According to standard guidelines, contraction joints should be spaced in feet equal to what factor of the slab depth in inches?

According to standard guidelines, contraction joints should be spaced in feet equal to what factor of the slab depth in inches?

• A. 1 times the slab depth in inches
• B. 2 1/2 times the slab depth in inches
• C. 3 times the slab depth in inches
• D. 4 times the slab depth in inches

Answer: (B)

Contraction joints are placed to control where cracks form as concrete shrinks during curing. To effectively relieve shrinkage stresses, guidelines specify that the spacing, in feet, should equal 2 1/2 times the slab depth, in inches. This means a 4-inch slab would have joints about 10 feet apart, and a 6-inch slab about 15 feet apart. A smaller multiplier would create joints too frequently, while larger multipliers risk cracking occurring between joints. So the recommended spacing is 2 1/2 times the slab depth in inches.

Contraction joints are placed to control where cracks form as concrete shrinks during curing. To effectively relieve shrinkage stresses, guidelines specify that the spacing, in feet, should equal 2 1/2 times the slab depth, in inches. This means a 4-inch slab would have joints about 10 feet apart, and a 6-inch slab about 15 feet apart. A smaller multiplier would create joints too frequently, while larger multipliers risk cracking occurring between joints. So the recommended spacing is 2 1/2 times the slab depth in inches.