Full Depth Reclamation Using Portland Cement Helps to Ease Budget Crunch
January 28, 2011
By Don A. Clem, P.E. (Colorado), Executive Director Portland Cement Association–Rocky Mountain Cement Council
Engineers at Spanish Fork City, Utah decided to explore an alternate construction process when faced with the reconstruction of 300 South from 700 East to 900 East. This particular stretch of roadway was requiring an increased amount of maintenance each winter. The city had estimated that the two-block reconstruction project (57,000 SF) would cost approximately $155,000. By specifying the full depth reclamation (FDR) process using portland cement as the stabilizer, the city realized an actual cost of $121,150, a savings of over 21 percent.
The project was originally scoped using conventional reconstruction of the existing roadway, which was in poor condition. Those plans called for removal of the existing structure and construction of a new eight inch aggregate base course with a three inch asphalt wearing surface. Trapper Burdick, Design Engineer, decided instead to investigate a new approach that involved reclaiming the existing road in place, stabilizing the reclaimed material with four percent portland cement (by weight of dry material), and capping the reclaimed base layer with a three inch asphalt wearing surface.
Burdick involved Spencer Guthrie, Ph.D., Brigham Young University (BYU), in design of the cement-treated layer and in development of the project specifications. The city was pleased when the project bid came in very close to the construction estimate and decided to proceed. The pavement section selected for construction using the reclamation process was three inches of an asphalt wearing course placed on eight inches of reclaimed, stabilized base. The cost per square yard for the reclamation was $9.40, including the cement. The contract was awarded to Staker Parson Companies.
Following the initial reclamation, the contractor pushed the reclaimed material to the side of the road and removed three to four inches of subgrade to make room for the new asphalt wearing course. About a week later, the cement slurry was placed using a slurry spreader that attached to the chute of a ready-mixed concrete truck. This spreader was developed by BYU in cooperation with John Coyle, Salt Lake City Corporation engineer, and the Portland Cement Association. After the slurry was mixed into the reclamation material, the base was compacted using a vibratory smooth drum compactor and then graded. Following a three day cure period, a vibratory roller was again used to microcrack the new cement-treated base layer to reduce the chance of reflective cracks developing in the asphalt wearing course in the future.
Reflecting on the project, Design Engineer Burdick opined that the project went very smoothly, exceeding his expectations. Further, Burdick was pleased that the FDR process cut truck traffic during the construction process, reducing pollution and wear and tear on the surrounding streets. The citizens of Spanish Fork will be happy to learn that they saved over $33,000, and that they won’t see any more maintenance dollars spent on that roadway section for some time!