BOND OF EPOXY-COATED REINFORCEMENT - COVER, CASTING POSITION, SLUMP, AND CONSOLIDATION

The effects of concrete cover casting position, concrete slump, and de gree of consolidation on the reduction in bond strength between reinfo rcing bars and concrete caused by epoxy coating are described. Tests i nclude beam-end specimens containing No. 5, No. 6, No. 8, and No. 11 ( 16, 19, 25, and 36 mm) bars. Bottom-cast and top-cast bars with 1. 2, or 3 bar diameters of cover are evaluated. Concrete slump ranges from 2 1/4 to 8 in. (55 to 205 mm). Some specimens containing high slump co ncrete are not vibrated. The results of the study are used to develop improved development length modification factors for epoxy-coated bars . Epoxy coatings significantly reduce bond strength. However. the exte nt of the reduction is less than used to select the development length modification factors in the 1989 ACI Building Code and the 1989 AASHT O Bridge Specifications for bars with cover < 3 bar diameters (d(b)) o r a clear spacing < 6 d(b). The development length modification factor can be reduced from 1.5 to 1.35 for these bars. The relative bond str ength of epoxy-coated reinforcement increases as cover increases. As a result, the development length modification factor of 1.2 in ACI 318. 89 is realistic for epoxy-coated bars with a cover greater-than-or-equ al-to 3 d(b) and a clear spacing greater-than-or-equal-to 6 d(b) when combined with the 0.8 factor for bars with a clear spacing greater-tha n-or-equal-to 5 d(b) (ACI) or a center-to-center spacing greater-than- or-equal-to 6 in. (AASHTO). However the modification factor of 1.15 in the 1989 AASHTO Bridge Specifications is slightly unconservative for these bars and should be modified. The ratio of the bond strength of b ottom-cast bars to the bond strength of top-cast bars, B/T, is about t he same for coated and uncoated bars cast in low slump concrete. B/T i ncreases significantly for uncoated bars and decreases slightly for co ated bars as slump increases. As a result, the upper limit on the prod uct of the epoxy-coating factor and the top-bar factor can be reduced from 1.7 to 1.5. A lack of vibration has a negative effect on the bond strength of both coated and uncoated reinforcement in high slump conc rete. This is the third in a series of papers describing research at t he University of Kansas on epoxy-coated reinforcement. The research is aimed at gaining a better understanding of the bond of epoxy-coated r einforcement to concrete and developing design procedures that accurat ely reflect the changes in bond strength caused by epoxy coating.