Sustainability – AHMC’s Research
The Materials or Resource Intensity of a product is a combination of the energy, water, materials and quantity of materials used to make something and to dispose of it at end of life.
A construction material which has as its major ingredient a fast growing renewable resource is hard to beat when you are looking for the feedstock for a sustainable building material. Expanding farming of this high biomass fibre crop for housing also has the potential to make a significant contribution to Australia’s emissions reduction strategy. Contingent on the number of internal walls, an average 135 sq m home (without subfloor or roofing insulation) at a minimum contains between 2 – 3 tonnes of Hemp.
AHMC’s Binder materials were designed to minimise the carbon footprint of hemp construction and to maximise affordability. Our R & D was focussed on life cycle analysis and we investigated ways in which to minimise the materials intensity of the materials by replacing some of the mined, heated materials in the Binder with locally sourced sand. This gives our material the strength to be used for external walls at a thickness of 200mm. Locally sourcing sand avoids a drying process and minimises packaging and freight. Compared to some of the more commonly available European Binders for hemp construction, AHMC walling materials use 56 kgs per cub m less mined super-heated materials.
Australia has abundant high quality Hydrated lime deposits. While lime production does have a significant energy footprint in Hemp lime construction, the energy or carbon released in the lime production process is reversed as the building material carbonates and draws in carbon dioxide from the atmosphere to cure. ( Hydrated lime is heated to 900º C. Hydraulic lime is heated to between 950º C and 1200º C.)
All hemp lime construction materials include some pozzolanic or cementitious materials which are heated to greater temperatures than hydrated lime. These materials may be naturally occurring elements, as those that occur in Hydraulic lime deposits, or magnesium oxide, volcanic ash or other pozzolanic materials.
A good indication of the amount of these added materials is the speed with which the Hemp building material sets and cures. AHMC’s materials for infill walling are slower curing than most hemp building materials. However the material has no slump so if walls are protected from the elements, formwork can be removed quite quickly. It does mean as well, that our materials are usable for longer.
A big difference between Hemp masonry material and conventional masonry is that there is no kiln baking in the production of the final product. It is a low embodied energy building material.
SO WHY DEVELOP AN AUSTRALIAN HEMP BUILDING MATERIAL AND WHY INCLUDE SAND?
1. Reduced emissions associated with the overall build. Global shipping emissions have a huge carbon footprint and shipping is responsible for extensive ecological damage.
2. Reduced Materials Intensity – 56 Kg less per m3 kilned material used than comparable hempcrete materials. This results in less water use, less energy use, less mining, and fewer bi-products produced from mining.
3. By working with hemp that is processed differently, we create an airy but strong matrix that maximises the porous insulative nature of the hemp hurd rather than shattering the hurd.
4. Durability – Sand adds early strength to the wall matrix by filling some voids between larger pieces of hemp and adds strength over time by combining with the lime in the binder through ongoing carbonation (as occurs in the formation of stalagmites).
.5. Reduced freight of materials – we transport fewer products for a build. The sand used in our builds is locally sourced to avoid the costs and energy required for bagging, drying and freight.
6. Aesthetics -The use of some sand creates a range of opportunities in relation to the aesthetics of a hemp building. Walls can be left off form and they are beautiful to look at because of the striation patterns the materials form. Mineral oxides and coloured sands can be used effectively.
It also allows for using natural products such as Waterglass as a clear sealant. There is a reaction between the Waterglass and the sand called silification. Few if any other hemp building materials are used in this way.
Our building materials can be reused or recycled.