ACCELERATED CARBONATION MODELLING OF FLY ASH-BLENDED CEMENT PASTE

Author(s): A. Morandeau, M. Thiéry, P. Dangla and C.E. White
Book Title: RILEM International Symposium on Concrete Modelling - CONMOD 2014
Editor: Kefei Li, Peiyu Yan and Rongwei Yang
ISBN: 978-2-35158-139-1
e-ISBN: 978-2-35158-140-7
Publisher: RILEM Publications SARL
Publication year: 2015
Pages: 407-415
Total Pages: 9
Language: English

Abstract: The reaction of gaseous atmospheric CO2 with calcium-bearing phases in concrete infrastructure is known to cause a lowering of pore solution alkalinity, leading to depassivation and corrosion of steel rebars. The carbonation mechanism is quite well understood from a physico-chemical point of view, especially in the case of pastes made of CEM I. Nonetheless the impact of supplementary cementitious materials (SCM), such as fly ash or slag, on carbonation is still an active research field. The pozzolanic reaction between portlandite and fly ash implies a lower portlandite content together with an increase in the amount of calcium-silicate-hydrate. Since portlandite is buffering the pH, its lower content in these blended cements may lead to a lower resistance to carbonation and to a higher amount of calcium-silicate-hydrate, which in turn will impact the phase evolution of the pastes. Thus, this article aims to develop a numerical model describing the carbonation of these cementitious materials under accelerated conditions. The modeling platform Bil (GNU General Public License) developed at Ifsttar was used to develop a reactive transport model of atmospheric carbonation by employing a finite volume method. Phase evolution was quantified, taking into account the effect of the progressive decalcification of calcium-silicate-hydrate linked to their molar volume, as well as the quantity of water released by carbonation using experimental data. Combined with a kinetic formulation of portlandite dissolution, calcium-silicate-hydrate decalcification in blended cements was described by an original thermodynamic/kinetic modeling approach.

Online publication: 2015
Publication Type: full_text
Public price (Euros): 0.00