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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.

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.

The practice of prestressing steel has proven to be a very successful method of construction compared to conventional reinforced concrete in increasing load-carrying capacity, improving crack control, and slenderizing structural elements. However, corrosion in prestressed concrete has much more serious consequences than in normal reinforced concrete. Tendons are subjected to high mechanical stresses (often up to 70 to 80 percent of their tensile strength). Under an FHWA contract dealing with rehabilitation of prestressed concrete bridge components by nonelectrical methods, a comprehensive technology review focusing on corrosion of prestressing steel in highway structures was conducted and is summarized in this paper. Types of corrosion and recent theories explaining stress corrosion and hydrogen embrittlement are presented. Susceptibility of prestressing steel to corrosion in prestressed and post-tensioned concrete structures is covered. Factors such as concrete materials, prestressing steel, and environments, which may influence such corrosion, are categorized. Laboratory and field studies dealing with a variety of corrosion issues in pretensioned and post-tensioned concrete are also presented. These issues include the development and improvement of grout materials for bonded tendons in post-tensioned concrete members, use of epoxy-coated prestressing wires, and corrosion of unbonded tendons under severe exposure. Selected case histories and field evaluation of concrete bridges subjected to corrosion are also included. This study gives an overview of corrosion problems in prestressed concrete members and should help engineers to diagnose causes of corrosion and select the right methods and materials to be used for rehabilitation as well as in new constructions.

Calcium nitrite corrosion inhibitor has been commercially available in the U.S. since 1978. In that period of time, over 200 parking structures, 100 marine structures, and more than 230,000 m 3 (300,000 yd 3) of precast/prestressed bridge girders have been constructed with concrete containing calcium nitrite. In this paper, several of the oldest structures, along with several test sites, were evaluated to determine the corrosion performance. The condition assessment included a visual evaluation of the structure, determination of chloride and nitrite contents in the concretes, and determination of the corrosion activity. The corrosion tests consisted of corrosion potential mapping and polarization resistance testing to determine the corrosion rates at the time of the evaluation. These assessment techniques are applicable to all steel reinforced concrete structures with or without some modifications. The assessment showed that all of the structures with calcium nitrite are performing well. In two cases, there is evidence that corrosion is in progress on adjacent structures that were not protected with calcium nitrite. The nitrite analyses document that calcium nitrite is stable in concrete and remains at the reinforcing bars. Diffusion of chloride is not increased in the concretes with calcium nitrite, and there is evidence of a reduction in chloride penetration in some cases.

A field survey was made of the condition of prestressed concrete bridge elements located in adverse, potentially corrosive environments. A total of 12 bridges were included in the detailed study. Bridges were located in various regions across the U.S., including the states of Connecticut, Florida, Illinois, Michigan, North Dakota, Oregon, and Rhode Island. Locations included marine sites where elements are exposed to corrosive saltwater and sites where elements are exposed to deicing agents. Surveys utilized a variety of nondestructive testing and concrete sampling techniques. These included visual and photographic documentation, potential surveys, delamination detection, cover measurements, linear polarization measurements, petrographic examination, and analyses of chloride contents. Results indicated that exposures to corrosive agents varied significantly between inland and marine environments. In marine areas, the entire support structure is exposed to corrosive conditions, the magnitude of which vary with respect to proximity of the given element to the waterline and attendant spray conditions. In deicing areas, exposure is much more localized, occurring mainly at beam ends immediately below leaking expansion joints, or between beams in the case of box girder bridges. Properly maintained joints and drainage systems can help to eliminate manly problems that occur on prestressed bridges subject to deicing applications. In warm marine environments where elements are directly exposed to seawater, more positive protection systems may be needed.