In order to function properly, vertical and horizontal construction joints must be carefully located and built correctly.
WHERE TO INSTALL CONSTRUCTION JOINTS
The engineer or contractor should consider economy, appearance, strength, and durability when choosing joint location.
- Economy--Placing a construction joint in a practical spot, such as between footing and walls, avoids complex, costly formwork.
- Appearance--Construction joints often are installed in an inconspicuous position.
- Strength--A construction joint introduces a weak vertical or horizontal plane in an otherwise monolithic concrete member. This obvious slip plane may reduce the strength of beams, columns, and walls.
- Durability--The location of construction joints also is affected by whether or not water and salts can easily enter the joint.
ACI REQUIREMENTS FOR CONSTRUCTION JOINT DESIGN
Because construction joints are most likely to reduce shear strength, they should be located where shear forces are low. The American Concrete Institute (ACI) Building Code covers joint location and other related subjects, such as shear keys, diagonal dowels, and the shear transfer method.
HOW TO FORM CONSTRUCTION JOINTS
Deciding where to put construction joints is only half the job. The other half is forming them correctly and cleaning the joint surface before the next concrete placement.