N.D. Co. Hwy. 1 was a 6-mile repair project completed by Damon DeVillers, P.E., senior project engineer with Interstate Engineering of Wahpeton, N.D., and Merrill Engquist, Sargent County Hughway Superintendent assisting in the project.
According to DeVillers, the existing paved surface consisted of 2 in. of cold mix over approximately 2 in. of aggregate base. The minimal amount of base was suspected to be in poor shape. It was apparent that numerous seal coats had been applied to the roadway over the years. The pavement was rutting and it had a significant amount of transverse and longitudinal cracking. Bleeding was evident in major portions of the roadway. Alligator cracking and pavement breakups also were present in numerous areas. Isolated areas of subgrade failure were evident. The cross section was inconsistent and the road ride was very rough. This roadway is classified as a major collector. It receives a fair amount of truck traffic since it is a route from local farms to the elevators.A few options were looked at, including:
- A 1.5-in. bituminous overlay with an additional 0.5 in. to help fill some of the ruts at a cost of $621,000;
- A 3- to 4-in. bituminous overlay with 20-year life span at a cost of $947,000;
- A mill and blend with new and existing aggregate base; add a base stabilization chemical and two bituminous seal coats at a cost of $808,000;
- Reconstruct the entire roadway to new design standards, which would cost $1.5 million.
Sargent County decided to utilize the blended base and chemical stabilization method. This would provide the most benefit for Co. Hwy. 1, according to DeVillers. After the low bid for the blended base project came in at $1,068,710, the county decided to reject all bids and complete the project with their own forces.
With the blended base there would be no grading; therefore, there would be no environmental issues. New gravel would be added and blended with the existing bituminous pavement and aggregate base. Team Laboratory Chemical Corp.'s Base One Aggregate Base Stabilizer would be applied and two bituminous seal coats would provide a surface course. An MC-3000 oil would be used for the seal oil and a North Dakota Class 5 aggregate was used for the seal-coat aggregate to provide more stability to the roadway. All current problems would be corrected. It also was a good opportunity to try Base One with minimal risk, as the proposed typical section would provide a good base without the additional strength provided by Base One.
Future maintenance costs of the blended base roadway will be approximately the same as they would be for a bituminous paved roadway. According to Devillers, the county was able to complete the project for an estimated cost of between $70,000 to $75,000 per mile, or $420,000 to $450,000 for the 6-mile project.
"The stabilizing chemical definitely improved the stability and strength of the aggregate base, as demonstrated by the ability of the aggregate to resist rutting and potholing. Fine grading of the treated aggregate base could not be completed without sufficient moisture. The motor grader operators reported that it was more difficult to blade the treated base than an untreated base," said DeVillers.
"Observations in the field indicated that there was less dust caused by traffic on the treated base than on an untreated gravel road," explained DeVillers. "The double sealcoat makes the roadway look and ride like a normal seal-coated asphalt pavement roadway."