Rheology and Shape Stability Control of 3D-Printed White Calcium Sulfoaluminate Cement Composites Containing Oyster...

Current 3D printing of cement-based materials faces challenges in shape stability and rheological control. While prior research has shown that admixtures can influence setting times and flow properties, the specific role of marine calcareous waste in white cement composites remains unclear. It was already known that oyster shell and cuttlebone contain calcium carbonate, but their impact on rheology and structural deformation in 3D printing had not been resolved. This gap motivated an investigation into how these materials affect printability and mechanical behavior. Existing studies often focus on synthetic admixtures, leaving a need for sustainable alternatives. The uncertainty around particle packing and thixotropic recovery in printed composites also required clarification. No prior work had resolved how varying concentrations of marine waste influence structural deformation. This study addresses these unresolved questions.

The aim of this study was to assess how oyster shell powder and cuttlebone powder affect the rheology and shape stability of white calcium sulfoaluminate cement composites used in 3D printing. The specific problem addressed is the lack of sustainable admixtures that improve printability without compromising mechanical strength. The motivation stems from the need to repurpose marine calcareous waste into construction materials. By evaluating setting time, rheological behavior, and structural deformation, the study sought to identify optimal admixture concentrations. The researchers also aimed to determine how these materials influence mechanical strength recovery. The study's focus was on achieving improved buildability and sustainability in 3D-printed cementitious structures. The goal was to provide a practical reference for using marine waste in cement composites.

The study used Vicat setting-time tests to assess the setting behavior of cement composites with varying oyster shell and cuttlebone powder content. Rotational rheological measurements evaluated the dynamic yield stress, while three-stage thixotropic recovery tests measured structural stability after printing. Structural deformation was quantified through deformation measurements, and mechanical strength was tested using flexural and compressive strength tests. XRD and SEM analyses were employed to examine microstructural changes. The researchers varied the admixture content from 0% to 24% to observe effects on rheology and shape stability. Each test was conducted in triplicate to ensure reproducibility. The combination of physical and chemical analyses provided a comprehensive evaluation of material behavior.

The incorporation of oyster shell powder and cuttlebone powder significantly shortened the setting time of white calcium sulfoaluminate cement composites. At 24% content, the initial and final setting times decreased to 17 min and 30 min for oyster shell powder, and 20 min and 33 min for cuttlebone powder. Dynamic yield stress increased from 48.83 Pa to 530.59 Pa for oyster shell powder and from 60.30 Pa to 1085.80 Pa for cuttlebone powder. Thixotropic recovery degree improved from 57.89% to 86.46% and 56.60% to 92.14%, respectively. Structural deformation decreased from 12.39% to 6.91% and 13.29% to 5.12% with increasing admixture content. Mechanical strength was initially reduced but recovered at higher concentrations due to improved particle packing. XRD and SEM analyses confirmed microstructural changes consistent with enhanced filling effects. These findings suggest that marine calcareous waste can improve printability and buildability in 3D-printed cement composites.

The study concludes that oyster shell and cuttlebone powder can enhance the shape stability and rheological properties of white calcium sulfoaluminate cement composites for 3D printing. The authors propose that these materials improve setting behavior and thixotropic recovery, which are crucial for printability. They also suggest that increased particle packing at higher concentrations contributes to mechanical strength recovery. The findings indicate that marine calcareous waste can serve as a sustainable admixture in cement composites. The researchers emphasize that the optimal concentration for both printability and strength is around 24%. The study does not claim that these materials are essential for all applications but highlights their potential in specific contexts. The authors state that their results provide a reference for using marine waste in sustainable construction materials. They do not propose broader implications beyond the scope of their findings.