Pozzolans, Pompeii, Naples, Thera, Santorini, Lost Atlantis, and Sophia Loren

摘要

We would have put solid admixtures into the title, too, but the romance and mystery would have been lost. Pozzolans can be considered admixtures, but so can many other materials. Pozzolans are substances that, under the usual definition, react with calcium hydroxide (Ca(OH_2)), a major Portland cement hydratjon product that occupies about 25% of the cement paste. The pozzolanic reaction converts this largely non- or very low-strength-producing compound into one providing useful properties. Pozzolans usually serve three purposes: (1) they increase strength and decrease permeability; (2) their use makes concrete a patriotic material because it serves as a useful "dump" for waste products; and (3) they provide an economic advantage by lowering concrete costs (because they are cheaper than portland cement).