Volumetric variations in concrete
During its life, concrete undergoes physico-chemical changes which are responsible for dimensional variations.
Hydraulic shrinkage, before and after hardening.
This is due to the rapid loss of a proportion of the mixing water, either by evaporation or by absorption. More than a litre of water per hour can be lost by evaporation from a fresh concrete surface.
Long term hydraulic shrinkage
This is due to the slow loss of excess water in a dry atmosphere. It varies from one cement to another (depending on nature and fineness) and is proportional to the absolute volume of water in the pure paste.
High density of the concrete or a curing treatment (a film which inhibits evaporation) limits shrinkage.
This is due to sudden reductions in temperature coming either :
* from the concrete itself, as its temperature may rise in early age due to hydration and then fall later,
* or from climatic variations in the environment.
In normal concrete, total shrinkage is of the order of 200 to 300 micrometres/metre.