Additional data: Submillimetre mechanistic designs of termite-built structures

Termites inhabit complex underground mounds of intricate stigmergic
labyrinthine designs with multiple functions as nursery, food storage, and
refuge, while maintaining a homeostatic microclimate. Past research
studied termite building activities rather than the actual material
structure. Yet, prior to understanding how multi-functionality shaped
termite building, a thorough grasp of submillimetre mechanistic
architecture of mounds is required. Here, we identify
for Nasutitermes exitiosus via granulometry and Fourier
transform infrared spectroscopy analysis, preferential particle sizes
related to coarse silts and unknown mixtures of organic/ inorganic
components. High-resolution micro-computed X-ray tomography and
microindentation tests reveal wall patterns of filigree laminated layers
and sub-millimetre porosity wrapped around a coarse-grained inner
scaffold. The scaffold geometry, which is designed of a lignin-based
composite and densely biocementitious stercoral mortar, resembles that of
trabecula cancellous bones. Fractal dimension estimates indicate
multi-scaled porosity, important for enhanced evaporative cooling and
structural stability. The indentation moduli increase from the outer to
the inner wall parts to values higher than those found in loose clays and
which exceed locally the properties of anthropogenic cementitious
materials. Termites engineer intricately layered biocementitious
composites of high elasticity. The multiple-scales and porosity of the
structure indicate a potential to pioneer bio-architected lightweight and
high-strength materials.