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Re: Slab on Grade and the Green Code

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My standard detail is a 5" slab w/ #4 at 12"oc on a heavy duty vapor barrier over 2" of compacted Class II base, over 5" of drain rock. This assembly was the recommendation of an ASTM working group headed by Tom Butt around 2000. Placement directly on a sand layer is the way the old-school slab finishers like it because it allows the concrete to be placed slightly wet & finished quickly with less shrinkage cracking. The sand layer creates a number of problems. However, placement directly on the membrane does need a wet cure to mitigate shrinkage. YMMV
Chuck Utzman, PE

On 12/5/2013 8:15 AM, Oshin Tosounian wrote:
Does anyone have a resolution to a conflict between the Green Building Code and the standard slab on grade base requirements, usually recommended by the soils engineer? The GBC requires the concrete to be placed directly on the vapor barrier which is directly placed over a 4" base of gravel. The standard practice and most soils engineers' recommendations is the placement of concrete over a sand base with the vapor barrier in the middle of the sand layer, then the gravel base.

Oshin Tosounian, S.E.

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