Contraction joints spacing: If slab depth is 6 inches, spacing should be every how many inches?

Contraction joints spacing: If slab depth is 6 inches, spacing should be every how many inches?

• A. 12
• B. 15
• C. 18
• D. 24

Answer: (B)

Contraction joints manage shrinkage cracks by giving them a controlled place to occur. The spacing of these joints is typically tied to the slab thickness, with a common guideline of about 2 to 3 times the slab depth. Using a midrange value of 2.5 times thickness provides practical spacing. For a 6-inch-thick slab, that yields 2.5 × 6 = 15 inches, so joints are placed about every 15 inches. The other options correspond to the ends of the typical range (12 inches = 2×, 18 inches = 3×), but 15 inches reflects the common midrange spacing used in practice.

Contraction joints manage shrinkage cracks by giving them a controlled place to occur. The spacing of these joints is typically tied to the slab thickness, with a common guideline of about 2 to 3 times the slab depth. Using a midrange value of 2.5 times thickness provides practical spacing. For a 6-inch-thick slab, that yields 2.5 × 6 = 15 inches, so joints are placed about every 15 inches. The other options correspond to the ends of the typical range (12 inches = 2×, 18 inches = 3×), but 15 inches reflects the common midrange spacing used in practice.