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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]

This paper studies the effects of recycled glass cullets as fine aggregates for the material in construction 3D printing. A reference material with natural river sand as fine aggregate was used as the control and recycled glass cullet of similar grading was used to replace the natural river sand at 25, 50,75 and 100% by mass. The effects of incorporating the recycled glass on the rheological properties such as the static yield stress, dynamic yield stress and plastic viscosity were studied. 3D printing investigation was also conducted on the mixtures to evaluate the materials printability (pumpability and buildability). Mechanical properties such as compressive strength and interlayer bond strength by splitting tensile were also examined. Results show that the static yield stress decreases while the dynamic yield stress and plastic viscosity increases as the recycled glass cullets content increases. The change in rheological properties also affected the printability of the mixtures. In the mechanical properties test, the increase in recycled glass cullets content also reduces the compressive strength and interlayer bond strength of the specimens. • Use of recycled glass cullets in construction 3D printing reduces demand for sand and provides a channel for waste glass. • Morphology and surface texture of recycled glass cullets affects the concrete's rheological properties and printability. • Hydrophobic nature of recycled glass cullets results in lower inter-layer bond strength of the concrete. [ABSTRACT FROM AUTHOR]