Evaluating the stiffening effect of CSA and sodium carbonate on the printability of OPC mortar

The printability of a material is the prerequisite of extrusion-based 3D concrete printing. This paper exams the printability of ordinary Portland cement (OPC) mortar with calcium sulphoaluminate cement (CSA) as the stiffening control agent. The flowability, shape stability, penetration resistance and real printing performance over time were measured to represent the printability of mixtures. Results indicate that CSA slightly decreases the initial flowability of mixtures and significantly increases the flowability loss with rest time. Besides, CSA improves the shape stability of mixtures and this improvement is increasingly prominent with rest time. In addition, CSA hardly influence the initial penetration resistance while it has a significant promotion on the growth of penetration resistance with time. Above results demonstrate that CSA has a moderate influence on the extrudability of OPC mortar mixtures and a prominent stiffening effect on mixtures, as a result providing a timely buildability for the printed layers. This influence is validated by the rheological properties and the kinetic analysis of cement hydration. Thus CSA acts as a favorable stiffening control agent for OPC mortar, which improves the printability of mixtures.