expansive cement[ek′span·siv si′ment]
the generic name for a class of cements that increase in volume during hardening. In most such cements, the expansion is due to the formation of highly basic calcium sulfoaluminate hydrates in the hydrating binder. The volume of these calcium compounds is 1.5 to 2.5 times greater than the volume of the initial solid components as a result of a large quantity of chemically bonded water. The total expansion ranges between 0.2 and 2 percent; the strength ranges between 30 and 50 meganewtons/m2.
In the USSR, the most widely used types are waterproof expansive cement, expansive portland cement, gypsum-alumina expansive cement, and stressing cement. All expansive cements harden best and exhibit the greatest expansion in the presence of moisture. Since they are highly waterproof, expansive cements are used for sealing joints between prefabricated rein-forced-concrete structural members, for reliable waterproofing in certain hydraulic engineering structures, and for manufacturing of reinforced concrete pressure pipes.