Recycled Glass to Foam Glass

Here's how ordinary, post-consumer recycled glass turns into a low embodied carbon building material. Recycled glass is prepared with cleaning and grinding, before mixing with a foaming agent and being kiln fired.

Glass Processing

Foam glass gravel begins its journey as post-consumer recycled glass. Amorphous container glass is received from local materials recovery facilities, where it’s crushed using a ball mill into a fine talc-like powder with <1% contaminant. Glass feedstocks can be cleaned to a lesser extent, but that results in a less consistent output. Cleaning glass to <1% impurity will give Glavel’s foam glass superior materials properties and ensure that each day’s production is exactly the same as the last. Upon being ground into a powder, it’s stored in a silo where it awaits being mixed and dosed with a foaming agent prior to firing. 

Recycled glass to foam glass. Photo: Oliver Parini

Glass Firing

The conversion of glass powder to foam glass continues at the mix and dose station, where the glass powder gets mixed with an environmentally friendly foaming agent. The mixture then drops onto a chain mesh belt to a thickness of 2cm, where it gets fed into the kiln. The kiln is 25m long, with a specific thermal profile that softens the glass powder and allows for a chemical reaction with the foaming agent. As the mixture expands, gases are released and trapped in the mixture as it hardens, creating a network of closed cell micropores, which are the basis of Glavel’s thermal insulation and weight profile.

Upon exiting the kiln, the foam glass slab is 8cm thick, and begins an additional 15m of cooling. Thermal stress from the slab cooling causes it to fracture into smaller pieces, which are fed onto a conveyor and prepped for delivery.

After cooling and breaking into pieces, Glavel’s foam glass is either packed into 3 cubic yard bags or loaded bulk into walking floor trailers for delivery. Even though foam glass gravel is physically a different product than glass, it still holds the beneficial properties of glass. It remains deformation-free, watertight, and inert, while becoming a broadly used building material. For more on foam glass gravel, find the products page.