Heart of glass

Slideshow photo credit: Matt Hagen

We may need to ditch that aphorism about throwing stones at glass houses.

Two engineering graduate students at the University of Washington have found a way to make bricks out of recycled glass that they say are stronger, lighter and better insulators than conventional building blocks.

Renuka Prabhakar and Grant Marchelli claim their VitroBricks require 80 percent less energy to produce because they’re fired at a much lower temperature for a shorter time. Most promising of all, according to the engineers, their invention can put to work the millions of tons of discarded glass that end up in landfills each year.

Sound too good to be true? It’s still an early-stage technology, and Prabhakar and Marchelli need to prove they can manufacture consistently and cheaply enough to break into the masonry industry.

But the students’ startup, EnVitrum (Latin for “out of glass”), has already drawn interest from UW research funders, brick makers and architects like Perkins+Will. Waste Management says it’ll pay them to take mixed-color waste glass off its hands.

Prabhakar and Marchelli say they were inspired by the surprisingly low level of glass recycling: Only 26 percent of the glass waste stream is actually reused, according to the United States Environmental Protection Agency.  Bottle makers can use only 10 percent to 35 percent recycled material and any impurity, including mixed colors, can render their products useless.

The grad students first tried using finely crushed glass for 3D printing – essentially stacking thin layers of glass– but found that the results resembled a Jell-O salad more than a brick. Then they experimented with sintering, a technique for fusing powderized materials. Prabhakar and Marchelli mixed in a binding agent they developed (they will say only that it’s not toxic or petroleum-based) and created a process for  heating the bricks at multiple temperatures.

“It’s not as simple as making a brick and putting it in the oven,” says Prabhakar.

The resulting product, though, has the heft and gritty texture of a clay brick. A glass brick can be designed to be highly porous, drawing water through capillary action. In hot climates, running water through a wall would produce evaporation, cooling a building.

The glass bricks’ unique porosity may also be useful for so-called living walls. The two engineers have developed prototypes with special cavities for plants, since many living walls so far have relied on felt or plastic containers with limited durability.

Gregg Borchelt, president of the Brick Industry Association, says plenty of would-be inventors try alternative materials for brick before running into, well, a brick wall when it comes to cost or durability.

He says cheap waste glass and lower energy costs for firing could be advantages for Prabhakar and Marchelli – if they can show their products are reliable and they can obtain a lot of glass.

“A typical plant will turn out 40 million bricks per year, so that’s a pretty big pile of material,”  notes Borchelt.

The next hurdles for Prabhakar and Marchelli are verifying their bricks can meet international standards for building materials and gaining independent verification of their manufacturing process. They hope to license the technology rather than go into the brick-making business themselves.

“We don’t really want to be masonry manufacturers,” says Prabhakar. “We’re both engineers and that’s what we love to do. We want to develop and scale and be problem-solvers.”