3. Possible choices for hydration calculations

There is only one hydration model in Code_Aster that allows to describe heat release as well as hardening, cf. [R7.01.12]. It is resolved using the THER_NON_LINE operator, and the “THER_HYDR” behavior. The model should only include concrete, modelled using solid or surface elements, preferably linear. The recommended models are 3D_ DIAG, PLAN_DIAG, and AXIS_DIAG (but 3D, PLAN, or AXIS are also possible). Sufficiently small time steps should be used at a young age (of the order of one hour until the peak of thermal heating, then the time steps can be gradually increased) to obtain a good quality solution, as an explicit discretization of the heat source is used.

Temperature and hydration can then be taken into account in the mechanical calculation in the form of control variables (TEMP and HYDR). In this case, it is advisable to solve the thermal problem with linear elements.

An example of solving such a problem is covered in test case FORMA41.

Note :

It is possible not to solve the thermo-hydration problem, and to define a hydration field analytically using the commands CREA_CHAM and CREA_RESU (In this case, the heating due to the thermo-hydration reaction is overlooked). Thus, the following formula, derived from calibration LCPC, is commonly used:

\(h=\frac{t}{b+t}\) , with \(b=1684800\mathit{s.}\) , if \(t\) is the time expressed in seconds.

(cf. test SSLA103 for an example of data layout) .