Beam-End Bond Tests and Bend Tests of Zinc-Clad No. 6 reinforcing Bars

Abstract

The bond strength of No. 6 zinc-clad bars was compared to that of uncoated conventional bars using beam-end tests performed in accordance with ASTM A944. The zinc-clad bars were also subjected to bend tests using bend diameters of 3.75, 4.5, and 6.0 in. (5, 6, and 8 bar diameters), as required for conventional and epoxy-coated No. 6 deformed bars, respectively, in accordance with ASTM A615 and ASTM A775. The zinc-clad bars provided bond strength equal to 94.9 percent of that exhibited by conventional bars from the same heat of steel. The difference in bond strength is not statistically significant. The two types of reinforcement exhibited similar force-bond slip behavior. The cladding exhibited significant local deformation and, in some cases, tearing following bond failure. Full-scale splice and bending strength tests on reinforced concrete members to compare the performance of clad and conventional reinforcement are recommended to develop design criteria for use in the ACI Building Code (ACI 318). The bend test specimens with the 3.75-in. bend diameter exhibited small transverse tension cracks in the cladding on the outside of the bend. Cracks ranged in length from 0.1 in. to one-half the circumference of the bar. One of six bend test specimens with the 4.5 in. diameter bend exhibited transverse cracking in the cracking at the outside of the bend. The crack was located on the cladding seam and had a length less than 0.1 in. No other damage was observed for the specimens with the 4.5 in. diameter bend. The bend test specimens with the 6.0-in bend diameter exhibited no visible damage to the cladding. To limit access of moisture and chlorides between the cladding and the underlying reinforcing bar, tightly fitting corrosion-resistant caps for the ends of the bars should be developed and marketed along with the clad reinforcement.