ORALS

SESSION: GeomechanicsFriPM2-R7	Schrefler International Symposium on Geomechanics and Applications for Sustainable Development
Fri Oct, 25 2019 / Room: Athena (105/Mezz. F)
Session Chairs: Patrizia Trovalusci; Christian Hellmich; Session Monitor: TBA

16:20: [GeomechanicsFriPM210] Keynote
A Non-equilibrium Approach to Modeling Chemical Deterioration Processes in Concrete Structures Exposed to Variable Hygrothermal Conditions
Dariusz Gawin¹ ; Francesco Pesavento² ; Marcin Koniorczyk¹ ; ¹Lodz University of Technology, Lodz, Poland; ²University of Padova, Padova, Italy;
Paper Id: 223 [Abstract]

Concrete structures are widely used in civil, environmental, and nuclear engineering. During their lifetime, the structures are often exposed to severe environmental conditions, causing various deterioration processes, which might significantly reduce their durability. The aim of this contribution is to present a general approach [1] to modelling various chemical deterioration processes in concrete, due to combined action of variable hygro-thermal, chemical and mechanical loads. For this purpose, mechanics of multiphase porous media and delayed damage theory are applied. The mass, energy, and momentum balances, as well as the evolution equations describing the progress of chemical reactions and the constitutive and physical relations are briefly summarized. The kinetics of physicochemical deterioration processes like calcium leaching [2], Alkali Silica Reaction (ASR) [3], and salt crystallization-dissolution [4, 5], are described by means of evolution equations based on linear thermodynamics of chemical reactions. The mutual couplings between the chemical, hygral, thermal and mechanical processes are presented and discussed, both from the viewpoint of physicochemical mechanisms and mathematical modelling. Numerical methods used for solution of the model governing equations are presented. For this purpose, the finite element method is applied for space discretization and the finite difference method for integration in the time domain. Some examples of the model application for analysis of transient chemo-hygro-thermo-mechanical processes in porous construction materials are presented and discussed. The first example deals with calcium leaching from a concrete wall due to chemical attack of pure water exposed to gradients of temperature and pressure. The second one describes cracking of a concrete element, caused by development of expanding products of ASR. The third example concerns salt crystallization during the drying of a wall made of concrete and ceramic brick, causing degradation of the surface layer due to development of crystallization pressure.

References:
[1] D. Gawin, M. Koniorczyk and F. Pesavento, Modelling of hydro-thermo-chemo-mechanical phenomena in building materials, Bulletin of The Polish Academy of Sciences: Technical Sciences 61(1) (2013) 51-63.
[2] D. Gawin, F. Pesavento and B.A. Schrefler, Modeling deterioration of cementitious materials exposed to calcium leaching in non-isothermal conditions, Computer Methods in Applied Mechanics and Engineering 198 (37-40) (2009) 3051-3083.
[3] F. Pesavento, D. Gawin, M. Wyrzykowski, B.A. Schrefler, L. Simoni, Modeling alkali-silica reaction in non-isothermal, partially saturated cement based materials, Computer Methods in Applied Mechanics and Engineering 225-228 (2012) 95-115.
[4] M. Koniorczyk, D. Gawin, Modelling of salt crystallization in building materials with micro-structure - poromechanical approach, Construction and Building Materials 36 (2012) 860-873.
[5] M. Koniorczyk, D. Gawin, B.A. Schrefler, Multiphysics model for spalling prediction of brick due to in-pore salt crystallization, Computers and Structures 196 (2018) 233-245.

SESSION: GeomechanicsFriPM2-R7	Schrefler International Symposium on Geomechanics and Applications for Sustainable Development
Fri Oct, 25 2019 / Room: Athena (105/Mezz. F)
Session Chairs: Patrizia Trovalusci; Christian Hellmich; Session Monitor: TBA

16:45: [GeomechanicsFriPM211] Keynote
A General Framework for the Numerical Modeling of Concrete Structures Behavior
Francesco Pesavento¹ ; Dariusz Gawin² ; Giuseppe Sciumè³ ; Marcin Koniorczyk² ; ¹University of Padova, Padova, Italy; ²Lodz University of Technology, Lodz, Poland; ³Université de Bordeaux, Bordeaux, France;
Paper Id: 222 [Abstract]

The prediction of the behavior of cementitious materials and concrete structures under severe conditions and/or for long time spans is of paramount importance in civil, environmental and nuclear engineering. Often, commercial tools do not provide a sufficiently accurate response, so it is necessary to use more sophisticated approaches. In this work, a general framework for the simulation of the non-linear behavior of concrete is shown and described. It is based on the mechanics of multiphase porous media. The mathematical model is developed by writing the relevant balance equations for the constituents at the pore scale, i.e. the local form of governing equations formulated at micro-scale, and by upscaling these equations to the macroscopic scale, taking into account thermodynamic constraints according to the so-called TCAT (Thermodynamics Constrained Averaging Theory) which assures that all the thermodynamics are properly up scaled from the micro to the macro level. Thanks to this approach, all the relevant quantities involved are thermodynamically correct, no unwanted dissipations are generated, and both the bulk phases and interfaces are taken into account. This procedure does not exclude, however, the use of a numerical multiscale approach in the formulation of the material properties. The numerical solution is obtained directly at the macro level by discretizing the governing equations in their final form. The resulting model can be usefully applied to several practical cases: evaluation of the concrete's performance at early stages of maturing massive structures [1-3], structural repair works [2,3], exposure of concrete to high temperatures, e.g. during fire [4,5], cementitious materials subject to freezing/thawing cycles [6], etc. In this work, the general model focuses on the specific situations described above and several examples are shown.

References:
[1] D. Gawin, F. Pesavento, B.A. Schrefler, Modelling creep and shrinkage of concrete by means of effective stress, Materials & Structures 40 (2007) 579-591.
[2] G. Sciume, F. Benboudjema, C. De Sa, F. Pesavento, Y. Berthaud, B.A. Schrefler, A multiphysics model for concrete at early age applied to repairs problems, Engineering structures 57 (2013) 374-387.
[3] F. Pesavento, B.A. Schrefler, G. Sciumè, Multiphase Flow in Deforming Porous Media: A Review. Archives of Computational Methods in Engineering 24 (2017) 423-448.
[4] D. Gawin. F. Pesavento, B.A. Schrefler , Modelling of hygro-thermal behaviour of concrete at high temperature with thermo-chemical and mechanical material degradation, Comput. Methods Appl. Mech. Engrg. 192(13-14) (2003) 1731-1771.
[5] D. Gawin, F. Pesavento, B.A. Schrefler, Towards prediction of the thermal spalling risk through a multi-phase porous media model of concrete, Computer Methods in Applied Mechanics and Engineering 195 (2006) 5707-5729.
[6] D. Gawin, F. Pesavento, M. Koniorczykc, B.A. Schrefler, Non-equilibrium modeling hysteresis of water freezing - ice thawing in partially saturated porous building materials, Int. Journal of Building Physics, in print.