Tarmac overlay

[snedrub2006]

I have a quick querie regarding overlaying an existing concrete slab (400m2+). The existing slab has expansion joints as would be expected. If I overlay the concrete with 25mm of 10mm wearing course how would I be able to reduce the risk of reflective cracking. Possibly using a geotextile along the length of each joint would help with any lateral movement but how do I deal with any upward/downward movement. Also if I have applied a tack coat, wont the surface of the tarmac tear as I have adhered one surface to another, meaning I have no independant movement. Could you please advise?

[bobbi o]

you shouldnt have any problems overlaying concrete as long as its only taking light vehicular traffic at most and you'd be better with 35mm depth.it wont adhere to concrete without tack coat.

ideally you should excavate the concrete and replace with type 1,but with above restrictions you should get 10yrs out of the surface,before any problems may arise.

[Tony McC]

There's a case to be made for projecting the existing movement joints through the new overlay, but if we can assume that thermal expansion/contraction is likely to be rather minimal, any overlay of less than 50mm depth should be far better able to cope with the lateral movement than the concrete beneath.

As for vertical displacement, I think you have to accept that if the concrete slabs/bays shift upwards/downwards, then they're going to tak ethe blacktop with them and there's eff all you can do about it!