This research deals with the carbonation phenomena in concrete for the first 28 days of the
concrete curing period. The reactions known as carbonation are those which take place with
the hydrated and un-hydrated components of the cement paste in the concrete mixture and the
atmospheric carbon dioxide (CO2).
A literature review of the chemistry of cement and concrete as well as the physical phenomena
of carbonation governed by Fick’s first law and the influential factors in the carbonation reaction
has been summarized. Moreover, information of different studies done at several conditions to
measure carbonation rates, have been gathered and compared with the experimental results
obtained in this research. Also, information regarding CO2 emissions from the calcination
reaction in the cement process was brought together in order to find out how much of the CO2
emitted can be absorbed by concrete the first 28 days of the curing period.
In order to study how is the process of concrete carbonation for the period of time specified,
concrete specimens right after being poured in cylindrical molds, were exposed to accelerated
carbonation conditions during 28 days, with controlled atmosphere of 5% CO2 vol., 30°C and
65%RH. Products of the carbonation reaction in the concrete were measured versus time, with
techniques such as Carbonation depth by phenolphthalein stain and Carbon Dioxide content by
Thermo Gravimetrical Analyses and Mass Spectrometry. Calculations of carbonation rate with
phenolphthalein data and CO2 absorption rates with TGA-MS data were done with the
information collected.
When phenolphthalein test and CO2 content by TGA and TGA-MS techniques were used, the
same tendency in the results was found; which coincides at the same time with formulations
done by Fick’s first law. The higher values of CO2 content achieved by the concrete were
consistent with the maximum availability of components to react within the concrete matrix.
Similar results were found between the data obtained in the literature review, especially when
laboratory set-up of accelerated carbonation conditions was simulated, and the measurements
obtained in this experiment. Measurements done in here to find out carbonation rate showed
that this value was smaller were compared with other studies in which the concrete was at
normal atmospheric conditions of exposure.
Results have shown that from data obtained by the different techniques used, the percentage of
CO2 absorbed during the first 28 days of the concrete curing period (with the specificities of the
concrete used and the calculations done) goes from 0.34% to 1% of that emitted in the
calcinations reaction of the cement process.