Effect of Aggregate Size on the Bond Behavior between Carbon Fiber–Reinforced Polymer Sheets and Concrete

The influence of maximum aggregate size on the bond-slip behavior between concrete surfaces and carbon fiber–reinforced polymer (CFRP) sheets was investigated. A total of 78 concrete prisms ($150\times 150\times 200\mathrm{mm}$ ) were cast, and six concrete mixes were prepared with different maximum aggregate sizes (25, 19, 12.5, and 9.5 mm) and concrete compressive strengths (20, 30, and 40 MPa). The specimens were reinforced with CFRP sheets and tested under a double-shear test. CFRP sheet strips with different lengths, widths, and numbers of layers were externally bonded to the concrete prisms using epoxy. The effects of each factor on the bond behavior were investigated through the bond stress versus slip curves and failure modes. Experimental results showed that the maximum aggregate size highly affected the bond behavior. Both the bond strength and maximum slippage increased as the maximum aggregate size used increased from 9.5 to 19 mm. After 19 mm, the aggregate size no longer had significant influence on the bond strength. The main failure mode for specimens was debonding at the interface between the fiber sheet and concrete surface. The bond strength model proposed in the literature has been modified to consider the maximum aggregate size. The modified bond strength equation is capable of accurately predicting the bond strength.