When rebuilding a heavily traveled road, time and safety are critical to the success of the project, and doing so in a cost-effective way bodes well for the road agency customer and taxpayers.
Dixon, CA-based Western Stabilization addressed all three factors this past summer as the subcontractor on Hwy. 166 rebuild through the Town of New Cuyama.
California Department of Transportation, better know as Caltrans, designed the project, which called for the existing asphalt roadway and aggregate base to be Cold Foamed In-Place Recycled (CFIPR) in preparation for a hot-mix overlay.
Granite Construction out of Santa Barbara served as the general contractor on the $17 million project, performing initial milling to correct the slope and profile of the road, supplying the oil used in the CFIRP, compacting the recycled material, and then placing five inches of hot mix over the widened roadway.
Located between Route 33 and Cottonwood Canyon, and running right through the Town of New Cuyama, Hwy. 166 carries a heavy truck traffic load as a farm-to-market, as well as other motorist who use it as a shortcut from I-5 and Hwy. 101.
The remote location of the project, almost an hour from the nearest major city, also proved a logistical challenge in supplying equipment and material required to execute the job.
Caltrans? design called for a recycling depth of 11 inches on most of the 30 lane miles to be rebuilt and 12 inches in front of two schools located along the project. The extra depth was required to accommodate heavy buses that provide service to the schools.
The CFIPR design specified an average oil content of 3 percent and cement content additive of 1.5 percent. The average existing asphalt depth of the old road surface varied from 4 to 5 inches.
According to Kevin Berry, business manager for Western Stabilization, the asphalt depth was much thicker in areas that had been patched over the years and much thinner in areas that had been milled to correct the slope. And along the shoulder areas more oil was required in the recycling process to accommodate the widening Caltrans called for in adding a 4.5-foot paved shoulder to the 12.7-foot travel lanes.
Using two Wirtgen 2500 reclaimer/stabilizers (one with a 10-foot-wide drum and one with an 8-foot-wide drum), Western Stabilization crews managed to recycle an average of 1.5 lane miles per day.
Approximately 30 lane miles were completed in 20 working days. Western Stabilization used 145,377 gallons of oil and 3,000 tons of cement to foam and stabilize approximately 301,400 square yards of road material at a cost of just under $1 million, which was a considerable savings for Caltrans.
The foaming process
The low-cost (as compared to a typical mill and fill or total rehabilitation) CFIPR process involved injecting a controlled amount of water into a hot penetration-grade asphalt in a series of individual expansion chambers of the recycling equipment used to pulverize and blend the road material.
The foamed or expanded asphalt technology stabilizes the existing road materials by increasing the surface coverage of the liquid asphalt binder required to hold the aggregate together after compaction. The process also allows traffic to return to the treated road as soon as compaction has been completed.
In the foaming process, small amounts of cold water injected into the hot asphalt cause the asphalt to rapidly expand to approximately 20 to 30 times its original volume, giving it a high surface area to bond all the aggregate and fines blended in the pulverizing and mixing of the road materials.
The foaming technology often requires additional minerals ? cement, lime or aggregate fines ? to be added during the pulverization/mixing process to improve the stabilization of the materials being blended.
In the case of the Hwy. 166 project, cement was spread over the original road prior to recycling to provide additional structure and strength to the materials being mixed and compacted.