2,000 years after it was installed, some Roman concrete is still holding strong. Why? That is the question that an international team of experts has answered through the study of the Pozzuoli Bay breakwater, at the northern tip of the Bay of Naples. The History Channel (History.com) has the story.
The team used the resources of U.C. Berkeley, as well as facilities in Saudi Arabia and Germany, to study the composition of concrete used for Roman underwater structures and found that the secret of the material was the use of volcanic ash. When mixed with lime, the volcanic materials "triggered a chemical reaction, through which water molecules hydrated the lime and reacted with the ash to cement everything together. The resulting calcium-aluminum-silicate-hydrate (C-A-S-H) bond is exceptionally strong."