Reconstructing Roads with FDR and CIR: A Combined Approach to Pavement Stabilization

When a roadway reaches the end of its service life, contractors face a critical decision: replace the entire structure or use in-place recycling methods that conserve materials and reduce environmental impact. The combination of Full Depth Reclamation (FDR) and Cold In-Place Recycling (CIR) offers a powerful alternative that restores deteriorated pavements while minimizing waste and disruption. These techniques have gained traction as agencies seek sustainable solutions that stretch limited transportation budgets. For context on how resilient construction principles apply across different building types, see Utility Building Design That Combines Resilience With Architectural.

Understanding Full Depth Reclamation and Cold In-Place Recycling

FDR and CIR are two complementary pavement rehabilitation techniques that have proven effective for restoring structurally failed roadways. Both methods recycle existing materials in place, eliminating the need for hauling debris to landfills and importing virgin aggregate. However, each method has distinct operational characteristics that determine its suitability for specific project conditions.

What Is Full Depth Reclamation?

FDR rebuilds worn-out asphalt pavements by pulverizing the existing pavement structure, mixing it with a stabilizing additive such as Portland cement, adding water, and compacting the mixture to produce a strong, durable base. The process typically operates at depths from 6 to 12 inches, depending on structural requirements. Dedicated reclaimer machines cut and pulverize materials in a single pass, mixing them with additives before depositing the blend back onto the roadway for grading and compaction by a motor grader.

What Is Cold In-Place Recycling?

CIR uses a specialized milling train to recycle thinner lifts of deteriorated asphalt, typically 3 to 5 inches. The process uses a down-cut milling head that keeps material in the cutting chamber longer than conventional reclaimers, resulting in more thorough mixing with additives. CIR trains include a milling machine, screening unit, pugmill mixer, and paver in a single continuous operation. The processed material is conveyor-fed to the paver, which lays the recycled mix to a specified grade without needing a motor grader.

Key Differences Between FDR and CIR

The Canvasback Road Project: A Case Study

Havre De Grace, Maryland, located at the confluence of the Susquehanna River and the Chesapeake Bay, faced a significant roadway failure on Canvasback Road. This residential feeder road served a large population and provided a shortcut to Maryland SR 40 and SR 155. Heavy school bus traffic compounded the deterioration, making reconstruction an urgent priority for the city.

Condition Assessment

A survey revealed a pavement structure of four inches of oxidized asphalt, zero to two inches of aggregate base, and a subbase of clay and unsuitable materials. The asphalt was severely deteriorated with potholes, alligator cracking, and soft yielding sections where subbase material pushed through. Stormwater penetrating the cracked pavement accelerated the damage cycle. The consulting engineer, Kercher Engineering of Newark, Delaware, consulted with E.J. Breneman L.P., a contractor experienced in pavement recycling technologies. Initial assessment identified several obstacles to conventional reconstruction:

• Inconsistent asphalt depth ranging from two to four inches, making milling depth control difficult
• Contamination of reclaimed asphalt pavement with soils, making it unacceptable at asphalt plants
• Limited aggregate base requiring full removal and replacement under traditional methods
• Unstable clay subbase requiring stabilization before any overlay could be placed
• Twelve intersecting roadways that had to remain open to traffic at all times
• Forty-eight water valve covers and twenty-eight manholes within the project limits

Selecting the Combined Approach

After a walk-through survey of the full 17,000-square-yard project, the team determined that FDR was appropriate for base stabilization. However, several site-specific factors led to using CIR equipment for the actual application. E.J. Breneman had previously used CIR trains with Portland cement on a roadway in Limerick Township, Pennsylvania, in 2002. That experiment at an 8-inch depth successfully demonstrated that CIR equipment could perform FDR-style stabilization when the depth of reclamation was within the equipment’s operational limits. For deeper insight into reconstruction methodologies in construction, refer to Detailed Analysis of 3d Reconstruction Technique in Civil.

Executing the Reconstruction

The design called for 8 inches of in-place Portland cement base topped with 2.5 inches of hot mix asphalt, with the finished surface flush to the existing gutter pans. E.J. Breneman used a Wirtgen milling machine with a 2-foot cutting head to excavate along concrete gutter pans to a depth of 10 inches immediately in front of the in-place cement train. This material was exported to a recycling center. All utilities were removed before major construction, with steel plates placed over utility areas to prevent debris from entering storm and sanitary sewers. Deeper-lying issues were repaired by cutting to solid base, placing stone to grade, compacting, and applying two inches of hot mix binder to stabilize the patches.

Technical Considerations for Combined FDR-CIR Application

Combining FDR and CIR techniques requires careful attention to geotechnical testing, equipment capabilities, and additive selection. Several technical factors determined the success of the Canvasback Road project.

Geotechnical Testing and Additive Selection

A geotechnical engineer evaluated existing materials before construction began. Samples were taken at the planned reconstruction depth of 8 inches, representing all materials from the asphalt surface down through the aggregate to the subbase soils. Portland cement was selected as the stabilizing additive after testing. Samples were mixed at different cement percentages, cured at 7, 14, and 28 days, and tested for compressive strength. Kercher Engineering used these results combined with average daily traffic, ESAL counts, and future development projections to establish the target strength for the roadway.

Depth Limitations of CIR Equipment

The CIR milling head uses a down-cutting drum that keeps material in the cutting chamber longer than conventional reclaimers. While this provides superior mixing of materials and additives, it limits the depth of cut. The deeper the cut, the more material is generated, and the cutting head can become overwhelmed with excess material that cannot be processed efficiently. Additionally, the paver can only handle a certain volume of processed material at a given time. For these reasons, the combined FDR-CIR approach is limited to depths of approximately 8 inches or less. Deeper structural issues require dedicated FDR reclaimers that operate without the mixing and conveying constraints of CIR equipment. For related reading on foundation reconstruction techniques, see Key Aspects of San Marco Bell Tower Foundation.

Compaction and Curing Requirements

After the paver placed the cement-treated base, compaction was achieved using a 12-ton steel dual-drum vibratory roller followed by a 25-ton pneumatic-tired roller. The dense-graded base material compacted well under this equipment. The base then received a prime coat of emulsified asphalt diluted with approximately 50 percent water. This prime coat prevented dust from rising and slowed the curing process, holding moisture in the mat to prevent premature cracking of the cement-treated material.

Advantages and Limitations of In-Place Cement Stabilization

The combined FDR-CIR approach offers several advantages over conventional reconstruction, but contractors must also understand its limitations before specifying this method. For additional perspective on reconstruction approaches, consult 3d Reconstruction Technique in Civil Construction Process and.

Key Advantages

• Elimination of motor grading: The paver lays material to final grade, preventing segregation of fines from larger particles and producing a finished surface comparable to paver-laid concrete.
• Environmental benefits: All existing pavement materials are recycled in place, eliminating truck hauling, reducing landfill disposal, and conserving virgin aggregate resources.
• Cost savings: The method avoids material removal, hauling, and disposal costs while reusing the entire existing pavement structure as a stabilized base.
• Time efficiency: The continuous train operation processes, mixes, and places material in a single pass, reducing construction time compared to staged removal and replacement.
• Reduced traffic impact: With proper sequencing, traffic can be maintained through the work zone, avoiding lengthy detours and community disruption.

Important Limitations

• Depth constraints: CIR equipment is limited to approximately 8 inches of processing depth, restricting its use to roadways where structural issues are confined to this range.
• Utility conflicts: Water valves, manholes, and other utility structures must be removed or protected before construction, adding planning and coordination requirements.
• Contamination sensitivity: Excessive soil content in the reclaimed material can compromise the strength and durability of the cement-treated base.
• Quality control demands: Continuous geotechnical testing is required during mixing and placement to verify moisture content, compaction, and strength development.

Project Outcomes and Lessons Learned

The project was completed in October 2011 by Goettner, a subcontractor to E.J. Breneman, who raised all utilities to the proper height and applied the final HMA wearing course. The 8-inch in-place Portland cement base provided the structural support needed for the 2.5-inch hot mix asphalt overlay and the traffic loading it would carry. Mike Polak of E.J. Breneman emphasized that this process is not a replacement for traditional FDR, but rather an additional tool suitable for specific site conditions where the depth of reclamation is within the CIR equipment’s capabilities.

E.J. Breneman, established in 1942, has applied green pavement technologies since 1983 and is a member of the Asphalt Recycling and Reclaiming Association. The Canvasback Road project demonstrates that combining FDR and CIR with Portland cement stabilization offers a viable, environmentally responsible reconstruction option for deteriorated roadways where site conditions align with the method’s capabilities. When pavement engineers evaluate reconstruction options for roads with limited aggregate base, contaminated RAP, and traffic management constraints, the combined FDR-CIR approach deserves serious consideration as a sustainable, cost-effective solution.