Full-Depth Reclamation Means Sustainable Paving
One of the most daunting tasks any county commissioner faces is maintaining a county's road system — and road maintenance is becoming an even larger challenge as state DOT maintenance funding shrinks and the cost of roadwork increases.
In years past, in Georgia's Coweta County as in many other Georgia counties, roads were built on what GDOT terms a sand/clay base. In other words, the asphalt for the roadway was placed directly over the underlying soil rather than being constructed on a rock/aggregate or soil/cement base.
Most of these roads performed well over the years. However, Coweta and many other counties are now experiencing exponential growth, which has led to much new development and greatly increased traffic counts and loads. Because these roads were not designed for current traffic conditions, they began to deteriorate. Signs of deterioration include the appearance of potholes and serious rutting along with alligator cracking, which can then lead to substantial failures.
"Resurfacing a roadway that has a failed base is a waste in time and money," said Bill Cawthorne, public works director. "We had to do something different."
When some of the county's major roadways began to show signs that resurfacing alone would not be adequate, Cawthorne adds, "We began to look for alternatives."
FDR appeared to be a possible solution. Wayne Kennedy, county engineer, directed Fred Landrum, transportation project manager, to look into the process. The eventual result? Last year, Coweta County awarded the state's largest-ever FDR contract to the Miller Group based in Morrow, GA. The $2.6-million FDR contract was for reconstructing five different major roads and nearly 10 miles of county roads.
FDR To The Rescue
For years, Coweta County had addressed its road problems by deep patching most of the isolated failures prior to resurfacing. But some of the roads were beyond having isolated failures.
"With deep-patching contracts now costing the county in excess of $100 per ton of asphalt, Full-Depth Reclamation using cement was an alternative that made sense," said Landrum. A traditional reconstruction can also take months, he said.
"FDR can rebuild the road in-place in a matter of days, and the cost savings are about one-third of traditional methods," said Landrum. "We can essentially rebuild an entire section of roadway for relatively the same investment of dollars spent for deep patching."
Do the new roads hold up? According to the 20-year research study of the FDR process by the Portland Cement Association, roads that were reconstructed using the FDR process have a life expectancy up to three times of non-treated roadways.
The FDR Process
Full-depth reclamation with cement makes the reconstruction of roads a largely self-sustaining process. The complete recycling process can be finished in one day, and traffic can be maintained throughout construction.
The process is straightforward. The old asphalt and any existing base material are pulverized, mixed with Portland cement and water, and then compacted to produce a durable base for either an asphalt or concrete surface. FDR incorporates the old asphalt and base material into the new cement-stabilized roadway base, so there is no need to haul in aggregate or haul out old material for disposal. Construction truck traffic is greatly reduced, and there is little or no waste of materials from the original roadway investment. FDR conserves virgin construction materials, saves fuel, and prevents truck loads from tearing up the road.
The process starts by evaluating the condition of the existing pavement including the sub-layers and mix design. Next, pulverization sizes the existing pavement into 2-inch minus material. An exact amount of Portland cement and water is blended into the pulverized material, and reshaping, proper compaction, grading, and curing follow. The resulting new base has the strength and durability needed for long-lasting, cost-effective pavements.
By addressing the entire pavement section, FDR is also able to correct delinquent cross sections, widen roads, and increase the load-bearing strength of the base — all while utilizing 100 percent of the existing materials. Substantial savings can be attained while meeting environmental goals. Cement stabilization increases the stiffness and strength of the base material, reducing deflections due to traffic loads and resulting in lower strains on the asphalt surface and sub-grades. A cement-treated base also forms a moisture-resistant layer that keeps out the water that routinely destroys untreated aggregate bases.
More FDR Ahead In Coweta County
Coweta County's first FDR project, constructed in 2005, was reclaiming a 1-mile section of Palmetto-Tyrone Road. The Miller Group was also the successful bidder on that project.
Initially, the county had been concerned about the cost and speed of construction. But after seeing the process and observing how the new roadway performed, Landrum says, "We were convinced that FDR using cement was a viable alternative to extensive deep patching."
Today, FDR is proving to be just what the county needs.
"Even before the cost of asphalt went sky high, FDR with cement was a better value than deep patching," said Landrum. "Now with the cost of oil now at $120 per barrel pushing asphalt prices to $65 ton and beyond, we are even more cautious on how we spend our road dollars. By utilizing FDR on our major roadways providing a stabilized, rigid base, we are expecting our asphalt investment to double or perhaps triple in longevity."
The county plans on bidding an additional 10-plus miles of FDR this year.
|Bob Nickelson is pavement applications director for the Southeast Cement Association.|