Finding optimized conditions for 3D printed high calcium fly ash based alkali-activated mortar

Alkali-activated material is a potential alternative building material. The conventional forming method of alkali-activated is casting. Recently, additive manufacturing technology, or 3D printing, has become increasingly attractive for use in construction due to its advantages in freedom of design, cost-efficiency, and less labor required. However, the proper characteristics of alkali-activated materials for 3D printing are still very limited. In this work, the 3D printing with high calcium fly ash alkali-activated using customized extruder was studied. The variables for the mix proportion were sand-to-fly ash ratio of 1.55, 1.65 and 1.75, and liquid-to-binder ratio of 0.45, 0.50 and 0.55; and printing speed of 140–160 mm/s, interval duration of 10, 20, and 30 min, and nozzle height of for the printing of 10, 11 and 12 mm for the printing. The results showed that for high calcium fly ash activated with sodium hydroxide and sodium silicate, the mix with a sand-to-fly ash ratio of 1.65 and a liquid-to-binder ratio of 0.50 was the most suitable one considering the fast-setting time of 56 min and ease of extruding the mixture with a flowability of 103 %. were the printing speed of 150 mm/s, interval duration between each layer of 3 min, and the nozzle height of 11 mm. The 28-day compressive strength of 23.9 MPa was obtained. The high calcium fly ash was shown to be suitable for 3D printing the presence of calcium reduced setting time and improve the buildability of the 3D printed mortar.