A Stronger Future for Rammed Earth?

What’s old is new again.

Rammed earth, aka compressed soil, has been used to make floors, walls and foundations for centuries. It’s still used today in some places. In fact, it’s experiencing a bit of a resurgence, and for good reason. It’s inexpensive, readily available, durable, sustainable, nontoxic and even fireproof. On the downside, it’s not a strong as it could be, limiting its applications. It’s certainly not as strong as cement-stabilized soil.

But a pair of researchers at the University of British Columbia has discovered a way to strengthen rammed earth without using carbon-emitting cement — and create a second life for landfill-clogging waste materials at the same time.

By adding calcium carbide residue and fly ash as binding agents, then compacting the soil, forming walls and curing them for 60 days in a temperature- and moisture-controlled environment, they created walls 25 times stronger than walls built the same way but without binders. 

The two binders were chosen for optimal strength but they also offer environmental advantages. “Fly ash is one of the residues of the cement industry,” said engineering professor Sumi Siddiqua, who led the research. “Calcium carbide residue is the waste material of the acetylene gas factory. Both residues are being stockpiled in landfills around the world.”

RELATED: Latest Strategies for Reducing Cement’s Carbon Footprint

Another advantage of rammed earth: It makes use of excavated soil. “Every construction site has excavated soil that ends up at the landfill,” said Siddiqua. “Now if we use locally available soil, it will help us to reduce cost and minimize environmental impact.”

What might the souped-up soil be used for? “Any construction industry can use it, for home, roads etc.,” said Siddiqua. It could replace conventional rammed earth and even cement-stabilized soil for applications that don’t require very high strength.

To build rammed earth walls, frameworks are needed for onsite use during soil compaction, and those frameworks can be removed and reused. Alternatively, explained Siddiqua, bricks can be precast in different sizes and shapes.

What’s next? “We would like to work with companies and builders to try this in their projects,” said Siddiqua.

Unlike so many building materials, earth is one resource that isn’t going anywhere (rammed earth uses subsoil, not topsoil) — and isn’t going to hurt the planet. A “green” way to strengthen it just might strengthen its resurgence.

Marianne Wait is an editor and writer who creates content for Fortune 500 brands. 

Image Credit: Clifton Schooley & Associates