Thoughts about drying shrinkage: Experimental results and quantification of structural drying creep

In this second article, we examine in greater detail the influence of concrete skin micro-cracking, linked with the non-uniformity of water content within the specimen. This cracking is responsible for the drying creep which results from a structural effect, also called “microcracking effect”, and which we prefer to call “structural creep” here. It is defined as the difference between the potential drying shrinkage of a specimen which does not crack and the shrinkage measured experimentally. We propose a simple experimental method making use of experimental curves of drying shrinkage as a function of weight loss and allowing the flanking and specification of certain properties of structural drying creep. We shall see that this method must also deal, in the interpretation of results, with the choice of the mechanical constitutive model allowing the processing of nonlinearities induced by concrete skin micro-cracking. Finally, to validate the hypotheses we have made, we shall base our approach on a probabilistic model of the cracking of concrete resulting from the work of Rossi, “coupled” with consideration of the drying of the concrete material in a sense that we shall specify. We shall see that this model is in satisfactory agreement with the curves of shrinkage as a function of weight loss. In addition, the results of simulations are very instructive, as regards the spacing and the width as well as the depth of cracks which appear in the drying shrinkage and creep tests.