Adding 4.5" of concrete on existing slab?
Adding 4.5" of concrete on existing slab?
(OP)
a client needs to elevate existing monolithic house slab with 4.5" of concrete to meet flood elevation to get permit from city in order to start building his house on top. The slab is on piles which used to support a 2 story house that was burned down. Just a slab on grade now.
I figured additional weight of concrete would add about 56 lb/ft^2 . slab is 46' x 30' , with 4.5" of concrete. which I don't think would be an issue as for as loading.
but how would you ensure a good bong between the two slabs? should rebar be doweled between the two? or the surface of the existing slab be roughen up? more importantly, should geotechnical tests be done to determine if additional concrete is ok? Not really sure how to approach this one...
thanks
I figured additional weight of concrete would add about 56 lb/ft^2 . slab is 46' x 30' , with 4.5" of concrete. which I don't think would be an issue as for as loading.
but how would you ensure a good bong between the two slabs? should rebar be doweled between the two? or the surface of the existing slab be roughen up? more importantly, should geotechnical tests be done to determine if additional concrete is ok? Not really sure how to approach this one...
thanks





RE: Adding 4.5" of concrete on existing slab?
The composite action would only possibly help the existing slab, and maybe the grade beams, depending on the existing slab to grade beam connection.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Adding 4.5" of concrete on existing slab?
RE: Adding 4.5" of concrete on existing slab?
Another option would be to remove the slab and place 4.5" of compaced fill then pour a new slab.
RE: Adding 4.5" of concrete on existing slab?
1. Existing concrete must be in good condition (poor material removed).
2. Existing concrete must be properly cleaned... and kept that way.
3. Existing concrete must have the proper moisture content (quite damp) when the overlay is placed.
If these basic steps plus an appropriate concrete mix and good workmanship are used the bond can be more that adequate.
Here is a "Guide to Concrete Overlays" (free .pdf download) by the National Concrete Pavement Technology center. The overlays described here are for highway use, but the principles and measures outlined are appropriate for most situations.
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RE: Adding 4.5" of concrete on existing slab?
If you have the plans of the structure (highly unlikely), or know where the post and bearing lines were (a maybe), it would be best to stick to those support points as closely as possible to avoid having to fully analyze the foundation.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Adding 4.5" of concrete on existing slab?
Rather than trying to bond the two slabs, could you put down a bond breaker between them, similar to white-topping a highway?
"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928
RE: Adding 4.5" of concrete on existing slab?
If the piles can't carry the load, I like Mike's idea.
RE: Adding 4.5" of concrete on existing slab?
RE: Adding 4.5" of concrete on existing slab?