RAP Recycling and High-Production Milling on Interstate Resurfacing Projects

Highway resurfacing projects on major interstate corridors demand careful coordination of materials, equipment, and scheduling to deliver durable pavements under tight traffic windows. The June 2010 mill-and-fill project on I-75 south of Valdosta, Georgia, stands as a textbook example of how modern cold milling technology, reclaimed asphalt pavement (RAP) recycling, and precision aggregate testing combine to produce high-quality results. With four contractors operating five Wirtgen cold mills across 17.25 miles of three-lane interstate in each direction, the project demonstrated what is possible when Aggregate Crushing Value Test Determine Aggregate Crushing Strength protocols and rigorous mix design procedures guide material reuse. The joint venture between The Scruggs Company and Reames & Son Construction Company milled approximately 155,000 tons of deteriorated pavement, with the reclaimed material going directly back into the new asphalt mix.

Cold Milling Operations on High-Volume Interstate Corridors

Equipment Configuration and Fleet Strategy

The milling operation on I-75 required a coordinated fleet of five Wirtgen cold planers, plus one spare machine standing by. Each machine served a specific role in the production chain:

• Wirtgen W 2200 – Full-lane head machine operated by Pavement Products & Services Inc. on the northbound mainline cut
• Wirtgen W 2100 – Mainline milling on the southbound lanes, operated by Oxford Construction Company
• Wirtgen W 2000 (three units) – One used for mainline cutting by Scruggs on southbound, one for 5-foot shoulder cutting by Oxford, and one on northbound with Pavement Products

Each pass removed 2 ¾ inches of raveling and deteriorated pavement that was approximately two decades old. This amounted to roughly 77,500 tons of material per direction. The mills began work at 7:30 p.m. each night, with paving operations starting approximately 45 minutes to one hour behind the milling train. Average production reached about 11,000 linear feet per night across all lanes.

Time Constraints and Night Work Logistics

The project operated under a strict 7 p.m. to 7 a.m. night window. Once a section was milled, traffic could not be permitted on it until paving was complete due to the 2 ¾-inch drop-off between lanes, which created a serious safety hazard. The last truck of hot mix asphalt needed to leave the plant by 5 a.m. and arrive on site by 5:30 a.m., with all equipment removed, traffic striping applied, and raised pavement markers installed by the 7 a.m. deadline.

The contract carried a $2,000 per hour penalty for failure to reopen lanes on schedule. This penalty clause drove the need for redundant equipment and the joint venture structure, which allowed backup mills and asphalt plants to be shared between contractors in the event of a breakdown.

Reclaimed Asphalt Pavement Testing and Recycling

Pre-Project RAP Characterization

Before the main milling work began, the project team milled a test section of the existing pavement and subjected the RAP to thorough Aggregate Properties Testing to determine its suitability for reuse. The existing pavement, though two decades old, still contained approximately 5.5% liquid asphalt content. Testing confirmed that the aggregate in the RAP retained adequate strength and gradation characteristics for incorporation into the new mix designs.

RAP Usage in Mix Design

RAP was permitted only in the stone matrix asphalt (SMA) intermediate course, at a rate of 10% by weight of the total mix. The porous European mix (PEM) friction course did not incorporate RAP due to its specialized open-graded design requirements. The ability to reuse RAP on the same project created significant cost savings for the Georgia DOT through what the contractor termed a big RAP credit. By reusing the existing aggregate and liquid asphalt on site, the project avoided the expense of mining, crushing, and transporting virgin aggregate while also eliminating the need to dispose of the milled material.

Aggregate Quality Requirements for RAP Mixes

When incorporating RAP into new asphalt mixes, the following aggregate properties must be verified through laboratory testing:

• Gradation of recovered aggregate from the RAP material
• Angularity and particle shape of the reclaimed aggregate particles
• Asphalt binder content and aged binder properties
• Moisture content of the RAP stockpile
• Deleterious material content and contamination levels

The Aggregate Impact Value test is one of several methods used to evaluate the toughness of aggregates recovered from RAP, ensuring they can withstand the compaction and traffic loading demands of the new pavement layer.

Pavement Design: SMA and Porous European Mix

Stone Matrix Asphalt Intermediate Course

The milled pavement was replaced with a two-layer system designed for both structural performance and surface drainage. The 2-inch SMA intermediate course served as the primary structural layer. SMA is a gap-graded mix that relies on stone-on-stone contact within the coarse aggregate skeleton to provide superior rut resistance and durability. The maximum allowable air void specification was 7%, but the contractor set an internal target of 5% to ensure long-term performance.

The Coarse Aggregate Concrete Construction principles that apply to concrete also inform SMA mix design, where the coarse aggregate fraction provides the primary load-bearing skeleton of the pavement. The quality of coarse aggregate is critical in SMA mixes because the stone-on-stone contact transfers traffic loads directly through the aggregate structure rather than through the mortar or binder.

Porous European Mix Friction Course

Above the SMA intermediate course, a 1 ¼-inch lift of PEM was placed as the riding surface. PEM is an open-graded friction course designed to contain approximately 20% air voids, which makes it highly porous. The key performance benefits of PEM include:

• Reduced tire spray – Water drains vertically through the pavement rather than remaining on the surface
• Enhanced drainage – Stormwater moves laterally within the pavement structure to roadside drainage systems
• Noise attenuation – The porous structure absorbs tire-pavement interaction noise
• Improved wet-weather friction – Reduced hydroplaning risk due to rapid surface drainage

The PEM binder was formulated with approximately 6.1% liquid asphalt content and 0.4% fiber additive. The project offered the option to use either polymer-modified binder or crumb rubber-modified binder, with the contractor selecting the latter. Crumb rubber modification, derived from scrap tire rubber, provides enhanced binder elasticity and rut resistance while also offering an environmental benefit through tire recycling.

Mix Design Parameters Comparison

Project Management and Quality Control for Night Paving Operations

Joint Venture Coordination

The project was delivered through a joint venture between The Scruggs Company and Reames & Son Construction Company, both headquartered in Valdosta, Georgia. This structure provided built-in redundancy for critical equipment. If one contractor’s asphalt plant went down or a milling machine broke down, the other contractor’s resources could fill the gap, avoiding the $2,000 per hour liquidated damages for lane closure overruns.

Milling subcontractors were used for portions of the work because large-scale cold milling was not the primary business of either joint venture partner. Oxford Construction Company handled southbound milling, while Pavement Products & Services Inc. handled northbound milling. This allowed the prime contractors to focus on paving operations while specialized subcontractors delivered the high-production milling required to meet the tight schedule.

Quality Control Protocols

Several quality control measures were critical to the success of the I-75 project:

1. Pre-project testing – Test sections were milled and the RAP was analyzed for mix design development before the main contract work began. This allowed the contractor to refine target gradations, binder content, and compaction procedures in advance.
2. In-process RAP sampling – Throughout the project, RAP was continuously sampled and tested to ensure consistency. Variability in the milled material was monitored so that plant mix designs could be adjusted as needed.
3. Void content verification – Both the SMA and PEM courses required rigorous air void testing. The SMA target of 5% voids (below the 7% maximum specification) ensured a durable, moisture-resistant intermediate course. The PEM’s 20% air voids were verified to ensure adequate permeability for drainage.
4. Temperature control – With a night work window from 7 p.m. to 7 a.m., ambient temperatures dropped during the overnight hours. Mix temperature at the plant, at the paver, and during compaction was monitored to ensure proper workability and density.

Lessons for Highway Contractors

The I-75 mill-and-fill project offers several takeaways for contractors undertaking similar highway resurfacing work:

• Invest in pre-project RAP testing to maximize recycling rates and reduce virgin material costs. Testing the existing pavement before bidding allows accurate mix design and cost estimation.
• Build redundancy into critical equipment paths. Joint ventures or subcontractor partnerships with backup plant capacity protect against schedule-killing breakdowns on time-sensitive night work.
• Match milling production to paving capacity. On I-75, milling was deliberately paced to stay slightly ahead of paving, avoiding both idle time and open milled surface exposure.
• Use gap-graded SMA and open-graded PEM in combination to achieve both structural durability and surface drainage performance in a single resurfacing operation.

The project was funded under the American Recovery and Reinvestment Act of 2009, demonstrating how federal infrastructure investment can support innovative pavement recycling and high-production construction methods on major interstate corridors. By combining advanced cold milling technology, rigorous aggregate testing, and collaborative contractor coordination, the I-75 project delivered a high-quality resurfacing that maximized the value of existing pavement materials while meeting the demanding constraints of live traffic on one of the Southeast’s busiest freight corridors.