• Andersson, Tom
• Ferreira, Rui Miguel
• Laukkanen, Anssi
• Pinomaa, Tatu
• Bohner, Edgar

Abstract

<p>Concrete in cold environments is subject to a unique combination of transport and deterioration mechanisms that have a synergetic effect on the deterioration of concrete. Freeze-thaw is well known to efficiently saturate concrete as a result of successive cycles, in addition to inducing internal micro cracking and surface scaling in the presence of deicing salts. Recent research has focused on the effects of freeze-thaw loading on the transport characteristics of chlorides in concrete. As a result, a three-dimensional finite-element method to model diffusion of chloride under freeze-thaw loading was developed, and presented in this paper. A stochastic methodology for generating a multiphase concrete microstructure was developed based on characterization inputs such as the aggregate grading curve, image processing results of morphological features and phase specific volume fractions. The microstructure was created as a composite of aggregates of different size, microstructural pores, larger voids and the cement matrix. The stochastic procedure combines tessellation of image based processing of morphological features and stochastic placement of individual geometric entities to create the material microstructure as a 3D image, subsequently meshed to provide the finite-element model. The material diffusivity was interpolated between the values in the continuous bulk concrete phase, and zero diffusion in the aggregate particle phase and the air entrainment. Diffusion during freeze-thaw was initially modelled by making the chloride diffusivity temperature dependent and neglecting water freezing. The model provides a microstructurally informed approach to assess chloride transport in concrete.</p>

Topics

• impedance spectroscopy
• microstructure
• pore
• surface
• phase
• composite
• cement
• void
• diffusivity