Optimizing Three-Dimensional Printing Binder Composed of Ordinary Portland Cement and Calcium Sulfoaluminate Cement with Retarders

Printability and open time are of great concern for three-dimensional (3D) printing of concrete. In this study, blends of ordinary portland cement (OPC) and calcium sulfoaluminate cement (CSA) were used as 3D-printing binders (3DPBs). Two organic salts-that is, sodium gluconate (SG) and potassium sodium tartrate (PST)-were selected as retarders to control the setting process of 3DPB. Effects of SG or PST dosages on 3DPB were characterized by measuring rheological properties, fluidity, penetration resistance, and bearing capacity. The underlying mechanisms were further revealed by zeta potential and thermogravimetric analyses. The results indicate that a blended binder with 90% OPC and 10% CSA is feasible as a 3DPB. Both SG and PST lead to the improvement of fluidity and a reduction of bearing capacity; however, the evolution of static yield stress highly depends on the dosages of retarders. Taking the open time, extrudability, and buildability into consideration, the optimal 3DPBs composed of OPC, CSA, and retarder are given.