Cracking and Creep Role in Displacements at Constant Load: Concrete Solids in Compression

The main assumption on the basis of the identifying model of the effective law, developed by the Author, is the impossibility of considering the specimen as a continuum, when an identifying procedure from load-displacement to stress-strain in uniaxial compression is attempted. Actually, a failure mechanism with propagation of a macro-crack was found to activate from the very beginning of the uniaxial compression test forth. This leads to considering the acquired dis-placements as composed by two quotes: one constitu-tive, due to the material strain, and one of crack open-ing. Since the ratio between these two quotes is not constant during the compression test, the properties of the displacement field (which attains to structural prop-erties) cannot be transposed to the strain field (which attains to material properties) through a mere scale fac-tor. In this context, also creep takes on a different meaning, in the sense that time-dependence is an effect observed in the displacement field that does not neces-sarily correspond to a property of the strain field, i.e., the creep. In other words, it is not possible to exclude a-priori that the time-dependence of displacements is induced by crack propagation alone. A time-dependent motion of crack opening could activate and affect the displacements acquisition. The aim of the present work is to investigate the role played in displacement time-dependence both by creep and crack propagation. Re-sults of an experimental program are presented here, stating the strict relationship existing between the in-creasing of displacement and the propagation of cracks at constant load.