Crushed Glass Fill at Little Rock Housing Project

Awards Evergreen Sustainable Development Standard (V1.2)

Crushed glass cullet was used as a 100% substitute for natural aggregates (e.g. sand and pea gravel) as fill/bedding material to construct a slab-on-grade foundation capillary break, and for waterline pipe zone bedding. According to the Clean Washington Center’s Construction Inspectors Guide to Recycled Glass Aggregate “glass aggregate and blends are strong, clean, safe and economical.”[1]

Glass cullet is manufactured out of crushed post-consumer bottles from municipal waste/recycling stream by secondary recycling processors and/or glass cullet supply companies, in this case Concrete Recyclers, Inc. of Tumwater, WA. It is crushed to a 3/8” minus size, sifted of debris and other impurities to create a consistent high-quality project with a ratio of coarse and fine material sizes which meets the WS DOT sieve test requirement[2] for the specified type of aggregate, the specification used by the building official as a requirement of approval.

Samples of product are sent to independent environmental laboratories to test for copper and lead content (samples collected according to ASTM D 75[3], tested using EPA method 3010[4]/ 6010[5]) and certified for total Lead content of no more than 250 ppm. The manufacturer supplied the test data and a Material Safety Data Sheet on the product to the subcontractor for material submittals. Using this data, the contractor warrants the product to satisfy the required specifications prior to delivery.

Field tests were also conducted to ensure the product conforms to allowable debris level (up to 10% by visual inspection, or 2% to 4% by weight using American Geological Institute[6] method).

Compaction was tested using the “roll test” method to ensure product is “firm and unyielding” under load. The use of the material was endorsed by the geotechnical engineer working on the project.

The residential and commercial building code has few specific requirements regarding the use of unbound aggregate for utility bedding, backfill, foundation materials, and drainage features (the applicable general code sections are International Building Code Sec. 1802.2 – 1802.6). Therefore the standard specification most cited in relation to the product is the DOT Standard, first adopted in 1994. However, this specification only allows a 15% blend of glass cullet with natural materials for foundation backfill and pipe zone bedding. While DOT’s quality specifications were used, the project deviated from the 15% limit due to the owners’ previous knowledge and experience, the subcontractors decision to use the product and the geotechnical engineer’s endorsement of the product as a 100% substitute material. The City of Tumwater inspector of the project approved the use based on contractor certification of the product.

The cost of glass aggregate is commonly 50-65% less than comparable natural sand and gravel material, offering a significant price advantage over natural materials when transportation costs are comparable. Hauling costs must be taken into account due to the fact that there are relatively few suppliers and distribution points for quality recycled glass aggregate material. Contractors who use the product report that a hauling distance of up to 30 miles farther than natural aggregate materials is viable.

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