Hemp as a substitute for concrete in the construction industry, contributing to the mitigation of climate change
Written by: Klayton Amai
“Sustainability represents a primary issue for the construction industry” 8. Construction of today’s modern buildings makes up around 40% of the energy use in developed countries 1, 10. Heating and cooling of buildings makes up approximately 60% of energy consumption in buildings 6. This is significant and therefore any improvement on these figures would also be substantial to mitigate the effects of climate change 1, 2, 5. So why not look at hemp or “hempcrete” (hemp lime concrete) as an alternative to the unrenewable concrete, which contains synthetic materials that results in the production of copious amounts of Carbon Dioxide (C02) and other waste products 1, 2, 9.
In terms of ‘embodied energy’ which refers to the emissions produced by the extraction, processing, manufacture, delivery of the materials and disposal 9. The synthetic materials such as glass and steel used to reinforce many mixes of concrete contributes to its current high embodied energy status 5. With naturally occurring strong materials which could be so readily available, why are they not utilised more? Well it appears times are changing for the better because such materials are being researched more profusely in recent years 2, 3, 5, 9.
Hempcrete is a material which utilises the hemp “hurd” or “shiv” found in the core of the stem with water and lime as a binder 2, 4, 9. It has been used in a few instances in New Zealand to build the outer walls of homes 2, 7. Although it is not as dense and strong as conventional concrete, it makes great external walls when used in conjunction with timber or steel framing 9. In addition, plaster is usually applied for weatherproofing the outside of the dry and hardened hempcrete to increase the lifespan of the material 3.
The thermal conductivity of hempcrete has the potential to be lower than that of conventional concrete 9. When the hempcrete mixture is further developed it has the potential to retain thermal energy better within a home, reducing energy consumption for heating 6, 9. When tested, the less dense hempcrete had a lower thermal conductivity compared to the stronger higher density hempcrete which had a lower thermal conductivity 4. In a separate study, values of 0.068 and 0.123 W/m K were found depending on density and are comparable to other building materials used for external walls 5. The lower the thermal conductivity the less heat energy can escape. Thus, there is a trade off in terms of strength and thermal conductivity.
Hempcrete, which may not compete in terms of structural integrity with conventional concrete on its own, definitely makes up for it in terms of thermal properties and a low embodied energy 2, 3. The processes associated with the production of hempcrete encapsulate the plant’s ability to extract carbon from the atmosphere and store it as a solid or liquid within the plant 5. The production of hemp and its lower embodied energy means not only are we able to have more sustainable homes but could reduce the overall greenhouse gas emissions 1, 2, 5. What is touched on here clearly does not scratch the surface but opens the mind to the endless possibilities of how we can adapt to slow the effects of climate change.
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