Eric Urness, P.E., central regional vice president with Interstate Engineering in Mandan, N.D., was working on plans to reconstruct a 11.5-mile section of BIA Rte. 6 from 86th Ave. to 31st Street in Mountrail County, N.D. Due to the recent growth of the oil industry in this area there has been a huge increase in truck traffic, and this section of roadway needed to be upgraded to handle the additional load.
The new roadway’s original design section was to consist of 6 in. of Superpave FAA45 overtop 18 in. of aggregate base (NDDOT CL. 5) on top of 12 in. of cement-treated subgrade. This would provide a structural coefficient number (SN) equal to 3.96 for the project.
A value engineering proposal was evaluated, which consisted of 6 in. Superpave FAA45 over 8 in. of aggregate base stabilized with Team Laboratory Chemical Corp.'s BASE ONE base stabilizer over top of the 12 in. of cement-treated subgrade. This solution would provide an SN equal to 4.68. The owners of the project selected the valued engineering option for the project because of the cost savings.
The 12 in. of subgrade material was treated with approximately 5% cement additive. Then the 8 in. of new aggregate base material was placed and shaped with a motor grader, and rolled like normal gravel laying procedures. Then the 8 in. of base material was injected with the BASE ONE stabilizer, and a pad foot compactor followed for the initial compaction. The surface was shaped with a motor grader and compacted to density with a steel drum and rubber-tired rollers. The project was completed by adding a 6-in. bituminous surface.
American Engineering & Testing Inc. conducted a falling weight deflectometer (FWD) test and used ground-penetrating radar on the roadway to collect data. The results are shown in the table below.
In the end, the stabilized base layer provided a good platform for placing pavement. By utilizing BASE ONE, the team was able to use aggregates from a nearby source, thus saving the additional costs that would have been spent to haul in the original specified Class 5 material.
The stabilized material outperformed the standards of non-stabilized material. By eliminating 10 in. of aggregate base in the design section, the owner was able to save approximately $2 million on the 11.5-mile, $21 million project and obtain a higher structural number than the original design intent.