We recently experienced some problems on a bridge deck repair project that required partial- and full-depth patches. Two months after completion, the repairs were inspected, and the surface of many of the patches were worn and scaled. Compressive strength testing was done on cores taken from the patches, and some of the breaks were low. Throughout the project, heavy traffic was allowed to continue on the bridge. Could vibration of the deck caused by allowing traffic to continue have affected the concrete quality?
The effect of continuous vibrations on concrete quality was reported in "Traffic-induced Vibrations and Bridge Deck Repairs," Concrete International, May 1986. The study concluded that traffic-induced vibrations appear to have no detrimental effect on compressive strength in bridge deck repairs if high-quality, low-slump concrete is used. In fact, compressive strength appears to increase slightly for low-slump concretes when vibrated. However, for concrete having slumps greater than about 4 inches, the study found that vibration can be detrimental to compressive strength. The study suggested that higher-slump concrete will have significantly more bleedwater, which will rise during vibration. Therefore, high-slump concrete test specimens will have a layer of high-water-cement-ratio, low-strength concrete at the upper end of the cylinder. During the compression strength testing, this weaker concrete should dominate the cylinder strength.