International Concrete Abstracts Portal

SP-151 The Philip D. Cady International Symposium was held in Minneapolis, Minnesota, on November 9 and 10, 1993. The symposium volume includes 15 papers on concrete bridges in aggressive environments. The papers address the performance, protection, assessment, and the repair and rehabilitation of concrete bridges. The performance papers include the corrosion protection afforded by concrete bridge deck overlays, corrosion in prestressed concrete bridges, and the use of calcium nitrite in field structures. Protection papers address the performance of silane sealers, coatings, and waterproofers. Condition assessment technologies include measuring the corrosion rate of steel in concrete and the diffusion of chloride ions in bridge decks with overlays. Experiences in the repair and rehabilitation of concrete bridges by practitioners is also presented. The Philip D. Cady Symposium was sponsored by ACI Committees 345, 222, 515, and 201.

Describes investigation and design of repairs to the approach decks of the Verrazano Narrows Bridge in New York City. In addition, all the joints will be replaced, electric manholes and pull boxes will be rehabilitated, and new power and communications cables will be pulled. These bare concrete decks exhibit extensive deterioration in the form of spalls, cracks, leakage, and efflorescence. A total of approximately 787,000 square feet of deck area will be repaired; this includes approximately 150,000 square feet of deck replacement. Total estimated cost is $45 million, and the construction duration is 5 to 6 years.

Explains the technology developed by Alberta Transportation and Utilities for field prestressing repairs to precast, prestressed concrete bridge girders. This repair technique restores structural integrity quickly and cost effectively. Applications regarding high load impact damage and corrosion of prestressing strand are discussed, based on Reid Crowther's experience and application of this repair technique.

In the early 1960s, the city of El Paso constructed the Texas, Piedras, Raynor Street Bridge, a mile-long, four-lane artery leading to the center of downtown, and a main road important to many businesses and merchants. Time and the effects of chloride penetration from road salts, plus carbonation, took its toll on this bridge. Corrosion of the reinforcing steel led to spalls on pier caps and corrosion of columns, in addition to massive spalling and delaminations of the bridge deck and parapets. Early in 1990, a complete structural repair of the bridge was conducted. Attempts to repair the bridge were unsuccessful. Cracks and delaminations in the substrate and in the areas that had been repaired were evident. Due to safety concerns, the bridge was closed for structural repairs. Repairs began again in November 1991. The first stage of repair consisted of removing the previous failed materials and all unsound concrete. Once all areas were prepared, the low-pressure spraying of a structural, one-component, high-strength fiber reinforced, shrinkage-compensated product began. Three men were employed in the batching and spraying of the material--two at the hopper/mixing unit, and one operating the spray nozzle. Using a pump for placement, the contractor was able to realize a maximum of 3 yd 3 per hr. Workers with trowels followed closely behind the nozzle man, and, using a finishing aid, were able to finish the placement quickly and efficiently. Circular bridge piers were finished with a template to maintain the design cross section. A water-based curing compound was applied to insure maximum moisture retention and full hydration of the mortar. All patches were covered with thermal protection for 7 days, to allow for cure. Because the sprayed material adheres well, it performed exceptionally on all of the vertical and overhead repairs required on this bridge. Its excellent bond strength, outstanding structural properties, and low permeability provided the needed characteristics for this job. The sprayability of the product meant less labor required on the job and faster turnaround. Since this was the second repair of this bridge, these characteristics were very important. The product performed exceptionally well and resulted in a hard and dense repair.

The service life of latex-modified concrete and low-slump dense concrete bridge deck overlays is estimated by extrapolating historical performance data obtained from the results of field research and investigations conducted in the U.S. and Canada. The data suggest that when concrete removal criteria are based on half-cell potential rather than actual damage, when removal of chloride-contaminated concrete is extended to below the reinforcing bar, and when the substrate is sandblasted to remove microcracking prior to cleaning, a mean service life of 30 to 50 years is likely.