May 20, 2004

It’s cost-effective. It saves resources. It fixes bad roads—and fixes them quickly. It can be done on asphalt roads and on composite roads. And, when it’s reached the end of its life, it can be done again. What is it? It’s in-place recycling.

It’s cost-effective. It saves resources. It fixes bad roads—and fixes them quickly. It can be done on asphalt roads and on composite roads. And, when it’s reached the end of its life, it can be done again. What is it? It’s in-place recycling.

What better place to recycle than right on the road? A train of equipment chews up the old road, recycles it and leaves in its wake a sound pavement ready for a new wearing surface. The construction goes quickly, minimizing user delays. Hauling expenses are lower. Rather than being treated as waste, the aged road is reused as valuable paving material. While many street and highway departments have used in-place recycling for years, newer and more dependable technologies for both cold and hot recycling are leading more and more street and highway departments to choose in-place recycling.

Performance enhancer

Washington Road in Tazewell County, Ill., was badly cracked and deteriorating in 2001. The county needed to fix the road, which carries 3,900 vehicles per day including 15% trucks. Norm Johansen, the county engineer, considered several alternatives including: (1) a thin hot-mix asphalt (HMA) overlay; (2) milling 1.75 in. off of the surface and filling with new hot mix; (3) milling 3 in. and filling with an HMA overlay; and (4) a new cold in-place recycling (CIR) technology followed by a 2-in. HMA overlay. All the alternatives (except the 3-in. mill and overlay) had similar costs, with the recycling just slightly higher. A life-cycle cost analysis, however, showed that the CIR would save the county at least $700,000 over all the other alternatives over the next 15 years. Recycling the pavement removes the existing cracking patterns, resulting in lower future maintenance costs. Based on this information, Johansen selected CIR for the project.

The recycling was specified using new performance-related specifications for strength, ravel resistance, moisture resistance and low-temperature behavior. Koch Pavement Solutions’ laboratory performed the engineered mix design. Not only was the life-cycle cost lower, but resilient modulus testing demonstrated the improvement in structural number is as high or higher than the alternatives. Indirect tensile tests (developed by the Strategic Highway Research Program) show that the asphalt emulsion recycled mix makes the road more resistant to cracking at low temperatures (with a cracking temperature more than 6°F below the alternatives).

RA Cullinan (UCM), the prime contractor, constructed the 5.5-mile project in the summer of 2001. Mid State Reclamation subcontracted the recycling and used a train of equipment to mill 3 in. of the pavement, screen and crush the millings to a minus 11?2-in. top size, and mix the millings with a new emulsion specially engineered for CIR and supplied by Koch. A paver placed the cold mix, with rollers compacting the surface close behind. The quick set and cure allowed almost immediate release to local traffic. An HMA overlay was placed later.

After two years, the project is doing very well. In October 2003, ERES performed falling weight deflectometer testing on the project, with an excellent resulting value of 400 ksi.

Handling wheat and heat

In the summer of 2001, Koss Construction recycled a 32.5-mile stretch of Kansas Rte. 140 from Salina to Ellsworth. K-140 is a truck route used by farmers to bypass I-70 to haul wheat during the very hot harvest season. Don Drickey, KDOT District 2 engineer, wanted a cost-effective solution for rehabilitating the surface layers, protecting the pavement structure and providing an acceptable riding surface. The project was unusual because it was done on a composite pavement. The portland cement concrete (PCC) pavement, originally built in the 1950s, had been overlaid with two lifts of HMA and several surface treatments. The pavement was stable, but the aged HMA surface had reached the end of its service life, with severe reflective and fatigue cracking. Approximately 4.5 in. of the old material was recycled, with traffic returning the same day. Venture Corp. placed 11?2 in. of a PG 64-28 hot-mix overlay on the recycled pavement as early as two days after the recycling. Although Koss has a lot of experience recycling, it was their first project using the engineered design and new emulsion. According to Kelly Moore of Koss, “This project went really well.” Jason Johnson, Koch Pavement Solutions’ Kansas representative, said, “There was excellent communication and coordination on this project. The quality control contributed to the overall success.”

On some segments of the project, the recycled pavement was left open to traffic for as long as 60 days before the HMA overlay. This was during the hottest part of the summer, with the temperature hitting over 100°F on many of those days.

While reflective cracking is to be expected in asphalt overlays on jointed PCC pavements, there are often fears of rutting, raveling, delamination and thermal cracking, especially with recycled materials. The engineered mix design executed for the K-140 project showed the recycled material had the strength to resist rutting and the low-temperature properties to resist thermal cracking.

After almost three years there is some reflective cracking over the concrete joints, but there are no signs of rutting or thermal cracking on the pavement, which is subjected to Kansas’ temperature extremes. In 2003, KDOT did an excellent job of sealing the cracks that had appeared over the old PCC joints, and, as of March 2004, the pavement has a very good ride. Since 2002 KDOT has used the new technology CIR to recycle over 500 miles of its highways, including a 2003 project on I-70.

Building off success

The Asphalt Recycling and Reclaiming Association gave its 2004 Charles R. Valentine Award for Excellence in Recycling to David Eller, Colorado Department of Transportation Region 3 materials engineer, for a cold in-place recycling project on State Highway 92 in Delta, Colo. Eller was cited as a leader within CDOT to improve specifications, constructability and the performance of CIR. Eller’s stated goal is to “develop dependable testing parameters and apply end-result specifications that can model anticipated performance.”

The new technology CIR described above met the needs for this project. Over 70 cores were taken from the existing pavement. These were evaluated and used for the engineered mix design, which examined different recycling products, varying emulsion contents and varying additive levels. The project was bid based on the mix design meeting the performance-related specifications. Elam Construction was awarded the bid, and Arizona Pavement Profiling Inc. was responsible for the recycling portion. The project recycled all of the existing hot bituminous pavement, which ranged from 3 to 4 in., using the CIR engineered emulsion supplied by Koch. Results from field verification during and after the project are being used to validate the design and specification methods.

The May 2003 project was finished with a 2-in. HMA PG 76-28 overlay. Following the success of the SH 92 recycling, CDOT has contracted for a 15-mile project on I-70 to be built in 2004 near Grand Junction using this process.

Engineered rejuvenation

The technology used for the Illinois, Kansas and Colorado CIR projects raises the level of reliability and performance of the process with the use of performance-related testing criteria and specifications for materials, construction equipment and workmanship. The engineered emulsion allows the appropriate amount of emulsified binder to be added to the mix based on design, resulting in better coating and longer durability.

Improved technology also is being used for HIR. Dustrol Inc. has developed new equipment and used a new emulsion developed by Koch Pavement Solutions’ laboratories for the process. The emulsion contains a mix of polymer-modified asphalt and rejuvenators designed to rehabilitate distressed asphalt surfaces.

HIR should only be done on structurally sound pavements with good base structures. Prior to recycling, any structural problems in the base should be repaired, and the existing pavement should be swept of deleterious materials. HIR is a continuous process, where a self-contained train of equipment heats and scarifies approximately 1 to 11?2 in. of the existing pavement surface. In Dustrol’s process, the scarified surface is treated with the rejuvenating emulsion, milled, mixed, replaced on the road with a vibratory screed and compacted. A surface course or treatment is usually applied after the recycling. During HIR, only the lane being recycled is closed, and it can be reopened quickly after the compaction is completed.

The process uses heaters to elevate the temperature of the pavement to approximately 300°F and softens the surface. The softened pavement is scarified to break apart the surface and prepare it for the application of the rejuvenator emulsion. The rejuvenating emulsion is metered and applied at a predetermined rate using a system calibrated for the correct shot rate.

Laboratory testing determines the optimal amount of emulsion for each hot in-place recycling project. The rejuvenating oils in the emulsion replace the chemical constituents of the asphalt that have oxidized and aged over time. The polymer modified asphalt used in the emulsion further improves the elasticity, coating, moisture resistance, rutting resistance and cracking resistance of the recycled pavement. The result is a durable mix for a longer lasting pavement.

The rejuvenator-treated surface is milled with a milling head and mixed with an on-ground pugmill to coat the milled material. The result is a black, completely coated mix. Dustrol places the rejuvenated mixture with a paver using a vibratory screed, resulting in a surface with a corrected profile. The newly recycled pavement is immediately compacted with conventional rollers and is ready for traffic return or for a surface treatment.

To study the new technology, the Kansas Department of Transportation contracted a project in 2001 which included sections using the new emulsion and a conventional emulsion used for many years for HIR. The Dustrol project, on state highway 170 near Reading, Kan., recycled the top 1 in. of the distressed pavement, followed by a 1-in. HMA overlay. The emulsion was supplied by Koch’s El Dorado, Kan., plant. More than 100 projects on 1,000 miles of pavement have been recycled since 2002 using this new HIR process.

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