Hemp lime construction and ecological sustainability
Hemp lime construction materials are amongst the most energy efficient materials available in the modern construction market because they are predominantly made from a renewable resource.
One of the best ways to manage high atmospheric carbon levels is through planting fast growing, high biomass fibre crops such as industrial hemp, which sequester or harvest large volumes of carbon from the atmosphere through their rapid and vigorous growth.
In a four month period an industrial hemp fibre crop can grow to 4-5m in height and produce a dry hemp yield of upwards of 10 tonnes per hectare. This is at as least an equivalent carbon sequestration rate to the sequestration rate of plantation forests over a year.
When the woody biomass from industrial hemp crops is combined with a lime based Binder and then locked up into durable housing materials these structures are effective carbon sinks. This form of construction provides excellent thermal efficiency and consequently energy efficient living and working spaces.
Our research goals at UNSW were to develop a lime based binder and a hemp lime building material that could be manufactured in Australia for the mainstream Australian construction market.
When we began the building materials research at UNSW in 2000 it was with a commitment to developing an Australian building material using Australian grown hemp. It was also with the understanding that the hemp in the long run would need to be grown regionally in multiple regions of Australia to reduce the carbon footprint associated with freighting materials. The company’s Managing Director, Klara Marosszeky works closely with Australian farmers to support development of regional farming initiatives.
Although life cycle analysis of products is only starting to be broadly discussed, sustainable products need to consider all the steps in their manufacture and distribution.
The aims of our research were to develop a product and identify a process that would:
a) maximise the renewable resource in the composite material
b) minimise the energy-intensive heated and mined materials (limes) in the Binder and
c) produce materials with the lowest possible materials intensity
d) incorporate process improvements based on the recommendations of leading researchers in Europe and the UK and on a lengthy period of field research in Australia on smaller trial builds.
Traditionally in Europe the Binders used in Hemp Lime Construction have combined industrial hemp with hydrated lime (heated to 950º – 1060º C approx.) which sets or cures through carbonation (it draws in carbon dioxide from the atmosphere) combined with hydraulic lime, which sets through hydration (heated to up to 1200º C) and cementitious materials such as pozzolans, volcanic ash, fly ash or cement (heated to approx 1450 C). Across different manufacturers and the range of Hemp Lime products available globally, the cementitious component of the Binders can vary from 12% – 50%.
The research at the Australian Centre for Construction Innovation at UNSW resulted in the development of a Binder for Hemp Lime Construction in which more than 55% of the building material is hemp. Sand replaces a proportion of the lime based products in the Binder to contribute to the material’s early set and strength. Australian Hemp Masonry is amongst the most sustainable Hemp Lime Construction materials available globally.