Silica fume as a radon retardant from concrete

Radon is a radioactive gas that can be generated from concrete. Its concentration is enhanced in indoor environments, and tracheobronchial deposition of radon progeny can lead to lung cancers. Aggregates (granite) are known to be the radon source in concrete. Recently, silica fume is introduced as a partial substitution in Portland cement to produce high- strength concrete, it can set in the aggregate-cement paste interface and lower the porosity in the interface zone. It can also effectively fill up the voids between cement grains, which suggests its ability to retard radon emission from concrete aggregates. In the present work, radon exhalation rates from concrete cubes with silica fume were measured using charcoal canisters and γ-spectroscopy and were considerably smaller (by ~ 4 mBq m^{- 2} s^-1) than those from normal concrete (~ 9 mBq m^-2 s^-1). The indoor radon concentration reduction is estimated as ~17 Bq m^-3 using a room model, while the radon dose reduction is ~ 1 mSv yr^-1. Therefore, silica fume is a simple material to reduce the indoor radon concentration and the radon dose.