At least 17 streets in Baltimore were paved with recycled glass, creating road surfaces that could sparkle when sunlight or streetlights hit them.
uncertain
sunlight → pave → them
Baltimore's approach is part of a broader practice of using crushed waste glass in asphalt mixes.
asserted
approach → use → mixes
Properly processed glass can replace some of the conventional aggregate used in road construction.
asserted
glass → process → construction
Wearing surfaces containing 10 to 15% crushed glass have performed well.
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surfaces → wear → glass
According to the Federal Highway Administration, recycled glass has also been used in road projects elsewhere in the United States.
uncertain
glass → accord → States
New York City used about 225,000 metric tonnes of glass in resurfacing applications between 1990 and 1995.
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City → use → 1990
However, earlier projects found problems when glass was used in high percentages or as large pieces.
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glass → find → pieces
The guidance recommends using properly processed glass in suitable proportions for asphalt paving.
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guidance → recommend → paving
How did Baltimore’s recycled glass roads create a sparkling effect
Waste glass was tested for use in hot mix asphalt during field demonstrations in the United States in the late 1960s and early 1970s.
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glass → create → 1960s
Test paving strips were placed at about 33 locations across the United States and Canada.
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strips → place → States
Baltimore later used glass in at least 17 streets, producing a sparkle effect from reflected sunlight or street lamp light.
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Baltimore → use → sunlight
Early projects often used more than 25% glass and coarse particles.
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projects → use → glass
The guidance says high glass percentages and large particles probably contributed to stripping and raveling problems reported during those demonstrations.
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percentages → say → demonstrations
Glass does not absorb asphalt cement binder and bonds poorly to it.
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Glass → absorb → it
Moisture damage can become a concern when high percentages and large gradations are used in surface mixes.
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percentages → become → mixes
PC: AI Generated
How is crushed glass turned into a paving material
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glass → generate → material
According to the FHWA guidance, turning waste glass into a suitable paving material requires several processing steps before it can be mixed into the asphalt.
uncertain
it → accord → asphalt
Waste glass is first cleaned to remove materials such as metal, plastic, and paper.
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glass → clean → metal
It is then crushed and screened to produce smaller, more suitable pieces while removing flat, elongated, and sharp-edged particles.
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It → crush → particles
For surface pavements, the guidance recommends using glass smaller than 4.75 mm, or the No. 4 sieve, as a fine aggregate mixed with conventional materials.
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guidance → recommend → materials
Asphalt wearing surfaces containing 10 to 15% crushed glass have shown satisfactory performance.
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surfaces → wear → performance
Higher proportions, potentially up to 25%, may be suitable for base or binder courses, where the glass is not exposed directly at the road surface.
uncertain
glass → expose → surface
Crushed glass can affect the strength and performance of asphalt
Well-crushed glass can also affect the performance of asphalt mixes because of its angular shape and high friction angle.
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glass → crush → shape
The guidance says these properties can contribute to good lateral stability, with tests reporting stability comparable to, and in many cases better than, conventional mixes.
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tests → say → mixes
Waste glass also has a specific gravity about 10 to 15% below that of conventional aggregates, which can increase the yield of an asphalt mix.
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which → have → mix
Its low thermal conductivity may also help mixes containing glass retain heat for longer.
uncertain
mixes → help → heat
Skid resistance tests on pavements containing waste glass have produced results within recommended limits.
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tests → contain → limits
However, larger glass particles measuring more than 19 mm can become slippery when wet and should not be used in surface mixes.
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particles → measure → mixes
The guidance also notes that using more than 15% glass can increase pavement reflectivity and glare, particularly when the surface is wet.
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surface → note → reflectivity
What makes recycled glass suitable for asphalt paving
Asphalt mixes containing crushed glass can be designed using standard laboratory procedures.
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mixes → make → procedures
The guidance recommends testing the mix for stripping potential and says conventional pavement structural design methods are appropriate.
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methods → recommend → potential
Most highway departments allow 5 to 10% glass.
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departments → allow → glass
The guidance says performance is generally best when crushed glass is used as a sand or fine aggregate substitute.
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glass → say → substitute
The same methods and equipment can be used to store, mix, place, and compact asphalt containing waste glass.
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methods → use → glass
Field testing should follow the procedures used for conventional hot mix asphalt.
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testing → follow → asphalt
The guidance identifies a need for uniform specifications covering sizing, debris levels, and mix limitations.
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guidance → identify → sizing
It says a lack of adequate and consistent glass supply remains a major constraint on wider use.
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lack → say → use
The Aporia
