3.3.7 Strain Alleviating Membrane Interlayer (SAMI)
A strain alleviating membrane interlayer (SAMI), as with a SAM, alleviates mechanical strains that occur in a road pavement; however, SAMIs are placed as an interlayer beneath asphalt layers (Figure 3.10). They are not intended to be used as a permanent wearing course, and should be covered by asphalt within a few days.
SAMIs should only use aggregates of size 10 mm or larger, applied at a light spread rate that is sufficient to carry construction vehicles to place the asphalt layer. The binder in a SAMI is usually heavier in application rate and more heavily modified than a SAM binder.
Care must be exercised if allowing traffic onto a SAMI in extremes of hot or cold weather.
In hot weather, the heavy binder application in a SAMI can lead to rapid flushing. This can also occur during the delivery of asphalt if trucks are channelised into the same path during the asphalt laying process.
In cold weather adhesion between the heavily modified binder and aggregate is difficult to achieve which can lead to widespread aggregate loss. In cold weather the laying of hot asphalt over the SAMI will reactivate the binder in the SAMI.