Effect of Cylinder Size on the Compressive Strength of Concrete CO₂ Curing

This study was conducted to assess the effect of cylinder size on concrete compressive strength by CO₂ curing. The factors studied to evaluate the effect of cylinder size on concrete compressive strength were cylinder size, CO₂ concentration, curing pressure, curing time, and age of specimen at testing. Three different cylinder sizes (5 × 10 cm, 10 × 20 cm, 15 × 30 cm), three CO₂ concentration (50%, 75%, 100%), three curing time (1, 3, 6 h), three curing pressures (2, 4, 8 bars), and four testing ages (3, 7, 28, 90 days) were used in this investigation. A batch size of 0.18 m³ concrete was used to produce twenty 5 × 10 cm cylinders, twenty 10 × 20 cm cylinders, and twelve 15 × 30 cm cylinders. However, it was necessary that the specimens reach an initial set to demold before the CO₂ curing process was used because the dry CO₂ gas-stream would gradually take the free water away from the specimens. After the CO₂ curing duration, the concrete samples were assessed through the compressive strength, the pressure drop and the temperature expected to go down and rise in the chamber. In general, high early and late compressive strength of the CO₂-cured cylinders were obtained while its strength was mostly higher than the strength of normally water-cured ones. The k_s5 value obtained from 5 × 10 cm, and 15 × 30 cm cylinders by CO₂ curing ranges between 0.95 and 1.30, this is partly due to the fact that high early compressive strength of the CO₂-cured cylinders was obtained while its early strength was about equal to the 28-day strength of normally water-cured ones. Therefore, special care is still needed to compare the properties of concrete from the two different cylinder sizes by CO₂ curing.