An evaluation method for the printability of magnesium phosphate cement concrete for integrated mixing-stirring-extrusion rapid 3D printing

Abstract

This study examines a new 3D printing molding process for magnesium phosphate cement (MPC)-based materials. The process involves inputting dry powder and outputting wet material. The study proposes an evaluation method for the integrated 3D printer with functions of mixing, stirring, and extrusion for rapid-setting concrete is used for the research. The study proposes an evaluation method for the printability of materials based on the consistency of MPC paste measured by a Vicat apparatus. The study systematically examines consistency, setting time, extrudability, buildability, and mechanical properties of MPC concrete extruded by the 3D print head under different water-to-material ratios (mass ratio of water to dry mix). The results show that MPC concrete sets rapidly with setting times consistently within 4 min. The consistency of the printing paste decreases as the water-to-material ratio increases. When the extrusion consistency is between 25 and 34 mm, the 3D printed MPC concrete exhibits good extrudability, and when the extrusion consistency is between 23 and 34 mm, the 3D printed MPC concrete shows excellent buildability. A correlation has been established between the water-to-material ratio for rapid 3D printing of MPC concrete and the water-to-binder ratio used in traditional casting processes. The compressive and flexural strengths of the 3D printed MPC concrete generally decrease as the concrete consistency decreases. Under equal consistency and age, the compressive and flexural strengths of the printed specimens are approximately 1/3 and 1/2 of the casting strength, respectively. However, the printed specimens have better crack resistance than those cast. Therefore, the Vicat consistency could be used as an evaluation method for the printability of rapid-setting materials in the rapid-setting and hardening MPC-based material 3D printing process. When the extrusion consistency of MPC paste is in the range of 25–34 mm, the integrated mixing–stirring–extrusion 3D printing molding process for MPC-based materials can be realized. This method simplifies the operation process and procedures of the 3D printing equipment, ensuring accurate shaping and stability of performance of the 3D printed cement-based materials.