As the building construction market expands, so does the production of glass. According to one industry report, the global glass market reached $110 billion in 2023 and is expected to attain a value of $187 billion by 2033. As a building material, glass is typically associated only with windows and curtain walls. However, glass is well-suited for other applications, including novel load-bearing components.

Although glass blocks have waned in popularity in recent decades, life cycle factors have inspired renewed interest in this kind of application. While float glass and insulated glazing units (IGUs) have little tolerance for incorporating the impurities commonly found in waste glass, solid cast components have a high capacity for such inclusions. Current research and development efforts expanding the uses and capacities of load-bearing glass include process advances as well as life cycle considerations.

For example, a new 3D-printed glass module is gaining attention for its structural capacity and circular economy potential. MIT researchers have developed a robust engineered glass brick using the Glass 3D Printer 3 (G3DP3), a variant of the G3DP printer developed previously by the MIT Media Lab. The module’s figure-8 shape imparts greater rigidity, particularly from shear forces, than a rectangular shape of the same thickness. Additionally, the new glass brick exhibits similar structural performance as a concrete masonry unit and is endowed with vertical pegs to enable vertical interlocking with other modules. Because the bricks are composed of pure soda-lime glass without filler or reinforcing materials, they can be readily recycled into new glass products when desired.

The ReStruct Group at the Technical University of Delft in The Netherlands has also developed structural glass bricks with a focus on the circular economy. “Cast glass can escape the design limitations generated from the two-dimensional nature of float glass,” claim group researchers Telesilla Bristogianni and Faidra Oikonomopoulou.

Re3 Glass consists of stackable, interlocking glass modules that are easily disassembled. The units are composed of recycled waste glass, given that cast glass components allow for the material’s impurities without reducing mechanical or aesthetic performance. Instead of adhesives, which are problematic for recycling, the system utilizes a dry, transparent interlayer made of PVB and PU polymers. These layers accommodate dimensional differences and reduce stress concentrations between units.

The same group designed a pedestrian bridge made of structural glass components. The 14 meter-long Glass Truss Bridge, constructed over a canal surrounding TU Delft’s campus, consisted of struts made of bundled glass as well as cast glass truss nodes. The researchers designed the top surface to be composed of 2,000 S-shaped glass modules that interlock to form a shallow arch without adhesives.

Given the novelty of a glass truss bridge, the team over-engineered the structure to support twice the amount of live and dead loads. One bridge test, “performed by 60 students marching and dancing over it,” enabled the researchers to analyze the strain forces in the diagonal glass bundles.

In a different nod to the circular economy of glass, scientists have also determined a way to prepare waste glass as a sand replacement in 3D-printed, load-bearing concrete. Researchers at Singapore’s Nanyang Technological University (NTU) developed a print-friendly concrete mixture incorporating repurposed glass waste. The composite is easily extrudable from print nozzles and structurally sound after curing. The intrinsic hydrophobicity of glass also results in less water being required than in concrete with conventional sand.

The research team acknowledges sand scarcity as a primary motivator for this research. “Given that sand is being exploited at a rate much quicker than it can be replenished naturally, the prospect of using recycled glass in building and construction is becoming more attractive,” said NTU researcher Andrew Ting.

One downside to this approach is that the glass may not be easily extracted from the cured concrete for future recycling. However, this resourceful application—like the structural glass examples mentioned above—is a compelling and rare example of material upcycling in an industry accustomed to wastefulness.