Engineers replaced 20% of cement with powdered waste glass in a field project; 3 years later, the concrete showed no deterioration or material failure

A concrete slab that has spent three years exposed to freeze-thaw cycles, traffic, and weathering is showing no signs of deterioration. This concrete contains 20% of its cement replaced by finely crushed waste glass, the kind of glass that would otherwise have ended up in a landfill. An extensive field study titled “Long-term field performance of concrete produced with powder waste glass as partial replacement of cement,” published in December 2021 in the journal Case Studies in Construction Materials, found that after the concrete had been in service for three years, detailed physical examination showed no signs of deterioration or material failure.

Why this matters more than it sounds

Cement production is a major source of carbon dioxide. According to research by the London-based think tank Chatham House, cement production accounts for approximately 8% of the world’s CO2 emissions, which is more than the entire aviation industry. If the cement industry were a country, it would be one of the largest emitters on Earth. Most of this carbon comes from the chemical process used to make clinker, the main binding ingredient in cement, produced by heating limestone and other materials to around 1,450°C, a process that both burns fossil fuel and releases CO2 directly from the limestone itself. Because this chemical reaction is intrinsic to clinker production, the clearest way to cut emissions is to reduce how much clinker goes into concrete in the first place, which is where substitute materials like glass powder come in.

Glass recycling in the US has its own problem. According to the Environmental Protection Agency, only around 31% of glass containers are recycled, and that figure has stayed flat for years. Much of the uncollected or unsorted glass ends up in landfills because sorting and transporting it to a glass plant isn’t cost-effective at the volumes most municipal recycling programs handle. Meanwhile, the construction industry is under pressure to cut emissions. On paper, the two problems look complementary.

The science simplified

Grinding glass into a fine powder changes how it behaves chemically. Instead of acting as inert glass, the powder becomes a pozzolan, a material that reacts with the by-products of cement hydration to form additional binding compounds within the concrete. Three years after the field project was built, researchers extracted concrete cores from the site and ran laboratory tests. The results showed increased compressive strength, up to a 57% reduction in water absorption, and up to a 61% reduction in weight loss from abrasion, compared with ordinary concrete. In other words, the glass-modified concrete performed as well as or better than standard concrete.

This is not the first research into using waste glass powder in cement. Previous laboratory research, per a 2017 study titled “Waste glass powder as partial replacement of cement for sustainable concrete practice,” published in the International Journal of Sustainable Built Environment, showed that 20% is the ideal amount of cement replacement, without affecting strength. The new study has shown that after years of exposure to real-life conditions, 20% is still a good amount to use.

So why isn’t this everywhere yet?

Construction is a conservative, risk-averse industry, so one successful project rarely changes standard practice overnight. Turning waste glass into usable powder requires sourcing, crushing, and fine-grinding it to a consistent particle size, all of which cost money and energy. And while the volume of uncollected glass nationally is large, as noted above, that doesn’t mean every region has easy access to a reliably sorted, consistently processed supply of glass powder suitable for concrete production. Abundant raw waste and a dependable, ready-to-use supply chain are two different things: the first is a disposal problem, the second is a manufacturing one. Bridging that gap is part of why adoption has been slow, even though the research itself is promising.