In 2024, Michigan Tech used treated waste glass to build stronger roads; a 6% mix raised stability by 42.3% and skid resistance by 38.6%

In a road-building experiment, Michigan Tech researchers have uncovered a promising use for waste glass that would otherwise be discarded. In a study, researchers tested asphalt mixed with surface-treated waste glass and found that a 6% blend delivered a 42.3% increase in dynamic stability compared with a conventional mixture. That same blend also improved anti-skid performance by 38.6%, giving it the strongest friction result among all the glass contents tested. To achieve this, the team treated the glass with APTES, a silane coupling agent that helped it bond more effectively with the asphalt. The findings point to a genuine role for recycled glass in building stronger, safer road surfaces.How was waste glass treated for asphaltAccording to the study published in ScienceDirect, titled ‘Performance evaluation of surface treatment waste glass as aggregate in asphalt mixture’, the team compared two approaches: physical abrasion and chemical surface treatment. For the chemical route, they used 3-aminopropyltriethoxysilane, or APTES, a silane coupling agent designed to improve how well the glass and asphalt interact. Glass was immersed in an APTES mixture, then cured at a range of temperatures. Afterwards, the researchers examined the treated material using microscopy, energy-dispersive X-ray spectroscopy, boiling tests and contact-angle measurements.The treatment clearly made the asphalt adhere more strongly to the glass. According to the study, chemically treated samples outperformed those that underwent only physical abrasion, with APTES-treated glass showing adhesion rates above 90% across every curing temperature tested. Curing at 160°C produced the strongest adhesion work of all. The researchers concluded that silane treatment effectively bridges the gap between inorganic glass and organic asphalt, strengthening the bond at their interface.Why did 6% treated glass improve skid resistanceTo gauge how the mixtures held up under repeated loading at high temperatures, the team assessed dynamic stability. Compared with mixtures containing 6%, 8% and 10% surface-treated waste glass, tests were run at 60°C and dynamic stability was measured in cycles per millimetre. The conventional mixture recorded 4,158 cycles per millimetre. At 6% treated glass, dynamic stability rose by 42.3%. The gain was even larger at 8%, reaching 54.2%, and it recorded 6,412 cycles per millimetre, though at 10%, the improvement fell away sharply to just 3.1%. The researchers put this down to the treated glass strengthening the bond between aggregate and asphalt, producing a more compact, interlocking structure.That 6% mixture also stood out in skid resistance testing. Using a tyre-road dynamic friction testing system, the team measured the friction coefficient of specimens containing varying amounts of treated waste glass, against a conventional-mixture baseline of 0.44. At 6% treated glass, the friction coefficient increased by 38.6%; at 8% the gain narrowed to 29.5%, and at 10% it fell further to 18.2%. With a recorded friction coefficient of 0.61, the 6% mixture was identified as the optimal result for skid resistance, a result the researchers attributed partly to the larger frictional contact area the treated glass provided, along with stronger cohesion between glass and asphalt.What made 6% treated glass the optimal mixThe results suggest the most effective mixture wasn't simply the one with the most recycled glass. Although 8% gave the highest dynamic stability, the 6% mixture held up strongly across several measures, including the best low-temperature performance; the small-beam specimens at that content reached their highest low-temperature indicators. As the Michigan Tech record puts it: "incorporating surface-treated waste glass at an optimal proportion of 6% within the asphalt mixture led to a 42.3% increase in dynamic stability and a 38.6% enhancement in anti-skid performance compared to standard mixtures." The original study recommends APTES coating with a 6% waste-glass content by total aggregate weight; the researchers caution that long-term performance, including durability, environmental effects and cost, still needs further investigation.Catch the latest World News and Live updates. Download the TOI app.