Engineering explanation
Concrete shrinks as it cures and continues to move with changes in temperature and moisture for years afterward. If a slab were free to shrink without restraint, it would simply get slightly smaller and no cracking would occur. In practice a slab is restrained, by friction against the subgrade, by reinforcement bonded within it, by adjoining structure, and by its own shape where one part of the panel restrains another. Restrained shrinkage puts the concrete into tension, and concrete is weak in tension, so cracks appear where the tensile stress exceeds the concrete's capacity.
Crack control works by managing that restraint rather than by trying to eliminate shrinkage. Conventional reinforcement does not stop cracks from forming; it holds them tight once they do, distributing the movement across many fine cracks instead of one wide one. Post-tensioning takes a different approach, actively compressing the slab so that the concrete stays in compression through most of its service life, which suppresses shrinkage cracking far more directly.
Restraint also comes from the base beneath the slab. A high-friction subbase, an uneven surface, or point restraints from pits and penetrations concentrate stress at predictable locations, so those locations need specific attention in the reinforcement layout and joint pattern, not just a uniform response across the whole floor.
Conditions
The reinforcement or post-tensioning strategy, the panel size, and the curing method are analysed together against the concrete mix, the ambient conditions expected during construction, and the restraint the specific subbase and geometry will generate. A strategy that performs well on one subbase can behave differently on another with higher friction or different stiffness.
Curing has a direct effect: rapid early drying increases shrinkage and the risk of early-age cracking, so the curing method and timing are part of the crack-control design, not an afterthought handled entirely on site.
Limitations
No design approach removes cracking risk entirely; the objective is to keep cracks tight enough, and few enough, that they do not compromise the floor's structural or operational performance. Statements that a floor design eliminates cracking altogether should be treated with caution, since cracking risk is a function of many site-specific and construction-related variables that cannot all be fixed in advance.
Reinforcement and post-tensioning address restrained-shrinkage cracking; they do not correct problems caused by an inadequately prepared subgrade, incorrect concrete mix proportions, or curing that is not carried out as specified. Those factors need their own quality controls during construction.
Evidence and references
The mechanics of restrained shrinkage and reinforcement-based crack control in slabs-on-ground are set out in ACI 360R-10. BICP also contributes, as a participating author, to a national concrete-structure crack-control code (reference pending official publication of its final number), which addresses the same restraint and reinforcement principles for structural applications.