Flow calculation and thermodynamics in wet frost exposure of cement based materials

Title: Flow calculation and thermodynamics in wet frost exposure of cement based materials
Author(s): Stefan Jacobsen, Frank Melandsø, Hung Thanh Nguyen
Paper category : conference
Book title: International RILEM Symposium on Concrete Science and Engineering: A Tribute to Arnon Bentur
Editor(s): J. Weiss, K. Kovler, J. Marchand, and S. Mindess
Print-ISBN: None
e-ISBN: 2912143926
Publisher: RILEM Publications SARL
Publication year: 2004
Nb references: 51
Language: English

Abstract: The calculation of moisture transport from a wet surface and into cement based materials (CBM) exposed to frost is further studied, limited to a case with continuously wet surface and constant temperature gradient dT/dx. The pressure created during phase transition of pore water to ice in the highly saturated CBM is considered a major driving force. The pressure is first calculated and analyzed using reversible thermodynamics. The pressures measured in practice and deduced theoretically vary within a rather large span. This is discussed in relation to the involved quantities (volume of unfrozen water and ice, enthalpy). Transport is calculated using d’Arcys law in the described wet frost exposure. Gradients dT/dx of various wet frost tests, as well as realistic enthalpies and volumes are used. Predicted flow varies approximately two decades using the chosen realistic values of dT/dx (20 – 100 K/m) and observed freezing temperatures (255 – 263 K). Experimental flow data from a wide variety of concretes and wet frost exposure conditions have similar values as the calculated values, indicating that the proposed approach can be used. The driving force for flow and the disruptive pressure in the degradation of the material stem from the same thermodynamic phenomena. The implication of this is that service life calculation must be based both on the freeze/thaw transport (“pumping effect”) and on the subsequent degradation. Finally, further work in calculation/numerical simulation and experiments are discussed.

Online publication: 2004-03-25
Classification: Freeze-Thaw
Publication type : full_text
Public price (Euros): 0.00
doi: 10.1617/2912143926.053