Cause and Control of Transverse Cracking in Concrete Bridge Decks

摘要

Many concrete bridge decks develop transverse cracking and most of these cracks develop at early ages, some right after construction, and some after the bridge has opened to traffic for a period of time. Transverse cracks usually occur when concrete is set and widen with time. These cracks have been observed in most geographical locations, and on many superstructure types. It is estimated that more than 100,000 bridges in the United States develop early transverse cracks. These cracks are typically full depth located 1-3 m (4-12 ft) apart along the length of the span and are usually observed over transverse reinforcement. It has been reported that predominant form of deck cracking is transverse cracking. These cracks reduce the service life of the structure and increase maintenance costs, which is of paramount importance in highway maintenance activities. Transverse cracks accelerate reinforcement corrosion, especially in regions where deicing chemicals are applied. Corrosion damage has been observed even on epoxy coated reinforcing bars. Freeze-thaw cycles of water in cracks and leakage of water to supporting structures may also reduce service life of structure. Cracks in concrete occur when a restraint mass of concrete tends to change volume. Volume change in concrete depends on the properties of its constituents and their proportions as well as environmental conditions such as ambient temperature changes and humidity. Restraint, which is basically due to composite action of deck and girder, depends on design characteristics of the bridge (i.e., structural design factors). Construction techniques also contribute to volume change and/or to degree of restraint of concrete mass.