Role of interaction between molding pressure and CO2 pressure in carbonating cement block

Abstract

To improve the mechanical performance and boost the carbonation reaction, varying molding (casting) pressures (10, 15, and 20 MPa) and CO2 pressures (0.1, 0.25, 0.5, and 1 MPa) were applied to produce cement blocks, which were then subjected to 1 h of carbonation curing and subsequent 28 d of water curing. The results showed that higher CO2 pressure promoted both the hydration and carbonation processes regardless of molding pressure after 1 h of carbonation and thereby densifying the microstructure, which translated into improved compressive strength of the cement block. Cement blocks fabricated with a higher molding pressure showed a negative effect on the carbonation reaction, resulting in a similar strength between the 10 and 20 MPa samples after carbonation for 1 h under the same CO2 pressure. However, a higher molding pressure exerted a positive impact on the subsequent hydration reaction, resulting in a 324.9% increase in the compressive strength of the 20 MPa sample after a further 28 d of water curing. Overall, a 15 MPa molding pressure coupled with a higher CO2 pressure (≥1 MPa) was found to be the optimal regime for carbonation curing. In contrast, a combination of a higher molding pressure (≥20 MPa) with a relatively lower CO2 pressure (≤0.5 MPa) was conducive to the strength gain under further water curing after carbonation.