I thought it was a pretty simple thing to recycle asphalt: grind up highways, melt them down, and pave with them. It turns out it's best to have less than 15% recycled material.
"However, in the case when higher amounts of recycled ashpalt (i.e. greater than 25%) are used, the stiffness properties of the mixture increase (significantly in some cases) and it may be necessary to lower the performance grade of the binder or use blending charts..."
There are competing engineering concerns of the pavement getting too runny (forming ruts) or being too stiff and forming cracks in winter (thermal cracks, like the cracks on molasses cookies,) let alone environmental concerns of asphalt petrochemicals leaching into the water supply.
A recent paving project on Seattle's Vashon island, where environmental concerns run high, caused a lot of angst. Those keen to recycle wanted these truckloads of material to stay on the island. Those wanting protection of the Puget Sound watershed wanted the material trucked off the island - 1250 dump truck loads. Vashon has been designated a "critical aquifer recharge area," which means anything that could damage groundwater has to be reviewed and permitted.
It sounds like the contractor delivered the asphalt millings to local islanders to use as gravel, to save money, and is now being fined for it because of concerns that rainwater will leach chemicals out of the asphalt millings.
It will be interesting to see what happens - this asphalt was already sitting on the island as road surface, exposed to rain, and now it's finely ground so it has more surface area but otherwise it's the same substance that was on the roads, passing little new environmental concern.
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