Concrete Q&A: Concrete Cover for Unbonded Tendons


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Title: Concrete Q&A: Concrete Cover for Unbonded Tendons

Author(s): Post-Tensioning Institute (PTI) staff

Publication: Concrete International

Volume: 38

Issue: 1

Appears on pages(s): 72


Date: 1/1/2016

Q.I have a question regarding tolerances for concrete cover for unbonded tendons in post-tensioned concrete. Section of ACI 301-101 states: "Unless otherwise specified, concrete cover for the tendon end from the exterior edge of the concrete shall not be less than 3/4 in. for nonaggressive environments and 1 in. to the encapsulating device for aggressive environments." Section of ACI 301-10 also states the following regarding tendon tolerances: "Place tendons and anchorages within the tolerances of ACI 117 for reinforcement placement, distance between reinforcement, and concrete cover." However, ACI 117-102 does not appear to include any tolerances for the concrete cover for tendon ends in unbonded post-tensioning systems. Are there any such tolerances? Is there a separate concrete cover requirement for unbonded post-tensioned tendon ends that are angled at 45 degrees to the horizontal? I’m afraid that the stressing pocket might hold water if the building cladding allows moisture to penetrate to the slab edge.