Scientists reinvent concrete with ancient wisdom

Prototype walls made with a clay, lime and cement. Credit: EPFL/Salvatore Aprea.

In a world where the construction industry significantly impacts the environment, a group of experts is looking back to ancient techniques to create a more sustainable future.

A team from EPFL, ETH Zurich, and a Geneva-based architecture firm has taken a revolutionary step by developing a new type of concrete that uses stone offcuts instead of traditional, carbon-intensive cement.

This innovative approach is inspired by construction methods from centuries ago, discovered in historical archives.

Reinforced concrete is a staple in modern construction but it comes with a heavy carbon footprint. Interestingly, not all structures need reinforced concrete.

The research team, consisting of experts from EPFL’s Archives of Modern Construction, ETH Zurich’s Chair of Sustainable Construction, and the architecture firm Archiplein, found that some walls could be built using unprocessed quarry waste, drastically reducing environmental impact.

As part of the Circular Building Industry Booster, a program supporting eco-friendly construction initiatives, the team experimented with various construction processes and cement mixtures.

In late October, they constructed six load-bearing walls in Lucery-Villars, Vaud Canton, using recovered stone-quarry waste and fieldstone.

They created two sets of walls using two different methods and tested three kinds of mortar-based binders: one with a bit of cement, another lime-based, and the third made from infertile soil.

The construction methods were unique. For the first method, they put mortar in formwork before adding stones.

In the second, stones were laid first and then coated with mortar. The use of large stones in the walls led the experts to name their method “Cyclopean,” a nod to the massive stone constructions of ancient architecture.

Currently, stone-quarry waste is processed before reuse, consuming a lot of energy. Cement production, the traditional binder in concrete, is even more energy-intensive, requiring limestone to be heated to extremely high temperatures.

Another challenge is that concrete is made from limited inert materials.

Salvatore Aprea, head of the Acm research group, points out that for centuries, builders reduced costs by using less cement and incorporating recycled materials. “The goal now is to bring back these old methods, not to save money, but for our planet’s future,” says Aprea.

Marlène Leroux, a partner at Archiplein, is surprised that modern construction has forgotten how to build simple load-bearing walls with minimal environmental impact.

These ancient methods didn’t need additives, chemicals, or steel reinforcement bars.

To find inspiration for their project, the Acm group dug through technical archives from Roman times to the 18th and 19th centuries, mainly from France and Germany. They were on the lookout for old concrete and cement formulas that could utilize unprocessed stone offcuts and mortars with little or no cement.

They discovered experimental results where engineers had tested the strength of mortars with different lime concentrations, often made from locally sourced materials.

These findings were crucial in developing new mortar formulas that meet modern standards but are rooted in historical wisdom.

Prof. Guillaume Habert from ETH Zurich, along with Leroux and colleagues Francis Jacquier and Olivier Dahenne at Archiplein, developed computer models to identify these new mortar formulas.

Their next steps include developing standardized, low-carbon wall construction methods, building prototypes, conducting strength tests, and creating comparative tables. Their work is reminiscent of past engineers and scholars like Louis-Joseph Vicat, Jean Henri Hassenfratz, and John Smeaton, whose studies have guided this groundbreaking project.

This effort marks a significant stride in combining historical knowledge with modern technology to pave the way for a more sustainable future in construction.