Creep of Coated Reinforcing Bars in Concrete

Abstract

The creep properties of organic coated and uncoated No. 6 deformed steel reinforcing bars, embedded in concrete prisms, were measured for 2 yr with corresponding tensile stresses in the bars at the loaded ends of 15,000 psi (103 MN/m²) and 30,000 psi (206 MN/m²). Twenty-four reinforcing bars were included in the tests, consisting of: 18 bars coated (in duplicates) with nine different epoxy materials; two bars coated with a polyvinyl chloride material; and four uncoated reinforcing bars. Reforcing bars coated with six of the epoxy materials developed slip-time relationships (creep) after 2 yr of testing that were nearly the same as those for the uncoated bars. The remaining epoxy coated bars were judged to have poor creep properties. The excessive slip of the polyvinyl chloride coated bars in the concrete should preclude their substitution for uncoated reinforcing bars in concrete. The relative performance of some coated reinforcing bars in the creep study were different than those obtained in earlier pullout tests.