%, respectively.Test results showed that failure modes of CFRP/concrete bonded joints with initial frostdamage in concrete were the delamination of covercrete. By contrast the joints withoutinitial frost damage failed in a thin concrete layer as usual. Moreover, CFRP/concretejoints with and without initial frost damage showed different manners in their interfacebonding strength and stiffness. If the initial frost damage existed in concrete substratethe effective bond length of CFRP/concrete joints was increased due to the decrease ofthe bonding stiffness and interfacial fracture energy. Fatigue testing results indicatedthat the linear slopes of S-N curves of CFRP/concrete bonded joints were not influencedby the initial frost damage. The initial frost damage did not shorten the fatigue life ofCFRP/concrete joints if a same relative tensile stress level was kept in the FRP sheets,where the relative tensile stress level was defined as a ratio of the applied tensile forcein FRP sheets for the fatigue tests to the maximum static pullout one achieved in eachtest series.