Numerical Modeling of Concrete Carbonation based on Durability Indicators

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Title: Numerical Modeling of Concrete Carbonation based on Durability Indicators

Author(s): M. Thiery, V. Baroghel-Bouny, G. Villain, and P. Dangla

Publication: Special Publication

Volume: 234

Issue:

Appears on pages(s): 765-780

Keywords: carbonation; carbonation profiles; chemical reactions; durability indicators; mass transport; mathematical modeling

Date: 3/22/2006

Abstract:
This paper deals with a numerical modeling of concrete carbonation, based upon durability indicators (DIs), within the framework of a durability approach. Firstly, the methodology and the selected panel of universal DIs concerning carbonation are presented. Secondly, with the purpose of protecting structures against carbonation-induced corrosion, a model accounting for the coupled CO2-H2O-ionic transports, the carbonation reactions of Ca(OH)2 and C-S-H, the pH decrease, and the microstructure evolution is described. In this model, the DIs porosity, initial Ca(OH)2 content, and liquid water permeability are introduced as major input data. Complementary parameters are also used: Ca(OH)2 crystal size, C-S-H content and capillary pressure curve. The main numerical outputs are the carbonation kinetics, the residual Ca(OH)2 and newly formed CaCO3 content profiles, and the pH value. As a first step, the model is validated with accelerated carbonation data obtained on a cement paste and on three porous concretes. The carbonation depth and profiles, measured by means of phenolphthalein spray test and thermal analysis respectively, are in good agreement with the numerical simulations. The study is completed by a sensitivity analysis. The model, together with the test methods required for the assessment of the relevant DIs, could be included in a toolkit for durability evaluation and prediction of carbonation-induced corrosion of real structures.