Repair of Structures Using UHPC
Presented By: Peter Weber
Description: Conventional reinforcing and strengthening methods for bridges and structures are coming with many limitations. These include increased self-weight of structure which consequently requires additional strengthening of the support structure, limited lifetime of repair and short periods between repairs, uncertain strength of the reinforcement, extended time of repair and typically a heavy carbon footprint based on the materials used. Application optimized UHPC solutions have shown the potential to replace traditional methods over the coming decade. This is driven by the excellent mechanical properties of UHPC, superior bonding strength of UHPC to underlying concrete and steel, and the limited thickness of UHPC layer required. In addition, further protective layers against water/ chloride penetration are not required due to the denser, low porosity and lack of capillary water transport through the UHPC system. Based on overall cost of a given enhancement project, UHPC based solutions can already compete today but require certain specialized equipment and trained workforce creating real and perceived barriers. As availability of ‘standard’ UHPC solutions is increasing and contractors become more knowledgeable, these barriers will disappear to make room for advanced concepts of repair and strengthening. Changes in Building Codes will be required to take full advantage of the available benefits of UHPC based solutions.
Impact Damage Retrofit of RC Bridge Girder Previously Retrofitted with CFRP Fabric
Presented By: Issam Harik
Affiliation: University of Kentucky
Description: Following an over-height truck impact, Carbon Fiber Reinforced Polymer (CFRP) fabric was used to retrofit the exterior girder in Span 3 of a four-span Reinforced Concrete Deck on Girder (RCDG) Bridge. 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. 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. 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. The retrofit with spliced steel rebars and CFRP fabric proved to be an economical alternative to bridge replacement.
FRP Strengthening and Evaluation for Corrosion Deteriorated Bridge Bent Caps on US-80 Bridge near Dallas, TX
Presented By: Nur Yazdani
Affiliation: University of Texas at Arlington
Description: Deterioration of old concrete bridge bent caps due to spalling and rebar corrosion is a common occurrence. Compared to superstructures, the deterioration of bridge substructures and associated repair/strengthening/evaluation has received much less attention in the past. This study was focused on such a bridge, built in 1940 and located near Dallas, Texas. The bridge exhibited moderate to severe corrosion related concrete deterioration in the reinforced concrete bent caps. Eight such bent caps were selected for repair, carbon FRP strengthening for strength gain and confinement, long-term durability and evaluation. The investigation consisted of three aspects: static load testing of deteriorated bent caps before any repair/strengthening of the bent caps using an epoxy mortar and longitudinal/transverse CFRP laminates, and follow- up load testing after repair/strengthening. Test data comparison showed that the maximum flexural strains decreased significantly, in the range of 20 - 40%, after mortar repair and CFRP strengthening in the two bent caps with the highest deterioration, with both lanes loaded. However, the recorded strain readings under the applied live load were small, suggesting stiff bent caps with short spans, deep sections at D-regions and rigid monolithic pier supports.
FRP Retrofitting and Non-Destructive Evaluation for Corrosion-Deteriorated Bridges in West Virginia
Presented By: Wael Zatar
Affiliation: Marshall University
Description: Many aging concrete bridges across the United States have exhibited severe deteriorations and in urgent need of rehabilitation, retrofitting or replacement. The deterioration is caused by a combination of factors including corrosion of reinforcing steel, freeze-thaw damage and chloride/water ingress. Fiber-Reinforced Polymer (FRP) composite fibers, laminates, reinforcing bars and prestressed tendons have been successfully employed in civil infrastructure applications in the past three decades. The State of West Virginia has one of the highest percentages of structurally deficient bridges in the United States and this presentation covers a few case studies of the use of FRP composites for rehabilitating the State’s deficient bridges. Non-destructive ultrasonic pulse echo testing is employed to map reinforcing rebars and detect internal defects of three reinforced concrete slabs and to reliably evaluate the condition of FRP retrofitted bridge elements as well. A software, that employs the modified synthetic aperture focusing technique (SAFT) image reconstruction algorithm and signal processing, is developed to effectively visualize the reinforcing rebars, delamination, voids and debonding of rebars.
Bridge Substructure Repairs with Basalt, Carbon, and Glass FRP Internal Reinforcement
Presented By: Mohit Soni
Description: The restriction was in place for the usage of GFRP bars due to reaction of GFRP bar resin with chlorides. This project Lifted the restrictions on use of GFRP bars within the splash. The US 17/Trout River project in Duval County, FL. includes Utilization of GFRP bars in lieu of traditional grade 60 steel rebar in a variety of settings, including in conjunction with Shotcrete; in the splash zone; with traditional pour in place construction methods; and removal of concrete from GFRP bars. The SR 312/Matanzas in St. Johns County, FL includes Utilization of GFRP rebar and Basalt Reinforcing Mesh in lieu of traditional Grade 60 rebar in variety of settings including in conjunction with Shotcrete; in the marine environment; and with traditional pour in place construction method and opportunity to explore the removal of concrete from basalt bars. Innovations unique to this project includes: Use of GFRP in conjunction with Shotcrete, GFRP bar use in the marine environment, Use of Basalt Mesh in conjunction with GFRP, and Use of Ribbon Anode in Footings.
Shear Strengthening Sunshine Skyway Trestle Spans with CFRP
Presented By: Atiq Alvi
Affiliation: T.Y. Lin International
Description: Due to the appearance of diagonal cracks on the most exterior prestressed beam on the Sunshine Skyway low-level trestle span approaches, Florida DOT implemented three progressive shear strengthening rehabilitation projects between 2007 and 2019. The first beam strengthening project completed in 2009 was designed by SDR and was the first time large-scale beam strengthening used in Florida. A second project designed by PB in 2013 improved the CFRP shear strengthening by using through drilled anchor points to prevent disbanding at the inside angles of the beam bottom flanges. The latest and most extensive project designed by T.Y.Lin, was similar to the previous but also allowed an option of self-adhesive CFRP to improve quality control in the field. The contractor eventually chose the conventional wet layup method. Other findings from the design and construction will be presented.