Queensland Department of Transport and Main Roads (TMR) has historically included a sprayed seal (waterproofing seal) prior to asphalt surfacing. This seal was provided to ensure waterproofing of the underlying pavement layers. Due to a recent increase in the compaction standards for asphalt, the waterproofing seal may be replaced in some instances with a tack coat. However, de-bonding (between the asphalt surfacing and the underlying pavement structure) has been observed on some projects where a waterproofing seal was not included in the design. It appears that existing practice for tack coating may not be adequate to ensure bonding between asphalt layers.
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