(GRS 222) About the role of vapour transport during bentonite resaturation

Klaus-Peter Kröhn

Recent re-saturation experiments show in detail the time-dependent development of the water content distribution in bentonite, also considering exclusive re-saturation via water vapour. The VAPMOD code that was developed ad hoc to simulate re-saturation via water vapour showed - in comparison with the measurements of re-saturation using liquid water - the strong relevance of the diffusion of water vapour in the pore space to the re-saturation process. Although the dynamics of the re-saturation process had not yet been satisfactorily modelled, the results still suggested that this process could be reproduced with sufficient exactness by improved modelling of local re-saturation. The present report therefore shows two different ways to approach this target. The first way is to improve the very simple quantitative description of the hydration process in order to achieve with it satisfactory modelling results of re-saturation via water vapour. For this purpose analytical functions were developed from various different re-saturation experiments with water vapour which can be used to indicate the hydration rate as a function of the water content. However, the remaining discrepancies between improved model and experiment show that apart from hydration, the other major process involved in re-saturation – the transport of water within the pore space – may possibly not yet be correctly described.