A new multi-scale modeling approach based on hygro-Cosserat theory for self-induced stress in hydrating cementitious mortars

摘要

The present paper focuses on the modeling of internal stresses induced by the restrained autogenous shrinkage of hydrating cementitious matrix in cement-based mortars. At very early age (0-48 h), these self-induced stresses may be relatively high and even critical, especially for cementitious systems with low water-to-cement ratio, since the physico-chemical phenomena involved (hydration and self-desiccation) are particularly intense. To pursue the mentioned objective, an original multi-scale approach based on the application of hygro-Cosserat theory has been developed to model the self-induced stress variation in the cement paste surrounding the aggregates. In fact, the characteristic length scale parameter L_c in the Cosserat theory helps us to reduce the specimen size from macro-scale to micro-scale and even sub-micro-scale due to its explicit size effect features, which is not feasible in the classical theory, i.e. Cauchy-Bolzmann's theory. The self-shrinkage phenomenon at early age has been observed and modeled via the experiments and a freshly defined Cosserat Size effect number (CS) based upon the Representative Volume Element (RVE) concept. The proposed method is capable of treating the internal stress and could be followed by cracks appearance investigation in the cementitious matrix surrounding the sand inclusions, which should occur inside of the RVE of mortar subjected to self-desiccation shrinkage during the hydration process at early age. The occurrence of these micro-cracking networks are confirmed by Scanning Electronic Microscopy (SEM) observations at the interface cement paste/aggregate performed on different mortars at early age. By taking advantage of the time-dependent Finite Element Analysis (FEA), the numerical outcomes are well agreed with the experimental observations coming from SEM. It concludes that the inclusion creates high hygro-stress concentration around the grains: when the number of inclusions increases, this hygro-stress could lead to a micro-crack network through the matrix.