A new strategy to enhance 3D printability of cement-based materials: in-situ polymerization

Printability is a crucial attribute for 3D-printed cement-based materials, as it not only governs the material's printability but also directly impacts the quality of the final structure. A good printability indicates that the printed materials are flowable for transport and extrusion, followed by a rapid increase in strength to establish a stable structure. In this paper, a novel strategy is proposed to enhance the 3D printability of cementitious materials by leveraging the rapid strength enhancement of fresh mortar during in-situ polymerization of acrylamide (AM) in the matrix within 30-60 min of contact with water. Prior to extrusion, AM monomers are absorbed onto cement particles to enhance the flowability of mortar to approximately 185 mm, thereby improving pumpability and extrudability of printed materials. Shortly after extrusion, in-situ polymerization of AM monomers within the mortar takes place, resulting in a sudden albeit modest strength increases in the fresh mortar, enhancing the buildability of the printed mortar. Moreover, the flexural strength of 3D printed filaments with 5% AM are increased by 52.4% at 28d, respectively. Meanwhile, the interactions between the AM in-situ polymerization and cement hydration are comprehensively discussed. This innovative approach to enhance 3D printability is expected to drive the advancement of 3D-printed materials with enhanced adaptability and superior properties.