For decades, northern contractors have watched the calendar with anxiety as November approached, knowing that one hard freeze could end the paving season. But winter does not have to mean downtime. With the right equipment and techniques, asphalt paving can continue well past the traditional cutoff. One of the most effective methods involves using hot in-place heaters to prepare frozen or snow-covered subgrades, allowing crews to place and compact asphalt even when temperatures drop below freezing. This article examines the practical strategies, real-world case studies, and quality control measures that make cold weather asphalt paving a viable option for contractors and highway agencies alike.
The Challenge of Cold Weather Paving
Subgrade Freezing and Moisture
When temperatures drop below freezing, the aggregate subgrade begins to freeze. A frozen subgrade prevents proper compaction because the asphalt mix cools too quickly against the cold surface and because frozen soils lack the stability needed to support rolling equipment. In the case of the Gallagher Asphalt project on the I-80/I-90/I-94 interchange south of Chicago, the subgrade had begun to freeze by early November, and the frontage roads were covered with snow. Standard methods would have been impossible without intervention.
Rapid Mat Cooling
Asphalt mix must be placed and compacted while it remains above a minimum temperature, typically 175 to 200 degrees Fahrenheit depending on mix design and layer thickness. In cold weather, heat transfers from the mat to the cold subgrade and ambient air much faster, shortening the available compaction window from several minutes to sometimes less than a minute. This places enormous pressure on the paving crew to maintain a tight rolling pattern directly behind the paver.
Snow and Ice on Existing Surfaces
When placing an overlay or widening an existing roadway, snow and ice prevent proper bonding between the new asphalt layer and the existing pavement. Bond failure leads to delamination, cracking, and reduced pavement life. The surface must be dry and above freezing before asphalt can be placed.
Using Hot In-Place Heaters for Winter Paving
Hot in-place recycling (HIR) equipment is typically used to soften existing asphalt pavement for rejuvenation and reprofiling. However, as Gallagher Asphalt demonstrated, these same heaters can be repurposed for winter paving.
How the Heaters Work
Hot in-place heaters use propane or natural gas-fired infrared heating panels to deliver intense heat to the pavement surface. The heat penetrates several inches into the existing asphalt and underlying subgrade. In winter paving applications, the heaters serve three purposes:
- Thawing the subgrade: By heating the surface for 30 to 60 minutes before paving begins, thermal energy radiates downward and thaws the frozen subgrade, restoring compactability.
- Drying the surface: The high temperature evaporates moisture, melts snow and ice, and leaves the pavement dry and ready to receive new asphalt.
- Warming the base: A warm base layer reduces the temperature differential between the new hot mix and the existing surface, slowing the cooling rate and extending the compaction window.
Case Study: I-80/I-90/I-94 Interchange
Gallagher Asphalt, a Thorton, Illinois-based contractor working as a subcontractor to Lorig Construction, was tasked with placing a surface course on frontage roads, a 6-inch stabilizing asphalt base on the mainline interstate, and 4-inch base on several ramps. The work was scheduled for completion by the end of October, but delays pushed it into November. An early cold snap brought snow and freezing temperatures, threatening to halt the project.
Joe Ulanowski, senior project manager, proposed using the company’s hot in-place heaters to warm the subgrade and dry the paved surfaces. IDOT approved the approach. Over three weeks, on days when weather permitted, crews preheated the work area, paved, and compacted using a tight rolling pattern. The approach allowed completion of critical portions by December 20, extending the season by nearly a month. Dan Darden, vice president of construction, noted the heaters allowed the team to finish the work IDOT needed going into winter.
Quality Control Measures for Cold Weather Asphalt Placement
Extending the paving season requires more than heaters. Every aspect of the operation must be adjusted for cold weather conditions.
Tight Rolling Patterns
Rollers must follow the paver as closely as possible, often within 50 to 100 feet. The breakdown roller should make its initial passes while the mat is above 250 degrees Fahrenheit. Intermediate and finish rolling must be completed before the mat drops below the minimum compaction temperature. Multiple rollers working in echelon can help cover the width of the mat quickly.
Temperature Monitoring
Continuous temperature monitoring is essential during cold weather paving. Infrared temperature guns, thermal imaging cameras, and paver-mounted sensors should track mat temperatures from the screed through final rolling. This data helps the crew identify cold spots, adjust rolling patterns in real time, and document that compaction occurred within the specified range. For projects using pre-heaters, surface temperature should be verified before the first load is placed.
Mix Design Adjustments
Asphalt producers can adjust mix designs for cold weather placement. Common modifications include using a softer binder grade, increasing binder content slightly, specifying finer aggregate gradation, and adding warm mix additives that lower binder viscosity. These adjustments improve workability and extend the compaction window.
Transport and Logistics
Trucks should be covered with insulated tarps to retain mix temperature during haul. The plant should discharge the mix at the highest permitted temperature, typically 300 to 325 degrees Fahrenheit. Staging should be minimized so trucks move directly from plant to paver without waiting. Maintaining these logistics is critical for cold weather success.
| Factor | Recommended Practice | Benefit |
|---|---|---|
| Subgrade temperature | Preheat above 32°F using infrared heaters | Enables compaction, prevents freeze-thaw damage |
| Mix delivery temperature | 300°F to 325°F at plant | Extends cooling time by 30-60 seconds |
| Roller distance behind paver | 50 to 100 feet maximum | Captures compaction before mat cools |
| Ambient temperature limit | No hard cutoff with pre-heating | Extends season by weeks or months |
| Surface preparation | Dry, clean, above freezing | Ensures bond between lifts |
| Truck covers | Insulated tarps on all loads | Reduces heat loss, saves 5-10°F |
Equipment Considerations and Safety
Heater Maintenance and Fuel Supply
Hot in-place heaters require significant fuel, typically propane or LNG. Before the winter paving season begins, heaters should be serviced, burners cleaned, and fuel lines checked. Gallagher Asphalt relied on its existing fleet of pre-heaters used for its HIR operation, avoiding major capital investment.
Paver and Roller Preparation
Hydraulic systems need the correct viscosity oil for low temperatures. Screed heaters should be tested before each shift. Roller drums must be properly lubricated and vibratory systems checked, because cold metal is more brittle. All equipment should be stored in a heated area overnight when possible.
Crew Safety in Cold Conditions
Working in freezing temperatures presents risks including hypothermia, frostbite, and slips. Crews should wear layered cold-weather clothing, insulated boots, and gloves. Warming stations should be available near the work area. The proximity of hot equipment such as heaters and hot mix creates additional hazards that require constant awareness.
Cold Weather Equipment Maintenance
Diesel engines need special attention in cold weather. Contractors should use winter-grade diesel fuel, install block heaters, and ensure batteries are fully charged. Air systems need functioning dryers to prevent freeze-ups in brake lines. A pre-start inspection checklist can help catch issues before they cause downtime.
Conclusion: Making Winter Paving a Strategic Advantage
The Gallagher Asphalt project on the I-80/I-90/I-94 interchange proves that winter paving is a practical, proven approach. By using hot in-place heaters to thaw subgrades, dry surfaces, and warm the base, contractors can extend the paving season by four to six weeks or more. This allows highway agencies to complete critical work, avoid costly spring remobilization, and keep traffic flowing safely through construction zones during the harsh winter months. The technique also reduces the pressure to rush work during the regular season, improving overall quality on all projects.
For contractors considering cold weather paving, the keys to success are preparation, the right equipment, and adapting traditional practices. Investing in pre-heaters, adjusting mix designs, tightening rolling patterns, and monitoring temperatures all contribute to quality results in cold conditions.
For additional guidance on cold weather asphalt paving strategies that cover mix design and rolling patterns in greater depth, see our dedicated resource. Contractors should also review our guide on temperature monitoring for asphalt paving to ensure quality control in challenging conditions. Those interested in the equipment side can explore how hot in-place recycling preserves county roads and budgets, and for broader compaction guidance, see our article on achieving optimum compaction in asphalt paving.