Foamed asphalt technology is an in-place asphalt stabilization method that has been researched for several decades. A new development in this evolution, called expanded asphalt, is proving to be a technical success in the U.S., Europe and Africa.
Expanded asphalt technology is being developed and supplied to the industry by CMI Corp., Oklahoma City, Okla., and now promises to save millions of dollars for America's road rehabilitation programs. The idea has been applied in Norway, Sweden and Finland, and in recent months has proven itself at four sites: at a demonstration near Brownsville, Wis., in September 1996; on a street project in Edmond, Okla.; in Norway and in the Republic of South Africa.
The technique involves mixing hot asphalt cement (AC) with pulverized asphalt during stabilization. Key to the process is a small amount of water that is injected into the hot liquid asphalt being metered through a special reactor tube located on-board the asphalt stabilizer. When the water contacts the hot liquid asphalt, a significant expansion occurs in the mixture and creates expanded asphalt. Combining a bit of water with the liquid asphalt results in a stabilizing product that mixes effectively with reclaimed asphalt.
ÒThe process works well, and it has great potential as a low-cost, high-quality asphalt rehabilitation technique,Ó said Anthony P. Bodway, milling superintendent at Payne & Dolan, a Waukesha, Wis., contractor involved in the Wisconsin demonstration. ÒFor our first project here, we're adding two 2%, 2 1/2% and 3% of liquid AC 120/150 asphalt, which at 3% is approximately 1.54 gal/sq yd at a 4-in. depth.Ó
ÒIt's just like tossing drops of water onto hot cooking grease,Ó says Russell Freimark, project manager, Northeast Asphalt Inc., which helped sponsor the Wisconsin demonstration. ÒYou get a reaction similar to a small, contained explosion.Ó
While expanded asphalt does not fully coat all the aggregate, Bodway explains, the stabilizing product effectively disperses through the reclaimed asphalt. The rejuvenated material does not harden immediately; it can be graded and compacted for several hours following injection.
Tools and process
The use of foamed asphalt is not new. Recently, however, CMI has refined the process to employ its new expanded asphalt technology and its high production reclaimer-stabilizers for in-place asphalt reclamation. ÒFoamed asphalt has been around for nearly 30 years,Ó says CMI chairman Bill Swisher.
In September, the Wisconsin Asphalt Pavement Association (WAPA), the Dodge County (Wis.) Highway Commission, Payne & Dolan Inc., Northeast Asphalt Inc., CMI, Koch Materials Co. and Marquette University hosted a one-day demonstration of in-place asphalt rehabilitation techniques, including the expanded asphalt technology. Some 240 persons attended, including state highway officials from various states including Virginia and Louisiana, and contractors with headquarters ranging from the upper Midwest to Australia.
The program began at the Brownsville (Wis.) Community Center. Following opening remarks by Gerald Waelti, WAPA executive director, speeches were given by Payne & Dolan's Bodway; Dale Bohn of Koch Materials Co.; Dodge County Highway Commissioner Robert Henken; Bob Sindelar, Dodge County highway engineer; engineer Jim Crovetti of Marquette University and others. Meeting sponsors organized bus tours of four asphalt rehabilitation demonstrations on county road V south of Brownsville.
Four methods proven
In addition to expanded asphalt technology, Payne & Dolan demonstrated the effectiveness of three other in-place asphalt rehabilitation techniques. These methods and variations of them are saving millions of dollars in asphalt pavement rehabilitation for cities, counties and states across the nation.
ÒThe whole idea is to get the highest-quality finished product for the least amount of money,Ó said Robert F. Henken, Dodge County highway commissioner. He emphasized the value of partnering for innovation with contractors and equipment builders. ÒIf we work together we can come up with some good solutions that save money,Ó he noted.
Following are brief descriptions of the three methods demonstrated in Wisconsin.
-- Milling and relaying asphalt. A full-lane milling machine working at a depth of 5 to 6 in. removes existing pavement and transfers it to a reclaiming train that crushes the material to 1 1/2-in. minus, screens it and conveys it to a surge bin that passes it to a paver. In this segment of the Wisconsin demonstration, no emulsion or rejuvenator was added.
-- Cold in-place reclamation with emulsion injection. The existing asphalt pavement was pulverized to a depth of 5 to 6 in. with a CMI RS-500B reclaimer. Next, the same reclaimer, pushing an emulsion tanker, injected Koch Materials' HFE-300 emulsion to a 4-in. depth. While injecting, the reclaimer scooted along at about 80 fpm.
-- Koch had analyzed the aged asphalt and pegged the injection rate at 1 gal/sq yd of pavement at the 4-in. depth. With injection complete, a motorgrader shaped the renewed asphalt to its final grade and cross-slope. After compaction by both pneumatic and vibratory rollers, the base was complete and ready to receive its 2 1/2-in. thick mat of hot-mix asphalt.
-- Pulverize and relay the pavement. First, the RS-500B pulverized the asphalt to a 10-in. depth. The Wisconsin DOT requires a new split-lift compaction specification whenever existing pavement is pulverized to an 8-in. depth or greater. Following initial pulverization, a grader rolls half the reclaimed lift to one side. The exposed material is watered lightly; both vibratory and pneumatic compaction follow on the lower half of the existing base. Then a grader brings back the uncompacted material and places it atop the newly compacted lift. When that top lift is watered and compacted with both vibratory and pneumatic rollers, the base is ready for a mat of hot-mix asphalt.
Pulverization and shaping work costs about $200 per station, or 100 ft of two-lane pavement, says Ron Triemstra, vice president at Northeast Asphalt. To shoot emulsion adds $150 to $170 per station.
On the other hand, injection with liquid asphalt will cost just $80 to $100 per station, plus it may carry another dividend. In discussions following the demonstration, Triemstra said it's possible that expanded asphalt injection will permit counties to reduce hot-mix overlays by 1 in. of thickness--if ongoing strength tests at Marquette University show that beefing up the base produces an equivalent product.
ÒWe could save between $2,000 and $3,000 per mile in mix,Ó says Triemstra. ÒWe can use expanded asphalt to raise the structural number of the base, and maybe we can reduce the overlay from 3-1/2 in. to 2-1/2, which allows us to reduce the cost per mile of roadway and provide more miles with the same volume of hot-mix asphalt.Ó
For the Wisconsin project, CMI fitted up an RS-650 to inject expanded asphalt. Liquid asphalt at about 300 deg F was pumped from an insulated tanker through the reactor tube, where 1% water was added to the AC content.
An on-board microprocessor monitors and controls the asphalt flow rate into the spray bar mounted reactor. Application rates are based on the mix design by adding the required percentage by weight to obtain optimum properties for the compacted mix. The machine operator sets the microprocessor to the required number of gallons per linear foot of travel. The microprocessor automatically proportions the flow rate to the travel speed of the machine.
Flow can be directed to any or all of four sections of the asphalt distribution bar, depending on the width at which the machine is working. Digital readings on the instrument panel tell the operator the total number of gallons of asphalt injected, so it's easy to know the amount remaining in the tank. As well, there are readings for real-time flows of both water and liquid asphalt in gallons per minute.
In Wisconsin, The RS-650 rolled along at 60 to 80 fpm while injecting liquid asphalt. The machine injected the two-lane road in four passesÑtwo at 8 ft and two at 5 ft wide.
For the future, Dodge County officials plan to compare the various costs and structural strengths of roads rebuilt with the methods explained here. Indeed, Marquette's Jim Crovetti presented some preliminary strength results and wheeled out his falling weight deflectometer, a model KUAB 2m-FWD, to take readings as the Wisconsin project continued. Tests are being taken before reconstruction, during the process, and at completion.
The KUAB 2m-FWD is a non-destructive deflection testing device and meets specifications set forth by ASTM and the Strategic Highway Research Program. Dynamic loads up to 12 lb may be applied. Next, deflections are measured and recorded by six sensors placed up to 36 in. from the center of loading. Based on pavement thickness and surface deflections, officials can establish a structural number for the pavement. Subgrade strengths can be determined as well.
The falling weight deflectometer will enable Wisconsin officials to judge strengths of roads built with reclaimed bases then compare those figures to an all-new sugbgrade, base and hot-mix pavement. It's probable, says Northeast Asphalt's Triemstra, that reclaimed bases injected with expanded asphalt, compacted and repaved with hot-mix asphalt, can come close to, or equal, new pavement strengths, for a fraction of the cost of a new road.
The goal is stronger, cost-effective county roads. While farm-to-market roads in Wisconsin must stand up to heavy milk trucks, Òthey aren't IÐ80,Ó says Triemstra. Next spring, Marquette's Crovetti will have definitive results, and county officials can match them with costs.