�y��vlog

In 1775 he discovered in the Velay a rich deposit of pozzuolana, which in due course was worked by the government.

Hydraulic Cements.—It was well known to builders in the earliest historic times that certain limes would, when set, resist the action of water, i.e. were hydraulic; it was also known that this property could be conferred on ordinary lime by admixture of silicious materials such as pozzuolana or tufa.

They are mostly of volcanic origin, and include pumice, tufa, santorin earth, trass and pozzuolana itself.

They are not usually manufactured by the careful grinding together of the pozzuolana and the lime, but are mixed roughly, a great excess of pozzuolana being employed.

When lime is used as a matrix, certain natural earths such as pozzuolana or trass, or, failing these, powdered bricks or tiles, may be used instead of sand with great advantage.