Expansive cement compositions and novel expansion agents containing free lime for use in such compositions. The expansion agents are prepared by heating lime of particle size less than 250 microns in an atmosphere comprising water vapor at 100.degree. to 400.degree. C. or carbon dioxide at 350.degree. to 850.degree. C., or by heating a partially hydrated lime at a temperature of at least 100.degree. C. The encapsulated limes produced in this way are useful as expansion agents in hydratable cement compositions, the amount thereof generally being less than 30%, preferably 3 to 10%, based on the weight of the cement and additive. Cement compositions containing the novel expansion agents are useful in a wide variety of uses where shrinkage of the composition on drying has to be prevented or reduced.