By Greg Halstead Pavement Engineer, Portland Cement Association
As the lessons learned in Texas are exported across the nation, other states are beginning to realize that recycling failed flexible pavements with portland cement has many advantages.
In today's interest in saving the resources available, this construction method assures the conservation of non-renewable resources by reusing the materials that already exist in the roadway It eliminates for the need for new granular base material, reduces hauling and energy costs and eliminates bumps, dips, ruts, potholes, cracks and patches.
The new stabilized base course can be shaped to restore the desired surface crown and cross-slopes, preserve drainage flow at curb and gutter sections and retain adequate clearance at overhead structures.
Other areas of the United States are following the Texas lead in recycling rural county roads, local streets, and highways. Thousands of miles of state, county and rural roads in the U.S. are rapidly deteriorating and in need of immediate rehabilitation. Nearly three-fourths of these roadways were constructed with flexible-granular base materials and were often under-designed for the greater and heavier traffic loads that these pavements experience today Ruts, potholes and severe cracking are common problems that are usually maintained with asphalt patches or thin overlays, or often by simply grading and re-compacting an unsurfaced granular base. These problems cannot always be blamed on normal wear and most often are the result of a failed or inadequate base course.
Salvaging failed flexible pavements is a good practice because the pavements still contain good granular material that can be reused and recycled into a strong, durable new base. A process commonly referred to as Full-Depth Recycling (FDR), is a technique in which the old asphalt pavement and a portion of the underlying base, subbase or subgrade materials are pulverized and blended together to create an enhanced homogenous base material. FDR is performed on the roadway itself at depths ranging from 6 to 10 in. depending on the thickness of the existing pavement structure.
For decades, many FDR projects have been successfully constructed
in Texas at the state, county and municipal levels - with all benefiting from
the low cost and durability of the recycled roadways.
The success that Texas has experienced is being followed in other states across
the nation as well. For example, a recent project outside Rock Hill, S.C., was
undertaken by the South Carolina Department of Transportation to address one
of its deteriorating roadways. On this 6.74-mile section of State Route 223,
the old asphalt and base materials were pulverized in place on the roadway mixed
with cement and water and then compacted, shaped and surfaced.
The FDR process was performed at one-third the cost it would have been to remove and replace the existing roadway Like the Texas Department of Transportation, SCDOT is an ardent supporter of FDR and has approved specifications for cement stabilized base courses.
Portland cement is the key to reconstructing flexible pavements that have failed. The incorporation of portland cement with the old base course material provides a practical, cost-effective means of strengthening worn-out pavements. The cement binds the granular particles together to form a paving material capable of withstanding moisture infiltration and degradation. It increases the strength of the base without the need for removing the old material and hauling in large quantities of expensive new base materials.
Always on the cutting edge, Texas is one of the leaders in the recycling industry when it comes to the application of cement in a liquid, or slurry form. The cement slurry is simply a mixture of water and cement that is blended together and then applied to the pulverized material during the recycling process by means of a modified water truck Applying the portland cement in this fashion helps to reduce the amount of airborne dust and makes it a preferred method when working in urban areas.
The application of cement to the rehabilitation needs on Texas
roads and highways and the innovations in construction techniques has re-established
an old practice to modem requirements.
Greg Halstead is a pavement engineer with the Portland Cement Association. He is responsible for providing design, construction, technical assistance and guidance for cement stabilized soils, soil-cement base, roller-compacted concrete and full depth reclamation.
Prior to the PCA, Greg worked for the Georgia Department of Transportation in all areas of the DOT involvement. He worked closely with other departments of transportation, city and county public works departments, colleges and universities and design and construction personnel.
Greg is a graduate of Shippensburg Stale University, in Shippensburg, Pa., and received a civil engineering technology degree from Southern Polytechnic State University in Marietta, Ga.
©2005 Road Recycling Council
P.O. Box 17362 - Cambridge, MA 02141
phone: (857) 998-0119 fax: (617) 547-0042
www.roadrecycling.org