372
As concerns the initial condition, it is interesting to notice that the initial pressure head,
which was derived from the optimized hydraulic parameters and the estimated saturation degree
of 0.646 for concrete C-15-A is equal to 2100 m. The latter value is far from the one derived
from Eq. (2) when applying a relative humidity of 54% (as in the capillary absorption test), i.e. h
= 8500 m. This is an indication that the samples did not yet reach an equilibrium moisture
content nor a capillary pressure commensurate with the imposed vapour pressure boundary
condition, and hence that a much longer equilibration time is needed.
CONCLUSIONS
Of significant importance to long-term prediction of water and radionuclide migration in
concrete is the choice of a suitable hydraulic model and the determination of accurate
unsaturated hydraulic parameters. In a first part, we estimated the van Genuchten retention curve
parameters using experimental moisture retention data encompassing both the wetting and drying
branch. In a second part, numerical simulations of a capillary absorption experiment were
performed. Results showed a satisfactorily agreement between model and data when the van
Genuchten-Mualem parameters (
D
, n,m,
T
r
, K
s
, l) were fitted simultaneously to both water
retention data and capillary absorption data. Because optimized K
s
values resulted in a good
description of the capillary absorption test and are in agreement with literature values for similar
concrete and mortar, the K
s
values (5.67×10
-13
m/s and 5.87×10
-14
m/s for concrete and mortar,
respectively) are considered appropriate for use in saturated-unsaturated flow calculations.
ACKNOWLEDGMENTS
The authors acknowledge M. Th. van Genuchten for providing useful comments on a this
paper. Data was kindly provided by the Eduardo Torroja Institute for Construction Science,
Madrid, Spain. This work has been performed as part of the project on disposal of category A
waste – short-lived low and intermediate level waste (LILW-SL) – carried out by
ONDRAF/NIRAS, the Belgian Agency for Radioactive Waste and enriched Fissile Materials.
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