California Paving Milestone: Use of Rubberized Hot Mix Asphalt with Warm Mix Asphalt Technology on the North Coast

By Wesley Johnson and Michael Stapleton, Caltrans District 1 Materials

September 15, 2009, marked a paving milestone for the State of California.  The Rio Dell/Scotia Rehabilitation Project on U.S. Highway 101, 20 miles south of Eureka, was the first project in the state to add Warm Mix Asphalt technology into Rubberized Hot Mix Asphalt-Gap Graded (RHMA-G) in the traveled way.  This use of Warm Mix Asphalt technology was introduced for a one-day trial to evaluate RHMA-G production and placement at lower temperatures.  Success with this technology would mean many other projects using Rubberized Hot Mix Asphalt (RHMA) could have success in cooler environments in the future.

Placement of RHMA on the North Coast has always been challenging due to the low ambient air temperatures and wet, misty conditions.  In addition, air quality has always been a sensitive issue in this pristine environment and previous rubberized asphalt projects have met opposition due to odors emitted from the rubber product during production, transport, and placement.  Rubberized hot mixes provide a resilient, longer-life roadway and divert waste material (used tires) from valuable landfill space.  Warm Mix Asphalt technology in the rubberized hot mix production process allows the RHMA-G to be produced at lower temperatures, provides an overall energy savings, and lowers hydrocarbon emissions and off-gassing of noxious fumes.  The use of rubberized hot mix is a “win-win” for the environment and maximizes scarce road-maintenance dollars due using reduced required pavement thicknesses for pavement rehabilitation.

Manufacturing plant with truck in the foreground
Plant at Scotia – Note the lack of smoke.

Conventional rubberized hot mix asphalt (gap graded) is normally produced at between 315° F and 325° F at the asphalt plant.  However, during the one-day production of asphalt mix for the Warm Asphalt Mix test section, the plant temperatures were lowered to 230°F.  Despite these lower production temperatures, the new pavement’s density was an average of 92 percent compaction, which is within the required range of 91–96 percent.  District 1 staff sampled the Warm Mix Asphalt to provide material for future performance testing.  They will compare these test results against the rubberized hot mix asphalt (gap graded) control mix and evaluate them for characteristics affecting long-term performance.

Workers and equipment working on a road surface
The RHMA-G sampling process.

Overall, the day’s production and placement of RHMA-G with Warm Mix Asphalt technology went well.  We placed approximately 2,600 tons of new asphalt.  The future will likely bring more opportunities to use rubberized hot mix in the District, and we will most certainly use Warm Mix Asphalt technology to save money and protect the environment.