Orange County Branch Newsletter

April 2016

Sustainability Committee

Full Depth Reclamation with Cement: A Sustainable Roadway Repavement Technique


What is Full Depth Reclamation?

As defined by the Asphalt Recycling & Reclaiming Association (ARRA), "Full-depth reclamation (FDR) is a reclamation technique in which the full flexible pavement section and a predetermined portion of the underlying materials are uniformly crushed, pulverized, or blended, resulting in a stabilized base course. Further stabilization may be obtained through the use of available additives." One of the most common FDR techniques, chemical stabilization, is done by adding various chemicals to the pulverized material, including lime, Portland cement, fly ash, cement kiln dust, calcium/magnesium chloride, or other proprietary chemicals. The specific issues at each jobsite will determine which method is preferred. FDR has been in use for over 50 years and applies to all manner of asphalt-paved roadways, so long as the existing pavement depth is approximately 6 to 12 inches.

A typical street that deteriorated beyond what an overlay will effectively repair – a good candidate for FDR. Photo credit – Marco Estrada at Pavement Recycling Systems

The benefits of Full Depth Reclamation with Cement (FDR-C)

The benefits of using FDR-C instead of traditional remove and replace methods are the savings of time, energy, cost, community impact, and the increased performance of the newly stabilized section. These savings are achieved by leaving existing roadway materials in-place instead of hauling them out and replacing them with new materials. The reduction of trucking traffic when using FDR-C is on the order of 40:1 and projects are completed in approximately half of the time. Additionally, the cost of utilizing FDR is approximately 30% to 50% less than traditional methods. This is an efficient in-place re-use of materials that have already been paid for and continue to have value but are in need of reconditioning. Community impacts are reduced by not having to deal with the long timelines associated with traditional construction methods, high volumes of heavy truck traffic, and extended street and driveway closures. Using FDR-C, local traffic can drive on a treated road within a few hours. Finally, the finished roadway section benefits from the stabilized base; roads are be expected to last twice approximately twice as long as if reconstructed or overlayed over poor base materials. This is due to both the stiffer supporting structure as well as the reduced permeability of the base course.

Project selection

Using FDR-C solves several common problems with worn roadways, including issues with the surface, base or sub-base. Good candidates include roads that have excessive cracking (including alligator cracking), patching, rutting, shoving, potholing, or traffic overloading. Poor candidates include areas with high clay content soils (the use lime treatment instead of Portland cement should be considered) and roads with drainage problems, including flooding problems – these are “deeper” issues that FDR-C alone will not solve.

The FDR-C process

The steps to the successful completion of an FDR-C project include: 1) Sampling materials from the existing base and sub-base materials in order to determine what depth of reclamation and cement dosage rate will result in the best ratio of cost to performance. 2) Pulverizing the roadway to depths of 8” to 12” (and possibly deeper as needed.) 3) Cement is spread at the predetermined dosage rate, typically with dry cement, although a slurry is used in some areas. 4) Cement and water are mixed through the depth of the pulverized material by running over the area a second time with the reclaiming machine. 5) Compacting is done with sheep foot, smooth, or rubber tire rollers, depending on the material in the roadway. 6) Curing is done by wetting with a water truck or with the use of a waterproofing agent to keep the material moist to allow for full cement hydration. 7) The final step is to apply a wearing course of traditional hot-mix asphalt or concrete.

Local examples of FDR-C

Full Depth Reclamation with Cement has been used successfully in cities throughout southern California. The treated streets are in very good condition after many years of use and have generally not required additional maintenance since being treated. The following is a short list of example cities that have successfully used the FDR-C process: City of Buena Park, City of Westminster, City of Fullerton, and the City of Los Alamitos. In addition to these cities, Caltrans is currently finalizing direction that will identify the use of FDR as one of the maintenance and rehabilitation strategies for rural highways statewide; according to Tony Tavares, P.E., Chief, Division of Maintenance, Caltrans HQ, Sacramento, “Sustainability solutions for the maintenance and rehabilitation of our highways are paramount. FDR provides one more technical strategy to be considered for achieving long-term structural integrity on specific roadways throughout California. Caltrans appreciates working jointly with industry on issues that make engineering sense for the department and economic sense for the taxpayers of California.”

LEED and Envision credits available with Full Depth Reclamation

The U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) program and the Institute for Sustainable Infrastructure’s Envision Sustainable Infrastructure Rating System each have several credits that are applicable to projects utilizing Full Depth Reclamation with Cement in the areas of waste diversion, materials reuse, regional materials greenhouse gas reduction and others.

Additional resources available

There are a number of design and specification documents available for your use. If you would like additional information or resources on this innovative, sustainable, cost-saving, and time-saving technology, contact Nathan Forrest, P.E. of the California Nevada Cement Association at [email protected]. Further information may also be found in following report: http://cncement.org/wp-content/uploads/2014/04/R_FDR_SR016.pdf

 

A reclaiming machine mixing Portland cement into the pulverized base. Photo credit – Marco Estrada at Pavement Recycling Systems

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