Alum shale concrete

In the past, it was thought that building materials were the principal sources of indoor radon (UNSCEAR, 1977). However, most recent studies have shown that with the exception of some unusual materials such as Swedish alum-shale concrete, the effect of building materials on indoor radon is small. 

There are obviously higher values in Scandinavia than in southern Europe and in many local areas such as Cornwall in the United Kingdom (Cliff et al., 1987) there are some substantially higher concentration areas. In Sweden there is a clear effect of alum shale concrete on indoor radon levels both from the perspective of increasing the concentrations indoors, but also because of an increased percentage of the population living in houses of such construction (Swedjemark et al., 1987). Thus, the largest fraction of people live in houses with radon concentrations below 110 Bq/nr. 

Another difference between the 1950s and the 1980s is that people now live in other types of houses. 70 % of the population lived in wooden houses in 1950 compared with 40 % today. 3 % lived in houses built of aerated concrete based on alum-shale, in 1950. In 1980 the figure was about 10 %. These differences are also an indication on an increased collective radon concentration during the period. 

All these comparisons support the hypothesis of an increase. The arithmetic means and thereby the collective doses seem to have increased by about a factor of four to six. If the aerated concrete based on alum-shale had not been used, the country-wide average has been estimated to be 30 % lower (Swedjemark 1985). 

Typical activities of building materials, such as bricks and concrete, in the UK and USA are in a similar range (20 to 50 Bq kg-1) (Nero, 1983), but granite used in older houses in Cornwall has about 100 Bq kg -1 of radium (O Riordan et al., 1982). In Sweden, Hultqvist (1956) found about 1000 Bq kg-1 radium equivalent gamma activity in lightweight concrete made from alum shale. 

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