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Slab-on-asphalt?

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We are doing a small addition to an existing building here in Springfield, Missouri and the addition is located where part of the parking / drive area is now.  It is 1-story, slab-on-grade (or on asphalt… see below) with spread column footings and a stemwall / continuous footing around the perimeter.  The Contractor wants to dig through the asphalt for the continuous footing and spread footings, but simply place the slab on the existing asphalt parking lot.  His argument is “It’s been there for 20 years with car, truck and semi traffic and it is in great shape.”  I don’t know yet if any of that statement is true… hopefully we’ll be able to verify some or all of it. 

 

I have a few reasons why it would be better to remove all the asphalt in the building foot print, but nothing that is really a “smoking gun”.  At this point, there isn’t a geotech involved and I doubt there will be.  We typically use a 4” slab reinforced with 6x6-10/10 WWF over a 4” gravel drainage layer.  Can we place the slab on asphalt (no gravel… just a 4” slab with the 6x6 10/10 WWF?  Any advice? 

 

 

Bruce D. Holcomb, PE, SE

Structural Engineer & Vice President

Butler, Rosenbury & Partners

319 North Main, Suite 200

Springfield, MO 65806

417-865-6100

417-865-6102