MIT Engineers Discovered A New Way To Design 3D-Printed Concrete

A team of MIT researchers may have discovered a novel way to 3D print concrete that’s more effective and uses less material. To understand why that’s a big deal, let’s back up a little. Concrete is the second most widely used construction material in the world, beat out only by water. In the United States alone, about 260 million cubic yards is used, and consumed, per year. Globally, over 4 billion tons are produced each year. But it’s also one of the largest sources of carbon emissions, responsible for 8% of global CO₂ emissions thanks to the chemical process required for its manufacture and its sheer scale of use. 3D printing has the potential to significantly reduce that impact, lowering its carbon footprint, because it’s limited and efficient. 

Rather than making huge batches of concrete, and also generating a lot of waste, a printer precisely places the material to match the design of an blueprint. If you could, theoretically, come up with designs that are sound while using less of the material — think hollow or reinforced shapes versus solid blocks or bricks — that would go a long way towards mitigating the carbon footprint issue.

Unfortunately, most efficient designs using less material are too complex for large-scale commercial printers. The thick nozzles are somewhat unruly when following complicated designs and the machines cannot make a lot of turns or sharp movements — 3D prints have to be made in one continuous motion. A team of researchers from MIT may have just the answer. In a new report published in Additive Manufacturing, the team describes a framework that factors a machine’s fabrication limits into the designs. 

Given the limitations of 3D printing with concrete, the goal was to create a framework that nearly any large-scale printer can utilize, as efficiently as possible, and without requiring manual tooling or extra work. To demonstrate and test their idea, the team printed a working 7.6 foot bridge using a design that contains 14% less material than conventional methods and also offers a material weight reduction of over 76%.  The demo bridge was produced in 30 minutes with commonly accessible materials, weighs roughly 900 pounds, but can support over 2,000 pounds spread across it without bowing or bending.

The sharp angles and restricted movement were a key element of the framework’s development. The team took into account the thickness of the material beads, the turn radius of modern concrete printer nozzles, and the need to print in single contiguous sections. After some tweaking, 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 shrink the demo bridge’s size using their optimizations in a matter of minutes.

In short, the framework the team came up with helps identify the best and most efficient design that’s mathematically possible given the constraints of the printer. They can apply it to almost any build design. In addition, this method doesn’t require the use of molds or other structural add-ons, which means alongside using fewer materials overall, there’s less work involved even in larger prints.

Having tackled the efficiency and optimization problem, the team is now moving on to working with composite materials, or rather, reinforced concrete. Pure concrete is rare in modern construction. Yes, concrete is a composite material made of aggregates (there’s really only four ingredients in the average concrete mixture), but construction crews often use rebar and other reinforcement methods to add tensile strength and reduce breakages. Without these support options, concrete alone remains vulnerable to strong forces — it’s very brittle. The MIT team demonstrated this problem by lifting the test bridge from a corner, which easily broke. 3D printed concrete can be made more durable in various ways.

However, the team explains that working some of these methods into their framework, particularly the use of rebar, is quite challenging. But it would address the problem of pure concrete’s low compression strength, making the design method and framework more viable for real-world applications. It may be some time before we see this mathematical solution in use for material developments. This isn’t the first time concrete has been improved upon. Previously, scientists have come up with a type of concrete that’s 17 times more resistant to cracking than conventional forms. On the eco-friendly front, there’s also a method employing cardboard tubes and packed earth that turns out stronger than concrete.