Measurement of Early Age Shrinkage of Virginia Concrete Mixtures

About the report:

Concrete volume changes throughout its service life. The total in-service volume change is the resultant of applied loads and shrinkage. When loaded, concrete undergoes an instantaneous elastic deformation and a slow inelastic deformation called creep. Deformation of concrete in the absence of applied loads that result in a volume decrease is often called shrinkage and is related to moisture loss and temperature change. Drying shrinkage has been studied extensively; ASTM C 157 measures the shrinkage of concrete prisms over time. The specimens are cured and tested in a variety of ways; however, they are not tested for length change during the first 24 hr. after they are cast. Therefore, the magnitude of the early age (first 24 hr.) volume change is not measured using this standard. With the use of high-performance concrete and rapid setting cements, there is a potential for a significant early age volume change because of the increased cement content and heat of hydration within the first 24 hr after the concrete is cast. Therefore, there is a need to measure this early age volume change in order to determine its magnitude and its effect on the durability of the concrete structure. The first objective of this investigation was to develop a simple, accurate technique to measure the early age volume change of concrete. The second objective was to investigate the early age volume change of a variety of concrete mixtures used by the Virginia Department of Transportation using the developed technique to aid in determining if the mixtures tested had significant early age shrinkage, which could lead to a higher probability of concrete cracking. Measurements on a variety of concretes using the testing procedure developed showed that mixtures with lower early age shrinkage tended to have greater shrinkage at later ages relative to mixtures with greater early age shrinkage. By using this procedure, VDOT will be able to determine the total magnitude of shrinkage in various concrete mixtures, which will lead to a better understanding of the material being used. The result will be project specifications that will lead to a more durable, longer lasting, and safer concrete structure.

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