Bond Strength of Grouted Reinforcing Bars

Abstract

The effects of hole preparation method, grout type, hole diameter, bar size, embedment length, cover, reinforcing bar deformation pattern, bar surface condition (epoxy coated or uncoated), 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 pneumatic 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 11/z in. for No. 5 bars; ll/4 in. diameter holes are used for No. 8 bars. Embedment lengths range from 4 to 12 in. for No. 5 bars and from 6 to 15 in. for No. 8 bars. 11/z in. and 3 in. covers are used. Two deformation patterns bars are evaluated. Bar installations include vertical, sloped, and horizontal bars. Concrete strengths range from 2700 to 5900 psi. Test results are used to develop rational design and construction requirements. A standard test to, establish the Strength Class of a grout for anchoring reinforcing bars is proposed. In addition, a test method currently in use by one state department of transportation as a technique for prooftesting grouted reinforcement in the field is evaluated. 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 groutconcrete interface provide higher bond strengths than grouts that undergo failure at the groutconcrete 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 only slightly sensitive to reinforcing bar deformation pattern, and insensitive to the presence of epoxy coating. Vertically and horizontally anchored bars may exhibit different bond strengths, depending on the grout used. For the grouts tested, bond strength increases approximately with the square root of the concrete compressive strength. The proposed standard test method for establishing the Strength Class of a grout is incorporated in a conservative, easy-to-use design procedure. The test method evaluated for proof-testing reinforcement is not recommended because the failure modes are often different and the strengths are higher than those obtained under more realistic loading conditions. A modification to the test method is suggested.