GDOT continues cement stabilization program

Blount Construction Co., based in Marietta, GA, is leading the way for GDOT by providing the road agency an alternative to conventional reconstruction, thereby maximizing their road improvement budget with FDR. The reclamation process not only improves the safety and performance of distressed asphalt roads, but does so at about one third to one half of the cost of conventional reconstruction. Further, the entire process can be completed in a tenth of the time of conventional construction, thereby allowing the asphalt paving contractor more time to focus on what they do best, lay hot-mix asphalt.

In Jackson County, north of Atlanta, the asphalt recycling specialist recently completed reclaiming a severely distressed 1.7-mile stretch of Wayne Poultry Road through a process that blends a stabilization additive with the existing pavement and the underlying base material. While bituminous and/or chemical products can be used in the FDR process, in this case GDOT selected Portland cement based on their laboratory mix design process.

"This is the second year that GDOT has been specifying FDR stabilization to improve county and city roads with the intent to make them wider, safer and stronger at a cost that's well below conventional reconstruction," notes Blair Barnhardt, operations engineer for Blount's Reclamation Division. Counties such as Jackson look to the State DOT for State Aid financial support for their roadwork, hence the GDOT involvement.

Barnhardt comments, "While we're excited to see southeastern states such as Georgia implement 'new technology,' some western states such as Nevada DOT, have been recycling their distressed roads for over 20 years and saved over $600 million in that time."

Project Manager David Faust states, "On this particular project we estimated the rehabilitation of 22,000 square yards 8 inches deep. As with most distressed county roads in Georgia, we figured on their being a couple of inches of asphalt on a mixture of granular aggregate base (GAB) and underlying soil. On a typical road reclamation project that may be three miles in length, we can complete the project in less than three weeks including FDR and a 2-inch asphalt overlay. A conventional reconstruction approach of removing the old asphalt and a portion of the underlying base and replacing it could take over 6 months to complete and cost two to three times as much."

On the 23-foot-wide Wayne Poultry Road reclamation project, the mix design called for 42 pounds of Portland cement for an 8-inch stabilized base. The analysis conducted by GDOT specified the 8-inch stabilized base to provide sufficient structural strength for the increased traffic level of the road. "GDOT typically looks for 400 PSI in their laboratory and 300 PSI in the field from cement treated FDR," says Barnhardt.

"The original road structure consisted of two to three inches of hot mix asphalt pavement over an existing gravel/dirt road," Barnhardt says. "The area, like most in the Atlanta hub, has experienced tremendous growth, specifically with industrial type operations in this area. As a result, GDOT felt it was important to significantly increase the Structural Number (SN) with the cement stabilization process before resurfacing with a hot mix asphalt overlay. The FDR process provided the most economical way for GDOT to do that."

Barnhardt notes that with FDR, "We can often double or triple the SN literally overnight on most of the roads and parking lots where we perform this work on. Worth noting is that we often do this work on roads with traffic counts of 20,000 cars a day."

Barnhardt, a Certified National Highway Institute (NHI) instructor for the FHWA, is one of the instructors that have delivered the Asphalt Pavement Recycling Technologies #131050 two-day workshop to 16 State DOT locations across America. He comments about the course, "It's always very exciting to see so much interest in asphalt reclamation, yet we're only recycling 3 percent of America's infrastructure! We have a very long road ahead of us if we are truly going to maximize our potential in budget savings and increased life cycles."

The project
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."

Barnhardt, one of the Directors of Asphalt Recycling and Reclaiming Association (ARRA) suggests visiting the www.arra.org website for more information on the FDR process or to sign up for the NHI workshop www.nhi.fhwa.dot.gov.

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