Mechanical properties of irradiated cement pastes for immobilization of evaporator concentrates

The effects of γ irradiation on the properties of concrete or cement composites have been investigated by several authors. However, the behaviour of composites immobilizing radioactive evaporator concentrates may be significantly affected by the altered chemistry of the matrix material. A newly proposed binder intended for the development of a composite immobilizing evaporator concentrates was investigated in terms of changes in its' mechanical properties due to gamma irradiation. Three kinds of cement pastes - a reference Portland cement paste (PC), a proposed binder as a mix of cements (NP) and a mixture 'NP' containing a model evaporator concentrate (NP_C) - were irradiated by gamma source Co-60 in two subsequent experiments differing in conditions - non-sealed (on air) and sealed (in a glass box). Surface cracks appeared on the NP and NP-C samples after the first irradiation experiment, i.e. in non-sealed conditions, due to drying effects supported by high ventilation in the irradiation chamber. In sealed conditions, some smaller surface cracks also appeared probably due to radiolysis of water present in the material, however they did not have any effects on the integrity of the internal structure of the pastes observed by non-destructive measurements. Compressive strength was enhanced by irradiation in all cases, only flexural strength decreased due to the presence of surface cracks. It should be noted that surface cracks appeared also on non-irradiated NP_C samples when left on air to dry. Therefore, further development of the cement composites will be focused on the elimination of any volume changes due to drying. (author)