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Use of alien plants in construction: a study

by Madelein
Use of alien plants in construction: a study

The national government of South Africa has started a research initiative to address the environmental crisis of using concrete and cement in the building industry. The focus needs to shift to alternatives for these building materials to create a more sustainable future. This initiative is to use the mechanically chipped biomass of water-thirsty invading alien plants (IAPs) as a substitute for sand and stone as aggregate in conventional concrete.

Detail of wall cast with wood-chip cement

Water catchment areas

The clearing of these IAPs from water catchment areas can contribute to producing more sustainable woodchip cement, or “noncrete” building materials – ensuring water security, restoring natural ecosystems and creating labour-intensive jobs in impoverished communities.

Beneficial use of IAP biomass

The innovative use of IAP biomass in construction offers significant carbon sequestration opportunities, while also addressing the increasing demand for dignified and affordable housing across South Africa, which has the highest income inequality in the world.

  • Casting woodchip cement blocks on site.
  • Detail of wall cast with woodchip cement.
  • Construction on site with woodchip cement.

A recent study has shown that there is enough invading alien woodchip to meet the current housing shortfall three times over in South Africa. Combined with a low-cement binder, this woodchip cement is three times more fireproof than conventional building materials in South Africa such as cement or clay bricks; and has double the thermal insulating properties at half of the weight of conventional concrete.

A viable alternative construction method

The proposed structural system as a viable alternative construction method for housing is a demonstration of how structural geometry can significantly reduce resource consumption and enable the use of local and more sustainable, yet structurally adequate, building materials such as “noncrete”. Combined with structurally informed fabrication techniques, this system demonstrates the potential of providing safer and more dignified housing alternatives in an affordable and sustainable manner.

The barrel-vaulted roof consists of self-supporting bricks, which can be constructed on site with a minimal amount of formwork and without requiring expert labour. More importantly, the geometry of the roof and the interlocking system of the bricks eliminate the use of steel reinforcement. The weight of each brick has also been optimised to be handled easily by both male and female workers.

Model arches

Arch-profiled floors reduce the amount of material

The arch-profiled floors have shown how they can drastically reduce the amount of material compared to conventional slabs in buildings. The lightweight falsework and shuttering of the formwork system can be fabricated using local grasses and invasive reeds by local basket weavers. Such a system not only further reduces the overall environmental impact of the building as well as the construction process, but also supports market-driven demand for sustaining local tradition and craftsmanship.

Invasive alien plants used as aggregate

During an interview done by the European Culture Centre (ECC) team with Juney Lee @juney.lee from ETH Zurich, he mentioned: “In South Africa, there is an abundance of invasive alien plants that consume a lot of water from the natural ecosystem. For this project, we are using them as aggregate in the place of stone and sand that is typically used in conventional concrete.

“So, we are using something that is locally available, yet ecologically harmful in South Africa, and turning it into an ingredient for a more sustainable version of concrete. The invasive alien plants are first chipped into small pieces of wood, which are then mixed with water and binder to create the bio-concrete.”

Lee continues: “We’ve been working closely with our colleagues in South Africa. We are currently testing different ways of fabricating these self-supporting bricks with complex geometry. From the context of ETH Zurich, we can experiment a lot with digital fabrication methods such as 3D printing, which was used to generate some of the prototypes in the exhibition. On the other hand, we are also investigating how to fabricate them in much more humble and cost-effective ways with locally available resources in the South African context.”

Critical need for alternative building methods

The building industry is responsible for 40% of the global resource consumption, over 35% of waste generated worldwide and nearly 40% of human-caused CO₂ equivalent emissions each year. With the global population expected to increase by 2,1 billion people over the next 30 years, it is simply not possible to continue building the way it is done today if we want to reduce greenhouse gas emissions, slow the depletion of natural resources and minimise waste production. Nearly three-quarters of a typical building’s embodied energy is attributed to its structural mass – a sustainable future of the building industry ultimately requires a drastic shift in how structural systems of buildings are designed, fabricated and constructed.

For more information, contact The Block Research Group (BRG)
Tel: +41 44 633 3835
Email: paulson@arch.ethz.ch
Website: https://block.arch.ethz.ch

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