Concrete is a very popular building material, enough so that one of its key ingredients – sand – is in increasingly short supply. Scientists are thus now exploring the possibility of replacing that sand with glass waste that would otherwise end up in landfills.

Although glass is considered a recyclable material, it quite often doesn’t get recycled. This may be due to a lack of properly equipped recycling facilities, or the fact that glass waste frequently takes the form of numerous fragments that are too small to sort by color in a practical fashion – that sorting process is a requirement for recycling.

Seeking a use for non-recycled glass, researchers at Singapore’s Nanyang Technological University looked into utilizing it as a replacement for the sand commonly used in 3D-printed concrete structures. After all, glass is made of silica, which is a major component of sand.

For their study, the scientists crushed glass waste into five different fragment sizes – coarse, medium, fine, super fine and “moondust” – to replace the sand and gravel which ordinarily serve as aggregate in concrete. That ground glass was then combined with concrete’s other two ingredients, cement and water.

The mixture was subsequently extruded through the nozzle of an existing 4-axis gantry robotic 3D printer, to create a 40-cm tall (15.8-in) L-shaped concrete bench. Once the concrete cured, it was found to be similar in strength to traditional sand-containing concrete. Additionally, the researchers noted that the poured concrete didn’t deform or collapse before it cured, plus it was fluid enough to flow easily through the printer nozzle.

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