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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.

Penetrating concrete sealers are often used on highway bridges and parking structures to slow down the rate of chloride-related reinforcing steel corrosion, thereby extending service life and reducing life-cycle structure costs. Silane sealers are the type most commonly used and are evaluated. Presents data on the effects of several variables on the resultant dampproofing performance and penetration depth. These variables include substrate conditions that influence sealer penetration depth, total active silane content, and the effects of subsequent silane retreatments. The Alberta Transportation and Utilities (AT&U) sealer evaluation methods that are used to measure dampproofing performance and effective penetration depth are described. Data show that the permeability of modern high-quality, low-permeability concretes can be significantly improved by silane sealers, whereas porous, high water-cement ratio concretes may be more effectively sealed by barrier coatings that seal the surface of porous concrete and do not penetrate. The concept and method of measuring the effective penetration depth is explained. Increasing the concentration of the active silane in a penetrating sealer improves both the effective penetration depth and the overall dampproofing performance on modern, good-quality concrete. Periodic resealing of the concrete with lower concentrations of silane results in a similar effect. Resealing can be successfully done through the previously sealed surface without expensive methods of surface preparation as long as the surfaces are clean and dry.

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.