The effect of aging, humidity, and fly-ash additive on the radon exhalation from concrete

Radon exhalation rates of concrete samples have been periodically determined for 6-8 y after pouring the concrete. From the results, it can be concluded that the radon exhalation rate changes with the age of the concrete. The exhalation rate varies considerably in the first 6-12 mo after pouring with a factor of 1.5. After this period, the variation in exhalation rates is much less. Starting 1 y after pouring, the radon exhalation rate was decreased with increasing age of concrete to 0.3-0.6 of the maximum at the end of the observed period. Low humidity conditions dramatically reduce the radon exhalation rate of concrete. If 25% by volume of the cement is replaced by fly ash, the 226Ra concentration is elevated by a factor of 1.5. The radon exhalation rate of concrete made with Portland cement and fly ash was increased only slightly or even decreased, despite the higher 226Ra content. The results indicate that measurements of radon exhalation from samples of concrete have to be standardized on a certain humidity and age of the sample. Under certain conditions, the addition of fly ash to the concrete can reduce the radon exhalation.