Tavs Jorgensen develops cob bricks for low-carbon construction

Researcher Tavs Jorgensen has created a method of extruding cob into brick shapes, in an effort to make the low-carbon biomaterial more accessible.

Used to create bricks that can be stacked in interlocking patterns, the process involves pushing different samples of cob – a construction material made from earth and straw – through 3D-printed extrusion moulds known as dies.

It was developed as part of a research project at the University of the West of England's Centre for Print Research, where Jorgensen is an associate professor.

Cob is a natural and ancient building material made by combining subsoil, water and fibrous materials such as straw.

While Jorgensen's extrusion research initially explored other clay-based materials for different applications, he was drawn to cob construction because of the importance and need for sustainable building techniques.

"We were particularly keen to work with cob as there is very limited knowledge of extruding this material and were also driven by the opportunity to contribute with research to develop sustainable and low-carbon construction approaches, which are so badly needed," Jorgensen told Dezeen.

"The fibres bind the cob composite together, so firing is not necessary," he continued. "Avoiding firing makes cob bricks an extremely low-carbon building material."

"Unfired cob bricks can also easily be returned to the raw state of the components – basically just earth and composable fibres – so complete material circularity can be achieved with no waste at all."

Typically considered a labour-intensive construction process, cob is traditionally formed into monolithic walls and compressed. Jorgensen hopes that making the biomaterial available in brick form will make it more accessible.

"The extrusion process is one of the most efficient industrial methods for producing bricks and other architectural construction components, so making cob bricks in this way presents significant averages in terms of speed and low cost," he explained.

Multiple cob mixtures were made to test what worked best for the extrusion process and Jorgensen has developed both light and heavy versions of the bricks.

The light cob bricks are made with two parts liquid clay and three parts hemp shiv – the woody core of the hemp plant. Meanwhile, heavier bricks are made from one part sand to one part clay, which is then added to a mixture of barley straw and water.

"There are lots of other variations with different fibres, clay and fillers that could be explored," explained Jorgensen.

"The key challenge in using the extrusion process is that cob or earth composites need to have sufficient plasticity to be formed in this way."

The dies are made with interlocking shapes, designed to negate the need for mortar in construction. The extrusion process also allows the possibility of more complex geometries, including bricks with air cavities.

"We wanted to explore some new design concepts with the cob brick dies, particularly ways of creating interlocking bricks to avoid the need to build with mortar, which is typically the weakness in clay brick constructions," Jorgensen said.

"We also wanted to explore new aesthetic possibilities in earth building through the nature of the extrusion process," he continued. "The approach of using 3D-printed extrusion dies allowed for rapid and low-cost exploration of such ideas."

Supported by the Arts and Humanities Research Council and with funding from Research England Expanding Excellence in England, Jorgensen hopes the research could help encourage the industrial uptake of earth-based building techniques as a way to lessen the environmental impact of construction.

"The construction sector is still extremely unsustainable in terms of carbon footprint, toxic material usage and component circularity," he said. "Building with raw earth has one of the lowest environmental impacts of any construction approach and it would be an obvious way to address the extremely serious environmental challenges that are presented to us."

Other innovative bricks that have been published on Dezeen include water-permeable bricks made from ceramic waste and low-carbon bricks made from municipal waste.

Earlier this year, experts spoke with Dezeen about the sustainability of rammed earth. Typically considered a low-carbon building method, they raised concerns about the addition of cement into some rammed-earth constructions.

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