Project leader: Greg Isakson
Agency: Goodhue County Public Works
Problem: Counties run into a dilemma when the bituminous surface of older, narrow roads reaches failure but there are not sufficient funds to rebuild the road. Goodhue County uses full-depth reclamation on the old bituminous surface and places a new 4-inch mat of 2360 mix over the reclaimed material to improve the ride and obtain a desirable load capacity. But adding 4 inches to a roadtop with 3-to-1 side slopes will reduce the existing shoulder by 12 inches, which is undesirable for the safety of the finished roadway where the shoulders were narrow to begin with. The challenge was to increase ride and the load capacity of the road while maintaining or increasing the shoulder width.
Solution: The solution involves building strength down into the existing structure by adding an emulsion to the reclaimed surface materials compared to building strength by adding additional bituminous material above the existing structure. The experiment split a 6-mile road project with poor surface conditions into two segments for a comparison of these two procedures to determine if using the emulsion is a viable alternative to the existing rehabilitation procedure. The surface of the west half was refurbished using an emulsion and a thinner 2-inch overlay of 2360 mix, while the east half received the county’s conventional reclaim (with no emulsion) and a thicker 4-inch overlay of 2360 mix.
Procedure: Core samples were taken of the existing materials on the road, and mix designs with comparable GEs were developed. After milling 3 inches from the whole project, the west (emulsion) section was reclaimed to a depth of 6 inches and two additional passes were made to inject and incorporate the emulsion (at a rate of 4.5 percent). The east non-emulsion section was reclaimed to a depth of 4 inches.
Results: The final cost for the emulsified segment was $441,200 and the cost of the standard reclamation segment was $359,887. The surface of the emulsion-impregnated segment was rougher than the other because the reclaimed materials were not finished as well as the county would have liked before the emulsion set up. The final elevation of the emulsified section is 2 inches lower, which equates to a shoulder that is 6 inches wider.
Approximate Cost: $10,000
Implementation: This process could easily be implemented on other old road segments where a narrow shoulder is a major concern and regrading is not an option.
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