Bridge Deck Deterioration Study. Part 8. Special Study of Blue Rapids Bridge Deck

摘要

The location and progress of the spall and hollow plane type of damage occurring in a scale free air entrained concrete deck of a Pony truss bridge near Blue Rapids, Kansas was studied by 'tapping and mapping.' Maps were made twice each year between August 1961 and May 1964 to show the progress of the damage. These studies revealed that the damage increased far more during the winter than during the summer. Freeze-thaw of water entering a pre-existing plane was considered to be the major cause of the increase in damage. Freeze-thaw susceptible and alkali-reactive chert coarse aggregates caused popouts and contributed to the formation and extension of hollow areas and surface spalls. Vibrations due to live loads also contributed to the formation and extension of the fracture planes. Saw cuts were made through the concrete surface to the cleavage plane and a slab of the concrete surface was 'pulled out' to reveal the conditions in the plane. pH measurements revealed spots on the reinforcing steel of this and other bridges in Kansas that were quite acid with pH of e or less even though the pH of the concrete in general was 12 to 14. The low pH areas were usually associated with corrosion pits in the steel. (BPR abstract)