The Marquam Bridge in Portland, Oregon, provides a crossing of the Willamette River for the north-south I-5 freeway. After 17 years of service, the bridge, which was opened to traffic in 1966, had a badly worn deck and numerous deck expansion joints in need of repair. The bridge has a daily traffic count of approximately 86,000 vehicles. Because of lack of capacity of detour routes, complete closure to traffic could be permitted only during night hours. To correct the deck and joint problems, a contract was awarded in May 1983 for a latex-modified-concrete overlay and joint repair. On a previous job with a 3-percent grade, the tendency of the finished surface to shift downhill during the early cure stages was noted, and it was thought that this tendency could be a major problem on this structure with ramps on 6-percent grades and 0.10 ft/ft supers. Type III cement was suggested; it was tried and was found to be a workable solution. Narrow pour widths required by traffic staging were as significant a factor to surface irregularities as were the steep slopes. The pour widths also restricted the pour rate. Three years after completion of the overlay, a check on the wear was made. This found wide variation in the projected life due to traffic patterns and irregular wear in the individual wheel tracks. From the survey, a general conclusion can be made that the latex-modified-concrete has equivalent or possibly better wear resistance than the original concrete surface had. Also from this information and a similar survey on the I-205 Columbia River Bridge, a normal wheel track wear rate of 0.0313 In./yr per 10,000 average daily traffic (ADT) can be anticipated.
Samenvatting