MIT engineers discovered a new way to design 3D printed concrete

A team of MIT researchers may have discovered a new way to 3D print concrete that’s more efficient and uses less material. To understand why this is so important, let’s take a step back. Concrete is the second most used building material in the world, behind water. In the United States alone, approximately 260 million cubic meters are used and consumed each year. Worldwide, more than 4 billion tonnes are produced each year. But it is also one of the largest sources of carbon emissions, responsible for 8% of global CO2.₂ emissions due to the chemical process necessary for its manufacture and large-scale use. 3D printing has the potential to significantly reduce this impact, reducing its carbon footprint, because it is limited and efficient.

Rather than producing huge quantities of concrete and also generating a lot of waste, a printer precisely places the material to match a plan’s design. If you could, in theory, come up with strong designs while using fewer materials (think hollow or reinforced shapes rather than solid blocks or bricks), it would go a long way to alleviating the carbon footprint problem.

Unfortunately, the most efficient designs using less material are too complex for large-scale commercial printers. Thick nozzles are somewhat unruly when tracking complex designs, and the machines can’t make many turns or sudden movements: 3D prints must be completed in one continuous motion. A team of researchers from MIT may have the answer. In a new report published in Additive Manufacturing, the team describes a framework that factors a machine’s manufacturing limitations into designs.

Given the limitations of 3D printing with concrete, the goal was to create a framework that almost any large-scale printer can use, as efficiently as possible, and without requiring hand tooling or additional work. To demonstrate and test their idea, the team printed a functional 7.6-foot bridge using a design containing 14% less material than conventional methods and also providing a reduction in material weight of more than 76%. The demonstration bridge was produced in 30 minutes with commonly available materials, weighs approximately 900 pounds, but can support more than 2,000 pounds spread across it without tilting or bending.

Sharp angles and restricted movement were a key element in the development of the frame. The team took into account the thickness of the material balls, the turning radius of modern concrete printer nozzles and the need to print in single, contiguous sections. After a few adjustments, the result is something that can easily be modified and adjusted throughout the scope of a project to meet design needs or additional criteria. For example, just before printing, the team was able to reduce the size of the demo deck with its optimizations in just a few minutes.

In short, the team’s proposed framework helps identify the best and most efficient design that is mathematically possible given the constraints of the printer. They can apply it to almost any building design. Additionally, this method does not require the use of molds or other structural additions, meaning that in addition to using fewer materials overall, there is less work involved, even for larger prints.

After addressing the issue of efficiency and optimization, the team is now moving towards working with composite materials, or rather reinforced concrete. Pure concrete is rare in modern construction. Yes, concrete is a composite material made of aggregate (there are actually only four ingredients in an average concrete mix), but construction teams often use rebar and other reinforcement methods to add tensile strength and reduce breakage. Without these support options, concrete alone remains vulnerable to powerful forces: it is very fragile. The MIT team demonstrated this problem by lifting the test bridge from one corner, which broke easily. 3D printed concrete can be made more durable in different ways.

However, the team explains that integrating some of these methods into their framework, particularly the use of rebar, is quite difficult. But it would solve the problem of low compressive strength of pure concrete, making the design method and framework more viable for real-world applications. It may be some time before this mathematical solution is used for materials development. This is not the first time concrete has been improved. Previously, scientists developed a type of concrete that is 17 times more resistant to cracking than conventional formwork. On an ecological level, there is also a method using cardboard tubes and compacted earth which is more resistant than concrete.