Modelling the sorption hysteresis and its effect on moisture transport within cementitious materials
| Main Author: | zhang, zhidong |
|---|---|
| Format: | Report |
| Bahasa: | eng |
| Terbitan: |
, 2014
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| Subjects: | |
| Online Access: |
https://zenodo.org/record/3244881 |
Daftar Isi:
- The durability of reinforced concrete structures and their service life are closely related to the simultaneous occurrence of many physical and chemical phenomena. These phenomena are diverse in nature, but in common they are dependent on the moisture properties of the material. Therefore, the prediction of the potential degradation of cementitious materials requires the study of the movement of liquid-water and gas-phase transport in the material which is considered as a porous medium. In a natural environment, structures are always affected by periodic variations of external relative humidity (RH). However, most moisture transport models in the literature only focus on the drying process. There are few studies considering both drying and wetting, although these conditions represent natural RH variations. Much fewer studies take into account hysteresis in moisture transport. Therefore, this work is devoted to a better understanding of how the moisture behaviour within cementitious materials responds to the ambient RH changes through both experimental investigations and numerical modelling. In particular, the consideration of hysteresis will be included in numerical modelling. In the research, a multiphase continuum model was recalled firstly. According to theoretical analysis and experimental verifications, a simplified model was obtained for the case that the intrinsic permeability to liquid-water is much smaller than the intrinsic permeability to gas-phase. The review of commonly-used hysteresis models enabled to conclude a set of best models for the prediction of water vapour sorption isotherms and their hysteresis. The simplified model was coupled with the selected hysteresis models to simulate moisture transport under drying and wetting cycles. Compared with experimental data, numerical simulations revealed that modelling with hysteretic effects provided much better results than non-hysteresis modelling. Among different hysteresis models, the use of the conceptual hysteresis model, which presents a closed form of scanning loops, showed more accurate predictions. Further simulations for different scenarios were also performed. All comparisons and investigations enhanced the necessity of considering hysteresis to model moisture transport for varying RH at the boundary. The investigation of moisture penetration depth could provide a better understanding of how deep moisture, as well as ions, can move into the material. Furthermore, this research investigated different methods to determine the liquid-water intrinsic permeability, including the inverse analysis with different boundary conditions and fitting measured apparent diffusivity values for different equations to calculate relative permeabilities.