Homes featuring walls which are made from cardboard and earth could form part of the solution to Australia’s housing sustainability challenge in low-rise construction.

(above image credit: RMIT University)

And the material – which is particularly ideal for regional areas in warmer climates – may help to lower transport costs and avoid waste going to landfill.

Inspired by New Zealand’s ‘cardboard cathedral’, engineers at RMIT have developed a new building material which is made entirely of cardboard, water and soil.

Known as cardboard-confined rammed earth, the product combines the durability of rammed earth and the versatility of cardboard to produce a material which is strong enough to support low rise buildings.

As thing stand, conventional rammed earth construction involves the compacting of soil to which cement is added for strength.

By contrast, cardboard-confined rammed earth is made by compacting the soil and water mixture inside cardboard formwork.

This can be done on site and can be done manually or with machines.

(image credit: RMIT university)

Huge benefits

According to lead author Dr Jiaming Ma from RMIT, the new material offers significant advantages compared with either traditional rammed earth construction or brick construction.

These include a lower carbon footprint, reduced transport costs/easier transport and the avoidance of sending cardboard to landfill.

Benefits are particularly significant for construction which occurs:

• in regional and remote areas where red soils (which are ideal for rammed earth construction) are in plentiful supply and where transport costs are particularly high; and
• in hot climates where rammed earth buildings are ideal as their high thermal mass naturally regulates indoor temperatures and humidity (as well as moderating noise).

Compared with traditional rammed earth supported with cement, Ma says that cardboard confined rammed earth involves only one-quarter of the carbon footprint and around one-third of the cost.

From an environmental viewpoint, this matters. Concrete accounts for roughly 8 percent of worldwide carbon emissions. Meanwhile, Australia currently sends around 2.2 million tonnes of cardboard and paper to landfill each year.

“The big practical win is logistics,” Ma said.

“Instead of trucking in heavy bricks, steel and concrete, you bring lightweight cardboard; nearly all the bulk material is already on site as soil. That cuts transport, simplifies site setup and avoids cement usage for traditional rammed-earth stabilization or the intensive firing process for bricks.

“The result is roughly one quarter of the carbon footprint and under one third of the cost compared to concrete.

‘Furthermore, the big mass of earth can moderate temperature and noise.”

The new material was inspired by New Zealand’s ‘cardboard cathedral’: image Shigeru Ban Architects)

Not just for remote builds

Asked about suitable applications for the material, Ma told Sourceable that the material’s ‘sweet spot’ lies in regional areas and in hot climates.

However, he stresses that the material could be used in metropolitan areas as plenty of traditional rammed-earth homes have been constructed in big city suburbs.

As for building typologies, Ma says that the material is strong enough for low-rise buildings.

Accordingly, buildings of one or two storeys are ‘well within its lane’, and the material would be perfect for typical suburban houses and duplexes.

(image credit: RMIT university)

Good fire performance

Asked about fire-related considerations, Ma said that cardboard is similar to timber in nature and that both have already been used in buildings such as the aforementioned Cardboard Cathedral.

As is the case with timber, cardboard can be fire-treated with fire resistant solvents and coatings/covers.

Furthermore, cardboard-confined rammed earth is around 90 percent rammed earth. This is inherently non-combustible and fire-resistant.

(image credit: RMIT university)

Formulated for strength, searching for partners

The mechanical strength of the material varies according to the thickness of the cardboard tubes.

Ma said the team has developed the formula for this strength design.

“We’ve created a way to figure out how the thickness of the cardboard affects the strength of the rammed earth, allowing us to measure strength based on cardboard thickness,” he said.

In a sperate study  which Ma also led, carbon fibre was combined with rammed earth, proving it had a comparable strength to high-performance concrete.

RMIT researchers are seeking industry partners to further develop the materials for broader use. (Companies seeking partnerships can contact [email protected]).

The latest study was published in Structures.

In addition to Ma, co-authors include Hongru Zhang, Vahid Shobeiri, Ngoc San Ha, Srikanth Venkatesan, Dilan Robert and Yi Min ‘Mike’ Xie.

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