Hot-in-Place Paving and Its Role in Modern Road Rehabilitation

[MikePhua]

What Is Hot-in-Place Recycling
Hot-in-place recycling (HIPR) is a specialized method of asphalt pavement rehabilitation that reuses existing road material by heating, softening, and remixing it directly on the roadway. Unlike traditional mill-and-overlay techniques, HIPR eliminates the need to haul away old asphalt and bring in new hot mix, reducing material costs, emissions, and traffic disruption.
The process involves a train of machines that heat the pavement surface using infrared or propane burners, scarify the softened layer, add rejuvenating agents or new asphalt binder, and then remix and relay the material using a paving screed. Some systems include a shuttle buggy or windrow elevator to transfer the recycled mix to a conventional paver.
Equipment and Process Configuration
HIPR trains typically consist of:

• Preheaters: Infrared or flame-based units that raise surface temperature to 300–350°F
  
• Scarifiers: Rotary or rake-style tools that loosen the softened asphalt
  
• Additive injectors: Systems that spray rejuvenators or emulsion into the mix
  
• Remixers: Auger or paddle mixers that homogenize the material
  
• Pavers: Screeds that lay the recycled mix to desired grade and slope
  
• Rollers: Vibratory or pneumatic compactors that achieve final density
  

Some advanced systems include robotic arms or mini excavators to expose manholes and drainage structures during paving. These integrated features reduce labor and improve finish quality.
Economic and Environmental Benefits
HIPR can reduce paving costs by 30–50% compared to conventional methods. The savings come from:

• Eliminating trucking and disposal of milled material
  
• Reducing new aggregate and binder consumption
  
• Lowering fuel use and greenhouse gas emissions
  
• Minimizing lane closures and traffic delays
  

In Philadelphia, HIPR was used on several arterial roads, saving the city over $1 million in resurfacing costs during a single season. In Saskatchewan, a pilot project covered 75 lane kilometers, with plans to expand based on performance and cost metrics.
Challenges and Limitations
Despite its advantages, HIPR faces several operational and technical challenges:

• Slow production rates: Typical speeds range from 3 to 5 feet per minute, limiting throughput
  
• High fuel consumption: Infrared heating requires large volumes of propane or natural gas
  
• Limited depth: HIPR typically addresses only the top 1.5 to 2 inches of pavement
  
• Weather sensitivity: Cold or wet conditions can reduce effectiveness and compaction quality
  
• Equipment complexity: Trains require skilled operators and coordinated movement
  

In New Mexico, HIPR was trialed on Interstate 25 in the mid-1990s. While the surface finish was smooth and aggregate blending improved, the method was deemed too slow for high-volume interstate work.
Regional Adoption and Industry Players
HIPR is used seasonally in regions like Queensland, Australia, where contractors deploy the method for three months each year. In New York, the state Thruway Authority has experimented with heater scarification followed by Novachip micro-surfacing, comparing results across northbound and southbound lanes.
Companies such as Highway Rehab Corp and former manufacturers like Enviro-Pave have contributed to the development and deployment of HIPR systems. Although some firms have exited the market, others continue to refine the technology and expand its use.
Operator Perspectives and Field Experience
Opinions among paving crews are mixed. Some appreciate the reduced material handling and environmental benefits, while others find the process tedious and less forgiving than conventional paving. One operator noted that the recycled surface often blends aggregate more evenly, reducing segregation and rough spots. Another commented that HIPR requires more patience and coordination but delivers a superior finish when done correctly.
A retired mill operator recalled working with HIPR systems in the 1980s and 1990s, describing them as “always in the game” despite fluctuating popularity. He emphasized the importance of training and equipment maintenance to ensure consistent results.
Conclusion
Hot-in-place recycling is a viable and increasingly relevant method for asphalt pavement rehabilitation. While not suited for every project, it offers compelling advantages in cost, sustainability, and surface quality when applied under the right conditions. As cities and contractors seek greener, more efficient solutions, HIPR stands as a testament to innovation in road construction—reclaiming the past to pave the future.