Engineers in Arizona have used an unusual material to expand a major interstate: tens of thousands of tonnes of crushed recycled glass.
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Engineers → use → glass
During the expansion of Interstate 17 north of Phoenix, construction crews used ultra-lightweight foam glass aggregate at 19 locations along a 23-mile section.
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crews → use → section
The material, made entirely from recycled glass, provided a lightweight structural fill that allowed existing drainage culverts, built decades ago for a two-lane highway, to support extra traffic lanes without being crushed by the added weight.
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culverts → make → weight
According to the Arizona Department of Transportation (ADOT), this was the first time foam glass aggregate had been used in a state infrastructure project.
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aggregate → accord → project
In an official agency publication, ADOT Communications representative Laura Douglas said the material was chosen because it combines high compressive strength, low weight and environmental benefits.
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it → say → strength
Solving structural challenges on a busy corridor
The 23-mile section of Interstate 17 between Anthem Way and Sunset Point is one of the region's busiest major routes, carrying more than one million motorists each year.
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section → solve → motorists
To reduce regular traffic jams and meet growing travel demand, state transport authorities began a major widening project.
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authorities → reduce → project
The work included adding third travel lanes between Anthem Way and Black Canyon City, as well as building dynamic flex lanes through the mountainous area leading to Sunset Point.
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work → include → Point
However, adding lanes meant widening the highway over old concrete box culverts built beneath the road.
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adding → add → road
These underground structures play an important role by carrying stormwater underneath the highway.
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structures → play → highway
The original culverts were designed to support only two lanes of traffic.
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culverts → design → traffic
Adding normal soil, stone or heavy concrete fill above them to support wider lanes could have placed too much weight on the structures.
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Adding → add → structures
Replacing or rebuilding the culverts would have cost much more and caused longer delays in the busy construction area.
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Replacing → replace → area
Engineers found an alternative in ultra-lightweight foam glass aggregate.
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Engineers → find → aggregate
By using the glass material instead of traditional earth fill, workers reduced the weight placed on the underground concrete boxes.
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workers → use → boxes
Manufacturing an ultra-lightweight fill
Although it is made from recycled glass bottles and containers, the finished material looks very different from ordinary glass.
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material → manufacture → glass
"Foam glass is made by crushing recycled glass into a powder and mixing it with a foaming agent," Douglas detailed in the ADOT report.
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Douglas → make → report
"The mixed powder is then sent through a kiln and softened.
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powder → mix → kiln
During this process, the foaming agent creates bubbles within the softened glass, which in turn creates the foam glass, an inert, non-leaching, rot-resistant, non-flammable, durable construction material."
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which → foam → glass
The heating process creates lightweight, porous, gravel-like pieces that weigh far less than standard stone aggregate while still being strong enough to carry heavy loads.
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that → create → loads
Because foam glass is made of closed-cell glass, it is also waterproof.
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it → make → glass
This prevents it from absorbing water and gaining extra weight over the underground structures during heavy rain.
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This → prevent → rain
The foam glass used along the Arizona highway was made in Florida and transported to the project in large bulk bags.
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glass → use → bags
The bags became a noticeable sight for motorists passing the construction area.
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bags → become → area
Promoting sustainability in highway engineering
The use of foam glass also supports wider sustainability efforts by keeping large amounts of glass waste out of landfills.
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use → promote → landfills
Glass collected through municipal recycling programmes can be difficult to turn back into new bottles because of sorting problems and mixed colours.
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Glass → collect → problems
Using the material in construction provides another way to reuse it.
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Using → use → it
"Foam glass is not only an innovative material for construction, it's sustainable and environmentally responsible as well," Douglas noted in the publication.
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Douglas → note → publication
The use of foam glass on Interstate 17 is part of a wider trend among US state transport departments looking for lightweight and durable fill materials for soft ground, retaining walls and bridge supports.
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use → look → walls
Similar materials have already been used in European infrastructure, while their use on North American highways has increased as transport agencies consider long-term costs and environmental effects.
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agencies → use → costs
Progress across the I-17 expansion project
The I-17 Improvement Project combines traditional construction methods with specialised materials.
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Project → combine → materials
Along with the foam glass, contractors recycled almost all of the rock removed during major blasting work in the surrounding mountains.
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contractors → recycle → mountains
The blasted rock was crushed on site and reused for aggregate base, embankment support and paving materials, helping reduce waste.
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rock → blast → waste
The project has a total investment of about $522 million (£395 million), funded through state highway money, federal infrastructure grants and local regional transport funding.
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project → have → money
By using lightweight glass aggregate over the existing culverts, construction crews avoided costly structural demolition while keeping the widened road safe and stable for heavy commuter and freight traffic.
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crews → use → traffic
The completion of the widening work and flex lane installation marks a major step forward for Arizona's transport network.
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completion → widen → network
The Aporia
