Thermo-hydro-ionic Transport Of Multi-species In Cement-based Porous Materials

The deterioration of cement-based materials are determined by mass transfer processes between porous materials and environment. Understanding multi-species transport processes under multi-field conditions is crucial for the assessment on durability and service life of cement-based porous materials and concrete structures. The present thesis aims to establish a comprehensive multi-field and multi-species transport model to make reliable assessment of long-term durability of structures using cement-based materials.The multi-field and multi-species transport theory is first studied considering multi-field, solid-liquid equilibrium and gas-liquid equilibrium in material pores. The multi-fields include ion concentration field, electric field, temperature field and moisture field. The electrical field consists of external artificial electrical field and local electrical one generated from multi-ions transport. The solid-liquid equilibrium pertains to the solid dissolution equilibrium and the adsorption equilibrium of ions. The dissolution of CH and C-S-H is solved by solid solution theory. The equilibriums between vapour and pore water, and between gas phase and liquid phase are described by using chemical potential and mechanical equilibriums. Then, a thermo-hydro-ionic(THI) model is established, taking into account the heat transfer, moisture and ions transport processes. Further, the radionulcides(RN) decay and transport processes are also included.The sorption properties of cement-based materials are studied through water vapor sorption isotherm(WVSI), RN sorption and immersion tests. The THI model is validated through literature data on leaching, chloride migration and RN migration experiments. Then the influence of binders and environmental conditions on the transport processes in cement-based porous materials is investigated by the THI model.The analysis indicates that:(1) materials using OPC binder provide better leaching resistance, but lower resistance against RN migration;(2) the higher environmental pH value reduces leaching;(3) the concentration of ions influences the RN migration through local electrical field in pores.The THI model is applied to one marine immersed tube tunnel with a service life of 120 years, and a high integrity container(HIC) for radioactive waste disposal with a disposal life of 300 years. The tunnel results show that: the leaching process can be neglected during service life, the impact of thermal gradient on ions transport is more important than sea water pressure, and the embedded steel has very low risk of corrosion during service life. The HIC results show that: the leaching can notably accelerate the RN release, the rise of internal temperature and pressure due to radiolysis reaction is to augment RN release, and the thickness of HIC wall is determinant for HIC safety.