Impact of Calcium Sulfoaluminate Cement on Printability and Early Strength Development of a Slag-Based 3D Printing Cementitious Material (2023-09)¶

Blast furnace cement (BFC) as a binder for 3D printing cement (3DPC) has potential to lower carbon-footprints, but its unstable workability and strength development hinder its application. In this article, blast furnace cement (BFC), a mixture of ordinary Portland cement (OPC) and ground granulated blast furnace slag (GGBFS) based binder was designed toward low-carbon 3DPC, and the impact of calcium sulfoaluminate cement (CSA) content on printability and early strength of printed materials was discussed. The researched components of the materials, GGBFS, OPC and CSA, were first designed based on the 24 h early strength development. Slugs test was utilized to investigate 3D printability, and adiabatic hydration temperature, compressive strength, X-ray diffraction, thermal gravimetric analysis, and solid Si-nuclear magnetic resonance were used to analyze the early strength development and hydration products. For 1 h of hydration, CSA played a significant role in the hydration, due to generation of rod-shape Aft, which resulted in increase of yield stress as indicated by the slugs test. For 24 h of hydration, when CSA is less than 20%, it is C-S-H gel provided the strength; when CSA content is more than 20%, AFt constructs the skeleton, and unhydrated material and AH3 fill in the voids of the skeleton, resulted in high early strength. Strength response surface results indicated that GGBFS, OPC and CSA mass ratio of 5:4:1 is the best in this research. The 3DP opening time is in the range of 20–40 min, and the compressive strength at 24 h reaches 14.43 MPa.