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June 01, 2015

Glass in Concrete

A collaborative essay between the Healthy Materials Lab and Sydney Mainster of the Durst Organization.

A new formula for concrete lessens its potential human and environmental health hazards and reduces landfilling of excess post-consumer recycled glass. It is making concrete stronger as well.

In this new formula, recycled glass, ground to a fine powder called pozzolan, replaces a portion of Portland cement. Portland cement has a large carbon footprint, so minimizing its use in concrete mixes helps to offset CO2 emissions. Portland cement also includes additives such as coal fly ash or silica fume that can be hazardous to human health. Replacing these additives with ground glass pozzolan removes these potential hazards.

At a June 2015 event of the Structural Engineers Association of New York (SEAoNY), a panel of industry practitioners and experts presented testing findings, market adoption, and code change efforts around the promotion and use of ground glass pozzolan in sidewalks, ready-mix, and cast-in-place concrete. (Ground glass is already utilized in CMU block and pre-cast structural members.) The audience included structural engineers and other building experts from across New York City.

The city of Montreal in Canada is testing a 10% min glass pozzolan design mix as a standard for all of its sidewalks, and the Department of Transportation will test 20%, 30%, and 40% ground glass pozzolan design mixes in sidewalks in Brooklyn, NY this fall. For structural uses, there have been surprising results with high strength outcomes using glass pozzolan as a percentage replacement for cement.

The panelists are all participants of a working group in the Building Product Ecosystem (BPE) initiative. The working group is composed of members from the construction industry, academia, the professional engineering community, manufacturers, processors, and the recycling industry, working together to find healthier solutions for building products.

The panel discussion was met with interest and excitement and the panel was eager to involve others in the project. During the event’s question/answer session, the panel’s moderator, Amanda Kaminksy, responded to a query with: “Maybe you can help us with that.?”— a statement and a question at once, welcoming others to contribute their expertise and available resources to the conversation.

Use of ground glass pozzolan in flatwork and formed concrete will take place in the United States for the first time this fall, with a hope for wider market adoption in the near future, thanks to the efforts of the working group.

(View related story here.)

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