International Concrete Abstracts Portal

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.

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.

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.

The importance of solvent- and plasticizer-free sprayable PU elastomers in the field of waterproofing of concrete structures has increased considerably over the last 10 years. Due to their excellent mechanical properties, their resistance to hydrolytic and microbial attack and chemical resistance, waterproofing membranes produced from spray-applied PU elastomers have proved to be very successful in many application areas in the building industry. Report deals with the chemical development of the PU system, the optimization of the processing technique, including the methods of preparing the concrete's surface to get good adhesion values and a seamless, watertight elastomeric membrane, the spray process itself, and the recommended machinery. Special attention is given to the influence of environmental conditions, such as temperature and relative humidity, on the mechanical properties and the performance of the waterproofing membrane in service. As the most important field application for spray-applied PU elastomers in Europe, bridge deck waterproofing membranes are discussed with special reference to the requirements set out in the regulations of the German "Bundesministerium fur Verkehr" and the "Bundesanstalt fur Materialprufung." The performance of spray-applied PU elastomers as waterproofing membranes for roofs, terraces, terracing in sports arenas, and car parks is discussed.