Basic Properties of Concrete Creep, Shrinkage, and Drying
Clear and unambiguous definition and characterization of material properties is the essential basis of analysis, although it has not been achieved in much of the literature. We begin by discussing the dependence of elastic modulus on the rate or duration of short-time loading and introduce the notion of asymptotic modulus for infinitely fast loading. Then, we define the basic creep as the creep at constant moisture content, introduce the creep coefficient as the ratio of creep strain to properly defined elastic strain, and proceed to discuss shrinkage and creep of cross sections at drying exposure. Our attention is then focused on common misconceptions in measuring, defining, and reporting creep and shrinkage data, such as initial strains incompatible with the elastic modulus. We warn about false extrapolations caused by plots in linear time scale and point out problems due to autogenous shrinkage in modern concretes. Finally, we emphasize the importance of updating long-term predictions on the basis of short-time measurements on structures.