Although newly constructed bridge decks on the state highway system contain epoxy coated steel, a possible avenue for corrosion remains because the epoxy coating may experience some deterioration prior to installation due to ultraviolet radiation or it may get chipped during shipping, storage at the job site, or installation. The corrosion problem may be even worse for South Dakota cities and counties as they use black steel (not epoxy coated). Beyond, the possible corrosion problem, newly constructed bridge decks and bridge deck overlays may be constructed with concrete mixes having a higher than desired permeability. Also, the mixes may not adequately resist sulfate attack, ASR, and drying and/or shrinkage cracking. Restrained shrinkage cracks are easily identifiable in newly constructed bridge decks when the forms are removed. These cracks occur frequently over the length of the deck (approximately every 5 to 6 feet).
Bridge deck overlays are a frequent form of maintenance for older decks. Most generally, these older decks contain black steel with the steel possibly having some degree of corrosion. The bridge deck overlay concrete should have a low permeability to minimize corrosion, resist sulfate attack, resist ASR, and have a low crack potential so that the deck's life can be extended for as many as 15 years.
Studies indicate that the inclusion of fly ash in concrete can result in a higher resistance to chloride intrusion (due to reduced permeability), less surface cracking, greater resistance to freeze-thaw deterioration, and resistance to ASR and sulfate attack. Therefore, there is a potential to reduce repair and replacement costs. Understanding the possible benefits of fly ash in concrete, SDDOT's Bridge and Materials Engineers have a desire to evaluate bridge deck and bridge deck overlay concrete that contains fly ash.
Although studies have indicated that Class F fly ash can improve the quality of concrete, trial bridge deck and bridge deck overlay fly ash concrete batches should be prepared and tested to determine if the properties are significantly increased beyond that of SDDOT's normal mixes. In addition, testing should be conducted to determine the effects of air content on permeability. If the optimized bridge deck and bridge deck overlay fly ash concrete mixes have significant improvement in the properties above, then the optimized mixes should be used in their respective field application. It is likely that the optimized bridge deck concrete mix could be used in the southbound structure on I-29 which will be monitored as part of SD98-06. A bridge deck overlay project would have to be identified so that the optimized bridge deck overlay concrete could be field tested and evaluated as part of this project.