versaengine
Geotechnical
- Jul 4, 2003
- 11
Trying to decide what to do. Called in to evaluate cracks in 3 month old floor. Here is the situation.
Pre-engineered metal building on concrete footings with concrete slab on grade floor. Building will house a community building with a ballroom, small kitchen, basketball court, bathrooms and offices. The floor will not have a finish floor material but is to be buffed, kind of like a wal-mart exposed concrete floor. The floor overall dimensions are 140' x 200'.
floor design was 4" minimum thick, 4,000 psi concrete, with 4" max slump and poly micro fibermesh and control joints in line with all columns each way spaced 20' x 25'. Soil subgrade is reportedly firm, non-expansive with 4"-6" thick clean crushed limestone base layer and vapor barrier above. There were 6 separate pours, the contractor claims dowels were placed between cold joints. Finish appears decent. They used a vibra-screed and power floats. I have asked for but have not received concrete tickets, to see how much water was added (hope I can trust if accurate?)
There are three long irregular cracks up to 3/16" separation with no vertical offset (this is what concerned the owner) that did not occur at cut joints. I believe these are drying shrinkage cracks and imo are not excessive,
BUT I found: in 2, 3/4" diameter hammer drills the slab was 3" and 3.5" thick. An impact-rebound hammer test suggests strength of concrete is OK. The joints were cut only 1/2" deep. The concrete sub-contractor has no money. The general has no money but may have insurance.
I am going to definitely recommend more 3.75" diameter cores to better evaluate thickness. But I am concerned about long term performance. If the thickness is only 3.25" thick on average, should I recommend a strengthening layer? or just monitor? I am concerned the owner did not get what he paid for. Would a rebate be in order?
Any ideas?? Thanks for any suggestions.
Pre-engineered metal building on concrete footings with concrete slab on grade floor. Building will house a community building with a ballroom, small kitchen, basketball court, bathrooms and offices. The floor will not have a finish floor material but is to be buffed, kind of like a wal-mart exposed concrete floor. The floor overall dimensions are 140' x 200'.
floor design was 4" minimum thick, 4,000 psi concrete, with 4" max slump and poly micro fibermesh and control joints in line with all columns each way spaced 20' x 25'. Soil subgrade is reportedly firm, non-expansive with 4"-6" thick clean crushed limestone base layer and vapor barrier above. There were 6 separate pours, the contractor claims dowels were placed between cold joints. Finish appears decent. They used a vibra-screed and power floats. I have asked for but have not received concrete tickets, to see how much water was added (hope I can trust if accurate?)
There are three long irregular cracks up to 3/16" separation with no vertical offset (this is what concerned the owner) that did not occur at cut joints. I believe these are drying shrinkage cracks and imo are not excessive,
BUT I found: in 2, 3/4" diameter hammer drills the slab was 3" and 3.5" thick. An impact-rebound hammer test suggests strength of concrete is OK. The joints were cut only 1/2" deep. The concrete sub-contractor has no money. The general has no money but may have insurance.
I am going to definitely recommend more 3.75" diameter cores to better evaluate thickness. But I am concerned about long term performance. If the thickness is only 3.25" thick on average, should I recommend a strengthening layer? or just monitor? I am concerned the owner did not get what he paid for. Would a rebate be in order?
Any ideas?? Thanks for any suggestions.
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