INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING Int. J. Numer. Meth. Engng 2010; 84:1009–1037 Published online 21 May 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/nme.2924 A continuous–discontinuous approach to simulate physical degradation processes in porous media P. Moonen 1,2,3,4, ∗, † , L. J. Sluys 2 and J. Carmeliet 3,4 1 Laboratory of Building Physics, Department of Civil Engineering, Katholieke Universiteit Leuven (KUL), Leuven, Belgium 2 Department of Civil Engineering and Geosciences, Delft University of Technology (TUD), Delft, The Netherlands 3 Institute of Technology in Architecture, Swiss Federal Institute of Technology (ETH), Zürich, Switzerland 4 Laboratory of Building Technologies, Swiss Federal Laboratories for Materials Testing and Research (Empa), Zürich, Switzerland SUMMARY A macroscopic framework for the simulation of physical degradation processes in quasi-brittle porous materials is proposed. The framework employs the partition of unity (PU) concept and introduces a cohesive zone model, capturing the entire failure process starting from the growth and coalescence of micro-defects until the formation of macro-cracks. The framework incorporates the interaction between the failure process and the heat and mass transfer in the porous medium. As an example, physical degradation of an outside render is studied. The analysis illustrates that both material and interface failure can be investigated with this formulation. Depending on the boundary conditions, either one dominant crack or a network of small cracks is formed. Copyright  2010 John Wiley & Sons, Ltd. Received 26 October 2009; Revised 9 March 2010; Accepted 30 March 2010 KEY WORDS: failure; damage; fracture; cohesive zone model; PU; X-FEM; heat transfer; mass transfer; multi-physics; continuous–discontinuous framework 1. INTRODUCTION Coupled hygro-thermo-mechanical (HTM) processes are the main cause of physical degradation of porous (building) materials, they are the determining factor in many biological and chemical processes, and they are prevalent in various geophysical applications, such as underground storage ∗ Correspondence to: P. Moonen, Institute of Technology in Architecture, Swiss Federal Institute of Technology (ETH), Zürich, Switzerland. † E-mail: moonen@arch.ethz.ch Contract/grant sponsor: Flemish Institute for Science and Technology; contract/grant number: IWT-SBO project 30175. Copyright  2010 John Wiley & Sons, Ltd.