Improving durability of bridge decks by transverse prestressing

The principal objective of the study was to examine the concept of improving bridge deck design by the application of transverse prestressing and to specifically examine the improvement of durability due to protection from chloride-induced corrosion. The secondary objective was to provide structural design related recommendations for proper use of modern prestressing systems to ensure effective distribution of transverse prestress throughout deck slabs. To fulfill these objectives, the research was divided into three areas. The first area was the durability phase, in which the primary emphasis was the experimental investigation of prestressed concrete specimens exposed to an aggressive chloride environment. The second area was the structural phase in which both experimental and analytical studies were conducted to investigate the structural aspects of transverse prestressing. The final phase was the formulation of design recommendations for transverse prestressing which incorporated the findings from the structural and durability studies. The results from the durability study indicate that current specifications for the design of reinforced concrete decks which implicitly permit crack widths under service loads of 0.011 in. are inadequate for protection of steel reinforcement from chloride-induced corrosion. Transverse prestressing is effective in reducing corrosion because it permits a "crack-free" slab under service loads. However, to reduce the risk of corrosion from long-time exposure to an aggressive chloride-containing environment, a minimum concrete cover of about 2.5 in. over steel reinforcement and a maximum water-cement ratio of 0.45 in the concrete is needed. In addition, special attention must be given to the prestressing system to ensure full encapsulation and thus prevent penetration of aggressive corrosion-producing substances. The results from the structural study indicate that diaphragms have a significant effect on the distribution of stress in transversely prestressed bridge decks. To overcome the effects of diaphragms on transverse stress distribution, either the diaphragm can be prestressed or additional transverse prestressing in the deck slab over diaphragm regions can be used. The results from the design recommendation study indicate that transverse prestressing represents a viable and economical alternative for improving the durability of bridge decks. The proposed design recommendations should provide for a corrosion- and frost-resistant crack-free deck slab. The simplified procedures which were developed for determining slab and diaphragm forces required to overcome restraining effects should ensure effective distribution of transverse prestress throughout deck slabsCivil, Architectural, and Environmental Engineerin