3D concrete printing is an additive manufacturing technology that is attracting attention from the construction sector for its potential to increase productivity and product quality. In Indonesia, 3D concrete printing technology is uncommon in construction activities, in contrast to the developed countries. The main challenge with using 3D concrete printing technology is determining the composition of material mixtures that have good extrudability but still maintain sufficient strength.
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A previous study conducted by Antoni et al. experienced several problems, such as unsatisfactory extrusion process and cracks in the 3D printed material. In this study, the cement-to-sand ratio was reduced to reduce the cost of the material. Synthetic microfiber was used to reduce crack problems. The study aimed to investigate the effect of the cement-to-sand ratio, maximum particle size of sand, and addition of synthetic microfiber on fresh and hardened concrete properties including workability, initial setting time, extrudability, and compressive strength. The materials used were silica sand, calcium oxide (CaO), Portland cement, synthetic micro-fiber, admixtures such as accelerators and superplasticizers. Mix designs are shown in Table 1. The mixture with a higher cement-to-sand ratio had greater compressive strength and smaller flow diameter because of higher fresh mixture compaction and viscosity. However, an increase in the cement-to-sand ratio caused concrete to have slightly faster initial setting time. Using sand with smaller particle size resulted in faster initial setting time; however particle size did not affect compressive strength or workability of mixtures investigated in this study according to their findings .
Addition of synthetic microfibers accelerated initial setting time , reduced workability of mixture ,and decreased compressive strength of concrete by 5 percent compared to mixture without microfibers . Extruded concrete showed significant strength reduction compared to compacted cube specimen without compaction due lower density caused by trapped air voids . There was also an effect noted in the load direction on compressive strength of extruded concrete depending on bond between each layer ,extrusion pressure from subsequent layer ,and setting time fo mixture which all play a role controlling compressive strength . All mixtures selected met requirement for setting time and workabilty for 3D concrete printing process . Only some mixtures achieved desired properties for extrusion process; however depending machine setup and nozzle size ,mixture needs to be readjusted to have required workability.
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Original Scientific Paper