4. Possible choices for drying calculations#

It is possible to model the drying of concrete under the effect of the water gradient (simplifying hypothesis that makes it possible to model only drying by diffusion and not by advection for example) with the operator THER_NON_LINE, (cf. [R7.01.12]). The model should only include concrete, modelled using solid or surface elements, preferably linear (especially if we follow up with a mechanical calculation). The recommended models are 3D_ DIAG, PLAN_DIAG and AXIS_DIAG (but 3D, PLAN or AXIS are also possible). 4 laws are available to represent the evolution of the diffusion coefficient \(D\) as a function of water concentration and possibly temperature. The expressions for each are given in [U4.43.01].

  • SECH_MENSI, where \(D\) is a function of water concentration;

  • SECH_GRANGER which is equivalent to SECH_MENSI but takes into account thermal activation (i.e. the acceleration of drying when the temperature increases);

  • SECH_BAZANT, where \(D\) is a function of humidity (linked to water concentration by sorption function);

  • SECH_NAPPE which makes it possible to define any evolution for \(D\) in the form of a table as a function of water concentration and temperature.

Drying can then be taken into account in the mechanical calculation in the form of a control variable SECH, which corresponds to the water concentration in the concrete.

Note

For more complex drying cases (for example drying under the effect of a pressure gradient), it is necessary to use Thermo-Hydro-Mechanical modelling which treats the equations of the mechanics of continuous media using the theory of porous media that may not be saturated and considering that mechanical, thermal and hydraulic phenomena are completely coupled, see r7.01.10 and u2.04.05.

The identification of material parameters is based on a mass loss curve. An example is given for the law SECH_GRANGER in the TTNV101 test.