Post by account_disabled on Feb 19, 2024 3:21:42 GMT -5
If you don't maintain modern concrete structures for a few decades, they will begin to break down. However, the structures built by the ancient Romans are still standing after 2,000 years. Now, MIT engineers have discovered a secret ingredient that helps Roman concrete self-heal, and they have shown how we can recreate the recipe to make our new buildings last longer.
Concrete is the most used construction material in the world , but it is not immortal. Weather and stress can cause small cracks, which can grow into much larger cracks that threaten the integrity of the entire structure. This may require costly maintenance or replacement to avoid catastrophic failure.
Instead, ancient Roman structures have stood the test of time for more than two millennia . To find out how this was possible, scientists have long been examining samples of the material in detail to study its composition and discover the ingredients that give it its resistance.
Pantheon Rome
Image: TTstudio – Depositphotos .
Pozzolanic material, made from volcanic Phone Number List ash from a specific region of Italy, features prominently. So does lime, and in previous studies it was found to help concrete become stronger over time in marine environments such as docks. One common inclusion, millimeter-sized chunks of white minerals called lime clasts, isn't usually counted as a byproduct, but in the new study, researchers found they might be there for a reason.
I have always been troubled by the idea that the presence of these lime clasts was simply attributed to poor quality control. If the Romans put so much effort into producing an exceptional building material, following all the detailed recipes that had been optimized over many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be something more to this story.
Admir Masic, lead author of the study.
The team used various imaging and chemical mapping techniques to inspect the lime clasts much more closely, and found that they were made of types of calcium carbonate, which appeared to have formed at high temperature. This suggests that they were made by directly adding (or "hot mixing") quicklime, a more reactive form of lime than the ancient Romans are supposed to have used.
Hot mixing has two advantages.
First, when concrete as a whole is heated to high temperatures, it allows for chemistry that would not be possible if only slaked lime were used, producing high temperature-associated compounds that would not otherwise form.
Secondly, this increase in temperature significantly reduces curing and setting times, as all reactions are accelerated, allowing for much faster construction.
Admir Masic
But most importantly, these lime clasts play an active role in the self-healing of concrete . The hot mixing process makes the inclusions brittle, so when small cracks form in the concrete, they move through the lime clasts more easily than the surrounding material. When water penetrates the cracks, it reacts with lime, forming a solution that hardens again into calcium carbonate and plugs the crack. It can also react with the pozzolanic material and further reinforce the concrete itself.
So rather than being an unwanted byproduct, these lime clasts are there for a reason, the team says. This self-healing mechanism may be an important factor in the longevity of ancient Roman concrete structures.
To test the hypothesis, the researchers made hot-mixed samples of ancient and modern concrete, cracked them, and made water flow through the cracks for long periods. After two weeks, the old concrete sample had healed its cracks, preventing the passage of water. In contrast, the modern material had not been repaired at all.
Concrete is the most used construction material in the world , but it is not immortal. Weather and stress can cause small cracks, which can grow into much larger cracks that threaten the integrity of the entire structure. This may require costly maintenance or replacement to avoid catastrophic failure.
Instead, ancient Roman structures have stood the test of time for more than two millennia . To find out how this was possible, scientists have long been examining samples of the material in detail to study its composition and discover the ingredients that give it its resistance.
Pantheon Rome
Image: TTstudio – Depositphotos .
Pozzolanic material, made from volcanic Phone Number List ash from a specific region of Italy, features prominently. So does lime, and in previous studies it was found to help concrete become stronger over time in marine environments such as docks. One common inclusion, millimeter-sized chunks of white minerals called lime clasts, isn't usually counted as a byproduct, but in the new study, researchers found they might be there for a reason.
I have always been troubled by the idea that the presence of these lime clasts was simply attributed to poor quality control. If the Romans put so much effort into producing an exceptional building material, following all the detailed recipes that had been optimized over many centuries, why would they put so little effort into ensuring the production of a well-mixed final product? There has to be something more to this story.
Admir Masic, lead author of the study.
The team used various imaging and chemical mapping techniques to inspect the lime clasts much more closely, and found that they were made of types of calcium carbonate, which appeared to have formed at high temperature. This suggests that they were made by directly adding (or "hot mixing") quicklime, a more reactive form of lime than the ancient Romans are supposed to have used.
Hot mixing has two advantages.
First, when concrete as a whole is heated to high temperatures, it allows for chemistry that would not be possible if only slaked lime were used, producing high temperature-associated compounds that would not otherwise form.
Secondly, this increase in temperature significantly reduces curing and setting times, as all reactions are accelerated, allowing for much faster construction.
Admir Masic
But most importantly, these lime clasts play an active role in the self-healing of concrete . The hot mixing process makes the inclusions brittle, so when small cracks form in the concrete, they move through the lime clasts more easily than the surrounding material. When water penetrates the cracks, it reacts with lime, forming a solution that hardens again into calcium carbonate and plugs the crack. It can also react with the pozzolanic material and further reinforce the concrete itself.
So rather than being an unwanted byproduct, these lime clasts are there for a reason, the team says. This self-healing mechanism may be an important factor in the longevity of ancient Roman concrete structures.
To test the hypothesis, the researchers made hot-mixed samples of ancient and modern concrete, cracked them, and made water flow through the cracks for long periods. After two weeks, the old concrete sample had healed its cracks, preventing the passage of water. In contrast, the modern material had not been repaired at all.