International Concrete Abstracts Portal

A Sustainable built-environment requires a comprehensive process from material selection through to reliable management. Although traditional materials and methods still dominate the design and construction of our civil infrastructure, nonconventional reinforcing and strengthening methods for concrete bridges and structures can address the functional and economic challenges facing modern society. The use of advanced materials, such as fiber reinforced polymer (FRP) and ultra-high performance concrete (UHPC), alleviates the unfavorable aspects of every-day practices, offers many new opportunities, and promotes strategies that will be cost-effective, durable, and readily maintainable. Field demonstration is imperative to validate the innovative concepts and findings of laboratory research. Furthermore, documented case studies add value to the evaluation of emerging and maturing technologies, identify successful applications or aspects needing refinement, and ultimately inspire future endeavors. This Special Publication (SP) contains nine papers selected from three technical sessions held during the virtual ACI Fall Convention of October 2020. The first and second series of papers discuss retrofit and strengthening of super- and substructure members with a variety of techniques; and the remaining papers address new construction of bridges with internal FRP reinforcing and prestressing in beam, slabs, decks and retaining walls. All manuscripts were reviewed by at least two experts in accordance with the ACI publication policy. The Editors wish to thank all contributing authors and anonymous reviewers for their rigorous efforts. The Editors also gratefully acknowledge Ms. Barbara Coleman at ACI for her knowledgeable guidance.

A reinforced concrete bridge built in 1940 and located in Dallas, Texas, exhibited moderate to severe corrosion-related deterioration in the concrete bent caps. The damaged bent caps were repaired with epoxy mortar and externally strengthened with carbon fiber reinforced polymer (CFRP) laminates. Three-dimensional numerical models of the bent caps were created to better understand the cap behavior in bending and during various stages of the repair. The models were calibrated using data obtained from full-scale live load bridge testing. . The models were loaded until failure (rapid crack opening or CFRP debonding) to show the crack patterns, strain distributions and the bent cap capacities. The bent cap moment capacity increased by about 30% after repair/strengthening, because the original bent caps had extensive damage at the flexure-critical areas. The dowel-connected newer bent caps from the 1970 widened bridge contributed to the load sharing with the older bent caps.

Alternative reinforcement such as Glass Fiber Reinforced Polymer (GFRP) and Basalt (BFRP) are gaining popularity due to their corrosion resistant properties in extremely aggressive environments. The Florida Department of Transportation was concerned with the long-term durability of fiber resin systems in wet marine environments and restricted its use in submerged marine locations. This paper demonstrates the implementation of a pilot project after the thorough evaluation of a Fiber Reinforced Polymer resin prior to broader deployment of the alternative reinforcement. The paper focuses on the successful construction implementation to provide an archival reference document for future study and comparison to look at the long-term performance and integrity of the strengthening systems. During the execution of this pilot project, several lessons were learned and are demonstrated in this paper.

The Sunshine Skyway Bridge is recognized as the State of Florida’s “flagship bridge.” The goal of the Florida Department of Transportation (FDOT) and specifically its entity that maintains the Skyway Bridge, the District 1 & 7 Structures Maintenance Office (DSMO), is to extend the life of this bridge to 100 years. Beam cracking on the trestle spans have been noted since the 1990s. In 2005 the DSMO initiated an in-depth study to determine the cause of cracking and to recommend a repair procedure. Upon completion, a committee of FDOT staff from various key offices in the State, along with consultant experts, determined criteria to address these cracks. The repairs included epoxy crack injection, penetrant sealer, and carbon fiber reinforced polymer (CFRP) wrap installation. FDOT addressed the repairs in three phases. The first repair project was in 2009, the second in 2013, and the third and final began in 2019.

Following an over-height truck impact, Carbon Fiber Reinforced Polymer (CFRP) fabric was used to retrofit the exterior girder in a four-span Reinforced Concrete Deck on Girder (RCDG) Bridge on route KY 562 that passes over Interstate 71 in Gallatin County, Kentucky. The impacted span (Span 3) traverses the two northbound lanes of Interstate 71. While the initial retrofit was completed in May 2015, a second impact in September 2018 damaged all four girders in Span 3. The previously retrofitted exterior girder (Girder 4) suffered the brunt of the impact, with all steel rebars in the bottom layer being severed. Damage to Girders 1, 2, and 3 was minor and none of the bars were damaged. A two-stage approach for the containment and repair of the damaged girders following an over-height truck impact was implemented when retrofitting the bridge. The repair and strengthening of all the girders using CFRP fabric was the economical option compared to the alternative option of replacing the RCDG bridge. The initial CFRP retrofit was found to have failed in local debonding around the impact location. The CFRP retrofit material that was not immediately near the impact location was found to be well bonded to the concrete. The removal of this material and subsequent surface preparation for the new retrofit was time consuming and challenging due to traffic constraints. In Girder 4 all but one of the main rebars were replaced by removing the damaged sections and installing straight rebars connected to the existing rebars with couplers. One of the rebars could not be replaced. A heavy CFRP unidirectional fabric, having a capacity of 534 kN (120,000 lbs.) per 305 mm (1 ft.) width of fabric, was selected for the flexural strengthening and deployed to replace the loss in load carrying capacity. A lighter unidirectional CFRP fabric was selected for anchoring and shear strengthening of all the girders, and to serve as containment of crushed concrete in the event of future over-height impacts. The retrofit with spliced steel rebars and CFRP fabric proved to be an economical alternative to bridge replacement.