The cities of the future could be 3D printed
3D printed concrete can lead to a change in architecture and construction. Because it can be used to produce new shapes and forms that current technologies struggle with, it can change age-old processes and procedures that are still used to construct buildings, resulting in cost reduction and time savings. .
3D printed layers of a wall element. Mehdi Chougan, Author provided
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, at great cost to the environment. In general, the construction industry struggles with sustainability. It creates about 35% of all landfill waste around the world.
Our new search offers a way to limit this impact. We tested the use of recycled glass as a component of concrete for 3D printing.
Concrete is made up of a mixture of cement, water and aggregates such as sand. We tried to replace up to 100% of the aggregates 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, with more than half go to the dump.
We used brown soda lime drink glass obtained from a local recycler. The glass bottles were first crushed using a crushing machine, then the crushed pieces were washed, dried, crushed and sieved. The resulting particles were smaller than one square millimeter.
The crushed glass was then used to make concrete in the same way that sand would be. We used this concrete to 3D print wall elements and prefabricated building blocks that could be assembled to form an entire building.
If used in this way, waste glass can find new life as a building material.
The presence of glass not only solves the problem of waste but also contributes to the development of a concrete with superior properties to that containing natural sand.
The thermal conductivity of soda lime glass – the most common type of glass, found in windows and bottles – is more than three times lower than that of quartz aggregate, which is widely used in concrete. This means that concrete containing recycled glass has better insulation properties. They could significantly reduce the costs required for cooling or heating in summer or winter.
A prefabricated building envelope using the 3D printing process. Mehdi Chougan, author provided
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 set. 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 the carbon dioxide emissions into the environment.
Limestone is less dangerous and has less impact on the environment during its production process than Portland cement. It can be used instead of regular Portland cement in concrete for 3D printing without loss of quality of the print 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, reduced by up to 40% compared to other concretes 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, convert it to 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 an ultra-lightweight, well-insulated 3D building is possible – something that could be a vital step in our mission to net zero.