Experimental assessment of the thermo-mechanical bond behavior of NSM CFRP with cement-based adhesives

Abstract

Cement-based materials, which are incombustible and show low thermal diffusivity, show great potential as a valid alternative to polymeric matrices for bonding near surface mounted (NSM) carbon fiber reinforced polymer (CFRP) systems for the strengthening of reinforced concrete (RC) structures. The performance of these materials in different loading conditions, including high temperature exposure, still needs to be better explored. This paper presents a study on the characterization of the bond behavior using cement-based adhesives and CFRP strips with innovative surface treatment. The CFRP strips used in this study were manufactured specifically with sandtreated surfaces to improve the bonding performance between CFRP and cement-based adhesive by taking advantage of the better grip of increased roughness surfaces. The results of the pull-out tests in ambient conditions, as well as exposed to elevated temperatures, are presented and discussed. The effect of using sand particles of different sizes, adhered with two different resins on the CFRP strips surface embedded in different cement-based matrices, was compared. The obtained results showed that by applying a sand treatment on the surface of CFRP strips, the maximum pull-out force was up to 12 times higher than when using smooth surfaced strips. Pull-out tests showed that, by using the NSM sand treated CFRP strips and CFRP bars with cement-based adhesive, an average bond strength up to about 9 MPa and 11 MPa, respectively, could be achieved. Thermomechanical pull-out tests showed the proposed strengthening system is able to withstand up to 30 min of heat exposure before bond failure.