Functionally Hybridised Lightweight Concrete Components: Monolithic Building Construction Using Selective Paste Intrusion

This paper introduces a novel methodology for the design and Additive Manufacturing (AM) of functionally hybridised, lightweight concrete building components. Grounded in simplified, monolithic, and single-origin construction principles, the proposed approach leverages geometric freedom and the use of lightweight aggregates provided by the AM technology Selective Paste Intrusion (SPI). This method enables the seamless integration of insulating and load-bearing functions within unreinforced, prefabricated concrete elements. The concept envisions an interlocking three-dimensional puzzle, wherein manufactured components are transported to the site, assembled, and connected through custom interlocking joints, with the option of incorporating post-tensioning cables when structurally required. The SPI method involves a repeated dual-step process, including depositing a loose layer of a lightweight aggregate of expanded clay (LECA) in a particle bed, followed by selective binding with penetrating cement paste. This research explores the potential of trapping loose aggregate within the cavities of the bound structure, which exhibits lower thermal conductivity compared to the fully bound structure. Consequently, areas containing trapped lightweight aggregates enhance thermal insulation, while regions with bound aggregates provide structural support. Compared to cast lightweight concrete with uniform material properties, lightweight SPI allows for creating an internal closed-cell composition that can be functionally graded to meet individualised structural and thermal requirements within a single freeform component. To experimentally validate this concept, a section of an outer wall on a 1:1 scale was manufactured using an SPI printer. With this demonstrator, we highlight the key conceptual features of the design method, including the manufacturing strategy of large-scale AM components with interlocking joints and a functionally graded internal structure.