EIGHT centuries on, the flying buttresses of Bourges Cathedral in France still beguile engineers. The secrets behind this marvel of medieval masonry are now about to be laid bare, thanks to a group of researchers who are rebuilding it, brick by brick.

Using a laser scan of the cathedral, a team led by John Ochsendorf of the Massachusetts Institute of Technology have 3D-printed thousands of bricks and are building an exact 1:50 replica. The researchers hope to use the mock-up to devise a way to gauge the stability, and thus safety, of historical buildings built of brick and stone.

Modern buildings are usually constructed around a steel framework. The steel pieces are fused, so under stress from a sinking foundation or an earthquake, say, the framework behaves as a cohesive unit.

Masonry structures are much more complex. Removing a single brick can change the pattern of stresses throughout the building. This makes it difficult to capture the forces at play, says Mathew Bronski, a structural engineer at architecture firm SGH in Boston. Computer models and simulations help, but there are a lot of inherent shortcomings, he says.

“People have been drawing buildings forever, but they’ve often been making up the building as they go because they can’t measure it,” says team member Andrew Tallon at Vassar College in Poughkeepsie, New York. “With a laser, you can get into places that you couldn’t hope to reach without three months of scaffolding and shutting down the cathedral you’re working on.”

Building the replica is painstaking work, but Ochsendorf thinks the process itself may be as valuable as the mechanics uncovered. For students of architecture and structural engineering, hands-on experience has largely given way to computer modelling. Techniques like 3D printing could be a way of reconnecting them with the craft behind the science, he says.

“Until now [structural engineering] has been dimensionless,” says Ochsendorf. “‘Here’s a prototypical dome of this thickness and this span’ – but it wasn’t modelled off of any specific building.” As 3D printing becomes ubiquitous, he says, learning could become less abstract and students will increasingly work from real-world examples.

“As 3D printing becomes ubiquitous, students will increasingly work from real-world examples”

This article appeared in print under the headline “History comes alive in 3D-printed bricks”

THERE’S more to brewing than beer. A by-product of the process could be about to give an upgrade to a workhorse building material – red clay bricks. By blending in the grains left over from making beer, the bricks can be more environmentally friendly and better insulators.

Bricks are often impregnated with polystyrene as a way to enhance their heat-trapping abilities. This is appealing, because the bricks remain strong, and they can be built into energy-efficient buildings, says Eduardo Ferraz of the Polytechnic Institute of Tomar in Portugal. However, EU restrictions on carbon emissions have made it expensive to incorporate polystyrene and other synthetic materials into bricks.

Ferraz and his colleagues have now shown that brewery grains can be mixed into clay bricks to enhance their ability to trap heat, without compromising strength.

Spent grain for the process should be easily available, because commercial breweries produce huge quantities of it as a pulpy mixture that is usually used in animal feed or ends up in landfill.

With a clay paste containing 5 per cent spent grains, the team was able to create bricks just as strong as the conventional type, while reducing the amount of heat they lost by 28 per cent (). The reason for this, the team says, is that the grains make the bricks more porous, and so they trap more air, which increases heat retention.

One thing could stand in the way of using this process, though: the smell. Bill Daidone of the , one of the largest brick manufacturers in the US, says his lab abandoned experiments because the stench of the moist grains was overpowering. “We opened up the bucket and it was terrible,” he says. This problem vanishes once the bricks are fired, though, says Ferraz.

“The overpowering stench of moist grains vanishes after the bricks are fired”

Bricks that provide insulation without sacrificing strength could be a big boost to the brick industry, says John Sanders, a researcher at the at Clemson University in South Carolina.

“With the current concern for energy codes, I think the industry is open to change,” Sanders says.

This article appeared in print under the headline “Brewing benefits? Alcohol, hangovers and better bricks”