Comparing the environmental impact of stabilisers for unfired earth construction

Buildings account for approximately one third of the total worldwide energy emissions, of which approximately a quarter can be attributed to the embodied energy of the building. Current UK legislation for low-energy homes is only concerned with operational energy. Embodied energy, and carbon, is not currently considered but over the design life of an average building is expected to make a significant contribution to the total whole life energy used.

Earthen building materials contribute to reduce energy consumption in use through their passive regulation of temperature and humidity. In addition, there can also be significant embodied energy savings compared to other materials. Traditional methods of earthen construction, using locally sourced materials and manual labour require minimal energy for the transport and construction. A greater uptake of earth construction is likely to come from modern innovations such as industrialised manufacture. Extruded fired brick manufacturing processes has the potential to produce a high quality, low cost and low energy product suitable for the mainstream construction sector in both developed and developing nations. By not firing the extruded clay bricks, an embodied energy saving of 86% can be achieved, compared to fired clay, and 25% compared to concrete blocks.

However, there are limitations to the structural use of unstabilised earth bricks due to the loss of strength under high moisture content conditions. The use of traditional and novel stabilisation methods can be adopted to address the concerns over strength and durability. Cement and lime are widely used in some countries, but both significantly increase material embodied energy and carbon and can inhibit passive humidity regulation. The paper presents results from a study of the embodied energy of various stabilisers used for unfired clay materials. The Global Warming Potential (GWP) is a measure of the equivalent carbon dioxide that allows for the relative weightings of damaging greenhouse gasses. Both the embodied energy and the GWP figures of various stabilisers are compared and discussed.

The conclusion of the work is that there is a maximum quantity of stabiliser than should be used. Typically the quantities of stabiliser are quoted as the amount that gives the maximum strength, but this should take account of not only strength but the environmental impact of achieving the improvement.