Micromechanics Contribution to the Analysis of Diffusion Properties Evolution in Cement-Based Materials Undergoing Carbonation Processes Journées Scientifiques du Groupement MoMaS CIRM Marseille, novembre 2009 Eric Lemarchand (LMSGC – UR Navier – Univ. Paris Est)‏

Materials ability to avoid radioactive radionuclides migration Groundwater (Stora, 2006) Microstructure evolution Transport properties evolution (diffusion here) Industrial Issues – Storage of Radioactive Waste Carbonation Chemical reactions in Concrete  Leaching / decalcification processes  Precipitation (ettringite, calcite,…)

Atmospheric Carbonation / Steel rebar corrosion CO 2 from outside  rust formation   effective diameter  Expansion Couplings  Transport (CO 2, liquid water, ions)‏  Chemical Reactions (pores clogging)‏  Macroscopic loading effects

Project Outline‏ Hydration Model (curing conditions, microstructure morphology)‏ Transport Properties (Diffusion)‏ Carbonation (Portlandite, CSH,…)‏ Steel rebar corrosion Damaging, Durability ?

Outline  Hydration process and microstructure definition  Multi-scale description for cement-based materials application to diffusion coefficient estimates  Carbonation processes in cement-based materials  Microstructure evolution  New estimates for diffusion coefficients  Conclusions

Hydration/Structuration of cement-based Materials Anhydrous cement + water hydration Heterogeneous microstructure structuration Mature cement material Apparent macro-homogeneity hydration structuration (liquid, viscoelastic solid)‏ (porous medium)‏ Solid Phase: anhydres, hydrates Porosity: capillary, gel Partial saturation: water, air Ions released Dissolutions / Precipitations Microstructure Organization

Cement Paste – Hydration (Powers model)‏ We aim to be able to propose estimates for te evolution of (macroscopic) cement paste diffusion coefficient undergoing carbonation processes at different (microscopic) scales, depending upon the initial water-to-cement ratio (w/c) (cement paste initial definition)

Cement Paste Hydration (Powers)‏ Initial water Anhydrous grains (C3S, C2S,C3A,C4AF) w/c=0.5 Volume fraction Hydration degree Outer CSH Inner CSH Portlandite Water Aluminates Voids, big capillary pores

« Outer CSH » capillary pores (0.1-1 micron)‏ large capillary pores (>10 microns)‏ hydrated clinker (=10 microns)‏ CH Portlandite ( microns)‏ gel pores (5-50 nm)‏ « Inner CSH » gel pores (< 5nm)‏ Cement Paste - A multiscale material (Sanahuja & Dormieux, 2008)‏

Reinforced Concrete - Morphology CH Cement Paste Mortar Sand grains (0.1 – 1 mm)‏ homogenization Reinforced concrete Aggregates (1 cm)‏ Steel rebar

Fick’s Diffusion – Homogenization procedure Linear Problem

Micro-Macro Diffusion Coefficient Estimates CH « outer » CSH n

CH n Self-consistent Scheme n n +++ … Homogenized diffusion coefficient ? (« outer » CSH gel)‏ Micro-Macro Diffusion Coefficient Estimates

CH « outer » CSH gel + capillary pores Matrix/inclusion homogenization scheme (Mori-Tanaka)‏ Micro-Macro Diffusion Coefficient Estimates

CH Self-consistent Scheme n n +++ … Homogenized diffusion coefficient ? (« inner » CSH)‏ n Micro-Macro Diffusion Coefficient Estimates

CH Incomplete hydration  Inclusion/matrix model (Mori-Tanaka, 1973) matrix of « homogenized » outer CSH  Morphology Representative Pattern (Hervé & Zaoui, 1993) Complete hydration (inner CSH phase) CH Assume spherical Portlandite phase Micro-Macro Diffusion Coefficient Estimates

Total porosity [-] Macroscopic diffusion coefficient Model prediction Experimental measurements (Richet et al, 1997)

Carbonation of hydrated products  Carbonation of (small amount of) alkaline species  Carbonation of great amount of Portlandite  Carbonation of CSH (+ formation of silica gel) (Calcium carbonates precipitation + release of free water)

Mercury Porosimeter Results (Thiery,2009)

Microstructure evolution evidences very large capillary pores Capillary pores Outer CSH gel pores Inner CSH W/C=0.5 Portlandite Carbonation CSH Carbonation (Thiery, 2009)

Portlandite Carbonation - Observations Calcite grains precipitation Initial Portlandite Crystal Complete Calcite precipitation (Fully-Carbonated Portlandite Crystal)

Carbonatation de la Portlandite Non porous phase Porous phase Portlandite Carbonation   Volume increase (stochiometry arguments):  Equivalent diffusion coefficient (new calcite phase):

Carbonation shrinkage 50 nm 5-30nm Calcium Silicate Hydrates (CSH) Carbonation nm <20nm

Calcium Silicate Hydrates Carbonation Calcite crystals precipitation yields gel pores and capillary pores clogging !

Effects of Carbonation on Diffusion (Model estimates) Total porosity [-] Macroscopic diffusion coefficient Non-carbonated Cement (model) Carbonated Cement (model) Non-carbonated Cement (Experiments, Richet et al 1997)

The key role of the diffusion within calcite aggregates Macroscopic diffusion coefficient Total porosity [-]

Effect of w/c on Diffusion coefficient (model) Diffusion properties of calcite need better understanding !

Project Conclusions and Coming Issues Objectives: A Multi-scale and multi-physics model for diffusion processes in cement-based materials accounting for chemical kinetics and possible couplings with mechanical loadings – application to carbonation processes  Behavior analysis in absence of chemo-mechanical couplings  Behavior (poroelasticity, creep) [Sanahuja,2008]  Diffusive transport in saturated conditions (better informations required)  Diffusive transport in unsaturated conditions  Microstructure evolution: the kinetics point of view  Dissolution/precipitation uncoupled laws (known by chemo-physicists)  Mechanical couplings in local dissolution/precipitation laws (already identified)

Portlandite Carbonatation – Kinetics Aspects Dissolution kinetics of Ca(OH) 2 h : kinetics prameter s, R i : geometrical variables D : diffusion coefficient

Project Conclusions and Coming Issues Objectives: A Multi-scale and multi-physics model for diffusion processes in cement-based materials accounting for chemical kinetics and possible couplings with mechanical loadings – application to carbonation processes  Behavior analysis in absence of chemo-mechanical couplings  Behavior (poroelasticity, creep) [Sanahuja,2008]  Diffusive transport in saturated conditions (better informations required)  Diffusive transport in unsaturated conditions  Microstructure evolution: the kinetics point of view  Dissolution/precipitation uncoupled laws (chemo-physics)  Mechanical couplings in local dissolution/precipitation laws (already identified)  Extension to steel rebar corrosion processes  Damage analysis – Crack propagation …

Thank you for your attention !