<p>The use of alkaline waste in construction enables dual CO₂ removal, both through carbonation processes employed to enhance their properties as construction materials and by substituting them in cement production. However, despite their environmental benefits and demonstrated properties such as strength, water absorption, chemical reactivity, porosity, etc., these materials may contain natural radionuclides at elevated activity concentrations. Therefore, it is necessary to analyse these materials to ensure their safety from a radiological protection perspective for humans and the environment. The alkaline supplementary cementitious materials (SCMs) studied were a white steel slag (LFS), a biomass ash (BA), and a siliceous construction and demolition waste (CDW). This study presents the radiological characterisation via gamma spectrometry of the individual materials, hardened cement pastes fabricated with 80% ordinary Portland cement (OPC) and 20% of these alkaline SCMs, and ground hardened pastes. The alkaline residue BA exhibited high concentrations of ²¹⁰Pb and ⁴⁰K (around 5000&#xa0;Bq&#xa0;kg⁻¹), both with and without accelerated carbonation. However, the absorbed dose rates from external radiation of the final construction materials were lower than the natural background radiation level of 84 nGy h⁻¹. On the other hand, the emanation and exhalation rates of ²²²Rn, both in the individual materials and in the cement pastes containing 20% of the SCMs, were equivalent to those obtained with OPC cement.</p> Graphical abstract <p></p>