Nonlinear creep of concrete: Stress-activated stick–slip transition of viscous interfaces and microcracking-induced damage

With the aim to identify the mechanisms governing nonlinear basic creep of concrete under uniaxial compression, a micromechanics model is presented. Extending the affinity concept for nonlinear creep, it describes that every microcrack incrementally increases the damage of concrete, leading to a step-wise increase of its compliance. Experimental data are taken from the literature. Strain and acoustic emission measurements from a multi-stage creep test are used to develop the model. This includes identification of microcrack evolution laws for both short-term load application and sustained loading. Strain measurements from four single-stage creep tests are used for model validation. It is concluded that nonlinear creep of concrete is governed by two mechanisms: (i) stress-induced stick–slip transition of viscous interfaces at the nanostructure of cement paste , which is phenomenologically accounted for by the affinity concept, and (ii) microcracking-induced damage, which is of major importance once the stress exceeds some 70% of the strength .