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Definitions & History

Naturally obtained Hydraulic Cement

Hydraulic Cement: Around 1000 BC, the ancient Greeks were the first to learn the beneficial effects of mixing lime with fine volcanic ash (may be, as a result of some lucky accident).

Ash can be thought of as naturally calcined rock, having silicon in a chemically active state like the calcium in calcined limestone.

When this lime-ash mixture is slaked, a whole new substance viz. calcium silicate hydrate ( i.e C-S-H : approximately SiCa₂O₄ · xH₂O) is formed. C-S-H is an amorphous gel without any set crystalline structure. It hardens fast, even in water. And it is more durable than lime cement.

The ancient Greeks used this cement in a variety of ways. Some concrete cisterns built in that period survive to this day.

Later Greeks & Romans used volcanic ash & tuff mixed with lime & sand. Roman engineers mastered the technology and constructed seaports, aqueducts and temples of concrete as well. Some of these structures are as good as ever today, two thousand years later. The formula for Roman cement was not improved upon until the development of Portland cement in the early 1800s.

Some old Roman Structures
Foundations and columns of aqueducts	Arches of the Colosseum	Dome of the Pantheon