Recycled Glass in 3D Printing Concrete

Usually, concrete is created from a mixture of water, cement and aggregates such as sand. Scientists at Technische Universität Berlin (TU Berlin) and Brunel University have developed a way of turning 3D printing concrete into a more sustainable, robust building material by using recycled glass.

Scientists at Brunel University and Technische Universität Berlin (TU Berlin) have created a method of turning 3D printing concrete into a stronger and more sustainable material to build with. The method? Switching out parts of the sand in the cement used to manufacture concrete with recycled glass, plastic fillers and limestone. Through this the researchers have managed to substantially improve the thermal conductivity and robustness of the cement. With further research this could eventually be utilized to create better-insulated buildings in the future.

Making Concrete More Sustainable

To create concrete a mixture of cement, water and a combination of several separate elements forming a whole, such as sand, are used. However, sand is often acquired unsustainably from for example beaches or riverbeds. Furthermore, the researchers state that large quantities of costly admixtures are usually added to make sure that this cement has enough buildability and flowability for 3D printing. This in turn raises the cost of any buildings it’s used to create. 

“Vast quantities of natural sand are currently used to meet the world’s insatiable appetite for concrete, at great cost to the environment,” the researchers told The Conversation. “Our new research suggests a way to curb this impact. Our research shows that an ultra-lightweight, well-insulated 3D building is possible – something that could be a vital step on our mission towards net zero.”

Thus, a lot of time has been put into research, with the goal of replacing the binder in cement with a variety of natural aggregates or fillers. For example, in 2020, a team at the Tongji University has shown that it is possible to add sand recovered from demolitions in place of cement. This result was without it having an effect on its printing properties! Another example would be from engineers at NTU Singapore, who have shown the success of utilizing waste glass into concrete. Even though the material’s flowability was strengthened, the mixture revealed a weak point in terms of buildability while being tested. 

The team was inspired by these examples and have thus taken recycled glass bottles, crushed them down, washed, dried, milled and sieved them, to finally mix them into concrete. The scientists have further added small plastic spheres and limestone to the mixture with the goal of them acting as sustainable binders that provide structures with better thermal properties.

Future Buildings are Improved

In their first attempts, the scientists formulated six concrete mixtures that differentiated from each other, with each one having between 50 and 100% glass waste aggregate. Then they 3D printed them into a set of 40 x 40 x 160 mm samples. The result was surprising as by doing so, the team found that all of their mixtures had the flowability needed to retain their shape after printing. However, the ones which had microspheres took longer to set into shape. 

Furthermore, the scientists found out that introducing lightweight fillers into their material made it able to be deposited into samples with a 40% lower thermal conductivity than regular 3D printing concrete, while compressive strength testing showed that their resistance characteristics increased when more recycled glass was added. As insulation is supposed to reduce the need to cool down and warm buildings, the researchers see their material as perfect for helping build future low-carbon infrastructure. Furthermore, this concrete has the potential to become a pillar in construction 3D printing, a technology the researchers believe has sustainability advantages of its own. 

“Using 3D printing technology, we can develop a wall structure on a computer, convert it to simple code and send it to a 3D printer to be constructed,” concluded the researchers. “3D printers can operate for 24 hours a day, decrease the amount of waste produced, as well as increase the safety of construction workers.”

As concrete 3D printing is heading more and more toward mainstream building, researchers and market leaders have begun to contribute even more time and funding to optimize the technology of it. With further development this technology could lead to whole cities being built in a more sustainable way, making us look towards a brighter future. 

Do you think other materials could also make 3D printing of concrete more sustainable and durable? If so, which ones do you have in mind? Tell us in the comments!

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