Title:
Comparative Bond Strength of Coated and Uncoated Bars
with Different Rib Geometries
Author(s):
Bilal S. Hamad
Publication:
Materials Journal
Volume:
92
Issue:
6
Appears on pages(s):
579-590
Keywords:
bars; bonding strength; deformation; epoxy resins; pullout
tests; reinforcing steels.
DOI:
10.14359/9776
Date:
11/1/1995
Abstract:
The objective of this research program was to assess the effect of rib geom-etry on the relative bond-slip characteristics of coated and uncoated deformed reinforcing bars. The application of an epoxy-like paint coating, or any nonmetallic coating to the surface of a reinforcing bar would decrease the bond capacity by preventing adhesion between the bar and the surrounding concrete. Grade 60 plain round bars with a diameter of ,0.811 in. (20.6 mm) were machined to simulate #6 bars with a parallel or bamboo deformation pattern and with different deformation properties. After machining, and to simulate the effect of epoxy coating, a white enamel paint was applied to the bar to a thickness of around 8 mils (0.2 mm). ‘The bars were tested in rectangular eccentric pullout specimens. The variables were the bar rib face angle, rib spacing, rib height, and concrete strength. Failure of the pullout specimens was governed by splitting of the concrete cover over the anchored bar. Test results indicated that bond strength and bond-slip behavior of the coated bars varied with the bar rib face angle, rib spacing, and rib height. When the results were compared with tests performed on identically machined uncoated bars, optimum rib geometries were determined that would best improve the bond strength of coated bars relative to uncoated bars. The trends of the results were independent of concrete strength.