Clay minerals in earthen binders for Earth Additive Manufacturing (EAM) applications

With recent developments in the construction sector exploring more environmentally friendly solutions, clay-rich sub-soil, commonly referred to as “earth”, is currently being re-evaluated as a building material [1]. As traditional earth-building techniques are being adapted to modern setups, additive manufacturing shows great potential for combining modern digital automated techniques with highly recyclable and sustainable earthen materials [2]. Earth Additive Manufacturing (EAM) techniques require high reproducibility for both equipment and material. Failure to account for key material parameters leads to time-consuming trial-and-error approaches, which over time can also strain or damage the robotic equipment used in EAM. An often-overlooked parameter is mineralogy, as inconsistencies or a complete lack of mineralogical data can be observed across studies, and established standards of earthen construction [3]. The present study introduces a systematic investigation of the clay mineral components of earthen binders and its effect on emerging EAM techniques. The heterogeneity of clay-rich materials around Germany is first assessed through the collection of samples with a sufficient range of spread in composition. Commercial clay products with high purity are chosen to simulate the isolated clay mineral component of earthen material systems. Non-swelling clay minerals, kaolinite (K) and illite (I), were targeted for the present study and their ratio (K/I) is varied within a range of 0.33 – 3. The first stage focuses on investigating the material on a microstructure scale. This includes a full quantitative mineralogical and chemical characterization using X-Ray Powder Diffraction (XRD) and Inductively Coupled Plasma Mass Spectroscopy (ICP-OES). Further microstructure characterization is carried out with Specific Surface Area (SSA) measurements using the Brunauer-Emmett-Teller (BET) method, surface charge determination with Zeta Potential (ZP), grain size distributions collected with Laser Diffraction (LD) and Scanning Electron Microscopy (SEM) used for imaging. For the second stage, the microstructure is linked to geotechnical and mechanical parameters focusing on how the materials interact with water and perform in EAM processes. Two types of mixtures are prepared: simplified "mortar" (clay and sand) to isolate the role of clay minerals, and more complex "concrete” (clay, sand, fibres, and/or gravel) that simulates realistic earthen building materials. The mortar mix highlights the contribution of the clay fraction in the binder, while the concrete mix allows for direct testing under EAM conditions. Fresh-state properties such as workability (consistency) and buildability (layer stacking and bonding) are evaluated. Finally, hardened-state properties, including shrinkage, compressive strength, and flexural strength, are measured to connect the clay mineral composition to overall mechanical binder performance.     «

With recent developments in the construction sector exploring more environmentally friendly solutions, clay-rich sub-soil, commonly referred to as “earth”, is currently being re-evaluated as a building material [1]. As traditional earth-building techniques are being adapted to modern setups, additive manufacturing shows great potential for combining modern digital automated techniques with highly recyclable and sustainable earthen materials [2]. Earth Additive Manufacturing (EAM) techniques requ...     »