Abstract: A hydraulic cement composition is disclosed which utilizes as part of an expansive component novel coated particles of high alumina cement. The particles have a core of substantially unhydrated high alumina cement and an outer layer of hydration products of the core, which outer layer delays the reaction of the particles with other materials in the composition. By varying the nature and relative amounts of the coated particles the amount the cement composition may expand and the setting time of the cement may be varied. The coated particles may be formed by partial hydration, drying and grinding of a mixture of high alumina cement powder alone with water.