Seawater is the secret to long-lasting Roman concrete

[muriel_volestrangler]

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Modern concrete uses a paste of water and Portland cement, a fine powder made mostly of limestone and clay, to hold together small rocks. But it degrades within decades, especially in harsh marine environments. Instead of Portland cement, the Roman concrete used a mix of volcanic ash and lime to bind rock fragments. The Roman scholar Pliny the Elder described underwater concrete structures that become “a single stone mass, impregnable to the waves and every day stronger.” This piqued Jackson’s interest. “For me the question was, how does this material become a rock?” she says.

In earlier work, Jackson and colleagues reported some of the unusual chemistry of Roman concrete, such as the presence of a rare mineral known as aluminium tobermorite2. For the new study, the scientists took samples of Roman harbour concrete to the Advanced Light Source, an X-ray synchrotron at Lawrence Berkeley National Laboratory in Berkeley, California, and mapped out the location of minerals in the samples.

The researchers found a silicate mineral called phillipsite, which is common in volcanic rocks, with crystals of aluminium tobermorite growing from it. Tobermorite seems to have grown from the phillipsite when seawater washed through the concrete, turning it more alkaline. “It's a very rare occurrence in the Earth,” Jackson says. Such crystallization has only been seen in places such as the Surtsey volcano in Iceland. As tobermorite grows, it may strengthen the concrete because its long, plate-like crystals allow the material to flex rather than shatter when stressed.

Modern concrete-makers could learn from the ancient Romans’ knowledge, says Nele De Belie, a materials engineer at Ghent University in Belgium. She and her colleagues have used materials such as fly ash, produced during the burning of coal, to give concrete ‘self-healing’ properties, whereby the material closes up cracks after they form3. Fly ash is similar to the volcanic ash that Romans used in their mix.
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http://www.nature.com/news/seawater-is-the-secret-to-long-lasting-roman-concrete-1.22231

University of Utah write-up: https://unews.utah.edu/roman-concrete/

The paper: http://ammin.geoscienceworld.org/content/102/7/1435

[CentralMass]

1. Fascinating.

[JHan]

2. fascinating, thanks for sharing.

[brush]

3. So is it the sea water or the ash that turns it to stone?

[muriel_volestrangler]

4. The sea water, ash and lime - you need them all for this reaction (nt)

[BigmanPigman]

5. Ancient civilizations were so intelligent and advanced in so many areas. AMAZING!

I just wish more people would turn to history more often. A lot can be learned from them and perhaps we wouldn't make so many errors a couple of thousand years later.

[SCantiGOP]

6. fly ash

is a valuable waste product of coal-fired power plants. It is sold to cement manufacturers, who often locate their plants near power plants because of that.

[eppur_se_muova]

8. Typically contains toxic heavy metals, though. nt

[SCantiGOP]

9. Yep, you get the mercury for free

[flamingdem]

7. Romans rock(ed)