Effect of sulphoaluminate cement on fresh and hardened properties of 3D printing foamed concrete

Generally, we expect that cement-based materials for 3D printing can quickly obtain sufficient strength after extrusion to resist the pressure generated by the stacking layers to achieve good buildability. In this study, sulphoaluminate cement (SAC) was used to improve the printability of fresh foamed concrete (FC). The effects of different SAC contents on the foam stability, open time, and buildability of fresh FC, the interlayer interface, and porosity and mechanical anisotropy of hardened 3D printed FC (3DPFC) were investigated. The addition of SAC reduces the settlement of fresh FC and prevents defoaming by promoting the hydration process to accelerate the formation of pore structure. In addition, SAC reduces the bubble diameter of the fresh FC, which is attributed to the enhancement of yield stress of the mortar before doping foam. Meanwhile, the buildability of 3DPFC is improved, while the open time is reduced with the addition of SAC. The printability of the 3DPFC can be pre-dicted based on the remaining height of the FC from cylinder test and the flow diameter from jumping table test. When the remaining height is 74-80 mm, and the flow diameter is between 155 and 176 mm, the extrudability and buildability of the 3DPFC can be guaranteed simultaneously. With an increase in SAC content, the width of the interface area and the interface porosity of the 3DPFC increase, leading to the intensification of mechanical anisotropy. We suggest that the SAC content for 3DPFC should not exceed 10%.