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In Singapore, there is an increasing need for independence from manpower within the Building and Construction (B&C) Industry. Prefabricated Prefinished Volumetric Construction (PPVC) production is mainly driven by benefits in environmental pollution reduction, improved productivity, quality control, and customizability. However, overall cost savings have been counterbalanced by new cost drivers like modular precast moulds, transportation, hoisting, manufacturing & holding yards, and supervision costs. The highly modular requirements for PPVC places additive manufacturing in an advantageous position, due to its high customizability, low volume manufacturing capabilities for a faster manufacturing response time, faster production changeovers, and lower inventory requirements. However, C3DP has only just begun to move away from its early-stage development, where there is a need to closely evaluate the process parameters across buildability, extrudability, and pumpability aspects. As many parameters have been identified as having considerable influence on C3DP processes, monitoring systems for feedback applications seem to be an inevitable step forward to automation in construction. This paper has presented a broad analysis of the challenges posed to C3DP and feedback systems, stressing the admission of process parameters to correct multiple modes of failure. National Research Foundation (NRF) Published version This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Medium-Sized Centre funding scheme, National Additive Manufacturing Innovation Cluster, Singapore Centre for 3D Printing, Enviro Sand Pty Ltd., and Chip Eng Seng Corporation Ltd.

The varying physical property in a functionally graded material can be tailored to its specific requirements while using material resources effectively. 3D concrete printing can produce robust and lightweight functionally graded material for the construction industry. In this study, an approach was developed to create an objective tailored functionally graded concrete material by examining the filament material property correlations with the printing parameters. It was found that the physical property of the printed material is closely correlated to the flow rate and travel speed of the printer. Results obtained from the experiment show that the optimised structure achieved an approximately 50% improvement in the strength-to-weight ratio. This preliminary examination of the 2D optimised concrete structure opens the realm of possibility for future work in 3D optimised functionally graded concrete. National Research Foundation (NRF) Published version This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore, under its Medium-Sized Centre funding scheme, Singapore Centre for 3D Printing, Berkeley Education Alliance for Research in Singapore (BEARS) for the Singapore-Berkeley Building Efficiency and Sustainability in the Tropics (SinBerBEST) Programme.

The disposal of post-consumer glass has been a major issue due to its inert properties that may cause environmental effects, while recycling of these glasses is only feasible if the waste glass recovered is sorted into its different colour to prevent chemical incompatibility in the manufacturing process. 3D printing in building and construction has gain increasing attention in the past decade and provides a potential to sustainably utilize the recycled unsorted glasses. This paper examines the use of recycled glass as the fine aggregates for 3D concrete printing applications. Despite the several studies done on the use of recycled glass in concrete, there is a lack of focus on the rheology of the material which is essential to the performance of the material in 3D concrete printing. Although results have shown that the mechanical strength for the recycled glass concrete is lower than the sand aggregates concrete, yet the flow properties of the former is better than the latter. Nonetheless, a balance between the mechanical strength and flowability of the mix design should be studied. The future work revolves around the optimization of the mix design using a combination of sand and recycled glass, adjusting the gradation of recycled glass particles and addition of accelerators to improve its buildability and mechanical strengths. Accepted version

3D concrete printing (3DCP) is gaining much attention due to the absence of formwork, allowing more freedom in the architectural design, and reducing construction costs significantly. The lack of formwork configuration in the 3DCP technique requires the printable concrete to possess self-supporting properties. Furthermore, the yield stress evolution over time caused by the structuration build-up of the cement also allows a larger buildable height of the print. However, before the structuration in the material occurs, the concrete needs to possess high initial yield stress to maintain its shape upon extrusion during the early stage of the printing process. Although it is advantageous to have higher yield stress for the buildability of the concrete, the extrudability of the concrete should also be considered. When the yield stress of the concrete is too high, the pumping effort to cause flow in the concrete becomes too high and the extruded filament displays defects on the surface of the filament. This study aims to study the effects of various material parameters on the concrete extrudability and buildability to determine the extrudable region of the concrete mix design using a graphical approach. The material parameters that are being studied in this research includes aggregates fraction, attapulgite nano-clay content, and aggregates fineness. The results shows that the mix designs at the extrudable limit surface is most optimal for 3D concrete printing as it has the maximum buildability with the extrudable region. National Research Foundation (NRF) This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Medium-Sized Centre funding scheme, Singapore Centre for 3D Printing, National Additive Manufacturing Innovation Cluster, Enviro Sand Pty Ltd, Chip Eng Seng Corporation and Berkeley Education Alliance for Research in Singapore (BEARS) for the Singapore-Berkeley Building Efficiency and Sustainability in the Tropics (SinBerBEST) Program.

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. National Research Foundation (NRF) Accepted version This research is supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Medium-Sized Centre funding scheme, National Additive Manufacturing Innovation Cluster, Singapore Centre for 3D Printing, Enviro Sand Pty Ltd, and Chip Eng Seng Corporation Ltd.

Rheological studies are important for successful 3D concrete printing. The main challenge for successful 3D concrete printing is the complex characteristic the materials should possess. It should be flowable enough to be pumped and extruded through the hose, as well as gaining sufficient strength and stiffness for buildability after the layer by layer deposition. Existing literature has various mixtures proposed for successful 3D concrete printing. Most of these studies used rheometers to measure the dynamic yield stress and plastic viscosity. As the measurement with rheometer is sensitive to the protocols and is controlled by the rheologists, as well as data processing if non-standardized measuring geometries are used, results could vary significantly. This study used standardized field-friendly protocols to measure the slump and slump-flow of the mortars. The pumpability and buildability are evaluated in terms of the pumpability index and maximum height printed before collapsing. These result together with the slump and slump-flow values are used to define the printable region. Accepted version

Scalability is a problem common to most existing 3D printing processes, where the size of the design is strictly constrained by the chamber volume of the 3D printer. This issue is more pronounced in the building and construction industry, where it is impractical to have printers that are larger than actual buildings. One workaround consists in printing smaller pieces, which can then be assembled on-site. This workaround generates however additional design and process complexities, as well as creates potential weaknesses at the assembly interfaces. In this paper, we propose a 3D printing system that employs multiple mobile robots printing concurrently a large, single-piece, structure. We present our system in detail, and report simulation and experimental results. To our knowledge, this is the first physical demonstration of large-scale, concurrent, 3D printing of a concrete structure by multiple mobile robots. Accepted version

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. NRF (Natl Research Foundation, S’pore) Accepted version