Abstract
Fresh concrete used in 3D printing should ensure adequate yield stress, otherwise the printed concrete layer may suffer intolerable deformation or collapse during the printing process. In response to this issue, an analytical study was carried out to derive the initial yield stress and hardening coefficient of fresh concrete suitable for 3D printing. The maximum shear stress distribution of fresh concrete was calculated using a stress transformation equation derived from the equilibrium condition of forces. In addition, the elapsed time experienced by fresh concrete during the printing processes was estimated and was then substituted into the elapsed time-yield stress function to calculate the yield stress distribution. Based on these results, an algorithm capable of deriving both the initial yield stress and the hardening coefficient required for printing fresh concrete up to the target height was proposed and computational fluid dynamics (CFD) analyses were performed to verify the accuracy of the proposed model.
Highlights
Reinforced concrete (RC) structures have been widely utilized because they are extremely easy and economical to build
This study aimed to develop an algorithm to quickly derive the rheological properties needed to prevent the collapse of fresh concrete during the printing process
The fresh concrete was regarded as Herschel-Bulkley fluid and it was assumed that no deformation occurs before the maximum shear stress of layered concrete exceeds its yield stress
Summary
Reinforced concrete (RC) structures have been widely utilized because they are extremely easy and economical to build. Perrot et al [22] predicted the failure of fresh concrete during the printing process by reflecting the increase of the yield stress of fresh concrete over time and they proposed a model for calculating the optimal build-up velocity for concrete printing. The purpose of this study is to quickly obtain the initial yield stress and hardening coefficient required to prevent the deformation and collapse of fresh concrete during printing. To this end, the maximum shear stress distribution generated in fresh concrete during the built-up process was calculated using the force equilibrium condition based on the slump prediction model of Murata [15] and the concrete yield stress distribution considering the overtime was calculated using the elapsed time-yield stress equation. ANSYS CFX (ANSYS Inc., Canonsburg, PA, USA), a commercial software program for numerical analysis, was used to verify the reasonability of the proposed model by checking the deformation of layered printed concrete
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