By: Roads & Bridges
IIn the summer of 2009 a new Model 3800 CR from Wirtgen America Inc. was put to work by Dunn Co. to cold in-place recycle (CIR) Mason County Highway 15 in central Illinois.
In-place recycling saved money for the county, as Dunn reported an average cost on the job for the base course of about $26 per ton, compared to fresh hot-mix asphalt selling around $75 per ton at that time.
“Doing the standard mill-and-overlay was not an option for rehabilitating the road,” said Jim Schwarz, vice president, Dunn Co., Decatur, Ill. “But it was a very good project for CIR.”
Using only one machine saves both time and money on a project, Schwarz said.
“Fewer people and fewer equipment reduce the cost and time needed to complete the project,” he said. “Because the CIR process reuses the materials in the road, we’re conserving natural resources and fuel consumption. The process also goes faster, so traffic is restored sooner.”
Mason County documents for Highway 15 required that the cold in-place reclamation rework the existing asphalt structure plans using a CIR process. Following CIR, a structural (intermediate) course layer was to be placed, followed by a friction course. The project length on the two-lane blacktop road was 17.4 lane-miles, a total of approximately 112,000 sq yd.
The road was in bad shape. Some pavement sections were more than four decades old and the pavement was highly oxidized and alligator-cracked, with many irregular cold patches. Extensive transverse block cracking had occurred.
“Coring and as-built data showed the existing asphalt pavement thickness ranging from 5 to 6 in. in thickness,” said Mike Marshall, Wirtgen director of recycling products. “The project was to be divided into two recycling depths, 2 miles at a depth of 3 in. and the remainder at 4 in.”
The emulsion content was calculated on a medium-to-coarse gradation percentage as 2.25 to 3.75%.
The new Model 3800 CR from Wirtgen America Inc. offers the ability to cold in-place recycle a 12-ft-6-in. full lane of pavement in one pass, stabilizing with either foamed asphalt “green mix,” or any other stabilizing medium such as asphalt emulsion or lime or cement slurry, but with a twist: With a conveyor mounted, it also will serve as a full-lane cold mill.
In this compact recycling train, the 3800 CR pushed the emulsion tanker while simultaneously milling (downcutting) the existing pavement. The 3800 CR added the design percentage of emulsion, proportional to working speed, and a metered amount of compaction moisture to suit varying in-situ conditions, with water taken from an onboard tank.
The 3800 CR then placed the recycled, stabilized material with an attached screed to design slope. The 3800 CR used a Vogele AB425T screed with working width up to 14 ft. Compaction of the reclaimed, stabilized base followed immediately behind the screed using a new Hamm HD+ 120 VV HF high-frequency, double-drum vibratory roller.
On Mason County Highway 15, the average working speed was 28 fpm, including base recycling and stabilization, with resulting material paved to slope, pre-compacted, at a rate of approximately 410 tons per hour with minimal disruption to traffic.
