Bond Strength of Grouted Reinforcing Bars

Abstract

The effects of hole preparation method, grout type, hole diameter, bar size, embedment length, cover, bar surface condition (epoxy-coated or ncoated), orientation of the installed bar, and concrete strength on the bond strength of grouted reinforcing bars are described. Hole preparation methods, using a high-speed vacuum drill or a hand-held electric hammer drill, and cleaning methods, using a fiber bottle brush with water, a fiber bottle brush without water, or compressed air only are compared. Two capsule systems, two two-component grout systems, and two nonshrink grout systems are evaluated. Hole diameters range from 3/4 to 1-1/2 in. (19 to 38 mm) for No. 5 (16 mm) bars; a hole diameter of 1-1/4 in. (32 mm) is used for No. 8 (25 mm) bars. Embedment lengths range from 4 to 12 in. (102 to 305 mm) for No. 5 (16 mm) bars and from 6 to 15 in. (150 to 380 mm) for No. (25 mm) bars. 1-1/2 and 3 in. (38 and 75 mm) covers are used. Bar installations include vertical, sloped, and horizontal bars. Test results are used to develop rational design and construction requirements. The bond strength of grouted reinforcing bars is not highly sensitive to differences in the hole preparation or cleaning methods studied. Grouts that provide strong bond at the grout-concrete interface provide higher bond strengths than grouts that undergo failure at the grout-concrete interface. With the exception of bars anchored by capsule systems, the bond strength provided by grouts is not sensitive to hole diameter. Bond strength increases with increasing embedment length, cover, and bar size. The bond strength of grouted reinforcement is insensitive to the presence of epoxy coating. Vertically and horizontally anchored bars may exhibit different bond strengths, depending on the grout used.