Guide Design Specification for Bridge Temporary Works

DTFH61-91-C-00088Following the collapse of the Route 198 bridge over the Baltimore/Washington Parkway in 1989, the Federal Highway Administration (FHWA) established the temporary works research program. The program was guided by the Scaffolding, Shoring, and Forming Task Group as formed by the FHWA. The objective of this study has been to develop a guide design specification for use by State agencies to update their existing standard specifications for falsework, formwork, and related temporary construction. The guide specification was prepared in a format similar to the AASHTO Standard Specifications for Highway Bridge Structures

Final Report on the I-129 Missouri River Bridge Deck Condition Assessment Using Non-destructive Testing Methods [Project Title from Cover]

Field testing using various non-destructive testing (NDT) methods was performed on the reinforced concrete deck of the I-129 Bridge over the Missouri River in Sioux City, Iowa to provide a basis for comparing the NDT techniques and characterizing the current condition of the deck. The NDT techniques employed included visual inspections and sounding, infrared (IR) thermography, ground penetrating radar (GPR), impact echo (IE), and half-cell potential testing. The actual damage in the deck that was used to evaluate the NDT methods was estimated based on the mechanical sounding surveys, with core sampling to confirm these findings. In addition to confirming the NDT testing, core samples were also collected to determine chloride concentrations through the deck thickness. Based on this data and extensive measurements of concrete cover depths obtained using GPR, service life predictions were developed using a statistical model built on a finite difference-based approach for modeling chloride movement through the multi-layer deck of this bridge, which included a low-slump concrete overlay. Delaminations and spalls were observed in 1 to 2 percent of the deck top surface area; this damage was concentrated around transverse cracks and was typically caused by chloride-induced corrosion of the reinforcing steel. The low-slump overlay has effectively protected the reinforcing steel in the deck from chloride infiltration away from cracks, and service life analysis suggests that the service life extension provided by the highly impermeable low-slump concrete may be as high as 80 years when compared to typical bridge deck concrete alone. Repairs for this deck should focus on preventing further chloride ingress at cracked regions and on repairing existing damage. None of the survey techniques employed was wholly accurate. Aside from visual and sounding techniques, the two most accurate techniques, as applied to this bridge, were IE and IR thermography. IE testing was sensitive to misidentifying delaminations, in part due to the epoxy injection work performed previously on this bridge deck. IR thermography is inherently dependent on conducive weather, but was also adversely affected by epoxy residue on the deck top surface

Performance Evaluation of Recent Improvements of Bridge Abutments and Approach Backfill

TR-736A bump at the approach of a bridge is an undesirable characteristic that causes bad ride quality and high maintenance costs. To mitigate bump formation, the Iowa Department of Transportation (DOT) revised its standards according to a former study completed in 2005. This current study evaluated the effectiveness of these revisions by investigating eight bridges in Iowa constructed after 2005, two of which were stub bridges and six of which were integral bridges. One stub bridge and three integral bridges were subjected to a detailed investigation including visual and borescope inspections, coring, GPR assessment, and elevation surveying. The other four bridges were subjected to visual and borescope inspections only. The data showed that components of the abutments were generally in good condition and the joints in the approach slabs were in the poorest condition; many joints were in need of maintenance. GPR assessment detected voids under the approach slabs leading to the integral bridges, and showed that voids were more extensive at the shoulders than at the centerline of the pavement. The stub bridge investigated with GPR had relatively limited voids. Borescope inspection of the access ports confirmed the presence of the voids in the integral bridges. The relatively large extent of voiding under the integral bridges is attributed to cyclic compression of the backfill due to abutment movement and failure of the joint between the barrier and the approach slab due to large differential movements between the two components, which would permit bridge runoff to enter and erode the backfill. Despite the presence of the voids and failed joints, the bridge approaches performed well. Several recommendation were made to improve inspection practices and performance of approach slabs, including the use of GPR assessment to investigate voiding beneath the approach slabs, a new design detail for stub abutments, and sealing or eliminating the gap between the barriers and approach slabs

Use of Polymer Overlays or Sealers on New Bridges

5510GPolymer overlays and penetrating deck sealers are used as preventive maintenance options to extend the service life of concrete bridge decks. Overlays and sealers protect concrete structures from deterioration by inhibiting the ingress of chlorides, chemicals, and moisture and by slowing active corrosion. Identifying the optimum time for installation of overlays and sealers is key to maximizing the benefit to cost ratio of this type of maintenance. This report provides an overview and analysis of the use of polymer overlays and penetrating deck sealers to achieve extended service life objectives. It includes a description of the materials used as polymer overlays and sealers; recommended practices for application and installation; additional considerations for construction; service life modeling of various preventive maintenance options; and an analysis of the relative service life costs. The literature indicates that polymer overlays are often applied to bridge decks in good to moderate condition with a median age of 20 years, while for sealers the recommended practice is to apply sealers to new bridge decks 3 to 6 months after construction, with reapplication often scheduled after 4 to 5 years. Service life modeling and life-cycle cost analysis results indicate that the greatest extensions in service life of northern bridges with typical life of 50 years are obtained when sealers are applied shortly after construction and polymer overlays are applied within the first 5 years of service. For bridges with desired service life of 100 years, polymer overlays should be reapplied through the life of the deck, at 25 years interval or less. It is recommended that bridges with desired service life exceeding 50 years be analyzed on a case-by-case basis