Plant-Germination Ability and Mechanical Strength of 3D Printed Vegetation Concrete Bound with Cement and Soil (2023-10)¶

To facilitate the manufacturing efficiency of vegetation concrete and reduce relevant environmental footprint, a novel type of vegetation concrete was manufactured by using 3D printing with cement partially replaced by soil. Twelve mixes were prepared for the printing mortar where three types of cement, i.e., ordinary Portland cement (OPC), sulphoaluminate cement (SAC), low-alkalinity sulphoaluminate cement (LSAC), as well as soil were used as the binder. Cubic cells of the vegetation concrete were printed with two printing paths. After printing and curing, grass seeds together with soil were sowed in the gaps among the printing filaments of the specimens. The printability, plant-germination ability, mechanical strength, X-ray computed tomography reconstructed structures, stress distributions, pH, and crystal phases of the printed vegetation concrete were investigated. Results revealed that increasing soil content in the printing mortar benefited plant germination but reduced concrete strength. Furthermore, the plants germinated earlier in the higher-cement-content specimens due to lower porosity of the printed concrete which retained more water in the soil. However, such plants withered soon after germination due to high alkalinity. The compressive strengths of the printed vegetation concrete were between 0.03 and 21.19 MPa. The corners and the surface grooves between the layers of the printed vegetation concrete were weak points due to stress concentration. Moreover, the buildability of SAC and LSAC specimens was better than that of OPC specimens. This was attributed to the calcium sulfate in the SAC and LSAC specimens. On the other hand, portlandite and ettringite which were abundant in OPC specimens contributed more to the specimens’ higher alkalinity that is harmful to plant germination.