The knowledge of initial water saturation state of cementitious components of the proposed Dessel repository is of paramount importance as this provides initial condition for performance assessment calculations. The repository will remain exposed to the local climatic conditions during initial stages and thereafter it is expected to remain in a buried state for a very long time. This means the water saturation state of the cementitious components will evolve in time. To understand the evolution, for at least over few tens of years, this study analysed data of water saturation states of various laboratory and large scale concrete structures that were exposed to natural environment.
The degree of water saturation in concrete is governed by two main processes: (i) self-desiccation owing to the process of long-term cement hardening at the time scale of years to tens of years, and (ii) moisture transport in response to imposed (micro)-climatologic conditions at the concrete surface at the time scale of months to years (surface layers) or event tens of years (internal components). Several studies have indicated that self-desiccation will result in a gradual desaturation of concrete up to nearly 80%. Since this process of desaturation is governed by cement hardening, it will be rather uniform within a concrete structure, thus depending only on the amount of cement and less so on the climatological boundary conditions at concrete surfaces. Desaturation and resaturation processes will further progress at concrete surfaces in response to low or high relative humidity of ambient air and temperature. An outer shell of a few centimetres will be relatively quickly in equilibrium with the surrounding atmosphere: saturation degrees within this thin concrete layer can be very high (100%) or very low (≈20%). A drying or wetting front will then develop within the concrete, at a rate which is depending on the value of the hydraulic properties of the concrete porous medium.
Based on the available data, the estimated mean degree of water saturation for concrete components is in the region of 83%.
|Number of pages||33|
|State||Published - 1 Jun 2017|
|Publisher||Studiecentrum voor Kernenergie|