3.2. Mechanisms of CO2 diffusion in concrete
To understand the mechanisms of CO2 diffusion in concrete, the
microstructures of uncarbonated and carbonated concretes were
examined and the results are discussed in this section.
The major product of the carbonation reaction in concrete is the
formation of a non-soluble salt of calcium carbonate (CaCO3).
Formation and growth of CaCO3 would have an expansion ratio
to be about 11.7% [15]. To understand the impact of the carbonated
products on the microstructure of the resulting concrete, both the
carbonated and uncarbonated concrete samples were examined by
means of SEM observations. The SEM images were taken from the
surface of both carbonated and uncarbonated concretes. Since the
SEM results were found insignificantly different with different
grades of concrete samples, the SEM results of G30 concrete samples
were used for the analysis in the following discussion. Fig. 4
depicts an SEM image of the uncarbonated concrete (G30). It can
be seen that the microstructure of hydrated cement products without
carbonation is amorphous, fibroid and lumpy. The C–S–H gel
has formed a porous and tortuous network structure, whereas
the microstructure of carbonated concrete is characterised with
high porosity with large inter-connected pores. Using MIP method,
the porosity of uncarbonated concrete (G30) is 11.2%.
3.2. Mechanisms of CO2 diffusion in concreteTo understand the mechanisms of CO2 diffusion in concrete, themicrostructures of uncarbonated and carbonated concretes wereexamined and the results are discussed in this section.The major product of the carbonation reaction in concrete is theformation of a non-soluble salt of calcium carbonate (CaCO3).Formation and growth of CaCO3 would have an expansion ratioto be about 11.7% [15]. To understand the impact of the carbonatedproducts on the microstructure of the resulting concrete, both thecarbonated and uncarbonated concrete samples were examined bymeans of SEM observations. The SEM images were taken from thesurface of both carbonated and uncarbonated concretes. Since theSEM results were found insignificantly different with differentgrades of concrete samples, the SEM results of G30 concrete sampleswere used for the analysis in the following discussion. Fig. 4depicts an SEM image of the uncarbonated concrete (G30). It canbe seen that the microstructure of hydrated cement products withoutcarbonation is amorphous, fibroid and lumpy. The C–S–H gelhas formed a porous and tortuous network structure, whereasthe microstructure of carbonated concrete is characterised withhigh porosity with large inter-connected pores. Using MIP method,the porosity of uncarbonated concrete (G30) is 11.2%.
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