Development and evaluation of a functionally graded additive manufactured biocomposite envelope system

Abstract

The implementation of Additive Manufacturing (AM) in construction has been proposed as a viable alternative as it can help mitigate the environmental impact of the construction industry through material waste reduction, elimination of formwork and scaffolding, and quick building times; while also enabling the fabrication of environmentally, structurally and materially optimized geometry. Most AM technologies in construction use homogeneous cement-based mixes, which albeit efficient in material use are nevertheless energy-intensive; not entirely addressing the fundamental problem of cement’s widespread use and its high environmental impact. Incorporating sustainable materials into AM for construction is a way to address this issue and is currently at a research phase. This thesis proposes a biocomposite material consisting of cement, lime, clay and hemp to be used with AM through function-based material arrays. Fabricating composite envelopes that match specific functions to localized regions of the material, such as in Functionally Graded Materials (FGM), can meet performance requirements by integrating performative materials only at critical target regions, and substituting non-target areas with comparatively lower-Embodied Energy (EE) material components. The building system presented in this thesis furthers the concept of blurring edges between the various discrete materials and components comprising a conventional building assembly, merging them through a gradient transition into a multi-material, multi-purpose monolithic envelope unit to achieve useful and appropriate combinations of materials, generating minimal waste during the fabrication of environmentally, structurally, materially-optimized and customized buildings using low EE materials whose beneficial properties will allow for low Operational Energy (OE) consumption.

Results demonstrate that the proposed biocomposite has desirable insulative properties that are comparable to those of current building systems, and which can transition into more structural properties where desired. The material’s thermal diffusivity would depend on the quantity of reinforcement present in the mix, which is uncoupled from the compressive properties which depend on binder composition and aggregate quantity variation. The mass customization opportunity of AM allows for low embodied-energy facades that are unique and optimized in their material arrangement, using FGM to enhance environmental, structural and thermal performance.

A characterization of different instances along a material gradient in a hemp-reinforced clay-hydraulic-lime-cement biocomposite was made in order to evaluate their mechanical and thermal ability for construction use, as well as their ability to be used as environmentally benign materials that contribute in lowering the GHG emissions of the building industry. Physical testing was conducted for thermal diffusivity and compressive strength, while in parallel, an evaluation of the environmental properties of the materials, using literature, is presented. A design application is presented as a way to assess the material performance and depict a possible use of the biocomposite in an architectural context, iterating on previous concepts using FGM in AM: a structure-to-envelope unit.

A global population surge is expected during the upcoming decades, which will result in an extraordinary expansion of urbanized areas across the globe and a steady demand for building construction. The construction industry and the building sector are large contributors to Global Warming and climate change through their energy consumption and Greenhouse Gas (GHG) emissions, evidencing a critical opportunity for improvement. Reducing the environmental impact generated through the consumption of energy and resources, and the emission of GHG, can considerably alleviate the pressure from both current and future construction and operation of buildings.