Abstract
The self-induced stress in mortars caused by autogenous shrinkage phenomenon at very early age has been investigated by taking advantage of the experimental results and application of hygro-Cosserat theory. Three cement matrices, prepared with three different types of cement, have been considered to analyze the role of cement paste composition on the development of these initial stresses surrounding the aggregates. The induced bulk deformations around the aggregates have been thereafter scrutinized by means of hygro-Cosserat elasticity taking into account the size effect in an explicit manner and a newly defined parameter called Cosserat size effect number (CS). By taking advantage of the autogenous shrinkage experiments on the cement pastes, the parallel time-dependent finite element analyses have been achieved considering the aggregate-to-cement ratio. The aforementioned parameters are put into practice to create an analytical pseudo-stochastic geometry using a spherical-packing algorithm. The numerical outcomes were analyzed and compared to the experimental outcomes coming from the Scanning Electronic Microscopy observations at 48h after hydration.
Highlights
To cite this version: Hamidréza Ramézani, Pierre Mounanga, Jena Jeong, Marwen Bouasker
The early-age autogenous shrinkage curves generally show two main phases: a first phase with a high shrinkage rate that develops from the mixing to the setting period, followed by a second phase characterized by a lower strain rate
Seems to be less sensible to the early-age micro-cracking. These observations demonstrate that the measurement of free shrinkage is not sufficient to assess the risk of early-age micro-cracking of cement paste
Summary
The physico-chemical and micro-structural evolution of earlyage cementitious matrices are characterized by significant volume variations. The early-age autogenous shrinkage of cement matrices, if restrained, may cause damage to the material: at early-age, the driving mechanisms involved in the evolution of shrinkage (hydration and Le Chatelier contraction) grow quickly This fast change, coupled with a significant increase in stiffness of the material due to its hardening, induces the development of internal stresses, when the material is not free to deform. In concrete, this situation occurs around the aggregates: in this zone, the hindering effect pertaining to the cement paste deformations gives rise to the self-induced stresses. This risk is high at early-age, during the first days of hydration, when the tensile strength of the material is still weak
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