The results of activation studies of concrete ingredients for shielding structures of nuclear installations in the aspect of their decommissioning are given. It is shown that for the long-lived induced radioactivity of construction mineral materials irradiated for 30 years and cooled for more than one year such radionuclides as calcium, iron, cobalt, caesium and europium are responsible. Elemental content of the binding agent and raw material components for their production is obtained by neutron activation analysis. The results show that the type of the binding agent influences to a great extent the concrete shielding activity. The concentration of the above mentioned elements should be taken into account even at the stage of nuclear power plants design. It would allow one to make a prognosis on the volume and radioactivity of wastes as on the radioactivity effect felt by the staff engaged in the decommissioning.