Overview on bio-based building material made with plant aggregate by S. Amziane & M. Sonebi

hemp shiv (the woody core of the stem of the hemp plant) is probably the most widely used in alternative or eco-friendly building materials in Europe and is also representative of most of the aggregate coming from the stem of an annual crop. This is usually mixed with a lime-based binder and the resultant bio-concrete is known as hemp-lime
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(…) plant based materials have a valuable benefit for health, ecologic, comfortable habitat (moisture management, thermic and acoustic) and sustainable materials (…) can be qualified as environmental-friendly and efficient multi-functional (…) The use of crushed hemp (shiv), flax and other plants associated to mineral binder represents the most popular solution adopted in the beginning of this revolution in building materials (…) in particular, for hemp, for which the corners of the market are as varied as fibers for the automobile industry, foodstuffs for the grain or indeed the wood of the stem for construction (…) Indeed, many projects aim to create construction materials using one or more forms of lignocellular matter as a reinforcement to the structure rather than as a lightweight aggregate with an insulating purpose (…) More recently, projects used various sources of bio-aggregates, such as wood, coconut, sisal, palm, bamboo, or bagasse (…) Bio-based aggregate are coming from the stem of plants cultivated either for their fibers (hemp, flax, etc.) or for their seeds (oleaginous flax, sunflower, etc.)

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Agro-concrete: “A mix between granulates from lignocellular plant matter coming directly or indirectly from agriculture or forestry, which form the bulk of the volume, and a mineral binder”

Hempcrete is a mixture, in very changeable proportions, of two very different components: a plant-based granulate and a hydraulic and aerated setting binder. It exhibits multiphysical behaviour which is unusual in the domain of construction materials. Indeed, the particles of hemp wood are characterized by a high degree of porosity which results in a high capacity to deform, absorb sounds and have hygrothermal transfer ability: this is one of the essential characteristics which set hempcretes apart from tradition mineral-based concretes for which the granulates are considered non-deformable (…) the variability of the behaviour depending on the formulation enables us to adjust and optimize the performances of this material for diverse applications as a roof filling material, in walling or as flagging (…) It can undergo differential compression, contraction or dilation with no apparent cracking (…) Hemp-based materials are considered as phase-change materials (PCM): the thermal behavior reduces the amplitude of the variations in the ambient air temperature, whilst improving the thermal comfort by bringing down the surface heat of the material. Thus, the use of such materials is an excellent means of passively regulating the indoor temperature, and thereby decreasing the building’s energy requirements (…) these materials are able to improve summer and winter comfort, and stabilize the indoor temperature between day and night, whilst preventing the phenomena of condensation and dampness on the walls (…) 1.8 tons of CO2 are sequestered for every ton of hemp shiv used (…) there is a favorable impact on the greenhouse effect; the hempcrete wall constitutes an interesting carbon absorber for a duration of at least 100 years (…) Some studies have shown that wetting/drying cycles, used to simulate natural variations of humidity, had an influence on the mechanical and thermal properties of hempcretes (…) fungi may also appear at the surface of materials

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