Sumi Siddiqua, an engineering professor at the University of British Columbia’s Okanagan campus, and her graduate student Priscila Barreto are examining the potential of rammed earth construction as a viable modern construction material – and developing newer, stronger rammed earth formulations and methods.
Rammed earth, also known as compressed soil, is a construction technique that involves mixing damp earth with a binding agent, usually clay, and compressing that earth inside a pre-built mold. This construction method dates back thousands of years, and is still in wide use today; in 2014, nearly 40% of the world’s population lived or worked in structures that used soil as a building material.
“Conventional cement construction is [still] the principal building material for buildings, roads, pipelines and bridges around the world,” says Sumi Siddiqua, engineering professor at UBC Okanagan. “But builders today are seeking cheaper and more environmentally responsible construction materials. One such material may be compressed—or rammed—earth.”
While rammed earth construction costs less and consumes less energy than modern construction, traditional rammed earth does suffer from structural limitations. Siddiqua and Barreto have tested the addition of calcium carbide residue and fly ash as binding agents in rammed earth construction material in order to improve its strength. They found that once the walls constructed from this material had cured for 60 days, they were 25 times stronger than rammed earth walls structures without the added chemicals.
This improved strength improves the viability of rammed earth construction in modern structures. “The core of our challenge was to pinpoint the strongest composition of binding materials,” says Siddiqua. “While research shows that some amount of clay is required to stabilize soils, having a mechanism to better bind the soil grains is the key.”
Siddiqua says that there is a demand for improved rammed earth construction material in the Okanagan and in other small Canadian cities, where rammed earth construction has been used to build small residential homes. “We targeted rammed earth structures because local construction engineers have approached us looking to improve traditional rammed earth structures with stabilization techniques like ours,” Siddiqua says.
Rammed earth is also commonly used as a building technique in Barreto’s home country of Brazil, particularly in the northeast Sertão region. “The opportunity to enable people to build stronger and safer structures with natural soil is one of my central motivations for doing this research,” Barreto says.
