Keywords: hygro-thermo-chemo-mechanical performance of concrete, two scale model, internal curing, multiphase material, porous media mechanics.

In this work a novel numerical model of hygro-thermal and hydration phenomena in concrete at early ages is presented. This is a solidification-type model where all changes of material properties are expressed as functions of the hydration degree, and not the maturity nor equivalent hydration period as in the maturity-type models. A mechanistic approach, typical in the mechanics of porous media, was used to obtain the governing equations, by means of a hybrid mixture theory. The final equations, mass (water species and dry air), energy and momentum balances were written in terms of the chosen primary variables: gas pressure, capillary pressure, temperature and displacements. The model [1,2] takes into account full coupling between hygral, thermal and chemical phenomena, as well as changes of concrete properties caused by hydration process, i.e. porosity, density, permeability. Phase changes and chemical phenomena, as well as the related heat and mass sources are considered. For a more detailed description of the mathematical model, the governing equations and the constitutive relationships, see [1,2].

A method of two-scale modelling of concrete, based on the so-called numerical homogenization approach has been recently developed. The macroscopic, effective properties of the material are obtained by means of up-scaling of the results from the meso-scale. At the meso-level, the representative elementary volume (REV) of the material is modelled as a composite, made of the inclusions of water reservoirs and the surrounding maturing concrete. The simulations focus on up-scaling of the transport mechanisms of water from internal water-reservoirs into concrete and determination of the effective properties for macro-scale simulations. The detailed analysis of fluxes of thermodynamic quantities in REV is carried out in order to obtain the transport properties of the medium at the macro-level.

This model is applied for the analysis of hygro-thermal phenomena and deformation of cement based materials exposed to internal curing. Numerical simulations carried out, focus on the influence of pre-saturated water reservoirs dispersed in concrete (light weight aggregates or super absorbent polymers), upon the effective properties of the material and its performance during maturing and exploitation in different environmental conditions. The results of the numerical simulations are verified by comparison with some published experimental data.

1

D. Gawin, F. Pesavento, B.A. Schrefler, "Hygro-thermo-chemo-mechanical modelling of concrete at early ages and beyond. Part I: Hydration and hygro-thermal phenomena", Int. J. Numerical Meth. in Engng, 67, 299-331, 2006. doi:10.1002/nme.1615

2

D. Gawin, F. Pesavento, B.A. Schrefler, "Hygro-thermo-chemo-mechanical modelling of concrete at early ages and beyond. Part II: Shrinkage and creep of concrete", Int. J. Numerical Methods in Engineering, 67, 332-363, 2006. doi:10.1002/nme.1636

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