Using a Terex (CMI) 800 reclaimer, Blount's crews milled 8 inches deep on the initial grind to pre-blend and pre-pulverize the asphalt surface with the underlying road material. "The initial pre-pulverization really gives us a good feel for any problem areas that may require additional cement to help stabilize soil conditions as well as identify any hidden problems such as buried railway tracks or utility structures," Barnhardt says. "If we find a soft area during the pre-pulverization stage, we can make adjustments by increasing the amount of stabilizing agent specified to further stabilize any soft subbase soil conditions that are prevalent. Experience has shown us that on a typical reclamation/stabilization project, we usually have to add supplementary stabilizing agents to approximately three to five percent of the total roadway which we are contracted to reclaim.
"Also, whenever you find a thicker section of asphalt on a road, that's a pretty good indication of a problem area that a road agency often tries to solve by putting down more asphalt," Barnhardt adds. "And once we do our initial pulverization and begin to compact the blended material, our pneumatic roller operator can also detect soft conditions that will require additional stabilization." Once the initial bridging effect of the original asphalt pavement structure is eliminated, it is not uncommon for the 25-ton traffic roller to find some periodic soft subgrade conditions in the Southeast.
Once the initial pulverization and subsequent compaction is completed and any additional aggregate is added if required for widening, Blount's reclamation crews then spread the required cement over the roadway, adding additional cement to problem areas wherever needed. The stabilizer is then put back on the road to blend the cement with the pulverized 8 inches of asphalt and underlying base material.
Using cement as a stabilization agent is nothing new for GDOT projects and other site prep applications. In fact, soil cement has been used extensively for the past 30 years on projects south of Macon in new construction primarily due to the limited supply of aggregate available in that area.
"When you don't have sufficient aggregate to use in building a stable base for roads or other construction projects, you have to find another way to stabilize the base conditions and cement stabilization has been a primary solution for many projects in the southern part of Georgia," Barnhardt says. "Now with the FDR process, we are seeing Portland cement used all across the state, and North America."
FDR, an economic approach
Faust emphatically states that "this county and others in Georgia can't overlook the FDR process as a way to provide their rate payers significant infrastructure improvements quickly and economically."
While the soil cement process has helped to build rigid base structures for roads and other building projects in Georgia, it's only been recently that GDOT has decided to specify FDR with Portland cement to reclaim existing roadways.
"They're (GDOT) taking a progressive role in road preservation treatments that improve the quality of the system and provide an economical approach that allows more roads to be addressed, but they also realize cement stabilization has its limitations as well," Barnhardt notes. "The process will provide a rigid structure, but like a concrete pavement, that rigid structure is prone to cracking." However, in some instances cement treated FDR is the best candidate for the existing soil conditions. Senior Vice President, Dale Cronauer states that he has seen an increased usage in all types of stabilization agents across the Southeast, including but not limited to cement, quicklime, fly ash, engineered emulsions and foamed asphalt base stabilization.
In the case of the Wayne Poultry Road project, for example, Blount could have proposed other stabilization agents, but DOT funding dictated the use of a cement stabilization treatment in this case. Last year a successful FDR with quicklime stabilization project was completed under the direction of GDOT in Jones County. "GDOT is currently in the process of developing a matrix to determine which bituminous and chemical agents work best with certain conditions," Barnhardt says. "It's just their first step in taking a proactive approach to treating roads with the dollars they have earmarked for those types of improvements."
While reclamation represents approximately half of Blount's business, with site prep for heavy utilities and asphalt production representing the other half, the company's Reclamation Division's processes are evenly divided between lime, cement and bituminous additives. "We have four CMI pulverizers and a Roadtec milling machine, and we can put up to four different reclamation crews out into the field on any given day," Barnhardt says. "As for the type of stabilization treatment we use, it really depends on the soil conditions and the life cycle the client is looking to achieve."