Multilayered Plant-Growing Concrete Manufactured by Aggregate-Bed 3D Concrete Printing (2024-05)¶

A new type of multilayered plant-growing concrete was proposed in this work based on aggregate-bed 3D printing. Ordinary Portland cement (OPC) and low-alkalinity sulphoaluminate cement (LSAC) were used as binders for the printing mortar. The printing began by extruding the first layer mortar, and then coarse aggregates were spread on top of the mortar. Repeating these two steps multiple times finally manufactured the proposed plant-growing concrete where the plant seeds associated with soil were sown in the pores of the aggregate layers. Printability, pore structures, porosity, plant-growing quality, mechanical strengths, alkalinity, crystal phases, permeability, and stress distributions of the printed specimens were investigated. Results showed the printability of LSAC specimens was better than that of OPC specimens due to higher contents of sulphoaluminate in the LSAC specimens which consumed more water and thus resulted in drier and stronger printing mortar. The pores in the printed plant-growing concrete were connected into permeable networks allowing water to flow in and plants to grow in. The porosity and permeability of LSAC specimens were higher than those of OPC specimens due to the better printability of LSAC specimens which resulted in more connected pores, whereas the alkalinity of LSAC specimens was lower. All these led to the better plant-growing quality of LSAC specimens. Portlandite and ettringite, which were more abundant in OPC specimens, contributed more to the alkalinity of the printed concrete. The mechanical strengths of the printed plant-growing concrete showed distinct anisotropy, which was contributed by different layers playing critical roles in the strength tests. Nevertheless, ordinary materials and printing paths were used in this work, which can be varied and optimized in future studies and applications.