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 role of concrete in the corrosion of steel in reinforced concrete has received a considerable amount of attention in recent years. This is due to the recognition of the strong relationship between the nature of the concrete and its ability to protect embedded steel. Therefore, in addition to some of the commonly used corrosion protection methods that focus on either coating the concrete, increasing the cover of the concrete, coating the reinforcing steel, or the use of inhibitors that change the nature of the surface of the reinforcing steel, other methods should be included that emphasize the role of the concrete mix design. Paper deals with the contribution of concrete to the corrosion of reinforcing steels in reinforced concrete. Twenty-six mix designs that represent concretes that could be used today were selected for study. Variables included cement content, water content, amount and type of fly ash, the addition of superplasticizers, and air entrainment. Strength and macrocell current were measured as a function of chloride exposure. The results of 1 year of cyclical exposure to 3.5 percent NaCl solution revealed that the concrete influences the corrosion process greatly. Furthermore, modification of concrete can become another method of corrosion protection through a better understanding of the relationship between the corrosion process and concrete mix design.

In recent years, corrosion of the reinforcement caused by chlorides, carbonation of the concrete, or low quality of the concrete cover has caused serious damage to concrete bridges. Apart from other measures, one possible means of repairing damage at the concrete surface due to reinforcement corrosion is to apply a coating to the concrete surface to reduce the water content of the concrete. If the coating has a sufficient high-penetration resistance against water and if no water enters the concrete from other sources, the water content of the concrete will remain low after the application of the coating, or the concrete will dry out slowly, provided that water can evaporate through the coating or through the opposite concrete surface. A multi-ring electrode method for determining the water distribution within the concrete near the reinforcement and the steel surface has been developed at the Institute of Building Materials Research in Aachen, Germany. The electrode is used to determine AC resistance between nine noble metal rings, allowing the water content to be estimated at eight different distances from the concrete surface. To estimate the effect of different types of coatings, time-dependent changes in resistance following wetting of coated and uncoated concrete surfaces were monitored. Fundamental laboratory investigations of the influence of concrete compositions, carbonation, and chloride application were also carried out.

The concept of applying electrical current to concrete to move chloride ions away from the reinforcement has been known for many years, but only recently have practical techniques been developed. Paper describes, in chronological order, the treatment and performance of three structures in Ontario and a summary of theoretical and model studies undertaken in support of the field activities. In 1989, a section of a large bridge pier was treated with a commercial electrochemical migration process developed in Europe. The same process was used to treat the spirally reinforced columns on a freeway overpass in 1990. An alternative electrochemical migration process, developed under a SHRP contract, was applied to portions of the concrete abutments of a bridge in Northern Ontario in 1992. A novel aspect of the treatment was the use of lithium borate in the electrolyte to suppress any negative effects of the treatment on alkali-silica reactivity in the concrete. Recommended criteria for the selection of candidate structures and for treatment parameters are presented.

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.