Radiological Aspects in the Evaluation of Portland Cements with Fine Aggregate Additions

The incorporation of recycled concrete fines (F), limestone (L), and ground granulated blast-furnace slag (S) as Portland cement constituents in accordance with EN 197-6 requires the determination of naturally occurring radionuclides to ensure radiological safety from a radiation protection standpoint. This study carried out a radiological assessment of eight cement types with varying proportions of L, F, and S additions, including anhydrous cements and mortars cured for 2 and 28 days. The activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were determined by gamma-ray spectrometry using HPGe detectors and radiochemical separation. In addition, the ²²²Rn emanation fractions were measured by the accumulation method using an AlphaGuard detector. Finally, annual effective doses were calculated using the RESRAD-BUILD software for a standard dwelling of 35 m² occupied by an adult and an infant. Among the individual materials, S exhibited the highest activity in the uranium decay series (113 ± 24 Bq kg^-1 of ²³⁸U), while L and F showed comparably lower values. Cements containing S additions (CEM II/C-M, CEM VI (S-L), and CEM VI (S-F)) were higher than the reference average value for building materials of 50 Bq kg^-1, although all mortars remained below this value. Principal component analysis revealed significant correlations between S content, SiO₂, Al₂O₃, and ²³²Th. The maximum annual effective dose reached 0.32 mSv for infants (CEM VI (S-L)), with the dose due to ²²²Rn inhalation being predominant. All cements studied are radiologically safe, confirming their suitability for use within the objectives of the circular economy.