A method for quality assurance of seven-wire strand bond in portland cement concrete

Abstract

Achieving good bond between prestressing strand and concrete is critical to ensure proper performance of pretensioned components. Unlike deformed nonprestressed reinforcements, which rely primarily on mechanical deformations to assist with bond, seven-wire prestressing strand is produced in a smooth helical form and must rely on chemical adhesion, mechanical interlock, and friction. Changes in the surface condition of the strand or the concrete mixture can produce significant changes in bond. Various strand bond tests have been developed, all of which have deficiencies in applicability, ease of use, cost, or sensitivity. A new test using direct pullout of tensioned strands is compared with existing tests and is shown to provide a sensitive, accurate, and low-cost test method for identifying bond quality differences due to changes in concrete or strand surface. © 2015 PCI Journal.