Mix design, optimisation and performance evaluation of three-dimensional printable concrete

Three-dimensional (3D) concrete printing (3DCP) is a cutting-edge construction method that has recently received much attention. Most 3DCP research studies have focused on printer development, printable material mix designs and the complexity of geometry shapes. This research study primarily focused on determining appropriate mix proportions and suitable 3D-printable concrete (3DPC) mix designs using a trial-and-error approach. Experimental tests were carried out on 27 trial mixes made with different materials to determine printable properties such as flowability, buildability, extrudability and open time. Printed and cast samples were tested for compressive strength. The 3DPC mix with 19% ordinary Portland cement, 23% fly ash, 7% silica fume, 13% ground granulated blast-furnace slag, 4% limestone and 0.22% superplasticiser (% by mass of total binder) was found to be an ideal mix proportion, exhibiting the required 3DPC characteristics such as good buildability, easy extrusion, low setting time, mix cohesiveness and reduced deformation. The proposed mixing protocol and the suggested 3DPC mix design are encouraging for large-scale 3DCP. To demonstrate the application of the 3DPC mix, 3D-printed concrete furniture was fabricated with a nozzle of size 30 mm, an extrusion speed of 100 mm/s and a printing speed of 60 mm/s.