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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 linear polarization technique has been used in the laboratory for corrosion rate measurements of reinforcing bars in concrete, but some modifications are needed for its application to structures in the field. A new device has been developed, using this technique with a sensor-controlled guard ring to measure corrosion rates in concrete structures. Describes the performance of this device and its application. It also summarizes some results from reinforced concrete structures, including bridges, in Europe and the U.S.

A computer simulation study of the penetration of chloride through concrete bridge decks with overlays was undertaken. The chloride transport was modeled as apparent diffusion. The apparent diffusion approach was based on the analyses of chloride concentrations obtained from field measurements. Part of the field data included untreated concrete decks and decks overlaid with latex-modified concrete, low-slump dense concrete, or microsilica concrete. The overlay field data was limited in number and repair details. In particular, the overlay data base did not include three significant details: the amount of original deck material removed, the thickness of the overlay placed, and the resistance to chloride penetration of the overlay material versus the original deck material. Consequently, a computer simulation was used to investigate the impact these three repair details have on enhancing the service life of a deck repaired with an overlay. Quality of material was defined by the apparent diffusion constant, a measure of the resistance to chloride penetration. The ranges for apparent diffusion constants were estimated from the overlay data base. Service life was defined as the time required to reach a critical chloride threshold level.

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.