A predictive model for determining shear strength and shear fracture energy of FRP bars in alkali-activated slag seawater coral aggregate concrete

Abstract

Bond parameters between alkali-activated slag seawater coral aggregate concrete (ASSCAC) and fiber reinforced polymer (FRP) bars are necessary to be determined rationally for future service of the new concrete structures in marine environment. The intention of this paper is to develop a predictive model for determining the realistic local shear strength and shear fracture energy incorporating the heterogeneity and discontinuity in the interface region. First, central pull-out tests were performed to study the bond properties between FRP bars and ASSCAC. Ordinary Portland cement CAC (OPCAC) was prepared for comparison. It is found that the ribs on the bar surfaces were seriously abrased and the extent of damage was more serious in the ASSCAC. Subsequently, a microstructure characteristic parameter was introduced indicating the heterogeneity of the interface region and determined as the rib spacing on the bar surface according to the analysis of failure process. The shear crack propagation was discretized by a discrete number. The local shear strength and shear fracture energy were then linked to the maximum pull-out load via the microstructure characteristic parameter and discrete number. Once the maximum load was given from the test, the two bond parameters were conveniently predicted from each specimen. The results indicated that the predicted local shear strength was apparently higher than the maximum average bond stress which was usually used to represent the local shear strength in traditional methods. As the bond length-to-microstructure characteristic parameter ratio increased, the predicted local shear strength showed a certain reduction but the predicted local shear fracture energy was significantly enhanced because of the reduced boundary effect. Moreover, the predicted bond parameters of the FRP bars in the ASSCAC were generally larger than those in the OPCAC.