5 ms·

I just did a guesstimate: Combustion concentrates radioactivity by a factor of 5x to 10x [1]. Fly ash can replace 25-50% of cement [2]. A typical concrete is

by femto 9y ago

I just did a guesstimate: Combustion concentrates radioactivity by a factor of 5x to 10x [1]. Fly ash can replace 25-50% of cement [2]. A typical concrete is 16% cement (1 part cement, 2 parts sand and 3 parts gravel) [3]. Hence a concrete might be 4%-8% fly ash. If the ratio of fly ash is 'A', the concentrating caused by combustion is 'C' and the background radiation of other concrete ingredients is uniformly taken to be 'B', then the radiation count of concrete without fly ash will be: B and the radiation count of concrete with fly ash will be A.C.B + (1-A).B Plugging in values for A (0.04 to 0.08) and C (5 to 10), we find that fly ash increases the radiation from concrete by a factor of 20% to 70%. That strikes me as a significant proportion of the radiation from concrete. [1] https://phys.org/news/2015-09-radioactive-contaminants-coal-ash.html https://phys.org/news/2015-09-radioactive-contaminants-coal-... [2] http://www.theconcreteproducer.com/how-to/concrete-production/whats-the-allowable-fly-ash-limit_o http://www.theconcreteproducer.com/how-to/concrete-productio... [3] http://www.cementaustralia.com.au/wps/wcm/connect/website/packaged-products/home/hints-and-tips/FAQ-Working-with-Concrete/ http://www.cementaustralia.com.au/wps/wcm/connect/website/pa...

pmiller2 9y ago
But how radioactive is concrete compared to a similar volume of bananas? I would like to know this, but I'm on my phone at the moment. :)
- femto 9y ago
  An interesting question! Typical banana dose: 0.1 μSv per banana [1]. Typical concrete building dose: 100μSv per year [2] ie. 1 year in a concrete building = eating 3 bananas a day. I'm not claiming that fly ash laden concrete is going to kill anyone, but I think it's interesting that (given my assumptions) the concentrating effects of coal combustion are causing a decent proportion of concrete's radioactivity (even if the total is still negligible). [1] https://en.wikipedia.org/wiki/Banana_equivalent_dose https://en.wikipedia.org/wiki/Banana_equivalent_dose [2] https://www.euronuclear.org/info/encyclopedia/r/radiation-exposure-building-mat.htm https://www.euronuclear.org/info/encyclopedia/r/radiation-ex...
  - jballanc 9y ago
    My understanding is that more than direct exposure to radioactive materials in fly ash, the real risk is Radon. As Thorium and Uranium decay they will produce Radon, which can accumulate especially in low-lying areas with poor ventilation (e.g. basements, which tend to rely on concrete as a key building material). Since Radon can be inhaled, it has the potential to cause far more harm than anything "baked into" the concrete itself.
  - simonh 9y ago
    > I'm not claiming that fly ash laden concrete is going to kill anyone... That's the thing though, these low 'safe' levels of radiation do actually kill people. Every now and then somewhere, someone will be hit by a radioactive emission from Fly Ash that happens to hit one of their chromosomes and trigger cancer. If Fly Ash increases cancer cases in a year by x% then we can be pretty sure that x% of cancer patients were victims of Fly Ash, it's just that x is actually fairly small and we just don't know which ones they are. But they still have cancer.
    - ageofwant 9y ago
      If you can absolutely correlate the cancer to the presence of fly ash then yes. But that is going to be rather hard. How do you normalize for other equally chromosome-destroying environmental factors? Maybe drinking two cans of Coke a year less gives you exactly the same level of risk than someone living in a fly-ash free building?
    - wycx 9y ago
      You should probably compare the U content of fly ash with the rocks around you for some context. The average U content of the upper continental crust is between 2 and 3 ppm. Individual rocks will range lower and higher than that. If fly ash is only 4 ppm U, you have more to worry about from living on granitic rocks, or near a swamp than you do from fly ash. More context: if you live on the Chattanooga shale it has an average U content of 30-120 ppm. The extensive Alum Shale (runs the length of Sweden) has U contents of 100-300 ppm. Granites will have low-mid 10s of ppm U and Th. The report [1] linked in a comment above makes the comment Fly ash is commonly used as an additive to concrete building products, but the radioactivity of typical fly ash is not significantly different from that of more conventional concrete additives or other build-ing materials such as granite or red brick. One extreme calculation that assumed high proportions of fly-ash-rich concrete in a residence suggested a dose enhancement, compared to normal concrete, of 3 percent of the natural environmental radiation. [1] https://pubs.usgs.gov/fs/1997/fs163-97/FS-163-97.html https://pubs.usgs.gov/fs/1997/fs163-97/FS-163-97.html

by femto 9y ago

pmiller2 9y ago

But how radioactive is concrete compared to a similar volume of bananas? I would like to know this, but I'm on my phone at the moment. :)

femto 9y ago
An interesting question! Typical banana dose: 0.1 μSv per banana [1]. Typical concrete building dose: 100μSv per year [2] ie. 1 year in a concrete building = eating 3 bananas a day. I'm not claiming that fly ash laden concrete is going to kill anyone, but I think it's interesting that (given my assumptions) the concentrating effects of coal combustion are causing a decent proportion of concrete's radioactivity (even if the total is still negligible). [1] https://en.wikipedia.org/wiki/Banana_equivalent_dose https://en.wikipedia.org/wiki/Banana_equivalent_dose [2] https://www.euronuclear.org/info/encyclopedia/r/radiation-exposure-building-mat.htm https://www.euronuclear.org/info/encyclopedia/r/radiation-ex...
- jballanc 9y ago
  My understanding is that more than direct exposure to radioactive materials in fly ash, the real risk is Radon. As Thorium and Uranium decay they will produce Radon, which can accumulate especially in low-lying areas with poor ventilation (e.g. basements, which tend to rely on concrete as a key building material). Since Radon can be inhaled, it has the potential to cause far more harm than anything "baked into" the concrete itself.
- simonh 9y ago
  > I'm not claiming that fly ash laden concrete is going to kill anyone... That's the thing though, these low 'safe' levels of radiation do actually kill people. Every now and then somewhere, someone will be hit by a radioactive emission from Fly Ash that happens to hit one of their chromosomes and trigger cancer. If Fly Ash increases cancer cases in a year by x% then we can be pretty sure that x% of cancer patients were victims of Fly Ash, it's just that x is actually fairly small and we just don't know which ones they are. But they still have cancer.
  - ageofwant 9y ago
    If you can absolutely correlate the cancer to the presence of fly ash then yes. But that is going to be rather hard. How do you normalize for other equally chromosome-destroying environmental factors? Maybe drinking two cans of Coke a year less gives you exactly the same level of risk than someone living in a fly-ash free building?
  - wycx 9y ago
    You should probably compare the U content of fly ash with the rocks around you for some context. The average U content of the upper continental crust is between 2 and 3 ppm. Individual rocks will range lower and higher than that. If fly ash is only 4 ppm U, you have more to worry about from living on granitic rocks, or near a swamp than you do from fly ash. More context: if you live on the Chattanooga shale it has an average U content of 30-120 ppm. The extensive Alum Shale (runs the length of Sweden) has U contents of 100-300 ppm. Granites will have low-mid 10s of ppm U and Th. The report [1] linked in a comment above makes the comment Fly ash is commonly used as an additive to concrete building products, but the radioactivity of typical fly ash is not significantly different from that of more conventional concrete additives or other build-ing materials such as granite or red brick. One extreme calculation that assumed high proportions of fly-ash-rich concrete in a residence suggested a dose enhancement, compared to normal concrete, of 3 percent of the natural environmental radiation. [1] https://pubs.usgs.gov/fs/1997/fs163-97/FS-163-97.html https://pubs.usgs.gov/fs/1997/fs163-97/FS-163-97.html