Compressive Strength of CFRP Composites Used for Strengthening of RC Columns: Comparative Evaluation of EBR and Grooving Methods

In the present study, application of carbon-fiber-reinforced polymer (CFRP) composites with fibers aligned along the column’s axis to improve compressive strength of reinforced concrete (RC) columns has been investigated. Global buckling of fiber-reinforce polymer (FRP) composite with fibers along the column’s axis may result in debonding of FRP from the column’s surface, and thus, the compressive load carrying capacity of the strengthened column would not be increased considerably. To limit the global buckling of composite under compression, a newly introduced strengthening method, named as grooving method (GM), was utilized in the present study and compared with externally bonded reinforcement (EBR) method using conventional surface preparation and near surface mounted (NSM) method. For this purpose, 22 circular RC columns with 150-mm diameter and 500-mm height were tested under uniaxial compression. Two techniques of GM named as externally bonded reinforcement on grooves (EBROG, to be pronounced as /ebrΛg/) and externally bonded reinforcement in grooves (EBRIG, to be pronounced as /ebrIg/) were used in the present study. Experimental results showed that grooving method considerably enhanced the columns’ maximum loads. It was also observed that the maximum compressive stress capacity of CFRP based on average compressive stresses of fibers in the composite was impressively increased when grooving method was used. The results showed that in the columns strengthened by EBROG method, nearly 80% of the fibers’ tensile strength in direct shear test could be utilized as compressive stresses in fibers of longitudinal composite; this value was about 13% and 16% when EBR and NSM techniques were used, respectively.