HIR is best suited for aged, oxidized, structurally sound pavements. HIR is most effective as a maintenance/rehabilitation process. Major realignments, widening or drainage corrections may make HIR less logistically practical and less cost effective.
HIR is meant to treat non-load associated distresses and minor structural distresses that occur in the top 1-3 inches of the pavement structure and can slow the return of transverse or reflective cracking. The HIR processes are not meant to address structural failures of the pavement such as structural rutting or existing mixture instability. All three HIR processes can be used for minor consolidation rutting. When a minor amount of structural rutting is present the HIR processes can be used if the asphalt overlay thickness is sufficient to address the structural deficiency.
Not all three HIR processes can correct the same pavement distresses equally and the condition of the upper layers of the pavement can have a significant impact on the HIR process selected. The types of pavement distress which can be addressed with the three HIR processes are indicated in Table 6-1 from the BARM.
Originally, HIR was limited to low or medium traffic volume roadways but it is now routinely used on high traffic volume roadways, including interstates. On two lane roadways, one-way traffic through the construction zone will need to be maintained with appropriate traffic control such as flaggers, lane demarcation devices and pilot vehicles.
The presence, frequency and elevation of utility covers (manholes and valves) needs to be assessed, particularly in an urban setting. Manholes and valves can be raised, lowered or left in place as scarification tines and teeth are spring loaded and hot mills can be raised. Manholes and vaults should be checked for flammable gasses prior to HIR.
Crack seals and surface treatments such as chip seals, slurry seals and micro surfacing can have an impact on environmental and economic considerations. They can be incorporated into the HIR mixture but they will have to be accounted for in the mix design. If surface treatments and crack seal present too great a problem, they can be removed by cold planing (CP) prior to HIR. Thermoplastic lane markings should be removed prior to HIR by CP.
There are no climate restrictions for hot in-place recycling. HIR has been used successfully in all four climate zone, dry freeze, wet freeze, dry no freeze and wet no freeze. However, there are weather restrictions during construction. See Weather Requirements for more information.