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Modelling of macroscopical transient frost processes and microscopical driving forces
Author(s) -
Kruschwitz Jens,
Setzer Max J.
Publication year - 2008
Publication title -
pamm
Language(s) - English
Resource type - Journals
ISSN - 1617-7061
DOI - 10.1002/pamm.200810509
Subject(s) - porous medium , materials science , saturation (graph theory) , nanoscopic scale , frost (temperature) , penetration (warfare) , porosity , microstructure , thermodynamics , mechanics , nanotechnology , composite material , physics , engineering , mathematics , combinatorics , operations research
The artificial saturation phenomenon due to freeze–thaw cycles is described by a multi–phase and multiscale model [1,2,3] formulated within the Theory of Porous Media, [4]. It represents partially saturated concrete as a mixture of 5 interacting constituents φ α , namely the solid skeleton φ s , the bulk water φ l , the pore volume occupied by vapour φ v , the ice φ i and the gel water phase φ p . Most relevant for the model is the distinction between two length scales and their characteristic time scales. The boundary is marked where macroscopic bulk conditions change to surface physics and chemistry. Surface physics and chemistry acting on the nano–scale affect fundamental properties of concrete and consequently the durability of concrete against freeze–thaw. At the macroscopic scale the model describes transient conditions (i.e. water–uptake, heat transport, volume dilatation of 9%, phase change of first order considering hysteresis) which are characterized by a relatively long time period to reach equilibrium in contrast to the processes modelled on the microstructure. At the microscopic scale the model represents the nanoscopic CSH–gel system consisting of solid CSH and water as a linked system of both components basing on the concept of the “Solid–Liquid Gel System” [5]. In the constribution the numerical results of the model are presented with focus on the evaluation of the process zone during the penetration of the melting front into the matrix. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)