Effect of Nano-Clay on the Printability of Extrusion-Based 3D Printable Mortar (2023-09)¶

Extrusion-based 3D concrete printing (3DCP) requires a balance between high yield stress for self-support and the ability to extrude mortar filaments at larger buildable heights. However, a higher yield stress, while advantageous for buildability, can hinder extrudability as it affects material fluidity. Increased yield stress results in greater extrusion effort, leading to surface flaws in the filaments. Incorporating nanoclay into the mix can enhance yield stress without compromising flow properties. Nonetheless, due to evolving rheological properties over time, there are constraints on the timing and dosage of nanoclay for efficient utilization. To overcome these limitations, a printability box is developed, utilizing consistency and yield stress values to define feasible boundaries for extrudable and buildable 3D printable mortar with minimal surface flaws or shape alteration. The printable mortar composition includes cement, fly ash, basalt fiber, superplasticizer, and nanoclay, with a maximum aggregate size of 1.18 mm. Increasing nanoclay dosage improves printability by reducing layer modification and shape deformation while significantly boosting compressive strength. Considering the exposure of cement-based materials to compressive stresses in 3D printing applications, especially in lower layers, the study employs an unconfined uniaxial compression test (UUCT) to assess whether the printable mortar can sustain compressive stress without significant deformation. The compressive strength of fresh mortar filaments increases notably with higher nanoclay content compared to the reference. The objective of this study is to determine the optimal mortar mixture with the highest nanoclay dosage that maintains printability while enduring sufficient compressive stress during and after printing. This research contributes to enhancing the understanding and development of printable cementitious materials, ensuring their stability, and enabling successful 3D concrete printing applications.