Drying creep of concrete in terms of the age-adjusted effective modulus method

Abstract

The problem of drying creep of concrete is considered. It is emphasized that there is no single explanation of the paradoxical concrete performance known as the Pickett effect. The existing experimental data cannot clearly distinguish between the different mechanisms of drying creep, namely microcracking and stress-induced shrinkage. The phenomenological approach describing drying creep under tension as a sum of shrinkage-induced creep and creep-induced shrinkage is corrected by taking into account the swelling deformation of sealed concrete in basic creep tests. In such a way, the drying creep strain represents only the extra creep component, and therefore the mechanism of drying creep based on the stress-induced shrinkage is called into question. A new phenomenological approach to the problem of drying creep using the terms of the age-adjusted effective modulus method is demonstrated. The work done by a concrete element under simultaneous loading and drying is represented as restrained shrinkage in addition to basic creep under gradually developed stresses. It is shown that the drying creep strain depends on the values of the ageing coefficients for basic and drying creep and on the individual components of the concrete deformation; instantaneous strain, basic creep and free shrinkage. It is found that the instantaneous strain plays a minor role. The experimental data from the creep tests under tension are used to calculate the ageing coefficient ofconcrete for basic creep.