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Foam glass aggregate vs conventional granular fill

Ordinary mineral soils and aggregates weigh 1,520 to 2,400 kg/m³ (95 to 150 lb/ft³), and foam glass aggregate 160 to 400 kg/m³ (10 to 25 lb/ft³).[1] The difference matters most over soft ground, behind walls and above buried structures.[2][3]

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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.

Side by side

Foam glass aggregate vs conventional granular fill

FactorFoam glass aggregateConventional granular fill
Unit weight160 to 400 kg/m³ (10 to 25 lb/ft³) across the material class.[1] Enviro-Rock: 200 kg/m³ (12.5 lb/ft³) loose, 240 kg/m³ (15.0 lb/ft³) at 20% compaction.[4]1,520 to 2,400 kg/m³ (95 to 150 lb/ft³) for mineral soils and aggregates.[1] Michigan DOT uses 1,920 kg/m³ (120 lb/ft³) for sand backfill and 1,600 kg/m³ (100 lb/ft³) for open-graded stone.[5]
Settlement over soft groundOn a Virginia project reviewed for PennDOT, the estimated settlement at the deepest fill stations was 10 mm (0.4 in) with foam glass aggregate, within the 13 mm (0.5 in) limit.[2]No. 57 stone at the same stations had an estimated 15 to 18 mm (0.6 to 0.7 in), over the limit.[2]
Pressure on walls and buried structuresFHWA states that low weight and a high friction angle can reduce vertical and lateral forces by more than one-half.[1] Modelling found it cut the maximum bending moment in culverts by 25 to 70% compared with conventional fill.[3]Michigan DOT designs sand backfill with a lateral earth pressure coefficient of 0.30, and open-graded stone with 0.24.[5]
Friction anglePeak angles above 50° at low normal stresses in large-scale shear tests, falling as stress rises.[1][6] Agency design guidance uses about 38 to 45° depending on stress level, and Illinois caps the design value at 40°.[7][6] Enviro-Rock: 39° at 65 kPa.[4]In FHWA direct shear tests reported by the Illinois Tollway study, AASHTO No. 8 stone reached 61 to 64° peak secant friction angle, against 55 to 61° for two foam glass aggregates.[6]
Stiffness and traffic loadsResilient modulus of 69 to 145 MPa (10 to 21 ksi) in the literature. Illinois design guidance limits wheel load at the top of the fill to about 96 kPa (2,000 lb/ft²).[6] Enviro-Rock's installation guide places crushed gravel between the fill and the pavement.[8]Stiffer: the same report cites 110 to 177 MPa (16.0 to 25.6 ksi) for crushed aggregate.[6]
DrainageCompacted foam glass aggregate is a highly permeable, free-draining layer.[6] Producer datasheets list 0.038 to 10 cm/s, so use the product's own test.[7] Enviro-Rock's brochure gives 50% void space loose and 30% at 20% compaction, based on worldwide averages.[4]Depends on gradation. A study cited in the Illinois Tollway report gives average saturated hydraulic conductivity of about 0.32 cm/s for gravels and 0.014 cm/s for sands.[6]
InsulationNorway uses foam glass aggregate regularly as road insulation. In service, at about 20% moisture by weight, its conductivity is about 0.155 W/(m·K), higher than dry laboratory values, so the designer sets an in-service value.[9]An NTNU road study modelled crushed rock sub-base at 1.5 W/(m·K), about ten times the in-service value for foam glass aggregate.[10]
BuoyancyBuoyant, so designs keep it above groundwater and the 500-year flood level, or ballast it.[6] At Jim Lorimer Park, the Enviro-Rock design anchored the fill against uplift.[11]Heavier than water at 1,520 to 2,400 kg/m³, so uplift is not a design case.[1]

Where foam glass aggregate fits

When foam glass aggregate is the better choice

Foam glass aggregate wins where weight is the problem: soft or compressible ground, walls and abutments, and buried culverts. It weighs 160 to 400 kg/m³ against 1,520 to 2,400 kg/m³ for mineral soils and aggregates[1], and on a Virginia project reviewed for PennDOT its estimated settlement stayed within a limit that No. 57 stone exceeded.[2] Modelling found 25 to 70% lower bending moments in culverts than with conventional fill.[3]

In Kelowna, the geotechnical design for a six-storey building sub-excavates 1.8 m of soil and backfills with 1.2 m of foam glass aggregate to top of footing, with mineral aggregate above, naming Enviro-Rock as the basis of design. Expected settlement is under 25 mm over 50 years, down from a projected 85 to 115 mm without ground improvement.[12]

The same layer also drains freely and insulates.[6][9] Crushed rock conducts heat about ten times as readily.[10]

Where conventional granular fill fits

When conventional granular fill may be the better choice

  • Weight does not matter: the ground is firm, and no wall or buried service needs protecting. Gravel costs less per cubic metre at the pit but more to ship, as the Langley Advance Times reported.[13]
  • The layer carries traffic directly. Crushed aggregate is stiffer, and Illinois guidance limits wheel load at the top of foam glass fill to about 96 kPa (2,000 lb/ft²).[6]
  • The fill sits below groundwater or in a flood zone and the design cannot add ballast or anchoring. Foam glass aggregate is buoyant.[6]
  • The design depends on the highest friction angle. AASHTO No. 8 stone tested higher than two foam glass aggregates in FHWA direct shear tests.[6]

Questions

Common questions

When is lightweight fill cheaper than conventional fill?

Gravel costs less per cubic metre at the pit but more to ship, as the Langley Advance Times reported.[13] Depending on the project, Enviro-Rock's lower weight can save on structural requirements, equipment, labour, transport and installation.[14]

How much lighter is Enviro-Rock than gravel?

About 90% lighter than conventional crushed rock.[15] Enviro-Rock weighs 200 kg/m³ loose and 240 kg/m³ at 20% compaction, against 1,520 to 2,400 kg/m³ for ordinary mineral soils and aggregates.[4][1]

Can foam glass aggregate carry a road or a building?

With the right build-up. Illinois design guidance limits wheel load at the top of the fill to about 96 kPa, and Enviro-Rock's installation guide places crushed gravel between the fill and the pavement or concrete.[6][8] In the Kelowna design, compacted, geogrid-reinforced Enviro-Rock carries the footing loads, with bearing values set by the geotechnical engineer.[12]

Does foam glass aggregate hold water in the ground?

Enviro-Rock absorbs 7.2% uncompacted, and its closed cells limit water entering each particle.[4][16] Where surrounding soils drain more slowly, water can collect in the fill, so the Illinois design guide calls for drainage by grading or a pipe.[6]

Does foam glass aggregate crush under compaction?

It can if it is over-compacted, which Maine DOT's provision warns against.[17] Enviro-Rock is placed in 300 to 600 mm loose lifts under a static roller with no vibration, or 150 to 300 mm under a plate compactor with more passes rather than more vibration, and compacted 10 to 20%.[8][18]

Sources

  1. [1] Alternative Backfills for Highway Applications: State of the Practice (FHWA-HRT-23-110), Federal Highway Administration, 2024
  2. [2] Lightweight and Sustainable Materials in Engineered Fills (FHWA-PA-2021-011), PennDOT and Temple University, 2021
  3. [3] The Use of Foamed Glass Aggregate (FGA) as a Lightweight Fill Above Culverts, research brief, Mineta Transportation Institute, 2026
  4. [4] Enviro-Rock civil infrastructure brochure (metric), specification table, Enviro-Corp Recycling
  5. [5] How Low Can You Go: Various Materials Used by MDOT to Reduce Lateral Earth Loading Pressures, Michigan DOT, 2025
  6. [6] Applications for Foamed Glass Lightweight Aggregate, final report, Illinois Tollway Research Program, Washington State University et al., 2025
  7. [7] Guidelines for Using Lightweight Fills in Transportation Infrastructure Applications, Texas DOT and University of Texas at Austin, 2025
  8. [8] Enviro-Rock installation guide, Enviro-Corp Recycling
  9. [9] Field test comparing frost insulation materials in road construction, SINTEF and Norwegian Public Roads Administration
  10. [10] Design of roads using frost insulation materials: case study new E6 in Hedmark, Norway, NTNU, 2019
  11. [11] Case study: Jim Lorimer Park playground, Burnaby, Enviro-Corp Recycling
  12. [12] Case study: 6-storey building, Kelowna, Enviro-Corp Recycling
  13. [13] Abbotsford's Enviro-Corp Recycling transforming glass into rocks, Langley Advance Times
  14. [14] Enviro-Rock benefits, Enviro-Corp Recycling
  15. [15] Enviro-Rock benefits: lightweight, Enviro-Corp Recycling
  16. [16] Enviro-Rock benefits: closed-cell structure, Enviro-Corp Recycling
  17. [17] Special Provision Section 203, Ultra-Lightweight Foamed Glass Aggregate, Maine DOT, 2025
  18. [18] Enviro-Rock compaction equipment sheet, Enviro-Corp Recycling

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