Carbonation of concrete made from limestone-rich cement

Beschreibung

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.

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Steiner Sarah

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CO2 diffusivity Carbonation limestone-rich cement

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