From Soil to Site

Emerging Bio-Based Materials 

It goes without saying that there is an ongoing awareness in global environmental consciousness to place more scrutiny on industries to utilise sustainable practices. Within the construction industry alone, there is an increased emphasis to utilise alternatives materials that have a lower environmental impact than traditional materials, such as the ubiquitous concrete. 

Emerging bio-based materials have garnered quite the attention, spurred on by this heightened sustainability focus — particularly the need to reduce global CO₂ emissions. Unlike conventional bio-based materials, such as wood, emerging bio-based materials are contemporary materials that are partly or wholly made from substances derived from living organisms, and typically undergo bio-catalysis (the use of living systems or their parts to speed up chemical reactions). These materials are active subjects of current research and development, and breakthroughs in their possible applications are regularly occurring. 

At the forefront of emerging bio-based materials is mycelium — the thin, root-like fibres of fungi found in and on soil and other substrates. Mycelium acts as a ‘glue’ which complex web of fibres binds substrates such as sawdust, ground wood, straw, agricultural residues, or similar substances that might otherwise be discarded. Mycelium-based blocks are made by combining mycelium and a chosen substrate into a solution that is transferred into moulds. The solution is left to grow in favourable conditions (adequate temperature, humidity, and light) for about five days before it solidifies into a sturdy material. It is subsequently removed from the mould and placed in an oven to terminate any living microorganisms and prevent any further growth.  

Depending on the mycelium strain, growing conditions, and the composition and structure of the substrate used, the final mixture can be moulded to produce insulation panels, furniture, accessories, fabrics, packaging material, and blocks. The physical characteristics of mycelium-based material are similar to polystyrene, but with improved biodegradability. These blocks exhibit good thermal and acoustic properties as well as water, mould, and fire resistance. 

Then there is hemp. Hemp is derived from the cannabis plant but has a very low content of tetrahydrocannabinol (THC) — the substance responsible for the ‘high’ feeling associated with consuming Cannabis sativa. The misinformed, negative association with the very high THC content of ‘marijuana’ has hindered the adoption of hemp into mainstream industries. But as public opinion around cannabis softens and countries around the world, including South Africa, review and loosen their legislation, hemp and its many possibilities are being explored with fervour.  

Hempcrete is one of these possibilities. It is made from the woody inner parts of the actual hemp stalk called the ‘hemp hurds’. This is broken into fragments, removed of impurities, and mixed with a lime-based binder and water. This mixture can either be cast in situ or placed in a mould, where it is left to harden into a lightweight block or sheet. Like mycelium-based material, hemp-based material is biodegradable, has good thermal and acoustic properties, and is water, mould, and fire resistant. Furthermore, it is carbon negative as it removes and stores more carbon from the atmosphere over its lifetime than was used in its production and use. Cape Town will soon boast the tallest building in the world made with hempcrete: the 12-storey Hemp Hotel on 84 Harrington Street. 

Despite the promising developments within emerging bio-based materials, greater economic incentive is still required for their wide-spread use in our cost-driven society. Conventional building materials such as clay bricks and concrete are still cheaper in comparison. Moreover, emerging bio-based materials usually have load-bearing limitations, and therefore a conventional frame (using conventional materials) for structures is still needed. Then there’s also the questions around the scalability and regulation of such novel materials within the construction industry. 

Looking ahead, we’re in for an exciting decade where emerging bio-based materials are constantly being researched, tested, and implemented, which includes explorations with banana fibre, cork, and straw (just to name a few). What started off experimental is gradually shifting into the viable, common use of environmentally conscious construction materials.