Efficient carbon sequestration of seawater sea-sand recycled aggregate concrete: an experimental study

Carbonation has long been considered harmful to the durability of steel reinforced concrete structures especially with the increasing CO₂ and temperature globally. In coastal construction, the chloride ions even make it worse. By replacing the steel with chloride-insensitive reinforcement such as fiber reinforced polymer (FRP), sea sand is a potential alternative to river sand, even carbonation could be utilized due to the acid resistance of FRP. In this paper, seawater sea-sand recycled aggregate concrete (SSRAC) was prepared, which had different hydration and carbonation from ordinary concrete (OC). The test results showed that the carbonation depth at 28 days of SSRAC increased up to 179.13% of OC. A modified carbonation model based on pore evolution was established. On the other hand, the increasement of carbonatable material in SSRAC was up to 14.32%. Combined with this characteristic, the carbon emission and absorption assessment were carried out. It is found that the CO₂ absorption of SSRAC can be up to 325% of OC in 10 years’ service, and the total carbon emission including carbon sequestration over the whole life of SSRAC with a salinity of 4% is 45.73% of OC. This research verifies that it is expected to achieve more CO₂ sequestration rapidly in SSRAC, which could probably help design low-carbon concrete structures.