Bond evaluation of SRP strengthening system exposed to several harsh environmental conditions

Abstract

Bridge retrofitting is a billion-dollar industry. Thus, finding effective and economically feasible solutions to strengthen bridges that deteriorate to extend service life until replacement is feasible is a critical global need. There are several types of fiber reinforced polymers (FRP) based repair systems available now commercially to strengthen bridge members including systems that utilize carbon, glass, and now even steel fibers. The latter is a system most often referred to as steel reinforced polymer (SRP) and is considered fairly new to the bridge industry; yet a very promising system due to its close-to-carbon fiber strength, and close-to-glass fiber price. One current research gap for SRP has been the performance of this system relative to exposure to environmental conditioning and its overall durability resilience. In this work, the SRP strengthening system used both micro-fine galvanized and micro-fine brass coated steel fibers to externally reinforce concrete prisms using the recently published American Concrete Institute (ACI) 440.9R-15 approach to evaluate FRP bond behavior. Companion dog-bone style coupon specimens were also prepared using both SRP systems to examine tensile mechanical properties of the SRP system alone. Both types of specimens were exposed to several types of harsh environments including cycles of freeze-thaw, varying temperature, and cycles of humidity. The study investigated accelerated environmental exposure in an environmental chamber as well as direct real-time weather exposure. The environmental chamber involved subjecting the specimens to freeze-thaw cycles, cycles of varying temperature, and humidity cycles. For the real-time weather exposure, the specimens were exposed to daily weather for 12 months in Rolla, Missouri, USA where the city is moderately exposed to freeze-thaw, high-range of temperature fluctuation, and wide ranging humidity levels. The results of the flexural tests conducted indicated that the bond strength between the SRP and concrete interface was reduced by harsh environment. All conditioned specimens had a mode II or mode III bond failure, while the control specimens failed in mode I. Real-time weather specimens failed at lower deformation levels with less concrete-covered substrate than those conditioned in the environmental chamber. An ACI 440 style environmental reduction factor, CE, of 0.75 is suggested for wet-environment and 0.65 for highly aggressive environment based on the work undertaken in the overall study.