Al-tobermorite, long known to give Roman concrete its strength, can be made in the lab, but it’s very difficult to incorporate it in concrete. But the researchers found that when seawater percolates through a cement matrix, it reacts with volcanic ash and crystals to form Al-tobermorite and a porous mineral called phillipsite, they write today in American Mineralogist. So will you be seeing stronger piers and breakwaters anytime soon? Because both minerals take centuries to strengthen concrete, modern scientists are still working on recreating a modern version of Roman cement.
It's the reaction that occurs between the lime and the volcanic material that produces the stronger concrete, the researchers found. As the concrete hardened, strätlingite crystals formed in spaces around the sand and the volcanic gravel, making the structure stronger.
Can we do the same? Apparently some varieties of fly ash have similar composition to volcanic ash. Maybe the Three Gorges Dam will luck out.