pozzolana

[pot-suh-lah-nuh; Italian pawt-tsaw-lah-nah]

a porous variety of volcanic tuff or ash used in making hydraulic cement.

Also poz·zo·lan

[pot-suh-luh n] /ˈpɒt sə lən/, poz·zuo·la·na

[pot-swuh-lah-nuh; Italian pawt-tswaw-lah-nah] /ˌpɒt swəˈlɑ nə; Italian ˌpɔt tswɔˈlɑ nɑ/, puzzolan, puzzolana.

Origin of pozzolana

1905–10; < Italian < Latin puteolāna, feminine of puteolānus of Pozzuoli (< Latin Puteolī literally, little springs); see -an

Not only the walls but the vaults were built in this pozzolana concrete, and formed one solid mass.
Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 4
Various
This shows the utter unfitness of the pozzolana beds in which the arenaria are excavated for the construction of the Catacombs.
The Catacombs of Rome
William Henry Withrow