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Foam glass aggregate

What is foam glass aggregate?

Foam glass aggregate is a lightweight fill made by milling recycled glass to a powder, mixing it with a foaming agent and heating it in a kiln.[1] It weighs a fraction of ordinary fill and drains freely.

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Enviro-Rock at a glance

Loose dry bulk density
200 kg/m³
Angle of friction
39° at 65 kPa
Thermal resistance
R-2.4 per inch, dry
Up to, per B-train load
140 m³

From the Enviro-Rock specification table and delivery trailer sheet. Sources on the product page.

How it is made

Heated, the glass softens and expands into a lightweight cellular structure, which is cooled and processed into aggregate.[2] The result is angular and stone-sized; products for geotechnical use are specified as closed-cell.[3][4]

It is also called foamed glass aggregate, foam glass gravel or ultra-lightweight foamed glass aggregate. Cellular glass is also made into rigid insulation boards[5]; foam glass aggregate is the loose, granular form used as fill.[6]

Properties of the material class

Published values vary by producer and test method. These ranges describe foam glass aggregate in general; product values come from each supplier's data.

PropertyTypical rangeNote
Unit weight160 to 400 kg/m³ (10 to 25 lb/ft³)[1]Mineral soils and aggregates: 1,520 to 2,400 kg/m³ (95 to 150 lb/ft³)[1]
Recycled glass contentAt least 95 to 98% in state specifications[3][4]Share of the raw material that is recycled glass
Friction anglePeak values above 50° at low normal stress[1]Falls as normal stress rises; design for the expected stress[7]
Dry thermal conductivityAbout 0.08 to 0.10 W/(m·K) for European products[6][8]Rises with moisture in service[9]
DrainageHighly permeable, free-draining[7]Open-graded granular layer
BuoyancyBuoyant[7]Placed above the water table or held down with cover
FireClass A1 for a cellular glass loose fill[6]Non-combustible
CompactionTypical specifications reduced lift volume by about 8 to 17% in field tests[1]Order loose, design compacted

Where it is used

Its low weight and high friction can reduce vertical and lateral forces by more than one-half, which is why it goes over soft soils, behind walls and abutments, and over buried structures.[1] Its insulating value adds frost protection under roads.[9]

Track record and specifications

Foam glass aggregate has been used as lightweight fill in Europe since the 1990s and drew wider attention in the United States from 2017.[1][5] In Norway it is one of three products used regularly as thermal insulation in roads.[9]

New York and Indiana have published specifications for foam glass aggregate fill, and Maine DOT has used a project special provision.[10][4][3] No ASTM or AASHTO product specification has been published for it, and FHWA lists test standards as a research need, so owners write their own requirements.[1]

Enviro-Rock

Enviro-Rock is foam glass aggregate made in BC from 100% recycled glass, at about 200 kg/m³ loose.[11][12] It is an accepted lightweight fill product on the BC Ministry of Transportation and Transit Recognized Products List.[13]

Common questions

Is foam glass aggregate the same as cellular glass?

Both are foamed glass. Cellular glass insulation is usually made as rigid boards; foam glass aggregate is foamed and broken into loose granular fill.[5][6]

Can foam glass aggregate get wet?

Yes. It drains freely, but it is buoyant and its thermal conductivity rises with moisture, so designs hold it down where it could be submerged and use in-service moisture values for insulation.[7][9]

Is foam glass aggregate non-combustible?

Yes. A European Technical Assessment for a cellular glass loose fill declares reaction-to-fire Class A1.[6]

Is foam glass aggregate expensive?

Gravel costs less per cubic metre at the pit but more to ship, as the Langley Advance Times reported.[14] Shipping distance significantly affects the delivered price of foam glass aggregate[7], and depending on the project, Enviro-Rock's lower weight can save on structural requirements, equipment, labour, transportation and installation.[15]

Which DOTs have specifications for it?

New York and Indiana have published foam glass aggregate fill specifications, and Maine DOT has used a project special provision.[10][4][3] In BC, Enviro-Rock is on the Ministry's Recognized Products List as an accepted lightweight fill.[13]

Sources

  1. [1] Alternative Backfills for Highway Applications: State of the Practice (FHWA-HRT-23-110), Federal Highway Administration, 2024
  2. [2] How Enviro-Rock is made, Enviro-Corp Recycling
  3. [3] Special Provision Section 203, Ultra-Lightweight Foamed Glass Aggregate, Maine DOT, 2025
  4. [4] 904-M-076 Lightweight Aggregate, Indiana DOT, 2025
  5. [5] Guidelines for Using Lightweight Fills in Transportation Infrastructure Applications, Texas DOT and University of Texas at Austin, 2025
  6. [6] European Technical Assessment ETA-13/0549, cellular glass loose fill, DIBt, Germany, 2020
  7. [7] Applications for Foamed Glass Lightweight Aggregate, final report, Illinois Tollway Research Program, Washington State University et al., 2025
  8. [8] EPD NEPD-2012-889-EN, foam glass aggregate 10-60 mm (Norway), EPD-Norge, 2020
  9. [9] Field test comparing frost insulation materials in road construction, SINTEF and Norwegian Public Roads Administration
  10. [10] Item 203.03200017, Lightweight Foamed Glass Aggregate Fill, New York State DOT, 2023
  11. [11] Enviro-Rock cellular foam glass aggregate, Enviro-Corp Recycling
  12. [12] Enviro-Rock civil infrastructure brochure (metric), specification table, Enviro-Corp Recycling
  13. [13] Recognized Products List, Lightweight Fill Material (October 1, 2026), BC Ministry of Transportation and Transit
  14. [14] Abbotsford's Enviro-Corp Recycling transforming glass into rocks, Langley Advance Times
  15. [15] Enviro-Rock benefits, Enviro-Corp Recycling

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