A PRINTING UNIT FOR USE IN A 3D CONSTRUCTION PRINTING SYSTEM, A 3D CONSTRUCTION PRINTING SYSTEM, AND A METHOD FOR 3D PRINTING A CONSTRUCTION

A method for 3D printing a construction using a printing unit (2) is disclosed and comprises: I) obtaining a precursor printing material, the precursor printing material comprising a binder, water, and sand; II) forming a flow of the precursor printing material towards the printing unit (2) using a material pump (61); III) adding downstream of the material pump (61) an amount of a first additive via an additive outlet (9) to the precursor printing material; IV) optionally adding one or more additional additives; V) mixing the precursor printing material, the first additive and the optional one or more additional additives to form the printing material; and VI) extruding the printing material via the printing head (22). The invention also relates to a 3D construction printing system (1) and a printing unit (2) comprising a hopper (21) and a printing head (22).