Natural radioactivity of Australian fly ashes

In Australia over 5.4 x 106t of fly ash is generated annually, of which about 9% is used at present, mainly in pre-mixed concrete but also in the manufacture of blended fly-ash cement and as a filler in asphalt. The mean gamma-ray activity (radium equivalent activity, Rasub(eq)) of samples examined from the ten major power stations was 300 Bq/kg, which is below the proposed acceptable limit of 370 Bq/kg for building materials. However, large variations from 10 to 570 Bq/kg were measured in the activities of ashes from various locations. Since fly ash constitutes only about 4 to 5% by weight of concrete, the contribution of the ash to the total gamma-ray activity of concrete is relatively small. It may be appropriate, however, to monitor the radioactivity level of fly ash used for the manufacture of aerated concrete, bricks, blocks and similar products consisting mainly of fly ash. (author)