Accelerated ageing tests and long-term prediction models for durability of FRP bars in concrete

Corrosion of steel reinforcement is the major cause of deterioration of existing reinforced concrete (RC) structures, resulting in significant expenses for repair and maintenance, and leading to shorter service lives. To address the corrosion problem, fiber reinforced polymer (FRP) bars have recently emerged as a promising solution not only for the rehabilitation of existing structures but also for the construction of new and more durable RC structures. But due to their versatile applications in harsh environments and exposure to high alkalinity content of concrete, the durability performance of FRP bars and their bond with concrete are major concerns. In this dissertation the durability of both FRP bars within concrete and FRP-concrete bond interface are studied, and effective evaluation and long-term prediction performance methods are developed to provide guidelines for design applications in practice.;First, a comprehensive evaluation is conducted of simulated accelerated ageing test environments and test specimens and methods, and effective testing procedures are recommended. Then, accelerated ageing tests on durability performance of GFRP bars embedded in concrete beams, subjected to sustained load and saturated moisture under several controlled temperatures, are used to develop and propose long-term prediction models and master-curves to be used in design. The degradation mechanisms are examined by microstructure and chemical composition analyses of scanning-electron microscopy (SEM) and energy-dispersive analysis of X-rays (EDAX). Service-life prediction procedures based on Arrhenius concept are given, including analyses to verify the validity of accelerated ageing tests used to satisfy the requirement of consistent degradation mechanism induced. For the first time, predictions are given for the long-term durability performance of GFRP bars in saturated concrete subjected to sustained loading, and the predictions agree well with other short-term studies and limited field data available.;Finally, the bond behaviors of FRP bars under direct pullout test are studied for different material compositions and surface characteristics. The effects of moisture, elevated temperature, and thermal cycles on bond behaviors are investigated. The environmental effects on concrete compressive strength, FRP-bar constituent materials, and bond interface are examined. To simulate the pullout failure process, a new concept is proposed to determine the local bond-slip law for FRP bars in concrete. The predicted bond slip curves from analytical and Finite Element methods are in good agreement with the results of pullout tests