53 Hot In-Place Recycling Hot In-Place Recycling (HIR) is a pavement rehabilitation method that involves the treatment and reuse of the existing asphalt pavement material, conducted on-site and in-place. HIR renews the pavement by heating, softening and rejuvenating the asphalt surface layer, which can then be remixed, reshaped and compacted to create a restored pavement structure. The HIR process includes the following steps: 1. Heating: Specialized equipment heats the existing asphalt pavement to a temperature high enough (usually around 300°F) to make it pliable and workable without causing damage to the asphalt binder. 2. Milling or Scarifying: The top layer of the heated pavement is mechanically removed (milled) or scarified to a specified depth, typically 1” to 4”. 3. Rejuvenating: A rejuvenating agent is added to the milled material to restore some of the properties lost due to oxidation and aging of the asphalt binder. 4. Mixing: The reclaimed asphalt is mixed to ensure a uniform coating of the rejuvenating agent and to achieve the desired consistency and gradation. 5. Laying: The recycled mixture is then laid back down onto the pavement using a paver. 6. Compacting: The mixture is compacted using rollers to produce a dense, smooth pavement layer. 7. Applying an Overlay (if required): In some HIR processes, after the recycled layer has been placed and compacted, an additional new hot mix asphalt overlay may be applied to provide additional structural capacity and a smooth driving surface. The benefits of HIR include: • Environmental Stewardship: HIR reduces the need for new materials and the associated environmental impacts of extraction, production and transportation. • Cost-Effectiveness: By reusing existing pavement materials, HIR can be more cost-effective than conventional remove-and-replace methods. • Speed of Construction: HIR can be performed quickly, minimizing traffic disruptions and road closures. • Energy Efficiency: The HIR process uses less energy compared to producing new hot mix asphalt. • Enhanced Pavement Performance: The process can improve pavement performance by correcting ruts, cracks and other surface distresses, restoring flexibility and improving skid resistance. HIR is suitable for pavements where the distress is confined to the upper portion of the pavement structure. The process is not recommended for pavements with severe structural deficiencies, poor subgrade conditions or where full-depth reconstruction is needed.
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