Buch, Englisch, Band 48, 198 Seiten
Reihe: Dissertationsreihe Prof. Dr.-Ing. Carl-Alexander Graubner
CO2 diffusivity and alteration of hydrate phases
Buch, Englisch, Band 48, 198 Seiten
Reihe: Dissertationsreihe Prof. Dr.-Ing. Carl-Alexander Graubner
ISBN: 978-3-942886-25-3
Verlag: Technische Universität Darmstadt, Institut für Massivbau
The cement industry is accountable for about 5-8 % of the worldwide anthropogenic CO2
emissions. The substitution of Portland cement clinker by limestone powder can significantly
improve the environmental impact of cement. However, low clinker contents usually
decrease the resistance against carbonation, which may hinder the use of such ecologically
optimised concretes. The disadvantageous effect of the reduced clinker content can be compensated
by an adapted mix design, as other studies have shown.
The present study aims to further the development of concrete made from limestone-rich
cement by investigating the driving forces of carbonation, namely the chemical reaction of
CO2 with the carbonatable constituents, and the gas diffusion of CO2 in concrete. Concerning
the chemical aspects of carbonation, the reaction rates with CO2 were investigated on
synthesised single phases (portlandite, calcium-silicate-hydrate phases and ettringite).
Moreover, the change of the phase assemblage due to carbonation was analysed on cement
paste with various contents of limestone, which enables conclusions about the chemical
progress of carbonation. The results were validated with thermodynamic modelling (software:
GEMS). A submodel for estimating the CO2 diffusion coefficient in concrete made
from limestone-rich cement was derived based on the experimental analysis of the correlations
between the mix design (w/cl ratio and LS replacement level), compressive strength
and CO2 diffusion. Finally, a coupled analytical-thermodynamic model for estimating the
carbonation depth in concrete made from limestone-rich cement was developed.
