Opus Caementicium: stuck between a rock and another rock

 

No matter what site you’re visiting in Rome, you will almost certainly be surrounded by Roman concrete. This type of concrete is known as Opus Caementicium. Use of concrete began around 3rd century BCE and continues steadily throughout antiquity.

Ruins in which you can see the concrete core and the brick facing that hasn't survived in some spots. 

Image Credits: Alayna Krueger

It was popular for a few different reasons. One major advantage was the variability in how you could make the concrete. Roman concrete was made of three main ingredients: slaked lime, inert sand or a pozzolanic additive, and pieces of aggregate. Vitruvius even wrote about this concrete and how to make it, in 27-30 BCE.[1] By changing the type of aggregate that was mixed in, builders could control the density and weight of the concrete.[2] Having this type of control was beneficial because you could make really strong and dense walls but also ceilings that were light enough not to fall. It was also popular because the materials were readily available, Romans didn’t have to look far to find the materials they needed. 

An example of columns that were also made with concrete and stone facing.

Image Credits: Alayna Krueger

Many Roman walls consisted of concrete that was often faced with different types of stone, these walls kind of looked like a sandwich when you could see the concrete core and stone on each side. Sometimes, plaster was then added to the outside to create a more high end look. Although we didn’t get to see any so far, I would also love to see ancient Roman marine concrete, it repairs itself! Sadly, that’s a whole other can of worms that I don’t have time to dive into today.

---

[1] Elsen, Jan, Marie D. Jackson, and Encarnación Ruiz-Agudo. “Historic Concrete Science: Opus Caementicium to ‘Natural Cements.’” Elements 18, no. 5 (October 1, 2022): 301–7. doi: 10.2138/gselements.18.5.301.

[2] Ulrich, Roger B., and Caroline K. Quenemoen. A companion to roman architecture. Malden (Mass.): Wiley-Blackwell, 2013. 172.

Bibliography

Elsen, Jan, Marie D. Jackson, and Encarnación Ruiz-Agudo. “Historic Concrete Science: Opus Caementicium to ‘Natural Cements.’” Elements 18, no. 5 (October 1, 2022): 301–7. doi: 10.2138/gselements.18.5.301.

 

Ulrich, Roger B., and Caroline K. Quenemoen. A companion to roman architecture. Malden (Mass.): Wiley-Blackwell, 2013.