Figs. 5–7 show the SEM images of the same grade of carbonated
concretes (G30) under different CO2 levels (10, 20 and 50%) for
7 days. Similar concrete after exposed to CO2 concentration of
10% for 7 days underwent some carbonation showing some
remarkable difference in its microstructure. As shown in Fig. 5,
the porosity of the carbonated concrete is reduced and the pore
structure is modified showing smaller pores. This is mainly due
to the formation of CaCO3 particles deposited around the large
pores. Compared with uncarbonated concrete sample, the porosity
of carbonated concrete (G30) under CO2 concentration of 10% for
7 days had reduced to 9.8%.
In the case of concrete exposed to CO2 concentration of 20%, the
microstructure of the carbonated concrete is further modified,
showing a relatively dense network structure as revealed in
Fig. 6. The increase of CO2 concentration led to the formation of
more carbonated products, making the cementing gel denser,
reducing the porosity and the pore structure is modified showing
less pores. And the porosity of this sample is 8.7% which less than
9.8% porosity of sample under 10% CO2.
Fig. 7 shows the microstructure of carbonated concrete after
exposed to CO2 concentration of 50% for 7 days. Under high CO2
concentration, the concrete underwent a significant carbonation