The mud hut becomes a house

Words:
Stephen Cousins

Geopolymer turns local soil into strong sustainable bricks

ISSB brickbuilding
ISSB brickbuilding

Researchers at the University of Bath are investigating the widespread application of a sustainable ‘supermud’ brick designed to tackle the global housing crisis.

Over two billion new homes need to be built over the next 80 years to meet global demand, yet in many developing countries a lack of affordable low carbon construction materials is a significant barrier to achieving sustainable development.

Geopolymer-stabilised soil materials (GSSM) offer a low carbon alternative to energy-hungry concrete or brick by making use of locally available soil materials. They are hard and durable and have been proven in the construction of one and two storey dwellings.

The team at Bath’s Department of Architecture & Civil Engineering is experimenting with a range of soil types to understand the chemical reactions triggered during the GSSM production process and the resulting impact on strength. It is hoped the results will validate the technique for the construction of homes worldwide.

  • ISSB wall
    ISSB wall
  • A hut near Kumi, Uganda
    A hut near Kumi, Uganda Credit: US Army Africa
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Alastair Marsh, Postgraduate Researcher and project lead, told RIBAJ: ‘Soil is abundant but it is always slightly different at any location, which remains a big question mark in terms of wider adoption. Understanding the chemical behaviour is important to predict material strength characteristics; clay mineral content is the most important aspect.’

Bath is also working with researchers from the Indian Institute of Science in Bangalore as part of a joint UK/India government-funded project, looking to develop a commercial product using material resources in the Bangalore region.

GSSM is manufactured using a simple process: Soil is taken from beneath the surface layer and mixed with an alkaline activating solution, containing chemicals similar to those found in household cleaning products, to create an activating solution that dissolves clay minerals into their constituent atoms. Bricks are created by shaping the dough-like mix into moulds and heating them at 80-100°C. During firing the dissolved atoms rearrange to form a strong geopolymer. 

  • Mathare Valley Slum
    Mathare Valley Slum Credit: Claudio Allia
  • School in a Maasai village on the A109 road Kenya
    School in a Maasai village on the A109 road Kenya Credit: CT Cooper
  • Collapsed soil building
    Collapsed soil building
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The relatively low firing temperature, combined with the use of local and abundantly available soil, is critical to the material’s low carbon footprint. It has been estimated that GSSM bricks could have half the carbon emissions of concrete, and quarter that of conventional fired bricks.

Marsh comments: ‘Even using very efficient plant, cement has a high environmental impact because the chemical processes in production require the release of CO2, and firing involves high temperatures. Geopolymers don't have that  chemical requirement and require much lower temperatures. Broadly speaking, many soils look like they could provide a good reduction in carbon and embodied energy impacts over conventional brick or concrete. However, the exact range is likely to be variable,’ he concludes.

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