Pozzotive puts recycled glass to use as a cement replacement

For more than a decade, New Rochelle, New York-based Urban Mining Industries has been advancing a new use for recycled glass in the form of Pozzotive, a ground glass pozzolan used in concrete production. Like other artificial pozzolanic materials such as coal fly ash, ground glass can assume cement-like qualities when it reacts with a combination of water and cement. Patrick Grasso of the Grasso family, owners of Urban Mining Industries, says Pozzotive strengthens concrete and lowers CO2 emissions. In using locally sourced glass, Pozzotive also has ushered in a circular economy for the glass industry in Connecticut, where it is now being made.

Grasso, a partner with Urban Mining Industries, says his family has long been involved in the construction industry. The Grassos’ story starts more than 15 years ago with the family first obtaining a block manufacturing plant in upstate New York. After rebuilding the plant, they used it to make grey construction block. Louis Grasso Jr., Patrick’s nephew, wanted to find a way to distinguish their gray block from every other gray block made in America. After Louis was advised to include recycled content in the block, a series of trial-and-error tests were done to find a material that could meet this goal. It was decided that glass was the best choice. After realizing the use of bigger chunks of glass wasn’t the best approach, they eventually created a fine powder of ground glass that became Pozzotive.

“So, as a result of that block manufacturing plant, we were able to see the market way back then when no one else was willing to experiment with this kind of stuff,” Patrick Grasso says.

Pozzotive in Action

The magic of Pozzotive’s effect in concrete, Patrick Grasso says, starts with a chemical reaction when it is paired with water and cement. Before Pozzotive becomes involved, the hydration of cement introduces two key compounds. One is calcium silicate hydrate (CSH), which Grasso says is the “glue” that develops the concrete’s strength. The other product is calcium hydroxide (CH), which conversely weakens the concrete and causes porosity. When a ground glass pozzolan is introduced, it gives up a silica atom and joins the CH to become CSH. This pozzolanic reaction allows ground glass to gain cementing properties and act as a partial replacement to cement. In most mixes, Pozzotive replaces 20 or 30 percent of cement.

Photo courtesy of Urban Mining Industries

Initially, Pozzotive was produced in small quantities at a product validation plant in New York. Before 2022, the company was mostly focused on getting a solid footing in the pozzolan market. It took four years, Grasso says, to obtain an ASTM 1866 standard that specifically confirmed the viability of ground glass pozzolans in concrete. This process involved a committee of industry professionals that vetted and signed off on 3^rd party testing done with Pozzotive.

Since its inception, Pozzotive has been used in projects at various locations, most of which are in New York and Connecticut. Some of these include the ESPN Digital Center 2, the New York Police Academy and the Second Avenue subway station in Manhattan. During the UN General Assembly Building’s renovation, 60 tons of window glass were harvested from the building and used to create pavers with Pozzotive for the UN Plaza. Grasso says smaller projects in Connecticut that have used Pozzotive, including Ox Ridge Elementary School in Darien and New Canaan Library in Canaan, particularly demonstrate the significance of Pozzotive in building a local circular economy.

Impacting Industries

In addition to supporting a circular economy, Patrick Grasso says Pozzotive addresses other challenges in the glass recycling industry: the cleaning and separating of glass and costs associated with transporting and logistics if a processor is not nearby. A common route for recycled glass is turning it back into bottles, but complications can arise in this process as the glass needs to be separated by color and any ceramics need must be removed because of their different melting temperature. The color of the glass does not affect Pozzotive, and pieces of ceramics are welcome since they are pozzolanic as well. Pozzotive also can use glass from electronics that don’t contain lead, plate glass and demolition glass. The glass is taken through a cleaning and separating process and is milled into a pozzolan that is 95 percent smaller than 325 mesh, Grasso says.

A primary issue within the cement industry, Grasso says, is CO2 emissions. Cement production accounts for about 7 percent of all global carbon emissions, and the U.S. alone uses more than 100 million tons of cement per year, he says. Twice as much concrete is used in construction than wood, plastics and aluminum combined. Even though common postindustrial cement replacements such as fly ash and slag, which is residue from steel manufacturing, can create a lower carbon concrete, Grasso says he considers postconsumer ground glass an even better replacement.

“A glass bottle is a glass bottle pretty much anywhere in the world in terms of its chemical composition … you can make a very consistent finished product because of the feedstock you’re starting with,” he says.

Grasso says that every ton of cement generates almost a ton of CO2. Urban Mining Industries has done testing to replace up to 50 percent of cement in concrete with Pozzotive, reducing the carbon footprint by almost a ton–for–ton basis of the cement it replaces, he says.

Photo courtesy of Urban Mining Industires

Pozzotive has other benefits that exhibit how it enhances performance of concrete along with its sustainable qualities. Concrete with greater percentages of Pozzotive feature a brighter white color, meaning it can reduce the heat island effect in urban areas, where temperatures are higher in light of a greater abundance of manufactured surfaces that absorb heat. Grasso says Pozzotive does a greater job of preventing efflorescence—when a white powdery substance bleeds out of concrete—and shrinkage, which means less cracking. He says concrete with Pozzotive is five-times more powerful in reducing moisture and chloride penetration than a straight cement mix.

“I think it’s a holistic solution, a climate solution, a health solution—avoiding heavy metals and some of these other alternatives … and the circular economy issue about really just taking regenerative waste streams regionally and putting them back into those regions,” he says.

The Future of Pozzotive

Pozzotive has been used by different companies and organizations, including Torrington, Connecticut-based ready mix company O&G Industries. T.J. Oneglia, vice president at O&G, says he believes the use of pozzolans in general is likely on the rise in the concrete industry. Oneglia points to recent trends of using more recycled material and lowering buildings’ carbon footprint.

“I am seeing support in our local market from the designers, the architects, the engineers and also the owners and the end users of the concrete. [There is] a desire to build green, and so Pozzotive, just by its very nature, in my opinion, is greener than the other sources of materials,” Oneglia says.

Ground glass pozzolans in particular could experience higher demand due to potential supply issues with other pozzolans, Oneglia says.

He says O&G plans to continue using Pozzotive mixes, which are starting to be specified on school projects and municipal projects.

“We intend to supply it as an ingredient in our concrete wherever and whenever it’s specified,” Oneglia says. “And then, in addition to that, we intend to use it just as a part of our daily concrete when we’re able to.”

Patrick Grasso says Urban Mining Industries’ focus is now on further commercializing Pozzotive and using it for bigger projects. The first large scale Pozzotive plant was established in Beacon Falls, Connecticut, in 2021. Grasso says this is a good central location from a glass feedstock perspective and allows Urban Mining Industries to serve the greater metropolitan New York market while also expanding into the Boston market. The new facility will allow the company to produce an estimated 50,000 tons of Pozzotive, Grasso says.

“We had to go through this four-year process of getting an ASTM standard. And we’ve had to have this product in use now for over 10 years to make sure it wasn’t some fly-by-night thing, it was real. We had to have the first plant up that can produce it commercially, large scale, and so all of those steps are now in place. So, any market where there is a need of a glass solution of some reasonable size, we can be there,” he says.