Over the last decades, lightweight foamed concrete has gained recognition and widespread adoption in the construction industry, owing to its intrinsic multifunctionality and versatility. Notably, the ability to achieve a broad range of densities through mix design adjustments makes this material appealing for fulfilling different essential functions, including mechanical strength and thermal insulation. Moreover, recent studies exploring the application of foamed concrete in Additive Manufacturing processes underline the considerable advantage of combining the peculiar properties of foamed concrete with the benefits associated with automated procedures. In the present study the application of multi-density foamed concretes in the fabrication of multifunctional engineered building components through 3D Concrete Printing (3DCP) processes is investigated. The possibility of employing medium-density foamed concrete for 3D printing topologically optimized structural sections and ultra-lightweight foamed concrete for filling these sections with thermal insulation purpose is proposed. This innovative solution allows for the fulfillment of multiple performance requirements - high mechanical performance and excellent thermal insulation - within a single cohesive cementitious element, thus eliminating the need to assemble numerous monofunctional layers of different materials. The primary properties of the two proposed foamed concrete mixes were investigated. Compressive strengths of 7.04 MPa and 5.40 MPa were achieved for cast and 3D-printed medium-density foamed concrete, respectively. Thermal conductivities of 0.205 W/mK and 0.072 W/mK were obtained for medium-density and ultralight-density foamed concrete, respectively. A successful 3D printing application with medium-density foamed concrete was executed using a collaborative robotic arm, and the possible pouring of ultralight-density foamed concrete to produce multi-density building components was assessed.
