Numerical investigation of the effects of freezing on micro-internal damage and macro-mechanical properties of cement pastes

- A microstructure-based model to assess the micro-internal frost damage has been established.
- Coupled effects of water expulsion, in-pore crystallization and cryosuction are considered during freezing process.
- Reduction in mechanical properties of cement paste due to freezing/thawing has been evaluated.
- Hydraulic pressure model, ice crystallization pressure model and the newly established model in this study are discussed.

It is of significance to investigate the deterioration of cement-based systems subjected to freezing temperatures including intrinsic microstructure change and reduction in mechanical resistance. From the microstructure of materials in question, few computer models take the coupled effects of water expulsion, in-pore crystallization and cryosuction into account to assess the realistic internal damage due to frost action. By considering the coupled effects of thermal action, hydraulic pressure and crystallization pressure, this study has established a microstructure-based model to investigate the effects of freezing on micro-internal damage and the macro-mechanical property changes of cement-based systems. Two parts of work are carried out: (1) by coupling a microstructure model HYMOSTRUC3D with a 3D lattice fracture model, the freezing of water in pores and the response of cement paste to the water freezing are captured. Changes in the microstructure of cement paste, represented by the creation of microcracks, are illustrated. (2) Changes in the mechanical properties of cement paste after freezing/thawing are estimated, and the estimated Young's modulus and volume deformation during freezing are compared with those by experiment. In the discussion chapter, from the aspects of thermodynamic considerations, damage sources, crack pattern and deformation, the hydraulic pressure model, ice crystallization pressure model and the newly established model in this study are discussed.