Post-tensioned concrete slabs on ground are coming into use to prevent cracking, particularly when built on expansive soils. Post-tensioning usually is a two-step process. The common practice is to lightly post-tension the slabs at an early age to prevent early shrinkage cracking. At a later age, when concrete strength is high enough, the full post-tensioning load is applied. The procedure is costly in labor because it requires that the post-tensioning be done twice. If expansive cement is used, however, it is possible to eliminate the first post-tensioning operation and enjoy another advantage as well freedom from the early cracking that sometimes occurs in the two-step process.
With post-tensioned shrinkage-compensating concrete, placement patterns are recommended that provide as much external restraint against expansion as would otherwise be provided internally by reinforcing steel. If pour strips are used for tensioning purposes, their edge forms should be left in place until the post-tensioning force is applied. Placement of one slab directly against the other for restraint is encouraged to minimize the use of pour strips. It eliminates the double bulkhead and the necessary through-reinforcement on at least one edge of the pour strip. Tensioning can be done at those edges of the slab that are on the perimeter of the floor.
Precautions have to be taken against plastic shrinkage cracking, which can occur during finishing operations. Shrinkage-compensating concrete should be cured as soon as finished. The potential level and rate of expansion of shrinkage-compensating concrete is a function of the curing efficiency. In conventional Portland cement concrete curing efficiency influences drying shrinkage while in shrinkage-compensating concrete, expansion rate is influenced as well.