Shrinkage-compensating concrete is made with an expansivecement or expansive component system in which initialexpansion, if properly restrained, offsets strains caused bydrying shrinkage. Since the mid-1960s, shrinkage-compensating concrete has been used in many applications.
These applications include highway and airport pavements,bridge decks (Gruner and Plain 1993; Ramey et al. 1999),hydraulic structures, wastewater treatment plants, containmentstructures (Valentine 1994), post-tensioned structures(Hoffman 1980; Eskildsen et al. 2009), parking structures, andslabs-on-ground (Keith et al. 1996, 2006; Bailey et al. 2001).
Shrinkage-compensating concrete is used to minimizecracking and structural movement caused by drying shrinkagein concrete. Drying shrinkage is the contraction in theconcrete caused by moisture loss from drying concrete. Itdoes not include plastic volume changes that occur beforesetting when surface evaporation exceeds concrete bleedingrate or length and volume changes induced by temperature,structural loads, or chemical reactions.
The amount of drying shrinkage that occurs in concretestructures depends on the constituent materials, mixtureproportions, curing, drying environment, and restraint.Tensile stresses caused by restraint to drying shrinkage canoccur before concrete tensile strength is fully developed.When concrete is restrained by reinforcement, subgradefriction, or other means, drying shrinkage causes tensile stressesto develop.
When drying shrinkage stresses exceed the tensilestrength of the concrete, it cracks. The spacing and size ofcracks that develop in structures depend on the amount ofshrinkage, degree of restraint, and amount of reinforcement.Shrinkage-compensating concrete is proportioned soconcrete volume increases after setting and during early-agehardening.