The recommended levels of ionizing radiation from construction materials in effective dose is set to a maximum of 1 mSv/year, EC (1996, 1999, 2013), ICRP (2007), IAEA (2011). By using a theoretical model proposed by the European Union (1999), this is equivalent to I-index 1. By using of concrete slabs with dimensions of 1.5 m × 1.5 m × 0.15 m, an empirical approach is suggested for the calculation of the I-index of naturally occurring ionizing radiation from construction materials. Measurements of 40K, 226Ra, 232Th and the total gamma radiation were conducted and the I-index values were calculated for each concrete mix. A good linear relationship could be established between measurements performed by the Swedish Cement and Research Institute (CBI) and the laboratory results acquired from the Radiation and Nuclear Safety Authority of Finland (STUK) and Centre de Recherches Pétrographique et Géochimiques/ Le Centre National de la Recherche Scientifique (CRPG/CNRS). The results indicate that 60 % of the investigated construction materials are in agreement with the stipulated levels set out by the EC (1999, 2013). The cause for the higher levels of ionizing radiation is often elevated concentrations of all the radioactive elements measured. Regarding the concrete samples yielding values of I-index > 1, 232Th makes the largest contribution.

The reference level for effective dose due to gamma radiation from building materials and constructionproducts used for dwellings is set to 1 mSv per year (EC, 1996, 1999), (CE, 2014). Given the specificconditions presented by the EC in report 112 (1999) considering building and construction materials, anI-index of 1 may generate an effective dose of 1 mSv per year. This paper presents a comparison of theactivity concentrations of 40K, 226Ra and 232Th of aggregates and when these aggregates constitute a partof concrete. The activity concentration assessment tool for building and construction materials, the Iindex,introduced by the EC in 1996, is used in the comparison. A comparison of the I-indices values arealso made with a recently presented dose model by Hoffman (2014), where density variations of theconstruction material and thickness of the construction walls within the building are considered. Therewas a ~16e19% lower activity index in concretes than in the corresponding aggregates. The model byHoffman further implies that the differences between the I-indices of aggregates and the concretes' finaleffective doses are even larger. The difference is due, mainly to a dilution effect of the added cement withlow levels of natural radioisotopes, but also to a different and slightly higher subtracted backgroundvalue (terrestrial value) used in the modeled calculation of the revised I-index by Hoffman (2014). Onlyvery minimal contributions to the annual dose could be related to the water and additives used, due tot heir very low content of radionuclides reported.