This work describes a material that has improved mechanical and reactivity properties for use in thermochemical energy storage systems based on CaO/Ca(OH)(2) reversible reactions. The composite material uses sodium silicate as a binder of active CaO particles. The observed mechanical stability of the material is due to the formation of hard Ca silicates resulting from the reaction of the binder with the exterior of the CaO particles. A screening of the main synthesis variables affecting the composite was carried out, including Ca precursors of different particle size, a range of molar Ca/Si ratios, as well as the curing and calcination conditions. The most suitable material (containing CaCO3 with a particle size of 36-63 mu m as calcium precursor and a molar Ca/Si ratio of 4.8-6.2, calcined in air at 850 degrees C) was tested over many hydration/dehydration cycles (up to 500) in a thermogravimetric apparatus. The material sustained high molar hydration conversions (between 0.6 and 0.7) and crushing strength values of >2 N after 200 cycles, when dehydrated in pure steam.