, Associate Professor, UMD-Civil Engineering
Post-installed reinforcement is used to connect a new concrete member to an existing concrete structure. Typically, uncoated rebar post-installed with a chemical adhesive is used in these applications, which may lead to corrosion. Departments of Transportation and local bridge owners have used and continue to use epoxy-coated rebar in post-installed applications due to its inherent corrosion resistance. Unfortunately, chemical adhesive manufacturers provide tensile strengths of their products for use with uncoated rebar and not epoxy-coated rebar. This project examined what effects the epoxy coating had on the tensile pullout strength and compared the results for epoxy-coated and uncoated rebar. Two slabs were constructed. One slab contained epoxy-coated rebar post-installed using four different chemical adhesive products and the other slab contained uncoated rebar post-installed using the same four different chemical adhesive products. Results indicated that the epoxy coating slightly reduced the tensile pullout strength of the post-installed rebar. The ratio of the tensile pullout strength of the epoxy-coated reinforcing bars to the tensile pullout strength of the uncoated reinforcing bars ranged from 0.94 to 1.05 and varied based on the chemical adhesive manufacturer. Results from t-test analyses indicated that differences in the tensile pullout strength for epoxy-coated rebar compared to uncoated rebar were statistically different when using three of the four chemical adhesives during installation. Recommendations were made to include a modification factor when calculating bond strength for an epoxy-coated reinforcing bar post-installed using chemical adhesives and to raise the MnDOT-specified uncracked bond stress (τuncr) of 1,000 psi or use the manufacturer published values for τuncr.