The new paradigm of 3D-printed concrete could revolutionize the construction industry because it could be used to produce new shapes and forms that are difficult to accomplish with current technology, and it could change centuries-old processes and procedures that are still used to construct buildings, thereby reducing costs and saving time.

However, concrete has a significant impact on the environment. At present, a large amount of natural sand is used to meet the world's urgent demand for concrete, which causes great damage to the environment. Overall, the construction industry is struggling to achieve sustainability, as it accounts for about 35% of all landfills worldwide.

On March 10, 2022, Antarctic Bears learned that foreign researchers have proposed a way to mitigate this effect. They are said to have experimented with using recycled glass as an ingredient in 3D-printed concrete.

Concrete is a mixture of cement, water and an aggregate such as sand. The researchers tried replacing up to 100 percent of the aggregate in the mix with glass. Simply put, glass is produced from sand, is easily recycled, and can be used to make concrete without any complicated processing.

Demand from the construction industry can also help ensure that glass is recycled. In the U.S. in 2018, only a quarter of all glass was recycled, and more than half went to landfills.

The researchers used brown soda-lime drink glass obtained from a local recycling company. The glass bottles are first crushed with a shredder, then the crushed pieces are washed, dried, ground and sieved to produce particles less than a millimeter square.

The shattered glass is then used to make concrete, just like sand. This concrete is used to 3D print wall modules and prefabricated building blocks, which can be installed together to form a complete building.

Grey concrete structure, prefabricated building envelope using 3D printing process. Mehdi Chougan provide

Through secondary crushing and incorporation of concrete, waste glass can become a part of the building material to play a new role. The presence of glass not only solves the waste recycling problem, but also helps to develop superior properties over concrete containing natural sand.

Sodium-calcium glass - the most common type of glass, which you can find in Windows and bottles, conducts heat more than three times less than quartz aggregate, which is widely used in concrete. This means that concrete containing recycled glass has better insulation properties. They can greatly reduce the cost of cooling or heating in summer or winter.

Improve the sustainability of building materials

In addition, the researchers made other changes to the concrete mixture to make it more sustainable as a building material, including replacing some of the Portland cement with limestone powder.

Portland cement is a key component of concrete that is used to combine the other components together to form a mixture that can harden. However, the production of ordinary Portland cement results in the release of large amounts of carbon dioxide and other greenhouse gases. The cement industry is known to produce about 8% of all carbon dioxide emissions in the environment.

Compared to Portland cement, limestone is less hazardous in its production process and has less impact on the environment. It can be used instead of regular Portland cement in 3D-printed concrete without degrading the quality of the printed mixture.

3D printed wall layer. Mehdi Chougan provide

The researchers also added lightweight fillers, made from tiny hollow thermoplastic spheres, to the printing material to reduce the density of the concrete. This changes the thermal conductivity of the concrete, which is reduced by 40% compared to other concrete used for 3D printing. This further improves the insulation properties of the concrete and reduces the amount of raw material required.

Using 3D printing technology, it is easy to develop a wall structure on a computer, convert it into simple code, and send it to a 3D printer to be built. The 3D printer can run 24 hours a day, reducing the amount of waste produced while also improving safety for construction workers.

Using waste glass as a raw material for concrete printing shows that ultra-lightweight, well-insulated 3D buildings are possible and could be an important step towards the goal of net zero emissions.