This report presents the results of a research project to evaluate the performance of six full-depth silica fume bridge decks, constructed between 1997 and 1999. The Minnesota Department of Transportation (Mn/DOT) constructed these decks to compare their performance and constructability in Minnesota, which involves the use of a seven-inch structural slab followed by a two-inch low slump overlay. Researchers conducted air content and slump field testing, visual inspections, and laboratory testing on chloride permeability, compressive strength, and hardened air system properties. In addition, they compared initial costs between the current deck system and the full-depth silica fume decks. The overall performance of the silica fume bridge decks has been good; however, two of the bridge decks did have problems related to the development of silica fume balls. Laboratory testing has shown that silica fume concrete performs better in terms of chloride permeability and compressive strength. Field tests have shown that placement of the silica fume concrete is comparable to a conventional concrete mix. Finally, cost comparisons have shown the placement of a full-depth silica fume deck to be slightly lower than the current deck system.
A section of Trunk Highway 23 near Mora, Minnesota, underwent concrete rehabilitation in 1998, which included the installation of retrofit dowel bars over a portion of the project. The Minnesota Department of Transportation (Mn/DOT) established several different test sections to evaluate the performance of different dowel bar configurations, group materials, and dowel bar lengths. During dowel bar installation, researchers monitored and evaluated construction procedures. They also conducted pavement testing before and after installation of the retrofit dowel bars to determine any immediate improvements to the joint performance. As expected, early age testing has shown improvements in joint load transfer efficiency after installation of the retrofit dowels. Testing also revealed that the rapid-setting mortar performed better than Mn/DOT's standard 3U18 patching mix. After only two years, there has been no noticeable differences in ride quality or faulting at the joints between retrofit and nonretrofit joints. Testing of pavements and joint performance will continue on a yearly basis to determine the long-term performance of the retrofit dowels.
