Rubbilization and HMA overlay in Faribault County
by Matt Shinners, Antigo Construction, Inc., and Jill M. Thomas, P.E., MAPA Associate Director
Rubblizing the deteriorated PCC on CSAH 16 prior to HMA overlay
County State Aid Highway (CSAH) 16, east of Blue Earth, is one of the most heavily traveled roads in Faribault County. This road provides access to a large grain elevator and other businesses in Blue Earth. The last major maintenance on this segment was in the early 1980s, and it needed reconstruction. The old, narrow concrete pavement had been overlain several times but the joints and cracks in the concrete continued to reflect through the asphalt.
In 2004 Faribault County decided to reconstruct the roadway section and bring the road up to current standards. Concrete rubblization was chosen to minimize reflective cracks. The width of the paved Mn/DOT turnback roadway was increased from 20 feet to 26 feet and the grade was corrected in two areas to meet vertical alignment standards. The grade correction areas were 2,600 linear feet in length.
Ulland Brothers, Inc., Albert Lea, was awarded this 8-mile-long project, and subcontracted with Antigo Construction, Inc., for the concrete rubblization. The first step was to mill off the 6 inches of existing asphalt overlay. Antigo then rubblized the existing portland cement concrete (PCC) pavement, which had a tapered thickness of 9 inches to 7 inches, with one of its MHB Badger Breakers®. Antigo followed with a Z-grid vibratory roller over the rubblized concrete to further crush the surface particles and seat the rubblized layer of concrete. More than 80,000 square yards of concrete was rubblized in seven days.
Using a vibratory Z-grid roller for compaction
The roadway was then widened by 3 feet on each side using a 9-inch-thick layer of crushed concrete adjacent to the existing concrete. Edge drains were installed outside the widenings. New centerline culverts were installed and the grade was corrected in two areas. The base was now ready for the hot-mix asphalt (HMA) overlay. Ulland Brothers paved 6 inches of HMA in two lifts. “In summer 2005, 1½ inches of LVWE45030B mix was placed for the final wear course, and the project required a total of just over 55,000 tons of HMA,” said John McDonald, Faribault County Engineer.
The Faribault County project highlights some of the advantages of the concrete rubblization and HMA overlay process. The rubblized layer serves as a composite flexible base design and excellent drainable base for the new HMA. Breaking the concrete into small yet still tightly interlocked particles through the process of rubblization greatly reduces thermal and load-induced movement of the concrete slabs. The resulting layer is similar to a crushed aggregate layer but typically offers greater support due to the interlocking of the particles.
The speed of the process keeps road closures to a minimum and the cost is significantly less than total reconstruction. In essence, the process recycles the deteriorated PCC in-place. No right of way needed to be acquired in the rubblized portions of the project. In addition, traffic was able to use the road throughout most of the project. All of the existing materials (asphalt, concrete, aggregate shoulders) are recycled, thereby reducing cost and minimizing truck movements, and helping conserve nonrenewable resources. The final cost per mile was $361,360.
CSAH 16 prior to final 1½-inch wear course
What was once a rough-riding road with significant maintenance expenses has become a smooth-riding, low-maintenance, safe road. The widespread success of concrete rubblization and HMA overlay across the United States suggests that this option should be seriously considered whenever a concrete pavement is in need of rehabilitation.
More information is available on the Minnesota Asphalt Paving Association’s Web site, www.asphaltisbest.com, along with reference to MAPA’s Asphalt Paving Design Guide.