Naturally occurring radioactivity in some Swedish concretes and their constituents – Assessment by using I-index and dose-model

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Highlights

  • In line with RP 112 and suggested dose models of the EC.

  • Assessment of the I-index and dose model by investigating different constituents.

  • Input of cement yields 16–19% lower I-index of concretes compared to aggregates.

  • I-index of 1 for aggregates yield ∼0.65 in mSv per year in effective dose for concretes.

Abstract

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, EC, 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 40K, 226Ra and 232Th 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.

Section snippets

European regulations and directives

The European Commission (2014) recently declared, through the implementation of the EU's Basic Safety Standard (BSS), a reference level for dose from gamma radiation in building materials from the natural radioisotopes 40K, 226Ra (238U) and 232Th. The Construction Product Regulation, CPR (CE, 2011) views the building materials as construction products, including materials such as concrete. Hence, a construction product can have several constituents of different building materials. It is also

Laboratory gamma spectrometric analyses (STUK)

The methodology to compare different products, such as aggregates, cement and concrete was based on the laboratory analytical procedure described in Draft TS 00351014 (2012), using gamma-spectrometry to analyze activity concentrations of naturally occurring radionuclides. The Swedish Cement and Concrete Research Institute (CBI) has consulted the Radiation and Nuclear Safety Authority of Finland (STUK) that uses this methodology (Klemola et al., 2010) as an accredited test method.

The gamma

Results

Table 2 shows the gamma spectrometric analyses for the aggregates, water, additive, cement and concrete. The thickness of the concrete castings and the density of the aggregates are also included in the Table. The type of method is indicated in the “sample type” column, where A = crushed aggregate, A-S=Aggregate, natural sand, Amix = 2–3 aggregate particle size fractions combined according to the recipe and sent for analysis, Aw = mean value (wt%), calculated by CBI from single aggregate

Analysis and discussion

The approach of the paper was to emphasize the differences in radiation dose between a construction/building material (concrete) and its constituents (e.g. aggregate). There are, however, some uncertainties that need to be addressed. Sample four (Id-number 4) showed a significantly higher thorium content as part of the concrete samples, than in the aggregates (Table 2, Fig. 1). The concrete samples analyses were repeated three times for the concrete specimen of 150 mm and twice for the concrete

Concluding remarks

Aggregates used in concrete and the concrete containing the aggregates were empirically examined by laboratory gamma ray spectrometry. The calculated R2-values of the regression analysis of Fig. 1, Fig. 2, excluding sample 4, yield R2-values >0.95, are interpreted as trustworthy correlations in the linear regression models.

Calculations of I-indices of the aggregates and their respective concrete mix show an overall approximate decrease of the gamma radiation by 16–19%, when the aggregate is

Acknowledgments

Special thanks to the Swedish Consortium for Financing Fundamental Research in the Concrete Area, who has partly funded and supported the research and the project using empirical data. Specially thanks also to some native English speaking colleagues at Borås, who have assisted in the first critical review of the document in English with great patience. Finally, the authors wish to express their utmost appreciations to the colleagues at CBI Borås, who have contributed with strong efforts to cast

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