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Seawater-mixed concrete for 3D printing offers a promising solution for marine infrastructure construction in coastal and island regions facing shortages of freshwater and labor. However, the high chloride concentration in seawater accelerates the initial setting of concrete, thereby hindering pumping and extrusion in one-component (1 K) printing. The two-component (2 K) printing approach, which combines retarded cementitious mixtures with aluminate-based accelerators, enables set-on-demand behavior and provides a potential solution for seawater-based printing. Nevertheless, the early-age behavior of seawater-mixed cementitious materials incorporating aluminate-based accelerators, such as aluminum sulfate (A$) and calcium aluminate cement with anhydrite (CAC-C$), remains largely unexplored, particularly regarding their interactions with seawater ions and Portland cement. This study systematically investigates the structural build-up and early-age hydration of seawater-mixed cementitious materials incorporating A$- and CAC-C$-based acceleration slurries. Structural build-up was quantified using constant shear rate rheometry, while water state evolution, hydration kinetics, and phase assemblages were characterized using low-field 1H NMR, isothermal calorimetry, thermogravimetric analysis, and X-ray diffraction. The results demonstrate that ettringite (AFt) precipitation governs structural build-up in both systems due to its high water-binding capacity and voluminous needle-like morphology. Seawater significantly enhances AFt formation in the A$-based system, leading to rapid stiffening but a narrowed printability window. In contrast, seawater initially suppresses AFt formation in the CAC-C$ system due to delayed sulfate dissolution and the preferential formation of Friedel’s salt; this effect is transient, and AFt formation resumes at later ages. Consequently, the CAC-C$ system exhibits superior robustness and greater suitability for seawater-mixed concrete 2 K printing.
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Seawater-mixed concrete for 3D printing offers a promising solution for marine infrastructure construction in coastal and island regions facing shortages of freshwater and labor. However, the high chloride concentration in seawater accelerates the initial setting of concrete, thereby hindering pumping and extrusion in one-component (1 K) printing. The two-component (2 K) printing approach, which combines retarded cementitious mixtures with aluminate-based accelerators, enables set-on-demand behavior and provides a potential solution for seawater-based printing. Nevertheless, the early-age behavior of seawater-mixed cementitious materials incorporating aluminate-based accelerators, such as aluminum sulfate (A$) and calcium aluminate cement with anhydrite (CAC-C$), remains largely unexplored, particularly regarding their interactions with seawater ions and Portland cement. This study systematically investigates the structural build-up and early-age hydration of seawater-mixed cementitious materials incorporating A$- and CAC-C$-based acceleration slurries. Structural build-up was quantified using constant shear rate rheometry, while water state evolution, hydration kinetics, and phase assemblages were characterized using low-field 1H NMR, isothermal calorimetry, thermogravimetric analysis, and X-ray diffraction. The results demonstrate that ettringite (AFt) precipitation governs structural build-up in both systems due to its high water-binding capacity and voluminous needle-like morphology. Seawater significantly enhances AFt formation in the A$-based system, leading to rapid stiffening but a narrowed printability window. In contrast, seawater initially suppresses AFt formation in the CAC-C$ system due to delayed sulfate dissolution and the preferential formation of Friedel’s salt; this effect is transient, and AFt formation resumes at later ages. Consequently, the CAC-C$ system exhibits superior robustness and greater suitability for seawater-mixed concrete 2 K printing.
Thanks to the low cost and earth's abundant potassium resources, potassium ion batteries (PIBs) have attracted much interest as alternative energy storage devices. However, there is still a great challenge to develop suitable anode materials for PIBs with high specific capacity, fast charge/discharge and stable ion storage. Nowadays, conductive metal-organic frameworks (c-MOFs) with excellent physicochemical properties are employed for different electrochemical applications, but the study of their potassium storage performance remains unknown, and the detailed potassium storage mechanism needs to be explored. Herein, nanostructured Co3(HHTP)2 c-MOF (Co-CAT MOF, HHTP: 2,3,6,7,10,11-hexahydroxytriphenylene) is synthesized by a liquid-phase method and evaluated as the anode for PIBs. The active sites and open pathways in the conductive Co-CAT MOF promote ion diffusion and electron transfer, exhibiting high reversible specific capacity (332 mA h g−1 at 0.1 A g−1), excellent long-cycle stability (230 mA h g−1 at the current density of 1.0 A g−1 after 700 cycles) and outstanding rate performance (165 mA h g−1 at 4.0 A g−1), which is superior to the typical PIB anodes. Combined with different ex situ characterization techniques, the potassium storage mechanism based on 8-electron transfer is revealed. Furthermore, Co-CAT MOF exhibits excellent Li-ion storage performance. In the half-cell, the Co-CAT MOF electrode displays a high reversible capacity of 800 mA h g−1 at 200 mA g−1. In addition, the Co-CAT//LiCoO2 full cell cycles for 100 cycles at 200 mA h g−1. It is believed that Co-CAT MOF is a promising electrode material for potassium/lithium storage, and the proposed ion storage mechanism can be used to discover other MOF-based electrodes for energy storage.
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Thanks to the low cost and earth's abundant potassium resources, potassium ion batteries (PIBs) have attracted much interest as alternative energy storage devices. However, there is still a great challenge to develop suitable anode materials for PIBs with high specific capacity, fast charge/discharge and stable ion storage. Nowadays, conductive metal-organic frameworks (c-MOFs) with excellent physicochemical properties are employed for different electrochemical applications, but the study of their potassium storage performance remains unknown, and the detailed potassium storage mechanism needs to be explored. Herein, nanostructured Co3(HHTP)2 c-MOF (Co-CAT MOF, HHTP: 2,3,6,7,10,11-hexahydroxytriphenylene) is synthesized by a liquid-phase method and evaluated as the anode for PIBs. The active sites and open pathways in the conductive Co-CAT MOF promote ion diffusion and electron transfer, exhibiting high reversible specific capacity (332 mA h g−1 at 0.1 A g−1), excellent long-cycle stability (230 mA h g−1 at the current density of 1.0 A g−1 after 700 cycles) and outstanding rate performance (165 mA h g−1 at 4.0 A g−1), which is superior to the typical PIB anodes. Combined with different ex situ characterization techniques, the potassium storage mechanism based on 8-electron transfer is revealed. Furthermore, Co-CAT MOF exhibits excellent Li-ion storage performance. In the half-cell, the Co-CAT MOF electrode displays a high reversible capacity of 800 mA h g−1 at 200 mA g−1. In addition, the Co-CAT//LiCoO2 full cell cycles for 100 cycles at 200 mA h g−1. It is believed that Co-CAT MOF is a promising electrode material for potassium/lithium storage, and the proposed ion storage mechanism can be used to discover other MOF-based electrodes for energy storage.
