Engineers hope that a new type of precracking treatment will save money and improve recycling procedures over the lifetime of a one-mile stretch of asphalt roadway in La Quinta, Calif.
The city awarded San Bernardino, Calif.-based Mattich Corp. a $105,000 contract to microcrack a two-lane country road prone to large shrinkage cracks. The road will then be paved with a Full Depth Asphalt Recycling (FDAR) combination of asphalt and cement.
In the project, scheduled to begin March 21 with a completion date of April 1, crews will pulverize 6 in. to 12 in. of roadwayat times reaching the subgradeinto pieces smaller than 2 in. Dry or slurry cement will be spread over the top and water added to the aggregate-soil moisture. In the next day or so, a steel wheel vibratory roller will be applied at 2 mph to introduce a network of hairline cracks and reduce stiffness by 40%. This is expected to decrease development of large cracks, says La Quinta assistant city engineer Steve Speer.
The initial cost of the road is about the same as laying asphalt with fabric, but the process is expected to cut the lifetime maintenance cost in half because "the FDAR process recycles the material in place, saving the investment and the material," says Jeff Wykoff, the Ontario, Calif.-based manager of business development for cement manufacturer CEMEX. Removing the fabric layer, which can gum up the recycling equipment, will make it easier to recycle in 15 years, says Speer.
Engineers in Texas conducted the first U.S. experiment with the precracking method, using it on three roads in College Station in 2000. According to a paper by Tom Scullion, research engineer at Texas A&M University, "the microcracks will not impact the pavements overall structural capacity as the cracks will re-heal and the base will continue to gain strength with time."
The paper, which mentions that the technique was first described by Austrian researchers in 1995, generated industry interest when it was presented at a 2002 Transportation Research Board meeting. Using the precracking method on the one-mile, two-lane country road is "an opportunity to have a learning experience on a road without too much visibility or use," Speer says.
Wykoff touts the benefits of conserving resources and allowing the road to remain open longer because the repaving process is faster than removing existing pavement and placing new pavement. "Engineers at other agencies and private firms have all expressed interest about this project," he adds.
Steve Marvin, president of Santa Ana, Calif.-based paving and inspection firm LaBelle Marvin Inc., says it will use a Humboldt Stiffness Gauge, which is an electromechanical method of determining stiffness on the spot, along with conventional nuclear density testing methods as a control to determine strength of the roadway.