Admir Masic is Professor of Civil and Environmental Engineering at the Massachusetts Institute of Technology in Cambridge, USA. He conducted his latest study with colleagues at Harvard University and laboratories in Italy and Switzerland. They discovered previously unknown production methods for concrete from antiquity, which are said to provide important self-healing properties for the building material.
Mr. Masic, Roman concrete buildings have endured for thousands of years. Why is Roman concrete so durable compared to the building materials we use today?
Ancient Roman concrete is a very special material that enabled the Romans to create an architectural revolution. Instead of carving stones and joining them with mortar, they could create “pseudo-stones” of desired shapes and sizes by pouring concrete. This was possible thanks to a special composition of the concrete that they had developed. This material is able to gain strength over time.
What was the special ingredient?
For a long time, researchers believed the key lay in one ingredient, a special form of volcanic ash from Italy. But we overlooked the role of so-called calcareous clasts, another key component. These inclusions are not just a passive ingredient. They have the ability to strengthen themselves over time and even increase in strength. Our work shows that these calcareous clasts are important. Second, we believe that the Romans used a technique to make their mortar that had not been thought of prior to this work, namely hot mixing. This enabled them to systematically incorporate lime clasts into the concrete and mortar mix. And that eventually leads to its self-healing function.
With the mentioned self-healing function, the enclosed lime lumps close the cracks and pores in the concrete that appear over time through a chemical process. Water penetrating the cracks dissolves calcium from the chunks, whereupon it reacts with other components and “cements” the gaps again. How can this Roman recipe help with today’s rebar concrete?
We’re not saying that we want to build with this technology so that a building lasts 2000 years. Today we build with reinforced concrete. But Roman concrete’s self-healing properties could help with current problems, e.g. B. by slowing down the spread of water through cracks in the concrete structure, which attacks the material. Normally the water penetrates slowly through the pores and when the crack reaches the rebar it corrodes. This could be prevented much better with a self-healing concrete.
Professor Admir Masic at work.
(Image: MIT)
Would you say that today’s concrete is worse? And that at some point we forgot the methods that the Romans already had?
I wouldn’t say he’s worse, but he’s different. First of all, the Romans built with a concrete that was unreinforced. They built differently because the load had to be distributed differently, so they used arches and domes, for example. Our methods, design and construction require walls and ceilings that need reinforcement. That’s an important difference.
Can better formulations help reduce concrete’s carbon footprint?
In any case. We believe that the future of concrete is multifunctional concrete, where different functions are incorporated into the material. A material that is not only particularly stable, but also self-healing, for example. And that saves emissions. Imagine a paradigm shift: from a concrete that pollutes the environment to a concrete that could even become a carbon sink. It’s a really difficult task because we produce so much of this material. And the time for the necessary radical changes is very short, because we don’t have a technical solution for about half of these emissions. If concrete buildings lasted longer, that would really be an advantage.
Is Roman concrete helpful for new construction techniques like 3D printing?
3D printing is definitely another paradigm shift in construction and it takes a significant effort, especially from a research perspective, to find the materials that are really suitable for this particular application. It opens up a whole new dimension of what we can do with a space while reducing emissions in manufacturing. We want to use less material and put the material exactly where it is needed to meet all requirements. The self-healing properties can also be very helpful. We are in talks with 3D printing companies who are very excited about our study because it could feed directly into their R&D strategies.
How long will commercialization take?
It is difficult to answer such a question as the industry is known to be very resistant to change. I mean, innovation in the concrete industry is a big challenge. That’s because of the cost structure: They make money because they produce a lot. And if a completely new procedure is introduced, e.g. B. the self-healing by bacteria, as recently suggested by colleagues from Delft, for example, it needs to be re-certified. The good thing about Roman technology is that it’s something that has been tried and tested for ages.
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