The second largest cause of lung cancer is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI) has examined three concrete recipes where only an additive as well as fly ash were added as single constituents to a reference recipe and compared to a reference concrete. The inputs of an additive as well as a supplementary cementitious material (fly ash) were made as a mean to investigate their potential influence on the radon exhalation rates of the concrete. Measurements were performed with an ATMOS 33 ionizing pulsation chamber for at least five different occasions for each recipe during a 22 month period. The results indicate a reduction of the exhalation rate by approximately 30-35 % for each altered recipe. This means roughly 1.5-2 mSv per year decrease in effective dose to a human using an additive or a supplementary cementitious material such as fly ash in relation to the investigated standard concrete.

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The reference level for effective dose due to gamma radiation from building materials and construction products used for dwellings is set to 1 mSv per year (EC, 1996, 1999), (CE, 2014). Given the specific conditions presented by the EC in report 112 (1999) considering building and construction materials, an I-index of 1 may generate an effective dose of 1 mSv per year. This paper presents a comparison of the activity concentrations of (4)(0)K, (226)Ra and (232)Th of aggregates and when these aggregates constitute a part of concrete. The activity concentration assessment tool for building and construction materials, the I-index, introduced by the EC in 1996, is used in the comparison. A comparison of the I-indices values are also made with a recently presented dose model by Hoffman (2014), where density variations of the construction material and thickness of the construction walls within the building are considered. There was a ∼16-19% lower activity index in concretes than in the corresponding aggregates. The model by Hoffman further implies that the differences between the I-indices of aggregates and the concretes' final effective doses are even larger. The difference is due, mainly to a dilution effect of the added cement with low levels of natural radioisotopes, but also to a different and slightly higher subtracted background value (terrestrial value) used in the modeled calculation of the revised I-index by Hoffman (2014). Only very minimal contributions to the annual dose could be related to the water and additives used, due to their very low content of radionuclides reported.

QC 20160926

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The second largest cause of lung cancer in the World is related to radon (222Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of 238U from its constituents. The Swedish Cement and Concrete Research Institute (CBI), part of RISE (Research Institute of Sweden AB), has examined the effects of cracks in concrete on two different concrete recipes where an Ordinary Portland Cement, OPC-CEM-I concrete (REF) and an OPC concrete including a hydrophobic additive (ADD) were addressed. Two concrete prisms from each concrete recipe were examined. The radon exhalation rate was measured in the pristine state and after concrete cracks had been induced into the concrete prisms. Measurements were performed with an ATMOS 33 ionizing pulsation chamber. The results indicate a strong influence of cracks on the radon exhalation rate. An increase in radon exhalation rate was calculated for every test prism. The increase in radon exhalation rate varied between 80 and 260 %. The crack apertures may play a significant role on the exhalation rate. The concrete prisms with the largest apertures (ADD) also generated the highest radon exhalation rates. The results imply that there could be a substantial variation in the exhalation rate, due to numerous factors, but nonetheless, the results should, raise the awareness of the impact cracks in concrete structures, may have on the final exhalation rate of radon. The exhalation rate of the recipe with an additive (ADD) also showed a lower exhalation rate than for the reference recipe (REF), when compared in a pristine state. This was in part expected. However, the effect of induced cracks and its aperture, seemingly trumps the effect that an additive may play on the radon exhalation rate, when cracks are induced. The hypothesis is in part verified in view of the results of the prism for the ordinary Portland recipe (REF-prisms), were an increase of approximately 100 % would be expected due to the total surface increase. The results also indicate this. The major increase in the radon exhalation rate of the ordinary Portland recipe including an additive, implies however other factors, such as minor internal cracks, that may substantially contribute to the final exhalation rate.