Influence of Coarse Aggregate Size on the Bonding between CFRP Sheets and Metakaolin-Based Geopolymer Concrete and Ordinary Concrete

Abstract

Geopolymers have been employed as a replacement material for cement in construction because they are better for the environment than are other replacement material options. In recent decades, externally bonded carbon fiber–reinforced polymer (CFRP) laminates have been used to strengthen or repair structures and improve their durability. The efficiency and reliability of a fiber-reinforced polymer (FRP) application depends significantly on the effectiveness of the bond between the FRP and the concrete substrate. This study examines the effect of the size of the coarse aggregate (5–10, 10–16, and 16–20 mm) on the bond between CFRP and metakaolin-based geopolymer (MKGP) concrete. The failure mode, failure load, distribution of strain along the bond length, maximum interfacial shear bond stress, effective bond length, local slip at the maximum interfacial shear bond stress, and bond–slip relationship between the CFRP sheet and the concrete substrate are investigated. Results show that the failure loads and maximum interfacial shear bond stress of MKGP specimens decreased with an increase in the size of the coarse aggregate, which can be attributed to the decreased splitting tensile strength of MKGP concrete with increasing size of the coarse aggregate. It was shown that this size affected the bond capacity between the CFRP and the concrete substrate and increased the effective bond length of ordinary Portland cement (OPC) and MKGP concrete by up to 24.5% and 46.8%, respectively. The average local slip between CFRP and MKGP concrete at the maximum interfacial shear bond stress increased with the size of the coarse aggregate, due to the decreased splitting tensile strength of MKGP concrete. Experimental results were used to recalibrate prevalent models used to calculate the effective bond length. Models to calculate the effective bond length are proposed that consider the influence of the coarse aggregate size. Popovics’s equations were employed to develop a relationship between the local bond stress and local slip by incorporating the effect of the size of the coarse aggregate. The findings of this study may contribute to the tailoring of bond behavior between CFRP and geopolymer concrete for engineering applications.