Exploration of 3D Printed Concrete With Recycled Fine and Coarse Aggregates: Material, Equipment and Performance

The performance of 3D printed concrete (3DPC) is more complex than that of the cast one due to differences in the mix ratio, preparation and curing method. This paper focuses on the effect of material and equipment optimization on the improvement of 3DPC performance. In order to comprehensively consider the effects of recycled aggregates and the printing process on concrete properties, natural aggregate printed and recycled aggregate cast specimens were designed as control groups. The characteristics of 3DPC mixed with recycled materials were systematically analyzed from green state to post-hardening with the control group. The test results show that the alternative use of recycled aggregates effectively improves the deformation stability of the extruded concrete in the green state. Compared with the vertical nozzle without a scraper, the vertical nozzle with 40 mm height scrapers could reduce the vertical deformation of 3DPC by 20–25%. The maximum height and width deformation of the printed filament are only 3.20 mm and 0.72 mm, respectively, for a fully recycled aggregate replacement specimen. In addition, the porous nature of recycled aggregates makes them more suitable for on-site printing and maintenance due to the internal curing effect of water in the old mortar.