TABLE OF CONTENTS Thermal shrinkage will occur and the object of control joints, sometimes referred to as construction joints is to avoid the random cracking that often comes about when a concrete slab dries and produces excess tensile stress. Control joint spacing depends upon the slab thickness, aggregate size, and water content, as reported by the Portland Cement Association in their articles Concrete Floors on Concrete, second edition, 1983.
| Slab Thickness | Slump of 4-6 inches (101.6 mm-152.4 mm) | Slump less than 4 inches (101.6 mm) | |
|---|---|---|---|
| Max. size aggregate less than 3/4 inches (19.05 mm) | Max. size aggregate larger than 3/4 inches | ||
| 4" (101.6 mm) | 8' (2.4 m) | 10' (3.05 m) | 12' (3.66 m) |
| 5" (126.9 mm) | 10' (3.05 m) | 13' (3.96 m) | 15' (4.57 m) |
| 6" (152.4 mm) | 12' (3.66 m) | 15' (4.57 m) | 18' (5.49 m) |
| 7" (177.8 mm) | 14' (4.27 m) | 18' (5.49 m) | 21' (6.4 m) |
| 8" (203.1 mm) | 16' (4.88 m) | 20' (6.1 m) | 24' (7.32 m) |
| 9" (228.6 mm) | 18' (5.49 m) | 23' (7.01 m) | 27' (8.23 m) |
| 10" (253.9 mm) | 20' (6.1 m) | 25' (7.62 m) | 30' (9.14 m) |
The term control joint is often used as being synonymous with construction joint, however, there is a difference between the two. A control joint is created to provide for movement in the slab and induce cracking at that point, whereas a construction joint is a bulkhead that ends that day s slab pour. When...
