High-performance carbonatable cementitious systems: novel materials and processing methods
Production of carbonatable cementitious materials (CCMs) using mineral carbonation has been considered one of the sustainable approaches for addressing the anthropogenic CO2 emissions because of their potential to absorb environmental carbon dioxide (CO2) to form stable, durable, and environmentally friendly carbonate materials. Despite a wealth of literacy and the major technological developments related to CCMs in recent decades, the expanded use of these eco-friendly materials depends on addressing their fundamental limitations (i.e., chemical, physical, and processing barriers). The overall objective of this research is to develop novel materials and processing methods to address the key limitations of CCMs systematically. In Phase I of this study, the depth-dependent limitation of the external CO2 curing process was addressed by developing an internal carbonation acceleration process using impregnated hydrogels with enzymatic solution. The depth-dependent limitation becomes more pronounced in large-scale concrete members that may require longer carbonation time and higher CO2 pressures. 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 (approaching the maximum theoretical degree of carbonation of the binder). The developed CO2 curing process provides a uniform carbonation profile through depth, which is crucial in upscaling CCM systems. In Phase II, hydrogels impregnated with amino acid salt (AAS) solutions were incorporated into CCMs to evaluate their potential for CO2 curing. The AAS solutions facilitate CO2 capture through the formation of carbamate and bicarbonate ions within the interior of the cementitious matrix. A comprehensive set of multiscale experimental techniques was employed to evaluate the effects of the impregnated hydrogels on the microstructure, mechanical performance, and durability of the CCMs. After 14 days of carbonation, CCM-AAS samples containing 0.10% and 0.15% hydrogels reached compressive strengths of 28.3 MPa and 25.5 MPa, corresponding to approximately 77% and 59% higher strength, respectively, relative to the control. Additionally, the CCM-AAS samples exhibited lower porosity and reduced water absorption rates, indicating improved durability performance. Overall, this hydrogel-based approach for delivering AAS solutions within CCM systems demonstrates strong potential for enhancing carbonation reactions and advancing carbon capture and storage technologies in cement-based materials. Further, with the rapid advancement of concrete 3D printing in construction projects, developing 3D-printable CCMs has become essential to driving a more sustainable transition. In Phase III of this study, two ternary binder CCMs with wollastonite (WS), hydrated lime (HL), ordinary portland cement (OPC), and ground granulated blast furnace slag (GGBFS) were developed, and cellulose nanocrystals (CNC) were implemented to improve the fresh and hardened properties of 3D-printed CCM systems. The results demonstrate that the degree of carbonation of the 3D-printed CCMs can reach up to 60%-70% within 14 days, with calcite and aragonite being the primary phases. The flexural strength of the CCMs becomes comparable to that of 3D-printed control OPC samples after 14 days of carbonation (≈8.5 MPa), with CNC-based CCMs showing an additional 25% improvement. These 3D-printable CCMs with CNCs can significantly reduce the environmental impact of 3D-printed cementitious materials by minimizing or eliminating the necessity of chemical admixtures to enhance material consistency and stability while replacing 70–100% of portland cement.
Civil engineering, Calcium silicate binder, Carbonatable cementitious materials, CO2 sequestration, Concrete 3D printing, Hydrogels, Sustainability
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