What is the secret behind those ancient Roman concrete buildings which are over 2,000-years-old and still hold up today, unlike our own modern buildings? Did the Romans create concrete differently than we do? Scientists have been amazed to discover that not only does their concrete hold up over time, but it actually becomes much stronger as time passes.
Scientists have finally answered the riddle as to why Roman buildings stand the test of time. The University of Utah has been researching the phenomenon of Roman concrete for many years now, with geologist Marie Jackson heading up their study. Thanks to many years of investigation, scientists have come up with a map of the old Roman concrete structure and now understand why it is so durable and apparently everlasting.
Our more modern concrete today is made out of a blend of portland cement, which is a combination of silica sand, clay, chalk, limestone, and other ingredients. These are all put together and then melted at scorching temperatures. As it turns out, the Romans created their own concrete in a much different way.
Romans made concrete with a mixture of lime, volcanic ash, and seawater. They were most likely aware of the chemical reaction present in volcanic ash deposits known as tuff rocks which were cemented naturally and would have used the volcanic ash to their advantage when constructing cement.
When looking at samples of Roman concrete, scientists used an electron microscope so that they could map the samples and then drilled into them with X-ray microdiffraction and Raman spectroscopy. By doing this, researchers were able to see all of the different mineral grains that were in the ancient concrete. Marie Jackson was especially surprised by the presence of aluminous tobermorite in the Roman cement, of which there is a lot of. This is a silica-based mineral which is reportedly both quite rare and also hard to create in a lab, as Science Alert note.
“We can go into the tiny natural laboratories in the concrete, map the minerals that are present, the succession of the crystals that occur, and their crystallographic properties. It’s been astounding what we’ve been able to find.”
The longevity of Roman cement. https://t.co/qmL6heo7yU
— Dr Sophie Hay (@pompei79) July 4, 2017
This explains why Roman concrete continues to thrive even in sea water since aluminous tobermorite, as well as the mineral phillipsite, start to grow in the concrete as a direct result of being battered by sea water.
“The Romans created a rock-like concrete that thrives in open chemical exchange with seawater.”
With the modern concrete of today, however, this does not occur. Our concrete erodes when the steel reinforcements rust and the compounds that hold the concrete together get washed away by the water. If we were able to create concrete today in the same way the Romans did, it would survive much longer if it was a structure near the sea.
The only thing scientists believe we can do today is to try and reverse engineer the manufacture of Roman concrete based on what we know about its chemical properties since we still do not have the exact recipe. Also, we don’t have the same access that the Romans had to volcanic materials, which plays a large part in the construction of their concrete.
“Romans were fortunate in the type of rock they had to work with. We don’t have those rocks in a lot of the world, so there would have to be substitutions made.”
While we may never be able to recreate the longevity of Roman concrete in our architecture today, reverse engineering the ancient Roman process of creating cement is something that we may be able to do in the future if we have the correct materials available.
[Featured Image by Hassan Ammar/AP Images]