Time-varying work performance of cementitious 3D printing mortar: Effect of SAC, H-PC and HPMC

Appropriate working performance of cementitious 3D printing materials is a crucial factor in the feasibility and efficiency of the 3D printing construction process. The time-varying performance of mortar is essential for designing and conducting a continuous printing process, and the quantification of the time-varying work performance of cementitious 3D printing materials is indispensable. In this study, cementitious 3D printing mortar was prepared from binding materials (52.5 portland cement (PI52.5) and sulfoaluminate cement (SAC)), aggregate (0.5-1 mm silica sand), additives (polycarboxylate superplasticizer (H-PC), hydroxypropyl methylcellulose ether (HPMC)), and polypropylene fiber (PP-F). Measuring the representative node performance, setting time, time-varying performance, fluidity, extrudability, continuity, shape retention, and deforming-bearing capacity of mortars with varied SAC, H-PC, and HPMC contents. The extrudability and continuity of mortar are characterized by measuring the feedback force and continuous nonbreaking length during the extrusion process, respectively. Meanwhile, autogenous deformation and feedback force under continuous deformation were detected to represent the autogenous deformation and deforming-bearing capacity of the 3D printing mortar, respectively. The results showed that the order of influence on setting time and open time was SAC > H-PC > HPMC. Increasing the SAC content not only reduced the autogenous deformation but also accelerated the increasing rate of bearing capacity, while increasing the H-PC content gradually slowed the development of the bearing capacity, and changing the HPMC content had little effect on the development of the deforming-bearing capacity. With the use of selected materials to print solid components, the compressive strength of the printed samples was approximately 30% lower than that of casting mortar.