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Validation of FEM models describing moisture transport in heated concrete by Magnetic Resonance Imaging

S.J.F. Erich1, A.B.M. v. Overbeek1, G.H.A. v.d. Heijden2, L. Pel2, H.P. Huinink2 W.H.A. Peelen1, A.H.J.M. Vervuurt1
1 TNO Built environment and Geosciences, Delft, The Netherlands
2 Eindhoven University of Technology, Eindhoven, The Netherlands

Fire safety of buildings and structures is an important issue, and has a great impact on human life and economy. One of the processes negatively affecting the strength of a concrete building or structure during fire is spalling. Many examples exists in which spalling of concrete during fire has caused severe damage to structures, such as in the Mont Blanc and Channel Tunnel. Especially newly developed dense types of concrete such as HPC and SCC, have shown to be sensitive to spalling, hampering the application of these new concrete types. To reduce risks and building costs, the processes behind spalling need to be understood. Increasing our knowledge allows us to reliably predict the behaviour and take effective and cost friendly preventive measures. Moisture present in concrete is one of the reasons for spalling. When concrete is heated water will evaporate, which results in a high gas pressure inside the pores of concrete. This high gas pressure can induce spalling. To attain a better understanding of this process, a first step was taken to develop a finite element model (FEM) describing this transport of moisture in heated concrete. However, the validity of all current models (including our own) is unknown because of debatable input parameters and lack of experimental techniques to follow the transport process in situ. In cooperation with the Eindhoven University of Technology moisture transport in heated concrete can now be investigated with a home built dedicated 1D Magnetic Resonance Imaging (MRI) setup. Using the results of the MRI experiments the validity of our FEM models has been assessed for the first time. A general correspondence is observed. The FEM model described in this paper is a simplified FEM model compared to literature models. Already this simplified model shows a good correspondence with the MRI measurements.

Key words: Concrete, spalling, NMR, MRI, moisture transport, fire, FEM, modelling