Cities of the future could be 3D printed, using concrete made from recycled glass.
3D printed concrete can lead to a change in architecture and construction. Because you can change the age-old processes and procedures still used to construct buildings, resulting in reduced costs and time savings.
However, concrete has a significant environmental impact. Large quantities of natural sand are currently being used to satisfy the world’s insatiable appetite for concrete, to the detriment of the environment. In general, the construction industry struggles with sustainability. It creates approximately 35% of all landfill waste worldwide.
Our new research suggests a way to limit this impact. We tested the use of recycled glass as a component of concrete for 3D printing.
Concrete is made from a mixture of cement, water and aggregates such as sand. We try to replace up to 100% of the aggregate in the mix with glass. Simply put, glass is produced from sand, is easy to recycle and can be used to make concrete without any complex processing.
Demand from the construction industry could also help ensure glass recycling. In 2018 in the United States, only a quarter of glass was recycled and more than half went to landfill.
We use glass from a local recycling company. The bottles were first crushed using a crusher and then the crushed pieces were washed, dried, crushed and sieved. The resulting particles were less than one square millimeter.
The crushed glass was then used to make concrete in the same way it would be made from sand. We use this concrete to 3D print wall elements and prefabricated building blocks that could be assembled to form a complete building.
If used in this way, waste glass can find new life as a building material.
The presence of glass not only solves the waste problem but also contributes to the development of a concrete with superior properties to those containing natural sand.
The thermal conductivity of soda lime glass, the most common type of glass in windows and bottles, is more than three times lower than that of quartz aggregates, widely used in concrete. This means that concrete containing recycled glass has better waterproofing properties. They could significantly reduce the costs required for cooling or heating during summer or winter.
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We also made other changes to the concrete mix to make it more durable as a building material, including replacing some of the Portland cement with limestone powder.
Portland cement is a key component of concrete, used to bind the other ingredients together into a mixture that will hold. However, the production of ordinary Portland cement results in the release of significant amounts of carbon dioxide, as well as other greenhouse gases. The cement production industry accounts for approximately 8% of all carbon dioxide emissions to the environment.
Limestone is less hazardous and has less environmental impact during its production process than Portland cement. It can be used in place of regular Portland cement in 3D printing concrete without reducing the quality of the printing mix.
We also added lightweight fillers, made of tiny hollow thermoplastic spheres, to reduce the density of the concrete. This changed the thermal conductivity of the concrete, reducing it by up to 40% compared to other types of concrete used for 3D printing. This further improved the insulation properties of the concrete and reduced the amount of raw material needed.
Using 3D printing technology, we can simply develop a wall structure on a computer, turn it into simple code, and send it to a 3D printer to be built. 3D printers can operate around the clock, reduce the amount of waste produced and increase the safety of construction workers.
Our research shows that a well-insulated, ultra-lightweight 3D building is possible, which could be a vital step in our mission towards sustainability.
Authors: Seyed Ghaffar, Mehdi Chougan, Pawel Sikora