Hot In-Place Recycling

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Primary Resource

The inspector plays a vital role on every construction project ensuring that the completed operations comply with the plans and specifications. Recognizing that many agencies were inexperienced in performing hot in-place recycling, and hesitant to add the treatment to their pavement management systems because of their lack of familiarity, the Asphalt Recycling & Reclaiming Association worked with FHWA to develop the Basic Asphalt Recycling Manual (BARM). Copies of the BARM can be obtained at Information on where to obtain additional HIR resources can be found in the Additional Resources section. As with any construction process, if the owner agency is concerned with any part of the process, the owner agency should have a conversation with the contractor.

Inspection Guidelines

Inspection Guidelines

With HIR, like most paving projects, the primary goal is to produce a strong, durable wearing/leveling course from existing pavement materials. Inspectors can help achieve this goal by ensuring that the process is in accordance with the contract documents as follows: 

Mix Design: Verify representative samples were obtained throughout the project and that a mix design, if required, has been performed by a qualified lab and that the resulting mixture meets or exceeds the contract documents.

Surface Preparation: Walk or drive the entire pavement to be paved for the day to ensure the surface has been properly prepared and that all pre-construction repairs have been performed in accordance with the plans and specifications. Ensure pre-milling, if required, was performed satisfactorily.

Acceptable Weather: Measure the air and pavement temperature and check conditions for anticipated rainfall to determine if construction can start/continue.

For best results, ambient temperatures should be 45-50 oF (7-10 oC) and rising before starting HIR.

Traffic Control: Verify that the proper traffic control is in place to keep the traveling public safe and out of freshly placed HIR mat.

Quality Equipment: 

  • Verify that the on-board rejuvenating agent system of the recycling train is equipped with a meter capable of recording the rate of flow and total amount of each liquid being added to the rejuvenated material. 
  • Verify that the preheater units are of the required number and size to heat the pavement to the required temperature without undo damage to the existing pavement. 
  • Verify that the heater/scarification unit is removing the softened material to the required width and depth without breaking the existing aggregate. 
  • Check the rejuvenated mixture for uniformity and homogeneity as it is discharged onto the pavement and windrowed, or directly discharged into the paver hopper or screed. 
  • Verify that the compaction equipment is of the type, number and size required by the contract documents and that scrapers and spray bars are properly working.

Quality Workmanship: 

  • Verify that the pavement surface is being heated to the required temperature.
  • Verify that the tines or teeth are scarifying, or the milling drum is removing the existing pavement surface to the required treatment depth.
  • Verify that the rejuvenated mixture is being placed to the proper depth and cross-slope. 
  • Ensure that the longitudinal joints are straight and constructed with the required minimum overlap. 
  • Verify that a rolling pattern was established to determine the compaction procedures necessary to meet the contract requirements. 
  • Verify that the rolling procedure established is being followed and that the compacted density is within the specified range. Develop a new rolling pattern if the density of the recycled mixture is not in compliance with the specifications. 
  • Verify that traffic is not allowed back on the rejuvenated mixture until the surface can carry the traffic without damage to the mix.

White smoke is steam leaving the pavement. Excessive blue smoke is an indication of overheating the pavement.

Excessive broken aggregate is an indication of insufficient pavement temperature prior to scarification/augering/milling.

Application Rates: Periodic checks should be made to verify that the amount of material being added to the rejuvenated mixture is within the allowable tolerances of the contract documents. Spot checking the yield over a specific pavement area using the calibrated meters on the HIR train or by measuring the pavement area covered over a tanker load of material.

Additional Resources

  • Hot In-Place Recycling (HIR): ID 2590 – A Transportation Curriculum Coordination Council (TC3) web based training course for inspection of HIR pavements.
  • Hot In-Place Asphalt Recycling Application Checklist – A pocket guide to inspection of HIR projects (provided by ARRA, FHWA and FP2)