Effect of Dual CO2 Technologies on the Properties of Mortars with Slag Cement

This research study aimed to investigate the effects of combining CO2 liquid and CO2 gas on the properties of mortars, both with and without slag cement. The study involved eight different mixtures, varying in slag cement content (0% and 30%), water source (normal water (NW) or carbonated water (CW)), and water-to-binder ratios (w/b) of 0.45 and 0.55. Two curing types were employed: normal or conventional curing (NC) and 24-h CO2 curing (CC). Strength and durability measurements at 7 and 28 days as well as flowability assessments were conducted following ASTM standards. The results revealed that using CW in NC samples generally increased early strength by 2-12% at 7 days. However, this improvement did not translate into enhanced long-term strength at 28 days, as the studied mixtures experienced an average decrease between 2 and 5%. Additionally, combining CC and CW showed significant enhancements in both strength and durability for slag cement mortars. These enhancements ranged from 3 to 8% compared to the reference samples. It is worth noting that combining multiple CO2 approaches did not consistently produce a synergistic effect. Therefore, it is recommended to avoid employing more than one CO2 technology in concrete materials, especially when dealing with high w/b. These findings suggest that using CW can be beneficial when prioritizing early strength over long-term strength, such as in precast concrete plants. Furthermore, the combination of CC and CW offers the potential for producing slag cement mortars with performance comparable to those containing 100% ordinary Portland cement (OPC).