Processed glass aggregate (PGA), a material produced from recycled glass, may be a sustainable substitute for the traditional sand-based resources currently used for building roads throughout Vermont. Professor Mandar Dewoolkar is leading a team on a new TRC research project, supported by the Transportation Infrastructure Durability Center, that is investigating how PGA may be able to replace sand-based materials in transportation projects in Vermont, New England, and beyond.

Sand is the most commonly used material in much of the world’s transportation infrastructure, including roadways and bridges. In Vermont and other New England states, sand is an important part of a road’s subbase, which supports the pavement and must provide adequate drainage to protect from freeze-thaw cycles.  However, high quality sand that can be used in a road’s subbase has become increasingly scare in Vermont and across the globe. A combination of increased urbanization resulting in high demand for sand in construction materials and the naturally slow rate at which sand is being replenished by the weathering of rocks means that the world is quickly running out of this vital resource. Not only is sand becoming increasingly scarce, but the mining processes used to retrieve sand can degrade natural environments and water quality through land clearing, digging pits and dredging, particularly when done in or near water bodies where sand is commonly found. 

This project aims to increase the use of PGA as a replacement for mined “sand-borrow” in Vermont’s roadway infrastructure. PGA is already used in parking lots, sidewalks, and trails throughout the state, but its quality and performance has not been tested for widespread use in Vermont’s roadways. A particular concern is understanding how contaminants introduced in the recycling process (think of all the other items that end up in your recycling bin) impact PGA performance. TRC researchers will evaluate the performance of PGA produced from different regional recycling facilities and develop testing methods that can reliably measure the quality of PGA and assess its suitability for use in roadway construction. A better understanding of PGA performance and reliable tests to ensure quality control are expected to increase contractor confidence in using PGA as a replacement for natural sands.

The research team will also evaluate the potential economic and environmental benefits from replacing sand with PGA in transportation projects. For instance, using PGA will help recycling facilities by making use of a regional waste stream that is difficult to reuse locally and expensive to transport to other regions. In turn, this minimizes greenhouse gas emissions and reduces the amount of waste going to landfills: a win-win-win for the environment, the transportation sector, and recycling facilities.