Why did the Control Joints not work? 1

[TonyES]

I inspected a PEMB that had large (8'x8'x2') footings at each column. Columns were spaced 25' apart on gridlines that are 50' apart. The contractor poured the footings monolithically with the 5" slab on grade (#4 @18" ocew). Control joints were 15' square grids. I'm told that cracks began about 9' away from the columns in a circular pattern and than propogated throughout the building. Cracks go right through the control joints into all sections (a section being a 15' x 15' square area of the slab as outlined by the control joints). The slab was exposed to rain and snow for 3 months prior to the roof being placed. The cracks began (apparantly) 3 weeks after the initial pour and slowly progressed over months. Weather was not too cold or hot during these first three weeks. The roof is now on and its been 6 months and the cracks seem to have stopped. I would appreciate any thoughts on why this happened and how to prevent it. Why did they first crack and why didn't the control joints stop them from propogating? Inspections document that the contractor did things correctly but who really knows. I realize more info is needed and I thank you all for your input.

 

[hokie66]

Agree with demayeng. If you don't reduce the amount of reinforcement crossing joints, they often don't open.