The contribution of fly ash toward indoor radon pollution from concrete

Owing to concerns about radon exposure, there is a need for understanding risk associated with fly ash in concrete. Monte Carlo simulations were applied, based on the radium specific activity of concrete constituents taken from the literature, to predict probabilities for the radium specific activity and radon exhalation rate. The model was then used to predict the indoor radon concentrations and effective annual doses from two different slab-on-grade concrete floors, one with and one without fly ash, in a typical single-family home in the United States. Due to uncertainty in the literature-reported values, a sensitivity analysis was conducted varying the emanation fraction of the fly ash concrete floors. The results show that concrete floors made without fly ash and a 5% emanation fraction, resulted in 90% of the simulated homes having an indoor radon concentration of less than or equal to 2.3 Bq m−3 and an associated annual dose of less than or equal to 54 μSv y−1. This annual dose represents 4% of the total annual background inhalation dose. A 25wt% fly ash concrete with an emanation fraction of 3% achieved the same exposure probability, but higher assumed emanation fractions raised the exposure probability. In general, the predicted radon exposure from fly ash concrete suggests minimal population health effects. But, given the serious health effects of radon exposure the influence of fly ash on the emanation fraction and radioactive pollution indoors deserves further exploration.

► Fly ash specific activity is, on average, eight times higher than cement.
► Other concrete constituents can also contribute greatly to exhalation rate.
►  Radon emanation from fly ash concrete represents a small fraction of total dose.