Emergency I-85 Reconstruction: Warm Mix Asphalt Saves a Failing Freeway

When a highway begins to fail, contractors and transportation agencies rarely have the luxury of time. This was exactly the situation facing the South Carolina DOT in late 2015, when a routine mill-and-overlay project on Interstate 85 near the Spartanburg-Greenville corridor turned into an emergency full-depth reconstruction. The solution came through innovative warm mix asphalt technology that allowed crews to place deep lifts at night and reopen the freeway by morning. As with any complex structural challenge, understanding what lies beneath the surface is critical. Just as Attic Foam Watertight Decks Failing Expansion Joints Essential issues require proper diagnosis before repair, this I-85 reconstruction demanded a thorough investigation before any pavement could be placed.

When Milling Revealed a Deeper Problem

The project between mile markers 56 and 68 covered 12 miles of three lanes in each direction on one of the busiest freight corridors in the southeastern United States. What started as a typical surface intervention quickly escalated into a $51 million emergency reconstruction with work beginning in January 2016.

Discovering the Extent of Damage

The original plan called for milling two to four inches of deteriorated pavement. The work was supposed to proceed lane by lane, letting traffic run on the milled surface while other lanes were completed. But as Dennis J. Garber II, District 3 construction engineer for SCDOT, explained, the underlying layers began to ravel almost immediately after traffic was allowed on the milled surface. Within a weekend, the interstate was quickly falling apart. The project had to be shut down and a new plan of attack developed.

The root cause traced back decades. The pavements in this section were constructed in the 1950s and 1960s. Successive thin mill-and-fill overlays had accumulated over 50 years without addressing the structural deterioration beneath. Cores taken at half-mile intervals revealed the true scale of the problem:

• Left and center lanes: delamination found five inches below the surface
• Right lane (heavy truck traffic): delamination up to ten inches deep
• Surface cracks across the entire corridor extended eight to twelve inches deep
• Stripping of lower asphalt layers had occurred over decades of use

Moving from Band-Aid to Reconstruction

Chad W. Hawkins, state materials engineer for SCDOT, described the situation bluntly: two-inch, three-inch, and four-inch mill-and-fills over 50 years had caught up with the agency. Major reconstruction was needed rather than another temporary fix. The decision was made to mill out the entire driving course ten inches deep in the right lane and replace it with two consecutive lifts. An open graded friction course (OGFC) would follow in 2017, with completion scheduled for 2018.

The scope change triggered a broader investigation. SCDOT began studying the entire length of I-85 from the North Carolina line to the Georgia line, examining surface cracks to determine their depth and planning staged rehabilitation for the corridor.

Warm Mix Technology Made Night Work Possible

The single biggest constraint on the project was time. Interstate 85 carries roughly 100,000 vehicles per day through the busy Spartanburg-Greenville corridor, a critical freight and commuter route. The highway had to be open for morning rush hour traffic, leaving crews only a single night shift to mill, pave, compact, and cool the pavement. The penalty for failure was severe.

The Night Work Challenge

Milling began at 9:00 PM. Paving started around 11:00 PM. Crews had to be out of the road by 6:00 AM, meaning paving stopped no later than 4:30 AM. Under standard SCDOT specs, individual lifts were limited to three inches. Nine inches of pavement would have required three separate lifts with cooling time between, making single-night completion impossible. SCDOT would not allow traffic in a nine-inch trench, so the full depth had to be restored each night.

Evotherm Warm Mix Additive

The solution came through a provisional specification called WMA Intermediate B Special, which required the use of a chemical warm mix technology rather than foamed warm mix. The project used Evotherm, a liquid warm mix additive from Ingevity that provides lubricity to the liquid asphalt binder. At the microscopic level, aggregate surfaces contain many microscopic peaks and valleys. The Evotherm additive smooths these irregularities, creating slip planes that let asphalt particles glide past each other with less energy required for compaction at reduced temperatures.

How Evotherm enables deep-lift warm mix placement:

1. The additive is dosed into the liquid asphalt binder at the plant
2. Production temperatures are reduced to 270-275 degrees Fahrenheit
3. The mix is delivered to the paver at approximately 265 degrees Fahrenheit
4. At the screed, the mat temperature measures approximately 255 degrees Fahrenheit
5. The mix remains workable for compaction despite the lower temperature
6. Both lifts cool rapidly enough to open to traffic by 6:00 AM

Dr. Everett Crews of Ingevity noted that lowering production temperatures avoids degradation to the binder that can occur at higher temperatures, improving long-term pavement performance.

Two Deep Lifts Instead of Three

With the warm mix modifier, Sloan Construction could place two four-and-a-half-inch lifts in a single night shift instead of three three-inch lifts. Each night, crews milled and repaved approximately 1,000 feet of roadway. Mitchell Dodd, quality control and design lab manager for Sloan Construction, explained that Evotherm lets the lifts cool faster, permitting the second lift to be placed on top of the first in the same night. This table compares the standard and warm mix approaches:

Mix Design and Quality Control Behind the Fast Track

The WMA Intermediate B Special mix was developed specifically for this project. It was based on one of SCDOT’s existing surface mixes but modified for deep-lift placement, with a nominal maximum aggregate size of one-half inch. The design did not specify Evotherm by name, but required a liquid warm mix additive rather than foamed warm mix.

Key Mix Specifications

• Binder: PG 64-22, not polymer modified
• Binder content: 5.7 to 5.8 percent (versus standard 5.5 percent)
• Warm mix type: liquid chemical additive required
• Target air voids: lowered for thick lift performance
• One-half inch nominal maximum aggregate size

Density Results Exceed Expectations

Test strips and production runs delivered density numbers that satisfied the most demanding quality control requirements. SCDOT interstate density specifications range from 92.2 to 96 percent. Given the unprecedented four-and-a-half-inch lifts, the project team would have been satisfied with results in the lower end of that range. Instead, test sections delivered nearly 96 percent density.

Cliff Selkinghaus, asphalt materials manager for SCDOT, noted particular satisfaction with the cold longitudinal joints, which go down nine inches deep. These joints achieved 93 percent density, addressing initial concerns about the vertical joints created by cutting out delaminated asphalt.

RAP Processing and Reuse

Two mills and two paving crews worked the northbound and southbound lanes simultaneously each shift. Reclaimed asphalt pavement (RAP) from milling was stockpiled, processed through an impact crusher, tested, and returned to the Intermediate B mix. Of the total 340,420 tons of asphalt, 131,752 tons were Intermediate B Special, 116,976 tons Surface A, and 31,453 tons OGFC. RAP also went into the Surface A mix, while the OGFC used all virgin aggregate.

The Long-Term Pavement Strategy

How Trimble 3d Grade Control Helped Rescue a failing parking lot project through innovative technology shows how construction challenges can be overcome with the right approach. Similarly, the I-85 emergency reconstruction was only the first phase of a comprehensive rehabilitation strategy designed for lasting results rather than another temporary fix.

Phased Construction Timeline

1. Phase 1 (2016): Milling and replacement with Intermediate B Special warm mix, placed as two four-and-a-half-inch lifts in each night shift
2. Phase 2 (2017): Placement of two inches of Surface A mix across the reconstructed section
3. Phase 3 (2017-2018): Open graded friction course (OGFC), one inch after compaction
4. Final elevation: approximately one and a half inches above the existing pavement to allow proper drainage

The intermediate mix served as the riding surface for about one year until the final surface and OGFC could be placed. The existing cross slope of adjacent pavements addressed drainage concerns during construction, as both new and existing pavements had cross slopes to facilitate water runoff.

OGFC Benefits Enhanced by Warm Mix

South Carolina DOT favors OGFC for high-volume driving courses because of its ability to manage water on the pavement surface, reducing hydroplaning risk and improving visibility in wet weather. Statewide, 95 percent of the agency’s contractors already use warm mix in their OGFCs. Beyond the temperature advantages, Evotherm provides a significant additional benefit for these open-graded mixes: it stops liquid asphalt drain-down.

OGFC mixes lack fine aggregates, meaning there is little material to keep liquid asphalt in place within the open grading. Traditionally, fibers have been added to prevent drain-down at additional expense. Evotherm eliminates the need for these stabilizing fibers by preventing drain-down naturally, while also allowing placement at reduced temperatures with less premature aging of the binder at the plant.

Lessons for Infrastructure Maintenance

The I-85 experience shows that surface-level fixes on aging infrastructure eventually reach their limit. The original interstate sections built in the 1950s and 1960s received multiple thin overlays over five decades, but none addressed the underlying delamination and stripping. How to Find and Fix Leaks in Hydronic Heating Systems requires the same diagnostic discipline that SCDOT applied on I-85, using core samples at half-mile intervals to find hidden damage before prescribing a solution.

Why Your Halogen Bulbs Keep Blowing and How to Fix It follows the same principle: diagnosing the root cause rather than treating symptoms leads to more durable results. On I-85, the root cause was decades of accumulated delamination that no thin overlay could correct.

Key lessons from the project for contractors and transportation agencies:

• Thin overlays accumulate over decades without addressing root structural causes
• Warm mix technology extends the paving season into winter months, enabling urgent work
• Chemical additives enable thicker lifts that accelerate construction timelines significantly
• RAP processing creates sustainable construction material from failed pavement
• Night work on high-traffic corridors requires innovation in both materials and methods
• Core sampling and investigation prevent repeated band-aid repairs on aging infrastructure

Todd K. Carroll, resident construction engineer for SCDOT in Spartanburg County, summarized the project simply: crews produced mix efficiently every night and the project met the urgent needs of one of the region’s most vital transportation corridors. With OGFC placement in 2017 and completion in 2018, the rebuilt I-85 will serve the Spartanburg-Greenville corridor for decades, built on warm mix innovation and thorough structural investigation.