Materials Spotlight: Recycled Glass in Concrete

Subscribe to Stok Insights
Materials Spotlight: Recycled Glass in Concrete

The carbon impacts associated with the production of portland cement is not a new sustainability issue. But there is a new solution.

We sat down with Doug Jackson, President & CEO of Sioneer, a glass processing company that’s bringing a new product to market aimed at tackling the issue.


A Bit of Background

The common concrete mix is comprised of aggregate, water, sand, various chemical admixtures, and portland cement. The primary function of portland cement in the mix design is to create a binding agency which allows these various ingredients to become concrete.

The manufacturing of portland cement is highly carbon intensive, responsible for roughly 5% of global anthropogenic carbon emissions. It’s commonly substituted, at varying percentages, with fly ash and ground-granulated blast-furnace slag for increased performance and environmental benefit.

However, while fly ash and slag are more sustainable alternatives than utilizing 100% portland cement, they are not perfect solutions. Both are by-products of coal-powered electricity generation, thus procurement is an indirect support of a carbon intensive industry. Additionally, they contain heavy metals that cause adverse health and environmental impacts.

The North American supply of fly ash and slag is also on the decline, resulting in product price and quality inconsistencies. These materials are now being imported and shipped thousands of miles to end up in U.S. concrete, only adding to the carbon impacts of a material we rely so heavily on.

So, what’s the solution?

Our pozzolan product is helping to solve not only one, but two environmental issues. According to the U.S. EPA, 75% of glass each year is landfilled due to overwhelming volume and ineffective glass processing. Sioneer takes recycled glass, and sanitizes and pulverizes it, creating a reactive pozzolan end product. This pozzolan has a variety of uses, the primary one being: a portland cement replacement that’s made from 100% post-consumer recycled content, is non-toxic, and results in ultra-high strength concrete.

Beyond sustainability attributes, what are the key benefits of using glass pozzolan in lieu of fly ash or slag?

There are two main benefits. First, concrete mix designs can achieve a greater compressive strength. And second, due to the chemical composition of the glass pozzolan – amorphous silica – it mitigates the occurrence of Alkali-Silica Reaction (ASR), a chemical reaction that causes cracking in typical concrete mixes.

Have you ever wondered why the Roman Colosseum has lasted thousands of years while more modern roads and bridges haven’t? The Romans used volcanic ash to make their concrete. Volcanic ash is also amorphous silica – just like Sioneer’s glass pozzolan. The result is ultra-high strength concrete that doesn’t crack, making it last much longer.

There are three U.S. glass pozzolan suppliers, what’s different about your product?

There are three different proprietary steps in our manufacturing process. First, is the cleaning process – how paper, garbage, et. cetera is effectively and efficiently separated from the glass. The second is how the glass pozzolan is treated to make it more reactive in the concrete mix, which allows it to gain compressive strength faster. And finally, Sioneer’s equipment can grind the glass into a multitude of sizes, which allows the material to have a variety of use cases beyond glass pozzolan in concrete.

What’s the biggest barrier to widespread market adoption?

The biggest barrier for glass pozzolan use in concrete mix is lack of awareness. The use of fly ash and slag has become industry standard, so introducing a new portland cement alternative is difficult. Engineers need to get comfortable enough with the material to specify it, and then the contractor needs to be comfortable enough to communicate the ask to their concrete installation subcontractors and ready-mix suppliers. There is a chain of education that needs to occur in these early use stages.

The driver for use on projects to date has been from the owner, primarily due to alignment with corporate sustainability goals. We’re excited that key innovators like Google and Facebook are working with Sioneer to pilot glass pozzolan on their Silicon Valley development projects. As leaders continue to realize the benefits of using our product over traditional portland cement and its alternatives, we see it catching on industry wide.

Key industry collaborators are working to develop an ASTM standard for glass pozzolan use in concrete mix designs, which will solidify legitimacy of use and mitigate concerns with risk. The standard will be officially published later this year.

You’re opening its first manufacturing plant this year, what can we expect from it?

We’re just a few months away from opening our first manufacturing plan in Stockton, California. We’re thrilled to have a world class team bringing it to life, with Perkins+Will leading the design and DPR Construction breaking ground.

We plan to showcase our product within the facility’s design, with both the plant’s floor slab as well as over an acre of pavement made from concrete with varying percentages of glass pozzolan as portland cement replacement. We hope to use the plant to educate design and construction professionals on the material.

Part of the funding for the plant came from a grant received from the CalRecycle 2017 Greenhouse Gas Reduction Program for Recycled Fiber, Plastic, and Glass. The goal of this program is to lower greenhouse gas emissions by expanding existing capacity or establishing new facilities in California that use California-generated post-consumer recycled fiber, plastic, or glass to manufacture products.

What do you see for the future of glass in concrete?

Simply put, it’s going to be big. While there isn’t enough glass in the U.S. to replace all fly ash and slag use in concrete, that means there’s no excuse for any glass to end up in the landfill.

Glass pozzolan solves three different issues at once: eliminating glass going to landfill, making concrete last significantly longer, while at the same time dramatically reducing GHG emissions. Our vision is to hit that trifecta at scale.

What can practitioners do to learn more about using glass pozzolan in concrete?

Get in touch! We’re excited to share our story and help others realize the benefits of glass pozzolan.