11-16 access cover manhole

[Image above] Many current access covers are made from materials that are bulky and heavy. A new glass–polymeric composite developed by RMIT University researchers could offer a lighter option. Credit: Himbeerdoni, Flickr (CC BY-NC-ND 2.0)

While glass in theory is infinitely recyclable, the reality of our recycling systems can lead to contamination and color mismatches in recycled glass, which prevent its use in new glass containers.

Fortunately, there are other ways recycled glass can be used. Researchers have explored using glass waste in construction applications where color is not a requirement, including as a substitute for cement, sand, and coarse aggregate in concrete, and in environmental applications such as beach nourishment to help combat coastal erosion.

Finding new applications for recycled glass brings the material ever closer to reaching its sustainable potential. Recently, three researchers at RMIT University in Australia developed a new process to turn glass waste into a composite material for various building components.

The new process involves encapsulating glass particles within a polymeric matrix using polyurethane resin. Though detailed information of the process is not presented “as the technology was selected to commercialise by the industry partners,” the researchers write, the paper does provide a broad description of the methodology.

The glass–polymeric composite consists of several inorganic components (glass waste, inorganic filler, and pigment) and polymeric materials (isocyanates and polyols). The fabrication process consists of five main stages:

  1. Grinding—Glass waste is ground to specific particle sizes identified in the testing plan.
  2. Mixing—The ground glass is mixed with some inorganic components, polymeric reactants, and additives.
  3. Molding—The mixture is poured into a high-density polyethylene mold.
  4. Demolding and curing—Samples are removed from the mold after 24 hours and then further cured for 3–4 days.
  5. Cutting—Samples are cut to the shape required for mechanical tests.

Flexural tests showed that the strength and modulus of the glass–polymeric composites increased with larger particle sizes. The researchers contribute this finding to less space in the polymeric matrix for it to rearrange itself and deform when the particles are larger. Larger particle sizes also led to higher compressive strength and higher impact resistance.

Following mechanical tests, the researchers demonstrated the composite’s potential by creating access covers, or removable lids placed over man-made openings to restrict access for safety and security. They chose this application “due to its significance within the road infrastructure system, which is exponentially expanding worldwide,” and because many current covers are made from materials that are bulky and heavy, “representing a negative factor for maintenance in terms of occupational injuries.”

They created access covers that comply with class B regulation, according to the Australia Standard guide AS 3996 for access covers and grates. This type of cover is designed for footpaths and paved areas where vehicles may park accidentally.

Results of loading tests showed that the access covers could withstand loading pressures up to 37 kN (~4 tonnes), which is equal to the load of a light truck. For situations requiring higher loads, like medium trucks, the researchers suggest that future work could strengthen the covers by identifying a suitable geometric design.

“The new technology of glass recycling method can be highly versatile and hence can be used in multiple building applications as verified in the current study using access covers as example,” they conclude.

The paper, published in Construction and Building Materials, is “A new technology of transforming recycled glass waste to construction components” (DOI: 10.1016/j.conbuildmat.2021.125539).