Engineers turn waste cardboard into a low-carbon building material

Australia’s construction sector may be on the brink of a quiet revolution, one built from soil, water, and something most people throw away. Engineers at RMIT University have developed a new building material that dramatically cuts carbon emissions while giving waste cardboard a second life. The material, called cardboard-confined rammed earth, could reshape how homes and small buildings are designed, especially in a warming world under pressure to reduce emissions.

Concrete has long been the backbone of modern construction, but it comes with a heavy environmental cost. Cement and concrete production account for roughly 8 percent of global carbon emissions each year. At the same time, Australia sends more than 2.2 million tons of cardboard and paper to landfill annually. The new material tackles both problems at once.

Cardboard-confined rammed earth is made entirely from cardboard, soil, and water. There is no cement. The materials are reusable, recyclable, and largely available on site. Compared with concrete, the new system has about one quarter of the carbon footprint and costs less than one third as much.

Rammed earth is not a new idea. Builders have compacted soil into thick walls for thousands of years. Modern versions often rely on cement to boost strength, which adds emissions and cost. The RMIT team questioned whether cement was really necessary.

Lead author Dr Jiaming Ma from RMIT said the strength of rammed earth walls often comes from their thickness, not cement content.

“Modern rammed earth construction compacts soil with added cement for strength. Cement use is excessive given the natural thickness of rammed earth walls,” Ma said.

The new approach replaces traditional formwork with cardboard tubes. Soil mixed with water is compacted inside the cardboard, either by hand or with machines. Once set, the cardboard remains in place, acting as confinement that helps the wall resist cracking and failure.

By changing the thickness of the cardboard, the engineers can control the strength of the wall. Ma and his team developed a formula that links cardboard thickness to mechanical performance, making the system predictable and measurable.

“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,” Ma said.

One of the most striking advantages of cardboard-confined rammed earth is how practical it is. Construction can happen directly on site using local soil. Builders do not need to transport large amounts of bricks, steel, or concrete.

Study corresponding author Emeritus Professor Yi Min “Mike” Xie said this could change how projects are planned.

“Instead of hauling in tonnes of bricks, steel and concrete, builders would only need to bring lightweight cardboard, as nearly all material can be obtained on site,” Xie said.

“This would significantly cut transport costs, simplify logistics and reduce upfront material demands.”

The system may be especially valuable in regional and remote areas. Many parts of Australia have red soils that are ideal for rammed earth construction. Transporting heavy materials to these locations is expensive and carbon intensive. Cardboard-confined rammed earth flips that equation.

Rammed earth buildings offer more than structural strength. Their high thermal mass helps regulate indoor temperature and humidity. In hot climates, thick earth walls absorb heat during the day and release it slowly at night. This reduces reliance on air conditioning and lowers energy use.

Ma said this makes the material well suited to Australia’s climate.

“Rammed earth buildings are ideal in hot climates because their high thermal mass naturally regulates indoor temperatures and humidity, reducing the need for mechanical cooling and cutting carbon emissions,” he shared with The Brighter Side of News.

"As heatwaves become more frequent, passive cooling strategies like this are gaining renewed attention. Cardboard-confined rammed earth aligns with a global revival of earth-based construction driven by net zero goals and interest in local materials," he continued.

Cardboard has appeared in architecture before, often in temporary or emergency settings. Architect Shigeru Ban famously used cardboard tubes to build disaster shelters and the Cardboard Cathedral in Christchurch, New Zealand. Those projects showed cardboard’s surprising strength and flexibility.

The RMIT work builds on that legacy, but takes it further. By combining cardboard with rammed earth, the researchers created a system designed for durability, not just temporary use. The walls are robust enough to support low-rise buildings, opening the door to permanent housing applications.

The research team is not stopping with cardboard. In a separate study led by Ma, carbon fiber was combined with rammed earth, producing strength comparable to high-performance concrete. Together, these studies suggest earth-based materials can compete with conventional systems when designed carefully.

Ma and his colleagues are now looking to partner with industry to refine the technology and move it toward real-world use. The goal is not to replace all concrete, but to offer a credible alternative where it makes sense.

Cardboard-confined rammed earth, published in the journal Structures, shows how small design changes can lead to large environmental gains. By rethinking waste as a resource and questioning long-held assumptions about strength, the research points toward a leaner and more sustainable building future.

This work could help reduce emissions from construction, one of the world’s most carbon-intensive industries. By using waste cardboard and local soil, builders can cut costs, lower transport emissions, and reduce landfill pressure.

The material is especially promising for low-rise housing, regional construction, and hot climates where thermal mass improves comfort.

For researchers, it opens new paths in earth-based construction that rely on design and material science rather than cement.

Research findings are available online in the journal Structures.

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