Shrinkage of concrete

During the past years research has been underway at VTT to clarify the causes of concrete shrinkage and determine methods to prevent these harmful volume changes. Shrinkage is a normal property of concrete resulting from its drying and cement reactions. It is not possible to totally avoid concrete shrinkage but it can be significantly lowered by proper design and specifications. Excessive shrinkage can cause cracking and deflection of concrete structures. It is also harmful because the dimensions of the concrete element change, durability and abrasion resistance are worse, the appearance is poor, and other final concrete properties are affected. Shrinkage and damage can already occur a few hours after preparing the concrete structure, or will then occur a few weeks or months later. Concrete shrinkage happens during two stages: early age and long term. Early age shrinkage occurs from immediately after casting until the age of one day and the magnitude can be ten times that of long term shrinkage. It is most intense prior to the final setting time. This excessive shrinkage period can also be referred to as plastic shrinkage. Early age shrinkage can be significantly lowered by the material choice and on-site construction practice. Later age or long term shrinkage continues from one day onward for many years. Long term shrinkage is more well-known and is typically addressed in construction specifications and literature. This shrinkage is normally taken into account during structural design.