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RE: New concrete SOG on existing SOG

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I would suggest a sand or gravel layer between the two slabs to avoid reflective cracking.  Also, you may want to punch holes through the existing slab to allow drainage of any water that gets in the sand / gravel.  2" - 4" diameter holes at 10' o.c. may be reasonable, but this would depend on the potential for groundwater flow.  This may also allow you to see if there are any voids under the existing slab.

Bruce D. Holcomb, PE
Butler, Rosenbury & Partners
300 S. Jefferson, Suite 505
Springfield, MO 65806-2217
ph (417) 865-6100
fax (417) 865-6102

-----Original Message-----
From: Bill Marczewski [mailto:bill(--nospam--at)]
Sent: Tuesday, May 20, 2003 11:34 AM
Subject: New concrete SOG on existing SOG

I’ve been asked to design a (N) new concrete SOG foundation for a pre-eng. Metal building.  The site contains an existing warehouse with an (E) existing concrete SOG.  The owner wants to raise (E) SOG a total of 9” via (N) SOG, to be level with an adjacent building.  What are the lists thoughts on pouring a structural overlay slab on existing, should any sand layer be present between new and existing slab?  Owner doesn’t particularly want to pour 9” of concrete if something of a compacted road base between layers could be used.  I’m not familiar with doing this.  I’ll continue my research but would like to hear some of the rules of thumb for pouring such a slab.  Thank you.




Bill S. Marczewski, P.E.