Characterising the anisotropic nature of bio-composites

Buildings contribute substantially to our greenhouse gas emissions and energy demands both in their occupation and construction. Their construction also consumes large volumes of finite resources. Sustainable, low embodied energy, high performance crop based materials therefore offer great potential. Hemp-lime is a bio-composite concrete, mass infill material with a greatly lower embodied energy than equivalent traditional constructions. It also exhibits beneficial hygrothermal properties that can improve both a building’s energy performance and the comfort of its occupants by buffering humidity and temperature. It is however widely considered insufficient structurally, limiting its scope for application. A lack of understanding and acknowledgment that hemp-lime and other similar bio-composites are anisotropic, but instead have a directional internal structure, has hindered the development of stronger and more versatile products. In this work a range of methods based on digital image analysis and computer tomography were trialled with the aim of identifying the nature of hemp-lime’s internal structure and providing a methodology to classify it. The results from both digital imaging and computer tomography scanning indicate that the internal structure of the specimens considered was highly anisotropic; a strong directionality in the hemp particles was found to be induced by the construction process. The novel assessment methods developed to allow the numerical classification the internal structure that may be used in the future to allow the structural optimisation and modelling of bio-composites