Unlocking the Depth-Dependent Limitation of External CO₂ Curing in Carbonatable Cementitious Materials Using Enzymatic Solution-Impregnated Hydrogels

Carbonatable binders have received extensive attention in recent years because of their potential to absorb environmental carbon dioxide (CO2) to form stable, durable, and environmentally friendly carbonate materials. However, the expanded use of these eco-friendly materials is still staggered due to their fundamental limitations (i.e., chemical and physical reaction barriers). This paper addresses the depth-dependent limitation of the external CO2 curing process using impregnated hydrogels for carbonated cementitious materials (CCMs). The CCMs with enzymatic solution-impregnated hydrogels in the presence of external CO2 have better mechanical (up to 80% improvement compared to control CCMs) and durability performance, and the calcium carbonate precipitation can reach up to 15 times higher compared to control systems (approaches the maximum theoretical degree of carbonation of binder). The experimental results show that external CO2 influx acts as an accelerator of the catalytic activity of urease and promotes CaCO3 precipitation over depth. The kinetic model shows that the addition of impregnated hydrogels with enzymatic solution significantly improved the early age reaction kinetics by accelerating the nucleation and growth of carbonate crystals. The developed CO2 curing process provides a uniform carbonation profile through depth which is crucial in upscaling CCM systems. This work provides a new path for the development of high-performance carbon sink construction materials.