Keyed construction joints are not recommended for slabs subject to heavy wheel traffic or for slabs less than how many inches thick?

Keyed construction joints are not recommended for slabs subject to heavy wheel traffic or for slabs less than how many inches thick?

• A. 4
• B. 6
• C. 8
• D. 10

Answer: (B)

Keyed construction joints provide a mechanical interlock to transfer shear between adjoining slabs. Under heavy wheel traffic, the loads are large and dynamic, and if the slab is thinner than six inches, there isn’t enough concrete section to develop and transfer that shear effectively across the key. The result can be joint slippage, spalling, or differential movement, leading to cracking and a rough, unstable surface. Because of these risks, keyed joints aren’t recommended for slabs that will see heavy wheel loads or for slabs thinner than six inches. For such conditions, alternative joint details, reinforcement, or different construction approaches should be used.

Keyed construction joints provide a mechanical interlock to transfer shear between adjoining slabs. Under heavy wheel traffic, the loads are large and dynamic, and if the slab is thinner than six inches, there isn’t enough concrete section to develop and transfer that shear effectively across the key. The result can be joint slippage, spalling, or differential movement, leading to cracking and a rough, unstable surface. Because of these risks, keyed joints aren’t recommended for slabs that will see heavy wheel loads or for slabs thinner than six inches. For such conditions, alternative joint details, reinforcement, or different construction approaches should be used.