Is Portland cement considered to be hydraulic? (cement that cures underwater)

Question

Some say it is, some say it isn't. I'm wanting to create a vaulted tunnel below grade and I need it to be able to resist the standard tendency for cement fines to wash away in wet conditions.

Answer 1

Most construction cements today are hydraulic, and most of these are based on Portland cement, which is made primarily from limestone, certain clay minerals, and gypsum in a high temperature process that drives off carbon dioxide and chemically combines the primary ingredients into new compounds. Non-hydraulic cements include such materials as (non-hydraulic) lime and gypsum plasters, which must be kept dry in order to gain strength, and oxychloride cements, which have liquid components. Lime mortars, for example, "set" only by drying out, and gain strength only very slowly by absorption of carbon dioxide from the atmosphere to re-form calcium carbonate through carbonatation.