CO2 Curing on the Mechanical Properties of Portland Cement Concrete

This study was to evaluate the CO2 curing on mechanical properties of Portland cement concrete. Three different specimen sizes (5 × 10 cm, 10 × 20 cm, and 15 × 30 cm cylinders), three CO2 concentrations (50%, 75%, 100%), three curing pressures (0.2, 0.4, 0.8 MPa), three curing times (1, 3, 6 h), two water cement ratios (0.41, 0.68) for normal and high-strength concretes, and two test ages (3, 28 days) were used for this investigation. Before using the CO2 curing process, the concrete samples reached the initial set at approximately 4 h, and the free water in the samples was gradually removed when dry CO2 gas was injected. The test results show that the 3-day early compressive strength of normal concrete cured by CO2 is higher than that of concrete cured by water, but the difference is not obvious for high-strength concrete cured by CO2. In addition, there is a size effect on the strength of the 5 × 10 cm and 15 × 30 cm cylinders, and the strength conversion factor ks5 value obtained for the 28-day compressive strength is greater than 1.18. Compared to conventional water-cured concrete, the elastic modulus of carbon dioxide-cured one generally increases in proportion to the square root of the 28-day compressive strength. It was observed that there are only minor differences in the four EC empirical equations obtained by CO2 curing from 5 × 10 cm and 10 × 20 cm cylinders, respectively.