Foam on Bottom

Asphalt Article June 11, 2001
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Expanded asphalt (also called foamed asphalt base stabilization) base stabilization was introduced to the South this past year


Expanded asphalt (also called foamed asphalt base stabilization) base stabilization was introduced to the South this past year as an economical alternative to conventional repair methods for distressed roads and parking lots. This technology was offered to DOT forces, asphalt contractors, municipalities and property owners to rehabilitate their infrastructure. Typical candidates are roads and parking lots that are flat, cracked, potholed, rutted, flushed, heaved, too narrow or have insufficient base strength. The process is gaining in popularity.


Water born


Expanded asphalt was invented by Professor Ladis Csanyi in 1956 at Iowa State University, Ames, Iowa. Csanyi discovered how hot (350? F/177? C) liquid asphalt cement (AC) reacted when a small amount of cold water was injected into it. With the new idea in hand, contractors and agencies began to work on ways to use foamed asphalt in the field to bind road bases together.


While Mobil Oil had taken the technology and patented it in North America, the process was taken across to Europe where it was well received and eventually perfected. Here, the Europeans added standard design procedures and fine-tuned computerized field equipment. While very little work was done in the U.S. during this time, it is ironic that expanded asphalt work was performed in 1982 for the Georgia DOT (GDOT) on an experimental basis in Ware County.


Greg Halsted, statewide materials coordinator for GDOT, visited the 18-year-old expanded asphalt project recently and was impressed by the way the roads were holding up with only a triple surface treatment as the wearing course.


"We (GDOT) have used foamed asphalt on one of our worst types of soil conditions in Georgia and it has held up great—especially considering the fact that these roads have been used regularly by local logging trucks. Soil-cement base mix designs typically fail using the fine granular soils in some of the southeastern counties in Georgia, so foam makes a nice fit," Halsted said.


Foaming the hot liquid asphalt on the jobsite allows the AC to expand 10-12 times its normal volume. This, consequently, provides an excellent means of bonding pre-pulverized in situ road base materials as well as virgin sand and aggregates. Materials Engineer Michael Smith of the Federal Highway Administration said in a presentation, "Foamed asphalt does not coat the particles, rather, particles stick together and form a paste.


"The process is consistent with the Sustainability Philosophy: Growth while minimizing environmental impact."


Often the original profile of the road can be restored even after numerous overlays without having to remove excess material to landfill sites. Asphalt Recycling and Reclaiming Association (ARRA) reports tell us that RAP (reclaimed asphalt pavement) is by weight the No. 1 recycled material in the U.S.


Dale Cronauer, vice president of Blount Construction Co. Inc., Marietta, Ga., stated, "With lime and cement stabilization there is always a bulking factor, however, the foamed asphalt doesn’t bulk so we are able to restore original profiles in paved areas that have been resurfaced three and four times."


After grading and compacting, the newly created bases have structural layer coefficients in the 0.35 to 0.39 range (@ 1.8 GBE); this process provides a way to increase structural strength while maintaining the existing profile.


Worth a visit


It has been four years since modern expanded asphalt technology was introduced into the North American market. In 1999, Jefferson County, Wis., utilized foamed asphalt technology in an $800,000 project.


"Foamed asphalt offers an option for road reconstruction," said Jeff Haas, Jefferson County highway commissioner. "It has long-term benefits, with an anticipated average cost savings of 20 to 25% over standard methods, when used where appropriate."


Haas performed foamed base work again in 2000 and has additional work planned for the 2001 season. "Expanded asphalt shows great potential in my county."


While a few companies introduced foamed asphalt in the northeastern states, the biggest market growth to date has occurred in Ontario, Canada. This substantial market growth could be because there are actually three companies actively promoting the foamed technology there.


Foamed asphalt in a market where winters are severe will provide good long-term durability study results. John Emery, president of John Emery Geotechnical Engineering Ltd. (JEGEL), prepared a technical paper on a Wellington County expanded asphalt project for presentation at a recent ARRA meeting in Toronto. Regarding the road covered in his paper he stated, "We have been monitoring that road for several years, it actually appears to get better looking each time we visit it."


Cronauer predicted that the demand for expanded asphalt in Georgia and the surrounding states will follow a similar growth pattern once the initial marketing effort has been completed. "We have made quite a few of our local asphalt paving contractors happy as we are in a position now to rehabilitate large areas of distressed asphalt with foam base that would otherwise be unsuitable for overlays," he said.


"Bottom line is we are now providing them with more finished base for their hot-mix crews to pave top course asphalt on."


Lots of foamed asphalt


Bruce Ummel, asphalt production manager with Blount Construction, commented on his experience paving on a foamed base at a busy commercial parking lot in Kennesaw, Ga.


"Main Street Mall at Town Center was the quickest, most trouble-free complete reclaim and repave of a major shopping center I’ve ever seen. The foamed process was easy on the owners and their customers. We had no complaints while engaged in major site work at an open center. That’s because people there could see great progress being achieved on a minute-to-minute basis."


At the 24,000 SY Main Street Mall project, expanded asphalt crews began work at 3 a.m. dry pulverizing their selected area. The project was divided into five sections. By 8 a.m. they were injecting foam into that same area, and by noon traffic was allowed to drive on the freshly compacted foamed base. The foam crew finished the entire parking lot base in five days while Ummel’s asphalt crew completed the 2-in. hot-mix asphalt overlay directly behind them.


Timothy Hackett, general manager for Urban Retail, was impressed by the way the crew handled the work.


"You handled a project at a busy shopping center that could have been a logistical nightmare, and turned it into an agreeable solution for both the needs of the tenants and those of the customers coming to shop here," he said.


"We found that a considerable amount of time, money and disruption could be saved. One of the greatest side benefits of this procedure was the ability to have traffic on the expanded asphalt within a few hours of its placement. This allowed the tenants to continue with their normal course of business throughout the project," said Hackett.


Preliminary work at the Town Center project involved sampling of the in situ materials, running a "cold" Marshall mix design and staging of the production. Blount uses JEGEL for their expanded asphalt mix designs. JEGEL has been involved with foamed asphalt since its inception into the North American market. Specifications for the Town Center project included the addition of 2.5% Citgo supplied PG 67-22 AC (AC 30) to a mixture of 75% RAP and 25% GAB at 5 in. deep. Foaming equipment from CMI was used for the job.


Jeffrey Jack, senior project engineer for CMI, designed the expanded asphalt system for the RS 650.


"The process temperature range for the hot liquid AC is from 300? to 350? F (149? to 177? C) and the water is added at rates from 1.0 to 2.5% of the total process mass," he said. "Inside the expansion chamber, the water forms tiny bubbles throughout the process stream."


During production, Blount crews regularly fill a 5-gal pail with foamed asphalt from the chamber to verify foaming results. Typically, the liquid AC is expanded 10 to 12 times its normal volume with a half-life of around 35 seconds.


Compaction and moisture content was checked on site with a nuclear density gauge by QORE Property Sciences.


Typically any parking lot or road that requires more than 30% of its area to be repaired by removal and replacement is a good candidate for expanded asphalt. Once the costs of removing and discarding this amount of material in and around busy metropolitan cores such as Atlanta are taken into account, foamed asphalt becomes more economical. A foamed asphalt base can provide upwards of 5,000 lb of Marshall Stability.


Full half-life


Early last spring Blount was approached by Forsyth County, Ga., to analyze one of their roads to see if it was a suitable candidate for expanded asphalt base stabilization. County Engineer John Cunard and Assistant County Engineer Tim Allen were instrumental in getting officials on board with the expanded asphalt process. Metro Atlanta is currently the No. 1 immigration point in the country, and as a result the urban sprawl is creating quite a demand on the existing infrastructure.


One of the key reasons Cunard chose the expanded asphalt process is so that he could widen the road from 18 to 22 ft. For the most part there are no gravel shoulders in Georgia, so wider roads mean safer roads. The county forces had been doing some asphalt milling around the corner from the foamed asphalt jobsite. From this work, they gathered approximately 800 tons of RAP and stockpiled it at the foam project.


After the new section of roadway was laid out and centerline offset stakes were set, Blount went to work. Once traffic control was in place, a Caterpillar 140 grader did excavating work out a widening while the CMI 650 pulverized the existing asphalt at 40 ft per minute. As the 3 to 4 in. of in situ asphalt was sitting on a base that consisted of mostly red clay, special care had to be taken by the operation not to integrate too much dirt into the pulverized material. RAP was immediately placed ahead of the operation with dump trucks to fill in the widening and to supplement the in situ section of road.


The section of road was reshaped, sloped and realigned to prepare for the foaming process. Hot liquid AC was trucked to the site using a 2,000-gal distributor truck. Again, the AC used was PG 67-22 supplied by Citgo.


"Because of our Venezuela-based Boscan crude oil source, the quality of the AC is superb. Foaming with quality material provides a longer than average half-life, and as a result we can expect better coating than with other types of AC," said Ron Corun, technical support manager with the AC supplier. ("The Wirtgen Cold Recycling Manual" stated: Foamed bitumen is characterized in terms of expansion ratio and half-life. Expansion ratio is defined as the ratio between the maximum volume achieved in the foamed state and the volume of unfoamed bitumen. Half-life is the time taken, in seconds, for the foam to settle to half of the maximum volume attained. The "best" foam is generally considered the one that optimizes both expansion and half-life.)


The JEGEL expanded asphalt mix called for 2.5% AC added to the in situ blend along with a moisture content of 6%. All fieldwork was performed as per "GDOT Expanded Asphalt Specification 328 Draft Copy." QORE Property Sciences did onsite testing and took field samples back to the laboratory for mix design correlation. The specified material calibrations were entered into the CMI 650’s onboard computer and the prepulverized road base was taken up again into the mixing chamber. Foamed asphalt was injected into the reclaimed mix and breakdown rolling followed with a 25-ton Dynapac traffic roller.


Fine grading commenced and a 10-ton smooth drum roller in static mode finished the 5 in. expanded asphalt mat.


"The production of the foamed asphalt crew was even faster than I had anticipated," said Cunard. "I have more distressed roads that I would like to address with this process."


APAC-Georgia Inc., Atlanta, placed the 1 1/2 in. hot-mix asphalt overlay a few days later to complete the project. One of the biggest benefits of the expanded asphalt process is that overlays, whether chip seals or hot-mix asphalt paving, can be applied after just two days. Tim Allen, also with Forsyth County, said "The foamed project is holding up well and is a dramatic improvement over what we had."


Gaining acceptance


"Overall, the acceptance appears better than average for the process in the South," stated Garry Holton, president of Blount Construction. "Anyone that we have performed work for to date has immediately asked us to quote similar projects for them at other locations. Although it will take several years to see a return on investment with the amount of sophisticated equipment and workforce required for the process, I am optimistic that we have made the right decision to pioneer this process in the South."


It helps that GDOT and FHWA are both actively involved in the education process with the foamed asphalt. Recently, FHWA published a report titled "Recycled Materials in European Highway Environments." This publication summarized findings from a recent International Technology Exchange Program. In the section "Summary of Findings," some of the recommendations read: "Conduct recycling demonstration projects about foam bitumen . . . encourage AASHTO and state DOTs to involve contractors more in committees establishing specifications and . . . conduct a public awareness program on recycling."


The future for expanded asphalt reclamation in the South looks bright. As more and more people become aware of what the process offers, consulting engineers, property owners and DOT professionals can begin to integrate this innovative technique into their systematic approach to road restoration.


Recently Blount finished foaming parking lots at Universal Forest Products in Union City, Ga. and was working on a 30,000 sq yd project for Emory University in downtown Atlanta. Blount was hired to foam the existing distressed roads and parking lots at Emory West and overlay them with a 1 1/2-in. hot-mix asphalt overlay.


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