Construction of radiation shielding wall with superheavy concrete

The energy 36 times as high as Co-60 gamma-ray can be obtained with the pulsed radiation emitted from the radiation-generating apparatus in the Industrial Science Research Institute, Osaka University. The wall to shield this radiation requires about 5 m thickness when ordinary concrete (specific gravity 2.3) is used, but it must be limited to 2.5 m due to the surrounding conditions. In order to obtain the required shielding effect with this thickness, the specific weight of concrete must be increased to 3.5 t/m3. This specific weight is the largest so far, and can be obtained with fine and coarse aggregates of specific gravity more than 4.5. In case of the construction with this heavy concrete, pumping method was adopted to raise the work efficiency and to prevent the formation of cold joints. As the fine aggregate, magnetite from Yoshino Mine was selected, and as the coarse aggregate, magnetite from Kamaishi Mine was decided. The mixing ratio of heavy concrete was as follows: cement 314, water 182, fine aggregate 1383, and coarse aggregate 1777 kg/m3. The quality control for heavy concrete and the construction works for the shielding wall with 420 m3 volume are explained. Prior to the construction, various physical properties of heavy concrete were tested. During the solidification of heavy concrete, temperature was measured. (Kako, I.)