A building technique as old as dirt is being re-tested as a ‘new’ and feasible modern construction material.
Engineering professor Sumi Siddiqua (right) and graduate student Priscila Barreto (left). (Image credit: The University of British Columbia)
Compressed soil, also called rammed earth, is a construction technique that goes back several centuries.
UBC Okanagan engineering Professor Sumi Siddiqua, who has been studying the resurgence in rammed earth, says conventional cement is still the go-to for contemporary engineers.
Conventional cement construction is the principal building material for buildings, roads, pipelines, and bridges around the world. But builders today are seeking cheaper and more environmentally responsible construction materials. One such material may be compressed - or rammed - earth.
Professor Sumi Siddiqua
Soil can be used in numerous ways, explains Siddiqui, including earth bricks, rammed earth walls, and compressed earth blocks. In 2014, almost 40% of the world’s population still worked or lived in structures using soil as a construction material. The advantages of using these natural and locally-sourced materials include a reduction in both costs and energy consumption.
The rammed earth walls are typically positioned between molds and bound by clay. But Siddiqua says while the method is simple, it has major structural limitations.
To enhance this, Siddiqua and her graduate student Priscila Barreto tested the incorporation of fly ash and calcium carbide residue as binding agents in the rammed earth. They discovered that when cured for 60 days, the walls comprising binding agents were 25 times stronger compared to those without. The increased strength significantly enhances their potential for use in modern construction.
The core of our challenge was to pinpoint the strongest composition of binding materials. 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.
Professor Sumi Siddiqua
Barreto, an international student from Brazil, started this study while at UBC Okanagan as an undergraduate and pursued the work into her graduate studies.
In countries like Brazil and regions like the Sertão in the country’s northeast, rammed earth is commonly used as a building technique. The opportunity to enable people to build stronger and safer structures with natural soil is one of my central motivations for doing this research.
Siddiqua says there is obviously a demand for this type of material and the method has been used in small cities in Canada, including the Okanagan, where small residential homes are being constructed with easily available materials.
“We targeted rammed earth structures because local construction engineers have approached us looking to improve traditional rammed earth structures with stabilization techniques like ours.”
The study was reported in the journal Construction and Building Materials and was supported by both a Discovery and ENGAGE Grant from the Natural Sciences and Engineering Council of Canada.