In a 2015 Deakin University study, crushed waste glass replaced 30% of concrete sand; after 28 days, the recycled mix was 6% stronger than conventional concrete

Every time you toss an empty jam jar or a cracked drinking glass into the recycling bin, you probably assume it will be melted down into another bottle. But glass can also have a second life in concrete, including pavement and building foundations. A team at Deakin University in Australia tested what happens when waste glass is crushed into fine particles and mixed into concrete instead of sand. The research explored whether recycled glass could partially replace fine aggregate without reducing concrete strength, while also providing another use for waste glass.

A stronger mix than expected

Researchers M. Adaway and Y. Wang detailed their findings in the Electronic Journal of Structural Engineering. They trialled several replacement levels, swapping out 15%, 20%, 25%, 30% and 40% of the fine sand with crushed glass before measuring the concrete’s compressive strength. Strength increased as the proportion of glass rose, reaching its highest relative performance at the 30% replacement level. According to the paper, the 30% glass mix was nine per cent stronger than the conventional mix after seven days of curing and six per cent stronger after 28 days. At the 40% replacement level, the improvement was no longer maintained, suggesting that 30% was the most favourable replacement level among those tested.


The researchers linked the performance of the crushed glass partly to its physical characteristics. Unlike naturally occurring sand grains, which can have relatively smooth and rounded surfaces, crushed glass particles have sharper, more angular edges. These characteristics can affect how the aggregate interacts with the surrounding cement paste and may help improve the bond within the hardened concrete.

What the findings could mean

The results suggest that recycled glass could replace a portion of fine aggregate in some concrete applications without necessarily compromising compressive strength. Using up to 30% crushed glass in the tested mix could therefore provide a way to divert suitable glass waste towards construction materials while reducing the amount of conventional fine aggregate required.

There are also circular-economy benefits to using higher-value materials like glass as structural materials rather than low-value products. However, moving from laboratory testing to widespread commercial use would require further assessment, including how different types of recycled glass perform under varying mix designs and construction conditions.

The findings presented by Adaway and Wang provide a useful starting point for further work on recycled glass aggregates. Rather than showing that glass can simply replace sand in every concrete application, the study demonstrates that a specific replacement level produced favourable strength results under the conditions tested.

For councils, recyclers and construction companies exploring ways to reuse waste materials, the research offers a practical example of how discarded glass can be incorporated into concrete. The 30% replacement level produced the strongest relative result in the study, while higher replacement did not continue the same improvement.

The next time a jar or bottle goes into the recycling crate, its eventual use may not involve making another glass container. Research from Deakin University suggests that suitably processed waste glass can also serve as a partial replacement for sand in concrete, although its suitability for specific construction applications would need to be assessed separately.