Anisotropic Characteristics of 3D-Printed Geopolymer Mortars from End-of-Life Materials of Construction Industry

The demand for housing has grown exponentially, leading to an increased emphasis on rapid construction methods that align with circular economy principles. 3D concrete printing is emerging as a key solution to address the comon issues of affordable housing, accelerated construction processes, and the modernization of the construction sector. In order to embrace circular economy principles, which prioritize waste reduction and efficient resource utilization, it's crucial for 3D printable materials to support material recycling at the end of their useful life. This study focuses on investigating the mechanical properties of 3D printable geopolymer mortars derived from end-of-life materials (specifically brick masonry waste) in the construction sector. To assess the viability of 3D printable one-part geopolymer, the investigation involved analyzing the flowability and buildability properties of the mixtures, and, orientation-based mechanical investigation, including compressive, flexural, and splitting tensile strength assessments on 3D printed samples with different layer heights. The interlayer bond properties were examined using direct tensile strength and microcomputed tomography.
In summary, the study findings revealed the existence of anisotropy, a key indicator for ultimate performance. Specimens loaded perpendicular to the printing path demonstrated similar performance to those cast in molds, underscoring the importance of the intersection ratio between the interlayer bond region and the load transfer plane. Nevertheless, anisotropy can be mitigated to some extent by adjusting the layer height, resulting in reduced pore content and distribution, reducing problems associated with weak interlayer bond zones in stress transfer. The results obtained from this study are expected to constitute a significant contribution to the advancement and promotion of sustainable waste-based alterna-tives for 3D printing of concrete, an area that remains open to further development.