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Recycling Glass into Aggregate – Glavel

Glavel foam glass aggregate is a super-light insulating gravel. Courtesy photo.

George Harvey

Glavel is a company based in Burlington, Vermont. It sells foam-glass aggregate. Some people might look at it and ask what good it is. Others will be delighted with its possibilities.

Science is full of surprises. For example, in some ways, glass is stronger than steel. While it is true that you can use steel to smash glass, because glass is brittle, it is also true that most types of steel are not as hard as most types of glass.

The unusual properties of glass, including its hardness, make glass useful in some ways that are also surprising, and some of these are important for recycling.

Today, when glass is recycled, it is often put into a machine, which immediately smashes it. The bottles are not returned to a bottling plant for reuse, as they were in the past. Instead, they are just broken up into fragments, which are mixed. They are not separated by color or other properties. And that means that they cannot be used for many of the things we think of when we think of glass.

That is where the inherent strength of glass comes in. Though it might not make an attractive wine bottle and would be pretty useless for windows, the wreckage of old glass still has its core value of hardness, and good minds have found a use for that.

It is possible to heat the broken glass pieces to the point that they melt while introducing materials that will cause the mix to foam. When the glass solidifies, as it emerges from the kiln that melted it, it breaks apart into lumps. It looks rather like some sort of volcanic rock. It is very light, but importantly, it retains some of the strength of the glass. The gas bubbles in the glass are sealed off completely, which means that they will not allow water, for example, to penetrate, but they also make the glass into a really good insulator. It is inert, it is not toxic, it is extremely light, and it has a surprisingly high compressive strength. These are characteristics that make it valuable.

So, what would you do with a material that is essentially super-light insulating gravel? Well, one thing you can do is use it as super-light insulating gravel. I’ll put this another way – this is really neat stuff!

These days, when a building is built, the slab or basement floor is usually insulated from whatever is below it. This can be done by putting down a layer of gravel, carefully packing and leveling it, and then covering it with insulating material such as foam board. With Glavel foam-glass aggregate, we have the alternative of putting down the gravel and insulator in a single step, because they are combined.

Rob Conboy, the CEO of Glavel, gave us a rundown, comparing foam glass aggregate with the combination of gravel and foam insulation. The R-value of both is similar. The thickness is similar. The strength is similar. And the cost is in the same ball park with foam glass aggregate a little more expensive, though it is easy to see reasons why its cost would go down, but the competition’s costs would not.

Right now, the Glavel product is imported from Europe. Conboy told us that it will soon be made in the United States, which will give it a cost advantage. It will be made in an electric kiln, powered by electricity from 100% renewable resources. Also, he is moving to tweak the formulation, in the hope that it will have somewhat better insulating value.

The end result is that we have a new system that is just as good as the old in terms of performance and cost but is far superior for the environment. Glavel foam-glass aggregate will be using a problematic resource, recycled glass, that might otherwise go to a landfill, and it can be produced with renewable energy.

And by the way, Glavel foam glass aggregate has other uses. Because it is so light, it can be used as substrate for green roofs. It can be used for road construction, for embankments, to insulate pipelines, and in other places where its insulating qualities, light weight, and good drainage are valuable.

Glavel’s web site is

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