This work describes the synthesis and hydration behavior of dicalcium silicates doped with manganese. The syntheses were performed using silica obtained from rice hull ash. The solids (SiO2, CaO and MnO) were weighed in stoichiometric proportions to prepare silicates having a ratio (Ca + Mn)/Si = 2. Insertion of manganese varied from I to 10% (mol). Solids were grounded and water was added rendering aqueous suspensions. The suspensions were sonicated for 60 min in an ultrasonic bath. After drying, the resulting solids were grounded and burned at 800 degrees C. The preparation of calcium silicates containing up to 10% of manganese oxide was observed. Hydration degree of a dicalcium silicate and calcium silicate containing 5% of manganese was determined by thermal analysis. Both materials present similar behavior. Hydration degree reaches approximately 70% after 60 days. (c) 2007 Elsevier B.V. All rights reserved.