New concrete anchors for carbon fiber-reinforced polymer post-tensioning tendons - Part 1: State-of-the-art review/design

In post-tensioning applications, carbon fiber-reinforced polymer (CFRP) tendons are prone to premature failure when used with anchors developed for steel tendons. The sharp corrugations of the wedges of these anchors bite into the CFRP tendon that then splinters due to its low shear strength. It was decided to develop a new nonmetallic anchor for CFRP post-tensioning tendons to overcome the problem of premature failure and to provide a completely metal-free (noncorroding) post-tensioning system. As with conventional steel anchors, the new anchors hold the tendons through mechanical gripping but without the corrugations between wedges and tendons. Each anchor consists of an outer barrel with a conical bore and four wedges. The anchor components are made of ultra-high-performance concrete (UHPC) developed specifically for this anchor, and the barrel is wrapped with CFRP sheets to provide the confinement required to utilize the strength and toughness of UHPC fully. The new concrete has compressive strengths in excess of 200 MPa together with excellent durability and fracture toughness. Three mm chopped carbon fibers were incorporated into the UHPC to enhance its fracture toughness. A comprehensive review Of the state of the art of anchors for prestressing FRP tendons is introduced herein, followed by design of the new concrete anchors for post-tensioned CFRP tendons.