Dowel Spacing

Slab Depth in. (mm)	Diameter  (bar number)	Total length in.  (mm)	Spacing in. (mm) center to center
5" (126.9 mm)	#5	12 in. (304.8 mm)	12 in. (304.8 mm)
6" (152.4 mm)	#6	14 in. (355.6 mm)	12 in. (304.8 mm)
7" (177.8 mm)	#7	14 in. (355.6 mm)	12 in. (304.8 mm)
8" (203.1 mm)	#8	14 in. (355.6 mm)	12 in. (304.8 mm)
9" (228.6 mm)	#9	16 in. (406.4 mm)	12 in. (304.8 mm)
10" (253.9 mm)	#10	16 in. (406.4 mm)	12 in. (304.8 mm)

Maximum Spacing of Control Joints

	Slump of 4-6 inches (101.6 mm-152.4 mm)
Slab Thickness	Max. size aggregate  Less than ¾  inches (19.05 mm)	Max. size aggregate larger than  3/4 inches	Slump less than 4 inches  (101.6 mm)
4" (101.6 mm)	8' (2.4 m)	10' (3.05 m)	12' (3.66 m)
5" (126.9 mm)	10' (3.05m)	13' (3.96 m)	15' (4.57m)
6" (152.4mm)	12' (3.66 m)	15' (4.57 m)	18' (5.49 m)
7" (177.8mm)	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 mm)	25' (7.62 m)	30' (9.14m)

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 control joints are created by bulkheading off a slab pour, rather than saw-cutting after the slab has been poured, steel dowels are often inserted in the bulkhead to increase load transfer at this joint.

Control Joints

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.