Petition to stop the use of SMA

Being a highway engineer, i thought I would add my two pennies;

SMA or Stone Mastic Alsphalt is used more commonly then any other surfacing as it offers the best noise reduction. The reason for this is that it employs a "reverse texture". The best way to describe it is to imagine a cheese grater. The grating side is like normal old fashioned Hot Rolled asphalt with the lumps being the stones. Turn the grater over and now the depressions are the gaps between the stones ala SMA and its these depressions which absorb the noise making it quieter. In the dry the grip is about the same but in the wet with SMA you can get water retention in the deppressions, especially on flat roads. There is also concern amongst engineers over the first bad winter we have with a prolonged cold spell with black ice, as the feeling is that for the very same reason as the rain problem there is a risk it will become, put simply, bloody dangerous.


THe Stuff that unfortunately you dad died on is called surface dressing. IT seems that it is getting used more and more these days as a cheap repair when originally it was only used on low use country roads. Councils are always looking to cut the budget for maintenance and I can only guess that the engineers thought that to surface dress the road was better than leaving it in the state it was previously in with the little money they had.

The comment was made about the seepage of oils from SMA during the first month or so. This is partly right but applies to all surfacing not just SMA. when first laid there are residual oils left in the surfacing which only come out when it has been trafficked for a while. THere is no way at the moment to artificially age aurfacing at the moment, so if you know a road has recently been relayed take it easy for a few weeks.