Retrofitting and Rehabilitation of Bridge Components subjected to Predominantly Flexural Load using Thin UHPC shell

The number of bridges exceeding their design life is increasing every year and Federal Highway Administration estimates that structurally deficient and functionally obsolete bridges comprise almost 24% of total bridge inventory in the U.S. Besides aging, the existing bridges can sustain damages due to various factors including exposure to severe environment, deleterious chemicals, and overloading. To avert any catastrophic loss of property and life, it is imperative that the existing bridge inventory is rehabilitated and repaired at a minimal cost and at an expedited schedule using advanced construction methodologies and materials. One such advancement consists of the use of Ultra-High Performance Concrete (UHPC) which exhibits mechanical and material characteristics that can enhance the structural performance and durability. In addition, UHPC has low permeability, high durability and reduces the time of retrofitting which makes this material a good option for retrofitting the bridge elements. Despite superior properties, the material undergoes undesired failure modes warranting further research in methods to improve the bond characteristics. The objective of the research was to investigate the behavior of UHPC to retrofit existing concrete structures. To this effect, an experimental and numerical study on surface preparation techniques and bond mechanism with normal strength concrete was performed. The study also included a novel technique of surface evaluation which was developed using digital image processing and machine learning algorithms. Also, the durability of UHPC based on various percentages, orientations, and types of fibers was investigated. The outcome of these studies was used to design retrofitting of beam and deck elements. Different surface preparation methods were used to retrofit thirteen beams and results showed that mechanical connectors and sand-blasted surfaces can provide sufficient interface shear for composite action and resulting in an improvement of flexural performance. A large-scaled T-beam deck was also designed as a proof-of-concept to evaluate the feasibility of field implementation and carry out durability studies. To complement the results of experimental investigation and understand the mechanism of retrofitting methodologies, a comprehensive finite element model for simulating the UHPC mechanical characteristic and interface bond was introduced. At the conclusion of the study, design, and construction recommendations are provided for field implementation