prime coat vs tack coat?

[swazimatt]

An existing chip and spray road is going to be widened and given a 30mm continuously graded asphalt overlay.

I will specify a prime coat for the widened portions, where a new base (crushed stone base) and sub base layers (stabilised gravel) will be constructed, do i then need to specify a tack coat for where the asphalt will overlay the existing chip and spray surface?

 

[Debaser]

It looks like the concensus is use a tack coat unless the existing surface you are covering is less than 10 days old, or thereabouts.

http://www.techtransfer.berkeley.edu/newsletter/08-4_09-1/ptu_tack-coat-between-pavement-layers.pdf

 

[Drumchaser]

We do not tack over an existing chip seal before placing new ACP, unless it is severely deteriorated. The new ACP (300 deg.) usually livens up the old chip seal to the point where you do not need a tack coat.

As most overlays "here" are placed during hot to mild temp.s, a tack coat on a chip seal usually makes one hell of a mess with tracking and such. The shuttle buggy tires, the paver tires (tracks not so bad) and the delivery truck tires, all combine to make a mess with most of the tack coat ending up on everything except the roadway.

I would set up a chip seal for the widening sections (in addition to the prime)to seal the base course(s).

Side note...... we mostly see the tack coat as incidental to the ACP item, and is not a pay item.