Shrinkage of concrete is primarily due to drying of newly built concrete elements. Most concrete shrinkage takes place early in the life of the structure.
Creep (continuing shrinkage of concrete over time under constant compression loads) is present in all post-tensioned structure where the force of the post-tensioning tendon produces pre-compression of concrete elements. The rate of creep deformation is slower than the rate of shrinkage.
Concrete elements also expand and contract in proportion to temperature variation. The length of longer concrete elements will commonly vary by several inches due to the combined influences of shrinkage, creep, and temperature change.
If these effects are not fully recognized, and the volume changes are not accommodated either by design or by allowing for the expected movement, parts of the structure could be distressed. A typical example of restrained volume changes is a design that creates a short column in a relatively long structure. This often happens in parking decks, especially when sloping ramp geometry results in variable column lengths.
Designers and contractors need to recognize the effects of volume change not only in the construction of new concrete structures but also during the evaluation and repair of existing concrete structures.