INVESTIGATION OF ACCELERATED CARBONATION KINETICS THROUGH CO2 DIFFUSION TESTS CARRIED OUT ON PARTIALLY WATER-SATURATED SPECIMENS OF CEMENTITIOUS MATERIALS

Author(s): Ph. Turcry, F. Gendron, A. Deeb, A. Aït-Mokhtar
Paper category: Proceedings
Book title: CO2STO2019 - International Workshop CO2 Storage in Concrete
Editor(s): Assia Djerbi, Othman Omikrine-Metalssi, Teddy Fen-Chong
ISBN:
e-ISBN: 978-2-35158-232-9
Publisher: RILEM Publications SARL
Publication year: 2019
Pages: 185-194
Total Pages: 10
Language : English

Abstract: Atmospheric carbonation is an ageing phenomenon affecting the durability of reinforced
concrete structures. A positive side of carbonation is the sequestration of greenhouse gas
thanks to the combination of CO2 with cement hydrates. At the end of service life, carbonation
could be accelerated by the crushing of demolition wastes. The CO2 storage capacity of
concrete has however to be assessed.
Since carbonation is a reactive transfer phenomenon, models of carbonation should involve at
least two phenomena, i.e. gaseous CO2 diffusion and chemical reactions between dissolved
CO2 and hydrates. Gas diffusion is classically investigated by means of diffusion tests carried
out with inert gases such as oxygen. Literature models of CO2 diffusivity were so-designed
from diffusion test results. As far as chemical reactions are concerned, models parameters,
e.g. kinetics constants, are often fitted from experimental data, such as carbonation fronts or
profiles of carbonation products or reactants.
In the present study, an original method based on a CO2 diffusion test is proposed to
investigate accelerated carbonation kinetics of cementitious materials. To this end, a thin
cylindrical specimen of cement paste is placed between two chambers. In the upstream one,
a constant CO2 concentration is maintained constant while the time-evolution of the CO2
concentration due to the gas flow is recorded in the downstream chamber. When specimen is
dried prior to testing, no carbonation can occur during the diffusion test. The CO2 diffusivity
can thus be deduced from the Second Fick’s Law by inverse analysis. If the tested specimen
is partially water-saturated, a reactive transfer will occur due to the competition between CO2
diffusion and CO2 fixation by the cement matrix. The time-evolution of the CO2 concentration
in downstream can be interpreted by a chemo-physical model of carbonation.

Online publication : 2019
Publication type : full_text
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