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RE: SOG Cracks

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Differential settlement CAN be an issue.  But more likely is shrinkage and differential curling.  Clay soils with a sustained load would be more prone to differential settlement as opposed to sandy soils. 
Another factor is time.  The clock starts when it is placed.  You will not plateau out on the shrinkage until about 5 years time, but about 80 to 90% will happen in the first year.  The first 90 days will account for about 60% of the shrinkage. 
The above observations will apply to all aspects below. 
Sandy soils would be more prone to consolidation and could settle with vibrations. 

Regards, Harold Sprague

> Date: Wed, 21 Oct 2009 19:18:30 -0400
> From: akester(--nospam--at)
> To: seaint(--nospam--at)
> Subject: SOG Cracks
> Harold et al,
> This is a bit of a loaded question, but I just want to test the waters on this. I have my ideas...
> What are your opinions as to the possiblity of settlement (slight, say, less than 1" over 10ft or so) causing hairline to 1/16" wide cracks in typical, residential, concrete slabs-on-grade (I don't like the new slab on "ground")? What if there were micro to hairline existing cracks, do you think settlement could exacerbate them?
> I know there is a difference in a floating slab that buts against a CMU stem wall, but for the most part I mean single story, thickened edge monolithic slab-foundations, supporting wood frame and CMU.
> Part 2: what about standard residential pool deck slabs and driveway slabs? Take into account that many times the pool deck slab is placed over the pool shell wall and a bond forms.
> Part 3: Could ground vibrations due to construction activity cause or exacerbate cracks in concrete SOG?
> I know, who cares, all SOG crack and are non structural. Poor workmanship, not enough CJ, better design mix and curing, proper placement of WWR, etc etc. But please humor me...
> Could you direct CC me your opinions also at akester(--nospam--at) ?
> Thanks list,
> Andrew Kester, PE
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