The hydration reaction of high-alumina cement (HAC) at a temperature of 20-degrees-C and a water/cement ratio of 0.5 has been studied over a period of one month. The changes of the solid phase were followed by X-ray diffraction and thermal analysis. Besides, pore-solution was expressed by application of high mechanical pressure (500 MPa) during different periods of the reaction in order to study its chemical composition evolution as a result of the hydration process.