Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2009.Includes bibliographical references (leaves 90-98).Advanced composite materials become popular in construction industry for the innovative building design solutions including strengthening and retrofitting of existing structures. The interface between different materials is a key issue of such design solutions as the structural integrity relies much on the bond. Knowledge on durability of concrete/epoxy interface is becoming essential as the use of these systems in applications such as FRP strengthening and retrofitting of concrete structures is becoming increasingly popular. Prior research studies in this area have indicated that moisture affected debonding in a FRP-bonded concrete system is a complex phenomenon that may often involve a distinctive dry-to-wet debonding mode shift from material decohesion (concrete delamination) to interface separation (concrete/epoxy interface) in which concrete/epoxy interface becomes the critical region of failure. Such premature failures may occur regardless of the durability of the individual constituent materials forming the material systems. Thus, the durability of FRP-bonded concrete is governed by the microstructure of the concrete/epoxy interface as affected by moisture ingress. In this work, fracture toughness of concrete/epoxy interfaces as affected by combinations of various degrees of moisture ingress and temperature levels is quantified. For this purpose, sandwich beam specimens containing concrete/epoxy interfaces are tested and analyzed using the concepts of fracture mechanics.(cont.) Experimental results have shown a significant decrease in the interfacial fracture toughness of concrete/epoxy bond with selected levels of moisture and temperature conditioning of the specimens. The strength of adhesive joint degrades as implied by the failure mode shift from concrete decohesion in controlled specimens to interface separation in conditioned specimens. In this thesis, primary data on the mixed mode fracture toughness of concrete/epoxy interfaces are presented as a basis for use in the design improvement of material systems containing such interfaces for better system durability, and issues related to the structural implications are also discussed.by Tak Bun Denvid Lau.S.M
