Relationships Between Surface Roughness Indexes and Tensile Bond Strength Between CFRP Sheets and Concrete
Masakazu MITSUI, Kimio FUKUZAWA and Tatsuya NUMAO
Abstract:The FRP adhesion method which uses carbon or aramid fiber sheets for the strengthening of the flexural member of building or bridge has lately become a subject of special interest. The bond strength between the FRP sheets and concrete influences the structural properties of the concrete elements which are strengthened by this method. The strength may be classified into three types according to the direction of force : the shear bond strength, the cleavage bond strength and the tensile bond strength. The authors have reported on the relationship between the shear bond strength and the surface roughness of the concrete. The present study describes the experiments concerning the tensile bond strength and the relations between the bond strength and various surface roughness indexes. The surface roughness of concrete varied by changing the treatment methods, such as, sandpaper polishing, disk-grinding, sandblasting and chipping. Surface roughness indexes, the maximum depth Dmax, the superficial area St, the form factor k, fractal dimension Df and the bearing ratio curve were determined based on the 3D profile measurements of the concrete surfaces. The mechanism for bonding between the FRP sheets and concrete was discussed based on the surface roughness indexes and the observations of the fracture surface of the tested specimens. The conclusions which were obtained from this study are as follows : 1) The superficial area St has the greatest influence on the tensile bond strength among the surface roughness indexes, 2) the chipping treatment reduces the bond strength significantly, and 3) the tensile bond strength increases as the concrete strength increases. Key Words:FRP sheet, Tensile bond strength, Surface roughness index, Fracture surface, Surface treatment