Crushed glass cullet was used below a sidewalk as fill and leveling agent in place of sand and gravel at 304 West Bay Drive in Olympia, WA. The material is made up of glass otherwise unsuitable for typical glass recycling and is created at a local quarry. Due to knowledgeable building officials and engineering examiners in Olympia, the material proved to meet the IBC compaction requirements with no additional procedures to permit the project. The project was successfully completed and crushed glass cullet proved to be safe and cost effective.
Glass cullet is a familiar alternative substrate material in the Olympia area. Developers SMCI of Bremerton, WA used glass cullet infill in the construction of the sidewalk. Using the material did not slow the project timeline or add additional costs. Because glass cullet meets the compaction requirement of the IBC code used by the City of Olympia, the use of glass cullet is in compliance to the code regarding sidewalks. Because of familiarity of the product, knowledgeable engineers and building officials, permitting this project was not difficult as glass cullet is a previously approved substrate.
To comply with the regulations set by the International Building Code in regards to compaction rate of the fill material, glass cullet must be compacted to 90% of maximum density using the Modified Proctor Test. The Modified Proctor Test is used to measure the dry density and moisture content of a soil by compacting layers of the material at different moisture levels in a cylindrical mold. Data relating to compaction of glass cullet was supplied by Concrete Recyclers. In addition to passing the Modified Proctor Test, the glass must also pass a visual inspection allowing a maximum of 10% debris in the finished product. Debris, such as labels, decompose over time and at this level do not affect product performance. The use of blended aggregates requires project engineers’ approval prior to use. Additionally, imported products require a toxicity safety test.
Test results are available from the supplier of the material, who will certify that the product meets all compaction, sieve test and debris requirments. All types of aggregates will comply with the general requirements outlined in the City of Olympia EDDS report under Chapter 4 9-03.21(1).
Again because of knowledgeable building officials, engineers, and contractors in the area, using glass cullet has become more common and proven itself to be safe, cost effective, and strong. Though there are procedures to be taken when working with crushed glass, they have become streamlined which makes using the material no longer a challenge in terms of permitting a project.
Material for this sidewalk project was sourced from Concrete Recyclers in Olympia, WA. The glass is crushed into different sizes for different uses “arriving at the rate of about 800 tons a month from solid-waste companies in Thurston County and surrounding counties that collect it separately from other recycled materials.” (5) Approved by Washington State DOT for nearly 20 uses, crushed glass has proven to be a valuable resource which can be utilized in the surrounding area for many new projects.
To meet compacting requirements, the glass is applied in lifts (layers) not exceeding 12 inches. Typically recycled glass cullet is compacted with vibratory compaction equipment after each lift is applied. Due to the nature of the material and the requirements in Olympia’s EDDS report stated above, cullet should be applied in thin courses with compaction and nuclear densometer testing done for each.
Health and Safety Considerations
Just like any natural aggregate, there may be sharp edges that could potentially be harmful, though the glass cullet has been pulverized which softens these edges. There are some additional safety measurements to be taken when working with any aggregate material. Heavy pants, boots, and long sleeve shirts are highly recommended when working with glass and other aggregates. Dust from the glass is a concern for those working and though it has been noted as a nuisance dust (3) and not harmful or hazardous.
Additionally, there are cost benefits when using recycled glass. Because it is unnecessary to sort glass by color and is made up of material that would be otherwise unsuitable for typical recycling, the cullet is sold for a fraction of the price of natural aggregates. The use of 100% glass is particularly beneficial in that there is no additional cost or time dedicated to blending aggregates at the quarry or on site. There were additional savings due to sourcing the material from a local quarry.
The use of recycled glass at 304 West Bay Drive is just one example of how glass cullet may be used in new construction. The project was completed in 2003 and though the material was still fairly new, because of the results from the Modified Proctor Test, glass cullet showed to be a dream material for easy compaction. Owner Glenn Wells had little to do with the permitting process or application of the material. However, Wells reported satisfaction with it’s performance, and recommends it’s continued use as an alternative sidewalk substrate.