CONTROL JOINTS IN CONCRETE FLOOR SLABS
ISSUE:
Improve the quality of floor slabs by properly specifying control joints.
BACKGROUND:
ProCATS (Proactive Claims Analysis and Tracking System) data indicates that
extensive cracking may occur in a floor slab when control joints are not properly
specified.
DISCUSSION:
Industry standards require control joints every 400 square feet. Control joints every
20 feet in both directions work well for large slabs. However, for narrow slabs, such
as in corridors or lobbies, specifying control joints every 400 square feet would
result in poor quality slabs. In a recent situation, the control joints were placed
every 50 feet, for an 8 feet wide corridor, which met the industry standard and
contract requirement, but resulted in numerous cracks.
RECOMMENDATIONS:
1. Distance between control joints must not exceed the spacing between
columns or 24 feet, whichever is smaller.
2. Provide diamond shaped isolation joints at columns.
3. Control joints should be carefully detailed at floor depressions.
FOR ADDITIONAL INFOR MATION:
Contact Krishna Banga at 202-565-9370 in the Standards Service (187C), or Dan
Edwards, SRE, Marion, IN., at 317-677-3159.
12 JULY 1996
FM-187C-DA56
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