Laser Profilometry For Concrete Substrate Characterization Prior to FRP Laminate Application

The use of fiber reinforced polymers (FRP) for reinforcement of aging and deteriorating concrete members has emerged as a viable and cost effective alternative to traditional repair and strengthening techniques to upgrade deficient structures to meet today’s design standards (Crasto et al., 1996; Myers et al., 2000). The load carrying ability of structures such as beams and columns can be enhanced by externally attaching the FRP laminates to the concrete surface. FRP laminates have high tensile strength to weight ratios and high stiffness, and can be easily installed by a manual layup process. Because fibers and resins are noncorrosive, they are ideally suited for the repair and retrofitting of concrete bridges and parking structures where high concentrations of chlorides from de-icing salts are found. Externally applied FRP sheets or laminates are impregnated in-situ and bonded directly to a concrete surface with an epoxy (see Figure 1). These FRP materials are often applied to provide additional flexural or shear strength capacity for deficient structures or structures where a change in the occupancy or usage occurs. The overall performance of the system and the parameters that affect delamination (see Figure 2) depend highly upon the quality of the bond between the concrete and the laminate. Experience has shown that when delamination of the FRP sheets occur at the substrate level, the load bearing capability of the strengthened member is compromised except when FRP laminates are used to confine members in axial compression. Research has indicated that the bond strength between the epoxy adhesive and the concrete depends on a number of factors including the material properties of the epoxy as well as the properties of the concrete substrate (Miller and Nanni, 1999). The strength of the epoxy is affected by how it is stored, handled, installed and cured. The epoxy -concrete bond strength is affected by the strength, roughness, and cleanliness of the prepared concrete surface. Ongoing research at the Center for Infrastructure Engineering Studies at the University of MissouriRolla is focusing on ways to reduce the incidence of de-lamination of FRP’s by developing new specifications for FRP installation.