Fillcrete under slab-on-grade

[pbc825]

I specified granular fill under a new slab-on-grade. As our winter is more or less upon us in Saskatchewan, the contractor has asked whether the fill could be replaced with 5 MPa fillcrete. Our typical slab-on-grade includes reinforced concrete over a poly-barrier over at least 150mm of well compacted granular fill. Any weak spots identified during proof rolling to be excavated and filled.

As I've never specified fillcrete before I have a few questions/concerns:

1) Is fillcrete permeable like granular fill, or should that be a concern? There's a sandy/silt layer under the would-be granular fill.
2) Does fillcrete change in volume, or shrink, during curing? If so, is it any more so than compacted granular fill? Perhaps the most compaction will occur under the fillcrete.
3) Where should the poly barrier go; over or under the slab? Or do I no longer need a poly barrier?
4) Are there any special specifications or notes that should be included on the drawing set?
4) Are there concerns over and above the ones I have listed?

Thank you in advance,
Paul

 

[msquared48]

The purpose of the granular fill is not only load bearing, but to serve as a capillary break. I do not see this happening with what is termed "fillcrete", and that I see as basically CDF (Controlled Density Fill).

Without further information, I would have to say no.

Mike McCann
MMC Engineering

 

[pbc825]

Good point Mike. Thank you for your input.

 

[dik]

If you have poly between the CLSM and concrete slab, you should have no issues, except if the CLSM is non-uniform and you have 'soft' spots, or 'hard' spots. I've used CLSM in potash mines to 'smooth' the surface to place the concrete on.

As Mike notes, one of the purposes of granular material is to act as a bit of a capillary break... this is recognised by the Ontario Building Code as well... I haven't had much confidence in this, in particular, if your fine material is in the range of 7 or 8% or more.

Dik