New study unlocks the long-hidden secrets of ancient Roman concrete

Techniques used by Roman architects approximately 2,000 years ago could be used to create longer-lasting buildings and sea walls capable of withstanding the rising ocean levels expected due to global climate change, according to the authors of a newly-published study.

Writing in the latest edition of journal American Mineralogist, University of Utah geology and geophysics professor Marie Jackson and her colleagues revealed that they used X-ray technology to study samples of Roman concrete made from volcanic ash, baked limestone and seawater.

Their analysis revealed that the concrete contains tiny growing crystals which, according to the Washington Post, appears to interact with the environment to prevent the building material from fracturing. The concrete, they explained, undergoes a rare chemical reaction in which crystals of aluminous tobermorite grow out of a second mineral known as phillipsite.

Furthermore, the authors found that the driving force behind this reaction was seawater, which permeated through cracks in the concrete, reacted with phillipsite (a hydrated potassium, calcium and aluminum silicate) found in the volcanic rock used in the building material and caused it to become more durable.

“Contrary to the principles of modern cement-based concrete, the Romans created a rock-like concrete that thrives in open chemical exchange with seawater,” Jackson, lead author of the new study, said earlier this week in a statement. “This is a concrete that apparently grows aluminum-tobermorite mineral cements over millennia.”

Technique could be used to prevent damage from rising seas

Jackson and her colleagues used imaging equipment at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) to analyze concrete from an ancient harbors and breakwater sites, according to the Post. They hoped to discover the techniques used by Romans to create such long-lasting structures so that those methods could be replicated.

Roman concrete is “an extraordinarily rich material in terms of scientific possibility,” Philip Brune, a DuPont Pioneer scientist who has previously analyzed the engineering properties of Roman monuments but who was not involved in the new study, told the newspaper. “It’s the most durable building material in human history, and I say that as an engineer not prone to hyperbole.”

Jackson’s research, Brune added, is a “significant accomplishment” towards unlocking the secrets of this long-lasting construction material. The concrete, the researchers behind the new study said, behaves similarly to volcanic deposits found in underwater environments. Even more surprising, it appears to be stronger now than it was when it was originally building, indicating that the interactions with the seawater have increased the substance’s durability.

Currently, Jackson’s team is attempting to replicate the Romans’ results, but doing so has been challenging. As the study author explained to the Post, aluminous tobermorite is very difficult to produce, as extremely high temperatures are needed to synthesize small quantities. While Roman builders used a specific type of volcanic ash from an Italian quarry in their concrete, Jackson and her colleagues hope to replicate their results using volcanic rocks and California seawater.

They have already created several samples that are awaiting testing, the newspaper said, and if their efforts prove fruitful, they could lead to a material which could be used to build better sea walls in order to protect communities threatened by rising ocean levels. Unlike modern concrete, Roman concrete would grow stronger – not weaker – when exposed to ocean waves.

“[The research] opens up a completely new perspective on how concrete can be made – that what we consider corrosion processes can actually produce extremely beneficial mineral cement and lead to continued resilience, in fact, enhanced perhaps resilience over time,” Jackson told The Guardian. “ There are many applications but further work is needed to create those mixes. We’ve started but there is a lot of fine-tuning that needs to happen. The challenge is to develop methods that use common volcanic products.”


Image credit: J.P. Oleson