Additive manufacturing of concrete with low initial yield strength through controlled heating of printed layers

3D concrete printing has emerged as a promising construction technology. Concrete mixtures with initial yield strength greater than 1,000 Pa are generally printed. Mixtures with lower initial yield strengths can enable better bonding among printed layers. This paper presents a method to print concrete mixtures with a low initial yield strength (e.g., 30 Pa). To improve the buildability, the printed layers were heated using an in-house automated printing and heating set-up. Process parameters, namely, stable layer thickness and duration of heating, were determined through suitable experiments. Buildability of the printed concrete was determined using three alternate methods. The results were affected by the slenderness of the specimen, and the nature of heating. The buildability rose sharply soon after 60 seconds-long heating, which can be attributed primarily to the loss of moisture and partly to an enhanced hydration of concrete. The moisture loss leads to an increase in the solid content of the mixture. Besides, it also produces a suction effect. Shear strength of hardened concrete cubes tested parallel to the printed layers was marginally affected for an optimal heating. The method developed herein can enable a sharp rise in buildability of the printed concrete while enhancing the integrity of the printed specimen. Further, it can help avoid chemical accelerators, thereby reducing the pumping pressure and the risk of choking the printing apparatus.