Sunday, July 9, 2017

Did you hear about the Roman concrete?

This was one of those fascinating science news stories that just shows up every now and then.  The question that was being addressed was why seaside structures built by the ancient Romans (piers, jetties, harbor breakwaters, etc.) have lasted thousands of years, while modern concrete structures, presumably made with better "modern" construction methods, fall apart a lot faster.

Good question!

The answer, apparently, is in the recipe that the Romans used.  It leads to some fascinating chemistry.  They combined volcanic ash (available all around Italy), quicklime, volcanic rock -- and the key ingredient, seawater.  The dissolved ions in seawater fostered the growth of a crystal, aluminous tobermorite.  I have to admit, that's a new one for me.

The growth of the crystals strengthen the Roman concrete structures, and they continued to get stronger as the crystals grew.

Like I said, fascinating.

Why ancient Roman concrete lasts for millenia, but ours crumbles in decades (2017)

So you must be wondering what aluminous tobermorite looks like, right?  So was I, in fact.  So I have a picture below.  It comes from this article:  To improve today's concrete, do as the Romans did. (2013)

Now, I admit I was wondering why if they knew in 2013 that Al-tobermorite was what held the Roman concrete together, why there was another article in 2017 about it.  It looks like the researchers went a long way in four years in determining the reaction pathways (there's more than one) that lead to Al-tobermorite crystallization, rather than just knowing what the end product was.

If you want to get right to it, here's the 2017 article in American Mineralogist (it's also linked in the first article link I have above). Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete

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