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The advantage of 3DCP technologies is the ability to fabricate free-form structures. However, printing openings in concrete structures are limited by the presence of overhanging sections. While various 3D printing and additive manufacturing technologies have established methods for handling overhangs with temporary supports, many existing techniques for 3D concrete printing still rely on wooden planks and corbelling, which restrict the design flexibility and slope angles. The objective of this study is to develop a removable and sustainable support material with high printability performance. This support material serves as temporary support for overhang sections in 3D-printed structures and can be removed once the primary concrete has hardened sufficiently. This study observed that increasing the recycled glass content in the mixture raises both the dynamic and static yield stresses, with only mixtures containing up to 60% recycled glass remaining pumpable. Optimization of the mixture design aimed to balance high flowability and buildability, and the results indicated that a mixture with 60% recycled glass content is optimal. The effectiveness of the optimized support material was validated through the successful printing of a structure featuring a free-form opening and overhang section. [ABSTRACT FROM AUTHOR]

An advancing technology that combines the concrete extrusion with a motion control to create structures with complex geometrical shapes without the need for formwork is known as 3D concrete printing. Since this technique prints layer by layer, the time taken to reach the same position in the subsequent layer is important as it will create an anisotropic property that has a weaker tensile strength at the bond interface of the two printed filaments. Through rheological measurement, which reveals the material deformation and flow behaviour, it is possible to examine the material structural build-up due to time-gap effect by measuring at different time delay. This paper focuses on investigating the time-gap effect on the printed filament with rheological and observation at macroscopic-scale to understand the material behaviour of the initial and subsequent printed layer during its fresh phase. Rheological experiment findings reveal that the tensile strength of the printed specimen is correlated to the material modulus at the initial layer. [ABSTRACT FROM AUTHOR]