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Publication Detail
Multiscale Study of Ionic Diffusivity in Non-saturated Blended Concrete
  • Publication Type:
    Thesis/Dissertation
  • Authors:
    Liu C
  • Date awarded:
    28/09/2021
  • Awarding institution:
    University College London
  • Language:
    English
Abstract
Blended cements with supplementary cementitious materials (SCMs) have been widely used in concrete as binders to replace Portland cement, which can not only improve the sustainability by reducing CO2 emissions but also enhance the engineering properties and durability of concrete. Ionic diffusivity in concrete is a crucial parameter for predicting service life and assessing durability of concrete structures, which is highly dependent on its microstructure, moisture content and moisture distribution in pore network. The effects of SCMs on ionic diffusivity in saturated concrete have been extensively studied, while the ionic diffusivity in non-saturated blended cement concrete considering its 3D microstructural characteristics at multiscale from nano- to meso-scale has not been investigated. This thesis presents an integrated multiscale framework for modelling ionic diffusivity in non-saturated limestone/fly ash blended cement concrete accounting for the microstructural features, electrical double layer (EDL) effect, and 3D moisture distribution. The 3D structures of blended cement concrete at multiscale including calcium silicate hydrate (nano-scale), cement paste (micro-scale) including bulk paste and interfacial transition zone, mortar and concrete (meso-scale) is simulated, based on which the fluid-solid interaction and moisture distribution in pore network of concrete with various saturation levels are mimicked using a lattice Boltzmann multiphase model and the influence of EDL effect on ionic diffusivity in pore solution of concrete is estimated using an analytical model. A lattice Boltzmann-finite difference model for diffusion is developed to simulate the ionic diffusivity in concrete at multiscale. Results indicate that the ionic diffusivity in non-saturated concrete highly depends on degree of water saturation, water-to-binder ratio, binder type and multiscale structural characteristics including gel pores, capillary pores, interfacial transition zone and aggregate attributes. This research provides new insights into the mechanisms of ionic diffusion in non-saturated blended cement concrete and offers guidance for service life design and prediction of concrete structures.
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