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©2012 CivilComp Ltd 



A. Ilc^{1}, G. Turk^{2} and I. Planinc^{2}
^{1}Primorje d.d., Ajdovšcina, Slovenia
^{2}Faculty of Civil and Geodetic Engineering, University of Ljubljana, Slovenia
Keywords: early age concrete, numerical analysis, porous material, fully coupled problem, cement hydration, heat and mass transport, sorption isotherms.
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A numerical procedure for modelling fully coupled thermal, hygral and mechanical behaviour of concrete at an early age is presented. During the first days after casting, the hydration of the cement occurs which induces temperature rise, desiccation and changes in porosity, permeability, stiffness and strength.
While most researchers concentrate on concrete after the hydration is almost completed, in the papers by Gawin et al. [1,2], a fully coupled hygrothermomechanical model adapted to concrete at early age is described. The model is based on the mass, energy and linear momentum balance equations, supplemented by constitutive equations: Kelvin's law, Fick's law, Darcy's law and an assumption that moist air is a perfect mixture of two ideal gasses (dry air and vapour). Porosity, permeability, modulus of elasticity and creep compliance function are all agedependant. Deformations are proportional to the solid phase stress instead of the total stress. Creep is modelled by microprestressed solidification theory. The governing equations are expressed in terms of four primary state variables which are gas pressure, generalised capillary pressure, temperature and displacements of the solid phase and solved iteratively using a finite element method.
The present paper follows the model presented in the work by Gawin et al. [1,2], but incorporates different sorption isotherms, a different mathematical model of the hydration curve and some other changes.
A numerical example dealing with the adiabatic test is presented. In addition to the sorption isotherms suggested in [1], the calculation is repeated using different sorption isotherms (modifying formulas suggested in [3]) having parameters which are easier to determine. A good agreement between the experimental and numerical results shows the adequacy of the proposed model and of the novel sorption isotherms.

 1
 D. Gawin, F. Pesavento, B.A. Schrefler, "Hygrothermochemomechanical modelling of concrete at early ages and beyond. Part I: Hydration and hydrotermal phenomena", International journal for numerical methods and engineering, 67, 299331, 2006.
 2
 D. Gawin, F. Pesavento, B.A. Schrefler, "Hygrothermochemomechanical modelling of concrete at early ages and beyond. Part II: Shrinkage and creep of concrete", International journal for numerical methods and engineering, 67, 332363, 2006.
 3
 C.T. Davie, C.J. Pearce, N. Bicanic, "A fully generalised, coupled, multiphase, hygrothermomechanical model for concrete", Materials and structures, 43, 1333, 2010.
