Road planings under concrete

[Tim Lamb]

Is anyone aware of possible issues? Thread elsewhere.

I have some, put down 20 years ago. Compacted, covered with dpm and 6" of mesh reinforced concrete.

Odour? Chemical reaction? EU waste directive? or...?

[Andrew Mawson]

I've heard the same rumours - 'it degrades the concrete' - well if it does I have many examples here of concrete laying over planings ! Most have a membrane between but not all. How many roads have a concrete sub base with tarmac on top - very many including the M20. Not sure how it is supposed to degrade the concrete, after all the asphalt content is waterproof as is the contained agregate.

Andrew

[harry]

I have often used planings. Never heard of any such problems.

The main thing was the occasional big lumps that had to be smashed with a sledge hammer.

[John Rumm]

Its generally not recommended as a sub base because the particle sizes are not well controlled. So you can end up with sizeable voids in it next to large lumps, that will then allow fines to migrate into them over time. Obviously of its been down 20 years then this is going to be far less of a problem its probably consolidated properly and is unlikely to move further.

[Tim Lamb]

OK. It has had 20 years of grain storage, tractor movement, barn dances etc. without visible cracking.

In view of the current Permitted Development Rights I wondered if any of the tar constituents have been declared carcinogenic or lead to the concrete deteriorating in some motorway bridge fashion.

Local planning will use any excuse to refuse domestic conversions.

>

[newshound]

I'd be very surprised if bitumen based materials directly cause concrete to deteriorate. I think the motorway bridge problem is probably corrosion of rebar because of construction errors and/or concrete cracking. I suppose that incorrect surfacing might lead to blocking of drainage channels and water pooling sub-surface leading to rebar corrosion.

Obviously, who knows if some day anything containing tar will be deemed carcinogenic, but I think the general argument is that old tarmac has lost its volatiles, and also any residual "nasties" are pretty well trapped physically, rather like the asbestos fibres in asbestos cement.