NORM waste, cements, and concretes. A review

2.1. Types of radioactivity

Radioactivity is the result of spontaneous nuclide decay with the emission of radiation, i.e., α and β particles together normally in conjunction with electromagnetic waves in the form of γ-radiation and X-rays (1212. Kovler. K.; Fridman, H.; Michalik, B.; Schroeyers, W.; Tsapalov, A.; Antropov, S.; Bituh, T.; Nicolaides, D. (2017) Basic aspects of natural radioactivity. In Naturally Ocurring Radiactive Materials in Construction. Ed. W. Schroeyers. Elservier. Chapter 3. 13-16.
). In the International System the unit used to express radionuclide activity is the becquerel (Bq), equal to the activity of a quantity of a radionuclide spontaneously decaying at a rate of one nuclear transition per second. During decay, the so-called parent nuclide transitions to a different type of nucleus, known as the daughter, which may be a different chemical element or an isotope, depending on the type of decay. The energy emitted, either directly (α- or β-radiation) or indirectly (γ-radiation or X-rays) suffices to strip electrons off and thus ionising any atom in the path of radiation (1212. Kovler. K.; Fridman, H.; Michalik, B.; Schroeyers, W.; Tsapalov, A.; Antropov, S.; Bituh, T.; Nicolaides, D. (2017) Basic aspects of natural radioactivity. In Naturally Ocurring Radiactive Materials in Construction. Ed. W. Schroeyers. Elservier. Chapter 3. 13-16.
). A brief description of the above four types of radiation follows.

Alpha (α) radiation consists in α-particles containing 2 protons and 2 neutrons: i.e., it is identical to the nucleus of the He atom. Alpha particles are characterised by a relatively large mass and a positive elementary electrical charge of 2, an indication of low penetrating power. In biological tissues its path is no longer than a few tens of micrometres. Alpha radiation is ionising, generating more ions per unit length in the host matter than other types of radiation because the particles shed all their energy over a short distance. Alpha emitters induce primarily internal exposure via inhalation, ingestion or contact with the skin (1212. Kovler. K.; Fridman, H.; Michalik, B.; Schroeyers, W.; Tsapalov, A.; Antropov, S.; Bituh, T.; Nicolaides, D. (2017) Basic aspects of natural radioactivity. In Naturally Ocurring Radiactive Materials in Construction. Ed. W. Schroeyers. Elservier. Chapter 3. 13-16.
).

Beta (β) radiation comprises β-particles, either electrons with a negative elementary charge or, less commonly, positrons or particles with a positive elementary electrical charge equal to the electron’s negative charge. As an electron’s mass is about 8000 times smaller than α-particle mass, β-radiation has moderate penetrating power. Exposure to beta particles is more of an external and less of an internal radiation hazard than exposure to alpha particles. The external radiation attributable to beta particles is confined primarily to the epidermis or outer layers of skin, although it may also be harmful to the crystalline lens of the eye.

Gamma (γ) radiation consists in high-energy photons (electromagnetic waves) emitted by the nucleus. This type of radiation is only weakly ionising but has high penetrating power and can travel across hundreds of meters of air. Thick concrete or lead shielding is normally used as protection against γ-radiation, exposure to which primarily affects external body parts. Given the high penetrating power of gamma rays, the energy released in internal exposure is absorbed by a smaller volume of tissue than is impacted by alpha or beta radiation. Internal exposure to gamma radiation is therefore less of a health hazard than similar exposure to alpha or beta radiation.

X-rays are electromagnetic waves emitted from the atomic shell, normally carrying lower energy than γ-radiation.

Radiation can be classified from two perspectives: whether or not it is ionising and whether natural or artificial. Ionising radiation is electromagnetic or corpuscular. When interacting with matter it ionises its atoms, modifying the atomic structure of the host material and inducing chemical reactions. Non-ionising radiation, which lacks that capacity, generates electromagnetic fields and optical radiation (1313. Piedecausa García, B.; Chinchón Payá, S.; Morales, M.A.; Sanjuán Barbudo, M.A. (2011) Radiactividad natural de los materiales de construcción. Aplicación al hormigón. Parte II. Radiación interna: Gas radón. Cemento y Hormigón. 946, 34-50.
).

Natural radiation is the radiation present in the air, the Earth’s crust, outer space, foodstuffs and even inside animal and human bodies. Artificial radiation is generated by human activity, such as in the wake of nuclear explosions or accidents, industrial activity or medical testing. All exist in the environment and impact human beings and all other species. Humans receive both natural and artificial radiation in the mean yearly proportions illustrated in Figure 1.

2.2. Naturally occurring radioactive materials (NORM). NORM industries

As the name infers, naturally occurring radioactive materials (NORM) are radioactive materials of natural origin whose potential as a hazard in their unaltered state may be enhanced by human technological manipulation. Pastor et al. (1414. Pastor, A.; Dovorzhak, A.; Mora, J.C. (2016) Hacia un inventario español de industrias generadoras de residuos NORM. Radioprotección. 86, 28-32.
) define NORM waste (in Spain) as material for which the generator envisages no use and which exhibits a natural nuclide concentration higher than stipulated for exemption and clearence "exemption and clearanceas per Spanish Ministry of Industry, Energy and Tourism (IET) order 1946/2013 (1515. Orden IET/1946/2013, de 17 de octubre, por la que se regula la gestión de los residuos generados en las actividades que utilizan materiales que contienen radionucleidos naturales. 23 de octubre de 2013 (in spanish).
) (Table 1) (1414. Pastor, A.; Dovorzhak, A.; Mora, J.C. (2016) Hacia un inventario español de industrias generadoras de residuos NORM. Radioprotección. 86, 28-32.
). Such waste must therefore be managed bearing in mind both its nature as industrial residue and the characteristics intrinsic to NORM materials.

NORM waste may be generated by a number of industries, and most significantly those listed in Table 2 (1414. Pastor, A.; Dovorzhak, A.; Mora, J.C. (2016) Hacia un inventario español de industrias generadoras de residuos NORM. Radioprotección. 86, 28-32.
). Its management, the responsibility of the generators, entails determining the most suitable type of processing based on its radiological characterisation.

Granite is a naturally radioactive material used in building or as a component in concretes. It has a high activity concentration of certain natural radioactive series, including uranium, thorium, actinium and potassium (16-1816. Allam, M.E.; Bakhoum, E.S.; Gara, G.L.K. (2014) Re-use of granites sludge in producing Green concrete. ARPN. J. Eng. Appl. Sci. 9 [12], e2737. 2731-2737.
17. Condomines, M.; Hemond, C.; Allègre, C. (1988) UThRa radioactive disequilibria and magmatic processes. Earth Planet. Sci. Lett. 90 [3], 243-262.
18. Plant, J.A.; Saunders, A. D. (1996) The Radioactive Earth. Rad. Protec. Dosim. 68 [1-2], 25-36.
). A recent study conducted by the present authors (1919. Suárez-Navarro, J.A.; Alonso, M.M.; Gascó, C.; Pachón, A.; Carmona-Quiroga, P.M.; Argiz, C.; Sanjuán, M.A.; Puertas, F. (accepted 2021) Effect of particle size and composition of granitic sands on the radiological behavior of mortars. Bol. Soc. Esp. Cer. Vid. Available online 2 June 2021. https://doi.org/10.1016/j.bsecv.2021.05.001.
) showed that granite aggregate particle size distribution affects activity concentration, with smaller particle sizes inducing higher activity. This matter is discussed in greater depth in a subsequent section.

4.1. Coal-fired power plant fly ash and botton ash

Coal fly ash (FA) is a fine powder generated when coal is burnt to produce electricity, usually in coal-fired power plants. It consists primarily in non-combustible inorganic material but also contains some residual carbon sourced from partially non-combusted coal (5454. Argiz, C.; Menéndez, E.; Moragues, A.; Sanjuán, M.A. (2015) Fly ash characteristics of Spanish coal-fired power plants. Afinidad. 72 [572], 269-277. http://www.raco.cat/index.php/afinidad/article/view/305569/395407.
). Although fly ash particles are largely spherical, irregular or angular quartz or other grains are likewise often present in the ash. Coal fly ash is divided into two main groups: siliceous (V) and calcareous (W) in European legistation and Class C Fly Ashes in accordance with ASTM standard. V-type fly ash is pozzolanic whilst W-type ash generally exhibits hydraulic properties (2121. EN-197-1: (2011). Part 1: Composition, specifications and conformity criteria for common cements.
). V-type ash must have a reactive CaO content of less than and W-type greater than 10 %.

Both siliceous (type V in European legislation and type F further to ASTM) and calcareous (W) ash are used to manufacture CEM II ordinary Portland cement, CEM II composite portland cement, CEM IV pozzolanic cement and CEM V composite cement. Further to the data in Table 3, the proportion of fly ash in the 10 cement types defined in EN 197-1: 2011 (with these fly ashes): ranges from 6 % to 55 % and more specifically for CEM II/A-V from 6 % to 20 %; CEM II/B-V, 21 % to 35 %; CEM IV/A 11 % to 35 %; CEM IV/B 36 % to 55 %; CEM V/A 18 % to 30 % and CEM V/B 31 % to 49 %.

Siliceous fly ash with a low reactive CaO content is the type most widely used in cements and concretes. Due to ash pozzolanicity, early age mechanical strength is low in cements bearing a high content of the addition. The use of siliceous fly ash-additioned cements to manufacture concrete is nonetheless known to have beneficial effects, such as improved workability and significantly lower later age capillary porosity than the unadditioned material. That in turn induces higher mechanical strength and enhanced resistance to chlorides, sulfates and potential alkali-aggregate reactions (5555. Skibsted, J.; Snellings, R. (2019) Reactivity of supplementary cementitious Materials (SCMs) in cement blends. Cem. Concr. Res. 124, 105799 https://doi.org/10.1016/j.cemconres.2019.105799.
).

The natural radioactivity of fly ash depends on the geological age of the original coal bed, the combustion process used and ash particle size; being of interest due to the accumulation of radioactivity - polonium 210 - in the smallest particles of fly ashes (2020. Kovacs, T.; Bator, G.; Schroeyers, W.; Labrincha, J.; Puertas, F.; Hegedus, M.; Nicolaides, D.; Sanjuán, M.A.; Krivenko, P.V.; Grubesa, I.N.; Sas, Z.; Michalic, B.; Anagnostakis, M.; Barisic, I.; Nuccetelli, C.; Trevisi, R.; Croymans, T.; Schreurs, S.; Todorovic, N.; Vaičiukynienė-Palubinskaitė, D.; Bistrickaitė, R.; Tkaczyk, A.; Kovler, K.; Wiegers, R.; P.V.; Doherty, R. (2017) From raw materials to NORM by-products. In Naturally Ocurring Radiactive Materials in Construction. Chapter 6. Ed. W. Schroeyers. Elservier. 135-182. https://doi.org/10.1016/B978-0-08-102009-8.00006-2.
, 5656. Mora, J.C.; Robles, B.; Corbacho, J.A.; Gascó, C.; Gázquez, M.J. (2011). Modelling the behaviour of ²¹⁰Po in high temperatura processes. J. Environ. Radioac. 102 [5], 520-526. https://doi.org/10.1016/j.jenvrad.2010.10.006.
, 5757. Temuujin, J.; Surenjav, E.; Ruescher, C.H.; Vahlbruch, J. (2019) Processing and uses of fly ash addressing radioactivity (critical review), Chemosph. 216, 866-88. https://doi.org/10.1016/j.chemosphere.2018.10.112.
). US Geological Surveys show that coal containing phosphate minerals such as monazite or apatite have high radioactive ²³²Th concentrations, whereas coal containing both organic matter and mineral fractions have high levels of the ²³⁸U radioactive series (5858. Zielinski, R.A.; Finkelman, R.B. (1997) Radioactive elements in coal and fly ash: abundance, forms, and environmental significance, US Geological Survey, 2327-6932.
). The respective radionuclides are retained during coal combustion and concentrate in the fly and bottom ash, more profusely in the former. Uranium and thorium concentrations may be up to ten-fold higher in bottom and fly ash than in burnt coal, while fly ash may contain even higher ²¹⁰Pb and ⁴⁰K concentrations. In modern power stations around 99 % of the fly ash generated is typically retained (90 % in some older plants) (5959. World Nuclear Association. Naturally Occuring Radioactive Materials (july, 2015). https://www.world-nuclear.org/information-library/safety-and-security/radiation-and-health/naturally-occurring-radioactive-materials-norm.aspx.
). The finest ash particles have been observed to bear ²¹⁰Pb contamination. Higher concentrations of that isotope are found in fly than in bottom ash because lead volatises in the combustion chamber (6060. Karangelos, D.J.; Petropoulos, N.P.; Anagnostakis, M.J.; Hinis, E.P.; Simopoulos, S.E. (2004) Radiological characteristics and investigation of the radioactive equilibrium in the ashes produced in lignite-fired power plant. J. Env. Rad. 77 [3], 233-246. https://doi.org/10.1016/j.jenvrad.2004.03.009.
, 6161. Mora, J.C.; Baeza, A.; Robles, B.; Corbacho, J.A.; Cancio, D. (2009). Behaviour of natural radionuclides in coal combustión. Radioprotec. 44 [5], 577-580.
). ²²⁶Ra contamination has also been detected in the finer fractions, where the ²¹⁰Pb/²²⁶Ra ratio may exceed 3 compared to no more than 0.5 in bottom ash (2020. Kovacs, T.; Bator, G.; Schroeyers, W.; Labrincha, J.; Puertas, F.; Hegedus, M.; Nicolaides, D.; Sanjuán, M.A.; Krivenko, P.V.; Grubesa, I.N.; Sas, Z.; Michalic, B.; Anagnostakis, M.; Barisic, I.; Nuccetelli, C.; Trevisi, R.; Croymans, T.; Schreurs, S.; Todorovic, N.; Vaičiukynienė-Palubinskaitė, D.; Bistrickaitė, R.; Tkaczyk, A.; Kovler, K.; Wiegers, R.; P.V.; Doherty, R. (2017) From raw materials to NORM by-products. In Naturally Ocurring Radiactive Materials in Construction. Chapter 6. Ed. W. Schroeyers. Elservier. 135-182. https://doi.org/10.1016/B978-0-08-102009-8.00006-2.
).

Detailed information on the radionuclides in fly ash can be found in (2020. Kovacs, T.; Bator, G.; Schroeyers, W.; Labrincha, J.; Puertas, F.; Hegedus, M.; Nicolaides, D.; Sanjuán, M.A.; Krivenko, P.V.; Grubesa, I.N.; Sas, Z.; Michalic, B.; Anagnostakis, M.; Barisic, I.; Nuccetelli, C.; Trevisi, R.; Croymans, T.; Schreurs, S.; Todorovic, N.; Vaičiukynienė-Palubinskaitė, D.; Bistrickaitė, R.; Tkaczyk, A.; Kovler, K.; Wiegers, R.; P.V.; Doherty, R. (2017) From raw materials to NORM by-products. In Naturally Ocurring Radiactive Materials in Construction. Chapter 6. Ed. W. Schroeyers. Elservier. 135-182. https://doi.org/10.1016/B978-0-08-102009-8.00006-2.
) and (6262. Nuccetelli, C.; Pontikes, Y.; Leonardi, F.; Trevisi, R. (2015) New perspectives and issues arising from the introduction of (NORM) residues in building materials: A critical assessment on the radiological behaviour. Construc. Build. Mat. 82, 323-331. https://doi.org/10.1016/j.conbuildmat.2015.01.069.
, 6363. Kovler, K.; Haquin, G.; Manasherov, V.; Ne´eman, E.; Lavi, N. (2002) Natural radionuclides in building materials available in Israel. Build. Environ. 37 [5], 531-537. https://doi.org/10.1016/S0360-1323(01)00048-8.
, 6464. Piedecausa, B.; Chinchón-Payá, S.; Morales, M.A.; Sanjuán, M.A. (2011) Radioactividad natural de los materiales de construcción. Aplicación al hormigón. Parte 1. Radiación externa: índice de riesgo radiactivo. Cem. Horm. 945, 40-65.
). The uranium series (²²⁶Ra and ²³²Th) and ⁴⁰K concentrations (in Bq kg^-1) in several European countries graphed in Figure 2 vary widely and depend, as noted earlier, on the original coal, combustion process and ash particle size. Table 4 gives the concentration ranges for radionuclides in fly ash sourced from a series of widely differing coal-fired steam power plants. The data show that coal fly ash has a high radionuclide content and the highest radioactivity of all the SCMs listed in standard EN 191-1: 2011. Further to Directive 2013/59/EURATOM (5151. Council Directive 2013/59/Euratom of 5 December 2013 laying down basic safety standards for protection against the dangers arising from exposure to ionising radiation, and repealing Directives 89/618/Euratom, 90/641/Euratom, 96/29/Euratom, 97/43/Euratom and 2003/122/Euratom.
), ACI values (Equation [1]) should be calculated only for endproducts, not for their constituents such as fly ash. Nonetheless, based on its radionuclide concentration (Table 4), the ACI for that by-product would be on the order of 0.5 to 1.5 (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
).

4.2. Iron and steel mill slag

The iron and steel industry generates different types of by-products, most prominently blast furnace (iron) and steel (steel) mill slag. The former, when vitreous and finely ground, exhibits hydraulicity and hence is widely used in cement and concrete manufacture (7676. Puertas, F. (1993) Escorias alto horno: composición y comportamiento hidraúlico. Mater. Construcc. 43 [229], 37-48. https://doi.org/10.3989/mc.1993.v43.i229.687.
, 7777. Pellegrino, C.; Faleschini, F.; Meyer, C. (2019). Recycled Materials in Concrete. Chapter 2. Sustainability of Concrete. Modern Concrete Techonology Book 17. Routledge Ed.
). The latter is less frequent in construction in light of its high heavy metal content and radioactivity, along with its unbound CaO and MgO and dicalcium silicate (2CaO·SiO₂ or C₂S) contents that may pose expansion or soundness problems over time. Its poor physical properties (low polished stone value, PSV, and high aggregate abrasion value, AAV) further condition its use (2222. Puertas, F.; Blanco-Varela, M. T.; Palomo, A.; Vázquez, T. (1988) Reactivity and burnability of raw mixes made with crystallized blastfurnace slags. Part I. and Part II. Zement-Kalk-Gips; 41, (389-402) and (628-631).
, 7878. Liapis, I.; Papayianni, I. (2015) Advances in chemical and physical properties of electric arc furnace carbon steel slag by hot stage processing and mineral mixing. J. Haz. Mat. 283, 89-97 https://doi.org/10.1016/j.jhazmat.2014.08.072.
, 7979. Rodríguez, A.; Santamaría-Vicario, I.; Calderón, V.; Junco, C.; García-Cuadrado, J. (2019) Study of the expansión of cement mortars manufactured with landle furnace slag LFS. Mater. Construcc. 69 [334], e183. https://doi.org/10.3989/mc.2019.06018.
), which is restricted to non-structural works and road bases and sub-bases.

Blast furnace slag is the result of contact between the clay-like acid gangue from iron ore and the sulphur ash from (likewise acid) coke on the one hand and the lime and magnesium (both basic) from the more or less dolomitic limestone materials used as fluxes on the other. That combination of acid (SiO₂ and AI₂O₃) and basic (CaO and MgO) oxides at high (>1600 °C) temperatures yields slag. When the molten magma cools rapidly to ambient temperature via granulation or pelletising procedures, the resulting material is over 90 % amorphous. Such glassy, ground (GBFS) blast furnace slag is hydraulic, meaning that when mixed with water it can harden like cement (7676. Puertas, F. (1993) Escorias alto horno: composición y comportamiento hidraúlico. Mater. Construcc. 43 [229], 37-48. https://doi.org/10.3989/mc.1993.v43.i229.687.
). If it cools slowly, however, the result is a highly crystalline (crystallised slag), low reactivity material that can be included as a raw material in portland cement raw mixes (8080. Liu, J.; Yu, B.; Wang, Q. (2020) Application of steel slag in cement treated aggregate base course. J. Clean. Prod. 269, 121733. https://doi.org/10.1016/j.jclepro.2020.121733.
) or used as a filler in road bases and sub-bases (8181. Cooper, M.B. (2005) Naturally Ocurring Radioactive Materials (NORM) in Australian Industries- Review of Current Inventories and Future Generation. EnviroRad Serv. Pty. Ltd. ARPANSA. Melbourne.
). The majority chemical components of blast furnace slag include SiO₂ (27-40 %), CaO (30-50 %), Al₂O₃ (5-25 %) and MgO (1-15 %). Mellite, a solid solution containing gehlenite (2CaO·Al₂O₃·SiO₂) and akermanite (2CaO·MgO·2SiO₂), is the majority phase in crystallised blast furnace slag. The chemical and mineralogical compositions of the two types of slag depend on the starting iron ore, the type of processing applied and the coke and fluxes used.

GBFS is an SCM used to manufacture ordinary CEM II/A-S and CEM/IIB-S cements, in which it accounts for 6 % to 35 % of the total weight; in cements CEM III/A, CEM III/B and CEM III/C the values are 36 % to 95 %; and in cements CEM V/A and CEM V/B 18 % to 50 %.

Steel slag, a by-product of steel manufacture, is formed in the reaction between fluxes such as calcium oxide and the non-metallic inorganic constituents of steel or scrap metal. Two types can be distinguished:

The origin of iron and steel slag radioactivity lies in the iron ore and scrap metal used and the sintering processes deployed. Depending on the origin, iron ore may contain different radionuclides and heavy metals, with uranium concentration in the 20 Bq kg^-1 to 30 Bq kg^-1 range (8181. Cooper, M.B. (2005) Naturally Ocurring Radioactive Materials (NORM) in Australian Industries- Review of Current Inventories and Future Generation. EnviroRad Serv. Pty. Ltd. ARPANSA. Melbourne.
). In blast furnace slag, the source of natural radionuclide content has been confirmed to be not only the raw materials but the manufacturing process (type of furnace, for instance) (1818. Plant, J.A.; Saunders, A. D. (1996) The Radioactive Earth. Rad. Protec. Dosim. 68 [1-2], 25-36.
). Figure 3 graphs the radionuclide concentrations in the iron and steel mill slag used in cement manufacture, whilst Table 4 gives the range of ²²⁶Ra (uranium series), ²³²Th (thorium series) and ⁴⁰K concentrations in BFS and steel slag.

As the data in Figure 3 and Table 4 infer, blast furnace slag bears a much higher radionuclide content than steel slag, although the BFS values, with ACI generally <1, are lower than observed for coal fly ash (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
).

4.3. Other wastes and limestones used as supplementary cementitious materials (SCMs) in cement and concrete manufacture

Table 3 shows that in addition to type V and W fly ash and vitreous slag (S), waste and materials, such as silica fume, limestone, natural pozzolans and calcined shale are used as SCMs in the standardised ordinary cements listed in EN 197-1: 2011.

Silica fume (D) is a residue generated in electric arc furnaces producing silicon and ferro silicon metals. An inorganic product consisting in very fine spherical particles generated when coal reduces quartz, it is essentially (85 % to 90 %) amorphous SiO₂. With such a high amorphous SiO₂ content and large specific surface (around 20 000 m²·kg^-1), silica fume is highly pozzolanic. According to standard EN 197-1: 2011, CEM II/A-D cements may contain 6 % to 10 % silica fume. Blended Portland cements CEM II/A-M and CEM II/B-M as well as cements CEM IV/A and CEM IV/B may also bear up to 10 % of that type of waste.

Portland cement with silica fume (CEM II/A-D) is apt for manufacturing of prestressed concrete, concrete with reactive aggregates and shotcrete or fast-setting concrete. Silica fume pozzolanicity determines the high reactivity and early age strength development in those materials (8383. Argiz, C.; Reyes, E.; Moragues, A. (2018) Ultrafine portland cement performance. Mater. Construcc. 68 [330], e157. https://doi.org/10.3989/mc.2018.03317.
). Silica fume can also be used as a cement replacement or addition to prepare very high-strength, durable concretes (8383. Argiz, C.; Reyes, E.; Moragues, A. (2018) Ultrafine portland cement performance. Mater. Construcc. 68 [330], e157. https://doi.org/10.3989/mc.2018.03317.
, 8484. Goldman, A.; Bentur, A. (1993) The influence of microfillers on enhancement of concrete strength. Cem. Concr. Res. 23 [4], 962-972. https://doi.org/10.1016/0008-8846(93)90050-J.
), although it must not account for more than 5 % to 10 % of the total cement weight. The presence of this mineral addition in concrete has induced the development of so-called ‘high performance’ concretes. The large specific surface in silica fume determines the need for variable amounts of superplasticising admixtures in the respective concretes to lower the water/cement ratio while ensuring suitable rheology as well as the production of very high density, high performance and durable concretes (8585. Instrucción de hormigón estructural (EHE-08) (2008). BOE 203. https://www.fomento.es/nr/rdonlyres/e20dffb7-fd75-4803-8ca4-025064bb1c40/68186/1820103_2008.pdf" (In spanish).
).

The concentration ranges of ²²⁶Ra, ²³²Th and ⁴⁰K (in Bq kg^-1) reported in the literature for silica fume (Table 4) are relatively low for the former two former and somewhat higher for ⁴⁰K. This SCM would not in any event appear to be a very significant source of natural radionuclides in the end cements and concretes.

Natural pozzolans are siliceous, alumino-siliceous (or a combination of the two) geological materials. The term was originally applied only to the volcanic tuff found in the area around Pozzoli, Italy, and used by the Romans to prepare hydraulic concretes. For several decades it has also been used, however, to designate natural materials able to react with the portlandite generated during the hydration at ambient temperature of the calcium silicates present in portland cement. The pozzolanic properties characterising the strong cohesive end products have determined the evolution of the term from its original geological meaning to its present technological connotations (8686. Soria Santamaría, F. (1983) Las puzolanas y el ahorro energético en los materiales de construcción. Mater. Construcc. 33 [190-191], 69-84. https://doi.org/10.3989/mc.1983.v33.i190-191.974.
). Natural pozzolans, like aluminosiliceous fly ash and silica fume, exhibit the pozzolanic characteristics defined in standard EN 197-1: 2011, which describes two types of materials: natural pozzolans (P) and naturally occurring fired pozzolana (Q). Natural pozzolans are normally volcanic materials or sedimentary rocks with the chemical and mineral compositions specified, whilst naturally occurring fired pozzolans are thermally activated volcanic, clay, slate or sedimentary rocks.

These materials can be used to manufacture cements CEM II/A-P and CEM II/B-P, CEM II/A-Q and CEM II/B-Q with 6 % to 30 % pozzolan by cement weight, as well as cements CEM IV/A and B and CEM V/A and B. Content is defined in keeping with availability. The characteristics of cements with natural pozzolans are qualitatively similar to but more intense than observed in materials with greater pozzolanicity such as silica fume and type V fly ash. P-type pozzolans are also apt for the manufacture of alternative materials such as alkaline cements (8787. Robayo-Salazar, R.; Mejía de Gutiérrez, R.; Puertas, F. (2019) Alkali-activated binary concrete based on a natural pozzolan: physical, mechanical and microstructural characterization. Mater. Construcc. 69 [335], e191. https://doi.org/10.3989/mc.2019.06618.
).

The concentration ranges of ²²⁶Ra, ²³²Th and ⁴⁰K (in Bq kg^-1) reported in the literature for natural and naturally occurring fired pozzolans used in cement manufacture are listed in Table 4, where metakaolin (MK) has been included as an example of the latter. Further to those data, the ²²⁶Ra content may be higher and more variable in MK than in non-fired natural pozzolans.

Limestone (L and LL) is another material used as an addition in ordinary cements. It must also meet a series of chemical and physical requirements to be apt for ordinary cement manufacture. Its calcium carbonate content (CaCO₃), calculated of terms of calcium oxide (CaO), must be at least 75 wt%, the clay content must be lower than 1.20 g/100 and the total organic carbon (TOC) must not exceed 0.20 wt% in subtype LL or 0.50 wt% in subtype L (2121. EN-197-1: (2011). Part 1: Composition, specifications and conformity criteria for common cements.
).

Limestone is present in cements CEM II/A-L and B-L at 6 % to 30 % by cement weight and in the same proportions in cements CEM II/A-LL and CEM II/B-LL. Limestone has no pozzolanic or hydraulic properties, but neither is it a wholly inert addition as believed until not long ago. Its presence in cement induces a series of very distinct chemical and physical characteristics explained by such non-inertness. Its most prominent effects include improved paste workability, which lowers water demand; absence of any impact on early or late age strength when limestone content is under 10 % by cement weight; and lesser expansion at all ages (8888. Ivanović, M.; Kljajević, Lj.; Nenadović, M.; Bundaleski, N.; Vukanac, I.; Todorović, B.; Nenadović, S. (2018) Physicochemical and radiological characterization of kaolin and its polymerization products. Mater. Construcc. 68 [330], e155 https://doi.org/10.3989/mc.2018.00517.
). In contrast, thaumasite formation-related durability issues have been described in cements with high limestone contents (8989. Voglis, N.; Kakali, G.; Chaniotakis, E.; Tsivilis, S. (2005) Portland-limestone cements. Their properties and hydration compared to those of other composite cements. Cem. Concr. Comp. 27 [2], 191-196. https://doi.org/10.1016/j.cemconcomp.2004.02.006.
).

According to the concentration ranges of ²²⁶Ra, ²³²Th and ⁴⁰K (in Bq kg^-1) reported in the literature for limestone (Table 5), the material exhibits fairly low uranium and thorium series contents, but a much broader range of ⁴⁰K activity concentrations.

Table 5 also gives the ²²⁶Ra, ²³²Th and ⁴⁰K ranges (in Bq kg^-1) for other industrial waste/by-products such as red mud, biomass ash and waste glass which, while not standardised, can be used as portland or alkali-activated (geopolymer) cement additions.

Red mud is waste generated in Bayer process-mediated bauxite refining, in which ground bauxite reacts with sodium hydroxide at high temperatures and pressures. A highly alkaline (pH~10 to 12.5) slurry, it has a solids content of 15 wt% to 30 wt%. Its composition features fine silica, aluminium, iron, calcium and titanium oxide particles in proportions that differ depending on the bauxite ore, conditions governing aluminium extraction and quality control (1818. Plant, J.A.; Saunders, A. D. (1996) The Radioactive Earth. Rad. Protec. Dosim. 68 [1-2], 25-36.
). Its alkalinity, toxic element content and natural radioactivity (bauxite waste ACI is consistently over 1: Equation [1]) limit its use in construction (2020. Kovacs, T.; Bator, G.; Schroeyers, W.; Labrincha, J.; Puertas, F.; Hegedus, M.; Nicolaides, D.; Sanjuán, M.A.; Krivenko, P.V.; Grubesa, I.N.; Sas, Z.; Michalic, B.; Anagnostakis, M.; Barisic, I.; Nuccetelli, C.; Trevisi, R.; Croymans, T.; Schreurs, S.; Todorovic, N.; Vaičiukynienė-Palubinskaitė, D.; Bistrickaitė, R.; Tkaczyk, A.; Kovler, K.; Wiegers, R.; P.V.; Doherty, R. (2017) From raw materials to NORM by-products. In Naturally Ocurring Radiactive Materials in Construction. Chapter 6. Ed. W. Schroeyers. Elservier. 135-182. https://doi.org/10.1016/B978-0-08-102009-8.00006-2.
).

Burning plants, trees and seed waste sourced from a wide variety of species to produce electric power yields biomass ash, generally in the form of fly and bottom ash. The chemical, mineralogical and radiological composition of such ash is highly dependent on the material burnt and the process. Some types of plant ash, such as rice husk and bagasse, exhibit pozzolanicity and can be used in cement and concrete (9595. Maldonado-García, M. A.; Hernández-Toledo, U. I.; Montes-García, P.; Valdez-Tamez, P. L. (2018) The influence of untreated sugarcane bagasse ash on the microstructural and mechanical properties of mortars. Mater. Construcc. 68 [329], e148. https://doi.org/10.3989/mc.2018.13716.
, 9696. Pereira, A.M.; Moraes, J.C.B.; Moraes, M.J.B.; Akasaki, J.L.; Tashima, M.M.; Soriano, L.; Monzó, J.; Payá, J. (2018). Valorisation of sugarcane bagasse ash (SCBA) with high quartz content as pozzolanic material in Portland cement mixtures. Mater. Construcc. 68 [330], e153. https://doi.org/10.3989/mc.2018.00617.
) or alkaline cement manufacture (3434. Mejía, J.M.; Mejía de Gutiérrez, R.; Puertas, F. (2013) Rice husk ash as a source of silica in alkali-activated fly ash and granulated blast furnace slag systems. Mater. Construcc. 63 [311], 361-375. https://doi.org/10.3989/mc.2013.04712.
).Others such as olive tree ash, however, are scantly applicable as SCMs. Some of the present authors recently assessed the viability of biomass ash as an alternative alkaline activator in geopolymer manufacture (4343. Alonso, M.M.; Gascó, C.; Martín Morales, M.; Suárez-Navarro, J.A.; Zamorano, M.; Puertas, F. (2019) Olive Biomas ash as an alternative activator in geopolymer formation: A study of strenth, radiology and leaching behaviour. Cem. Concr. Comp. 104, 103384. https://doi.org/10.1016/j.cemconcomp.2019.103384.
). The very high ⁴⁰K content observed, with ACI values consistently >1, (Table 5), must not be overlooked when considering its use.

Other types of waste such as glass hold promise for possible application in cement and concrete manufacture either as aggregates (9797. Gupta, A.; Gupta, N.; Shukla, A.; Goyal, R.; Kumar, S. (2020) Utilization of recycled aggregate, plastic, glass waste and coconut shells in concrete - a review. IOP Conf. Series: Mat. Sci. Eng. 804, 012034. https://doi.org/10.1088/1757-899X/804/1/012034.
, 9898. Kou, S.C.; Poon, C.S. (2009) Properties of self-compacting concrete prepared with recycled glass aggregate. Cem. Concr. Comp. 31 [2], 107-113. https://doi.org/10.1016/j.cemconcomp.2008.12.002.
) or as precursors and/or activators in geopolymers (3232. Puertas, F.; Torres-Carrasco, M. (2014) Use of glass waste as an activator in the preparation of alkali-activated slag cements. Mechanical strength and paste characterisation. Cem. Concr. Res., 57, 95-104. https://doi.org/10.1016/j.cemconres.2013.12.005.
, 3333. Torres-Carrasco, M.; Puertas, F. (2015). Waste glass in the geopolymer preparation. Mechanical and microstructural characterisation. J. Clean. Prod. 90, 397-408. https://doi.org/10.1016/j.jclepro.2014.11.074.
, 3838. Torres-Carrasco, M.; Puertas, F. (2017) Waste glass as a precursor in alkaline activation: chemical process and hydration products. Construc. Build. Mat. 139, 342-354 https://doi.org/10.1016/j.conbuildmat.2017.02.071.
). These materials vary widely in terms of their composition, while sodium silicate-based glass is the most apt for use in geopolymers. Further to the radiological data in Table 5, this waste poses no natural radiation-related problems, for its uranium, thorium and potassium contents are all fairly low.

4.4. Gypsum and phosphogypsum

Gypsum and phosphogypsum have some similar characteristics but are conspicuously different chemically and radiologically. Gypsum, hydrated calcium sulfate (CaSO₄·2H₂O), is blended with clinker and SCMs in Portland cement manufacture. The most prominent of its various purposes is to react with the C₃A (3CaO·Al₂O₃) in the clinker and the water present in the early stages of cement hydration to form ettringite (3CaO·Al₂O₃)(SO₄)₃(OH)₁₂·31H₂O). That reaction constrains or impedes any direct reaction between C₃A and water, preventing flash setting by retarding some of the cement hydration reactions. Gypsum may also be found in calcium sulfate cement hemihydrate (CaSO₄·½H₂O) and anhydrite (anhydrous calcium sulfate, CaSO₄) or any combination of the two. Gypsum and anhydrite are present in nature and calcium sulfate may be generated as a by-product in certain industrial processes. The ceiling sulfate content in ordinary cements, expressed as % SO₃, is 3.5 % (in 32.5 and 42.5N cements) or 4.0 % (42.5R and 52.5 cements (2121. EN-197-1: (2011). Part 1: Composition, specifications and conformity criteria for common cements.
).

Phosphogypsum (PG), a phosphate industry by-product, is generated during the acid digestion of phosphate ore (2020. Kovacs, T.; Bator, G.; Schroeyers, W.; Labrincha, J.; Puertas, F.; Hegedus, M.; Nicolaides, D.; Sanjuán, M.A.; Krivenko, P.V.; Grubesa, I.N.; Sas, Z.; Michalic, B.; Anagnostakis, M.; Barisic, I.; Nuccetelli, C.; Trevisi, R.; Croymans, T.; Schreurs, S.; Todorovic, N.; Vaičiukynienė-Palubinskaitė, D.; Bistrickaitė, R.; Tkaczyk, A.; Kovler, K.; Wiegers, R.; P.V.; Doherty, R. (2017) From raw materials to NORM by-products. In Naturally Ocurring Radiactive Materials in Construction. Chapter 6. Ed. W. Schroeyers. Elservier. 135-182. https://doi.org/10.1016/B978-0-08-102009-8.00006-2.
). The industry is known to be vital to the worldwide food supply, given the role of phosphate fertilisers in extensive farming. Phosphate minerals carry high contaminating contents of uranium, radium, polonium, thorium and lead isotopes.

The ²²⁶Ra, ²³²Th and ⁴⁰K concentrations (in Bq kg^-1) for gypsum and phosphogypsum used in construction are given in Table 6, which shows that as a rule the U, Th and K series values are fairly low.

Approximately 70 % of the phosphate ore mined is processed in an acid medium to produce phosphoric acid, during which procedure substantial quantities of phosphogypsum are generated. Depending on the raw ore used, PG may contain up to 60 times the radionuclide content found in the pre-processed rock (100100. García‐Díaz, I.; Gázquez, M.J.; Bolivar, J.P.; López, F.A. (2016) Characterization and valoration of Norm wastes for construction materials - Chapter 2. Manag. Haz. Wast. 13-37 (2016). Ed. INTECH. https://doi.org/10.5772/63196.
). According to García-Díaz et al. (100100. García‐Díaz, I.; Gázquez, M.J.; Bolivar, J.P.; López, F.A. (2016) Characterization and valoration of Norm wastes for construction materials - Chapter 2. Manag. Haz. Wast. 13-37 (2016). Ed. INTECH. https://doi.org/10.5772/63196.
) up to 80 % of the ²²⁶Ra, up to 86 % of the U and up to 70 % of the Th may concentrate in PG. The radionuclide content in this material must be determined because ²²⁶Ra generates radon gas (²²²Rn), which with a short half-life of just 3.5 d is very active, i.e., emits intense radiation that may harm bodily organs.

This industrial by-product is scarcely used in construction due to its high radioactivity, although research has been ongoing for some time on its use in place of mineral gypsum and for other applications. A review of possible applications in building material production (101101. Dvorkin, L.; Lushnikova, N.; Sonebi. M. (2018) Application areas of phosphogypsum in production of mineral binders and composites based on them: a review of research results. MATEC Web of Confe. 149, 01012. https://doi.org/10.1051/matecconf/201814901012.
) cites setting control, mineralisation in clinker preparation and gypsum product manufacture as potential uses. A recent study (102102. Ngoc Lam, N. (2020) Eco-concrete made with phosphogypsum-based super sulfated cement. IOP Conf. Series: Mater. Scie. and Engi. 869, 032031. IOP Publishing. https://doi.org/10.1088/1757-899X/869/3/032031.
) addresses the use of phosphogypsum instead of gypsum in super-sulfated cement-based concrete manufacture. As noted, its use is conditioned by its high radon radioactivity and emissions. A few studies and patents suggest that phosphogypsum can be purified by eliminating heavy metals and ²²⁶Ra (104104. Kovler, K.; Dashevsky, B.; Kosson, D.S.; Reches, Y. (2017) US Patent. System and methods for removing impurities from phosphogypsum and manufacturing gypsum binder. US 2017/0022070A1.
), while others (8282. Gijbels, K.; Iacobescu, R.I.; Pontikes, Y.; Vandevenne, N.; Schreurs, S.; Schroeyers, W. (2018) Radon immobilization potential of alkali-activated materials containing ground granulated blast furnace slag and phosphogypsum. Construc. Build. Mat. 184, 68-75. https://doi.org/10.1016/j.conbuildmat.2018.06.162.
) assess the use of alkaline cement matrices to immobilise the radon in phosphogypsum.

As the uranium, thorium and potassium concentrations in phosphogypsum of different origins graphed in Figure 4 show, the numbers vary widely. The ²²⁶Ra, ²³²Th and ⁴⁰K concentrations (Bq kg^-1) reported in the literature for this by-product and listed in Table 6 also attest to enormous variability. The specific concentrations of naturally occurring radionuclides in phosphogypsum depend on the origin of the phosphate ore and the chemical process used (2020. Kovacs, T.; Bator, G.; Schroeyers, W.; Labrincha, J.; Puertas, F.; Hegedus, M.; Nicolaides, D.; Sanjuán, M.A.; Krivenko, P.V.; Grubesa, I.N.; Sas, Z.; Michalic, B.; Anagnostakis, M.; Barisic, I.; Nuccetelli, C.; Trevisi, R.; Croymans, T.; Schreurs, S.; Todorovic, N.; Vaičiukynienė-Palubinskaitė, D.; Bistrickaitė, R.; Tkaczyk, A.; Kovler, K.; Wiegers, R.; P.V.; Doherty, R. (2017) From raw materials to NORM by-products. In Naturally Ocurring Radiactive Materials in Construction. Chapter 6. Ed. W. Schroeyers. Elservier. 135-182. https://doi.org/10.1016/B978-0-08-102009-8.00006-2.
). In wet phosphoric acid production, the amount of radionuclide taken up by each fraction may vary with the technology. As a rule most of the uranium ultimately remains in the fertiliser, whilst radium is more evenly distributed among the (by-)products, with some possibly precipitating in the plant. Most of the polonium is eliminated with the phosphogypsum fraction (103103. IAEA. (2013) Radiation protection and management of NORM residues in the phosphate industry. Safety Reports Series 78. http://refhub.elsevier.com/B978-0-08-102009-8.00006-2/rf0225.
). With such variability the ACI values range from 0.5 to 4.0, although most are >1 (2020. Kovacs, T.; Bator, G.; Schroeyers, W.; Labrincha, J.; Puertas, F.; Hegedus, M.; Nicolaides, D.; Sanjuán, M.A.; Krivenko, P.V.; Grubesa, I.N.; Sas, Z.; Michalic, B.; Anagnostakis, M.; Barisic, I.; Nuccetelli, C.; Trevisi, R.; Croymans, T.; Schreurs, S.; Todorovic, N.; Vaičiukynienė-Palubinskaitė, D.; Bistrickaitė, R.; Tkaczyk, A.; Kovler, K.; Wiegers, R.; P.V.; Doherty, R. (2017) From raw materials to NORM by-products. In Naturally Ocurring Radiactive Materials in Construction. Chapter 6. Ed. W. Schroeyers. Elservier. 135-182. https://doi.org/10.1016/B978-0-08-102009-8.00006-2.
).

4.5. Cements and Concretes

This section draws a distinction between the more conventional cements and concretes based on portland or standardised materials and alternative cements and concretes (as a rule with a low or nil clinker content) such as alkali-activated products or geopolymers. The radiological behaviour of all these cements and concretes is described in great detail in a recent paper (88. Scrivener, K.L.; John, V. M.; Gartner, E.M. (2016) Eco-efficient cements: Potential, economically viable solutions for a low-CO₂, cement based materials industry. United Nations & Environment Programm, 2016.
).

4.5.1. Portland cements and concretes

 ⌅

Nuccetelli et al. (6262. Nuccetelli, C.; Pontikes, Y.; Leonardi, F.; Trevisi, R. (2015) New perspectives and issues arising from the introduction of (NORM) residues in building materials: A critical assessment on the radiological behaviour. Construc. Build. Mat. 82, 323-331. https://doi.org/10.1016/j.conbuildmat.2015.01.069.
) studied the uranium, thorium and potassium series radionuclides in anhydrous portland cements in 21 European countries. Their findings, summarised in Table 7, revealed that radionuclide concentrations are fairly low, with ACI values ranging as a rule from 0.1 to 0.4, far below the 2013/59/Euratom European Directive maximum of 1. Some authors (6060. Karangelos, D.J.; Petropoulos, N.P.; Anagnostakis, M.J.; Hinis, E.P.; Simopoulos, S.E. (2004) Radiological characteristics and investigation of the radioactive equilibrium in the ashes produced in lignite-fired power plant. J. Env. Rad. 77 [3], 233-246. https://doi.org/10.1016/j.jenvrad.2004.03.009.
) have reported higher ACI values for cements, however.

The presence of NORMs in industrial waste/by-products such as coal-fired steam power plant fly ash or vitreous blast furnace slag may raise the natural radionuclide concentrations in ordinary cements, along with their ACI values. The radionuclide content in standardised commercial cements (6666. Alonso, M.M.; Suárez-Navarro, J.A.; Pérez-Sanz, R.; Gascó, C.; Moreno de los Reyes, A.M.; Lanzón, M.; Blanco-Varela, M.T.; Puertas, F. (2020) Data in Brief. 33, 106488. https://doi.org/10.1016/j.dib.2020.106488.
) is listed in Table 8 and in synthetically prepared anhydrous cements in Table 9 (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
). The data denote an additive effect as well as proportionality between the radionuclide content and the percentage of ‘pure’ (unadditioned) cement and the SCM in each blend. Other authors report similar findings (7070. Kovler, K. (2012) Does the utilization of coal fly ash in concrete construction present a radiation hazard? Construc. Build. Mat. 29, 158-166. https://doi.org/10.1016/j.conbuildmat.2011.10.023.
, 9292. Turhan, Ş.; Gürbüz, G. (2008) Radiological significance of cement used in building construction in Turkey. Rad. Protec. Dos. 129 [4], 391-396. https://doi.org/10.1093/rpd/ncm454.
, 105-107105. Trevisi, R.; Risica, S.; D’Alessandro, M.; Paradiso, D.; Nuccetelli. C. (2012) Natural radioactivity in building materials in the European Union: a database and an estimate of radiological significance. J. Env. Rad. 105, 11-20. https://doi.org/10.1016/j.jenvrad.2011.10.001.
106. Sanjuán, M.A.; Suarez-Navarro, J.A.; Argiz, C.; Mora, P. (2019). Assessment of radiation hazards of white and grey Portland cements. J. Radioanal. Nucl. Chem. 322, 1169-1177. https://doi.org/10.1007/s10967-019-06824-y.
107. Sanjuán, M.A.; Suárez-Navarro, J.A.; Argiz, C.; Mora, P. (2020) Assessment of natural radioactivity and radiation hazards owing to coal fly ash and natural pozzolan Portland cements. J. Radioanal. Nucl. Chem. 325, 381-390. https://doi.org/10.1007/s10967-020-07263-w.
).

Table 8 also gives the radionuclide content in cements other than the ordinary materials listed in standard EN 197-1: 2011, including sulfate-resistant, white, calcium aluminate (CAC) and calcium sulfoaluminate cements. CACs exhibit the highest radionuclide concentration, particularly for thorium, with an ACI value of around 0.7 to 0.9, much higher than the 0.2 to 0.4 recorded for unadditioned OPC. Neither the radionuclide concentrations nor the ACI values for the other cements analysed vary substantially from the findings for ‘pure’ Portland cement.

Table 7.  ²²⁶Ra, ²³²Th and ⁴⁰K activity concentration in 2036 cement samples (6262. Nuccetelli, C.; Pontikes, Y.; Leonardi, F.; Trevisi, R. (2015) New perspectives and issues arising from the introduction of (NORM) residues in building materials: A critical assessment on the radiological behaviour. Construc. Build. Mat. 82, 323-331. https://doi.org/10.1016/j.conbuildmat.2015.01.069.
).

Country (21 EU_MS)	No. of samples	226Ra (Bq kg-1)	232Th (Bq kg-1)	40K (Bq kg-1)
Austria	18	27	14	210
Belgium	26	52	46	255
Bulgaria	1	29	19	160
Cyprus	20	23	8	136
Czech Republic	496	46	19	237
Denmark	6	20	12	90
Finland	11	40	20	251
France	1	35	21	24
Germany	23	86	73	170
Greece	183	85	19	257
Hungary	400	30	22	218
Ireland	3	60	11	131
Italy	200	41	63	357
The Netherlands	17	62	64	271
Poland	344	73	66	353
Portugal	8	31	19	256
Romania	55	44	27	233
Slovakia	6	35	18	223
Spain	182	70	49	273
Sweden	30	53	54	224
United Kingdom	6	22	18	160
Overall average		46 ( 22-86 )	32 ( 8-73 )	214 ( 24-357 )

Table 8.  Radionuclides in anhydrous commercial and standardised cements (6666. Alonso, M.M.; Suárez-Navarro, J.A.; Pérez-Sanz, R.; Gascó, C.; Moreno de los Reyes, A.M.; Lanzón, M.; Blanco-Varela, M.T.; Puertas, F. (2020) Data in Brief. 33, 106488. https://doi.org/10.1016/j.dib.2020.106488.
).

Radioactive series	238U (in Bg kg-1)					235U	232Th (in Bg kg-1)			40K (in Bg kg-1)
Anhydrous cement	234Th	226Ra	214Pb	214Bi	210Pb		228Ac	212Pb	208Tl		ACI
CEM I 52,5R	17.6 ±2.3	17.1 ±4.2	14.65 ±0.62	13.0 ±1.3	17.0 ±1.9	< 2.1	17.2 ±1.2	18.4 ±3.0	6.8 ±1.5	201.9 ±8.0	0.210 ± 0.015
CEM II/A-L 42.5R	< 3.5	26.7 ±3.6	27.1 ±2.9	< 0.9	27.3 ±6.0	< 1.18	5.94 ±0.35	5.80 ±0.75	2.14 ±0.32	43.7 ±2.9	0.133 ± 0.012
CEM II/B-V 42.5N	72 ± 20	66.8 ± 7.2	75 ± 10	68.8 ± 6.9	56 ± 19	3.3 ± 1.2	31.8 ± 3.1	34.6 ± 4.8	12.8 ± 1.5	211.7 ± 9.1	0.452 ± 0.029
CEM III/B 42.5N	99 ± 20	81 ± 15	91.9 ± 4.9	88.5 ± 2.7	< 10.6	3.8 ± 1.1	50.6 ± 2.0	52.6 ± 3.4	20.4 ± 1.0	184 ± 11	0.584 ± 0.051
CEM I 52,5 S/R	17.4 ±2.9	19.5 ±3.2	16.9 ±1.9	15.8 ±1.0	17.0 ±4.4	< 2.11	14.3 ±1.1	15.7 ±1.8	5.50 ±0.58	143.5 ±9.3	0.184 ± 0.012
White cement	58.5 ±3.2	-	57.15 ±0.81	-	-	-	4.81 ±0.52	4.36 ±0.31	1.36 ±0.13	84.6 ±3.4	0.2428 ± 0.039
White cement	23.7 ±3.8	23.5 ±3.6	23.1 ±2.6	21.9 ±1.3	27 ±10	< 2.13	16.8 ±1.2	17.8 ±2.1	6.55 ±0.70	146.3 ±9.1	0.211 ± 0.014
CAC	73.8 ±6.2	-	64.9 ±0.96	-	-	-	131.2 ±1.6	137.4 ±1.2	42.42 ±0.59	41.4 ±5.8	0.886 ± 0.0088
CAC	< 19.0	83 ±11	82.0 ±8.8	< 1.2	38.9 ±8.3	< 12.9	118.4 ±5.7	123±14	45.6 ±4.0	< 6.8	0.871 ± 0.046
Calcium sulfoaluminate	13.1 ±4.0	15.7 ±2.9	14.7 ±1.7	10.1 ±5.6	14.2 ±3.8	< 2.02	3.85 ±0.84	5.01 ±0.61	1.73 ±0.21	105.0 ±7.1	0.107 ± 0.011

CAC: calcium aluminate cement
Reproduced with kind permission of Elsevier

Table 9.  Radionuclides in anhydrous synthetic cements with different SCMs (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
).

Anhydrous cement	Radionuclide concentration (Bq·kg-1)
	226Ra	232Th	40K	ACI
OPC	19.23 ± 0.54	19.13 ± 0.32	237.9 ± 5.2	0.2382 ± 0.0045
OPC + 10% SF	17.49 ± 0.69	18.41 ± 0.46	230.6 ± 5.4	0.2186 ± 0.0041
OPC+ 50% FA	72.90 ± 0.80	74.70 ± 0.70	277.6 ± 5.0	0.6951 ± 0.0060
OPC+50% S	83.85 ± 0.90	32.40 ± 0.50	158.3 ± 3.7	0.4892 ± 0.0049
OPC+50% L	17.91 ± 0.35	9.65 ± 0.31	119.8 ± 2.9	0.1465 ± 0.0018

OPC: CEM 52.5R; SF: silica Fume; FA: fly ash; S: ground blast furnace slag; L: limestone
Reproduced with kind permission of Elsevier

Studies of hydrated Portland cement paste radiological behaviour, i.e., their ²²⁶Ra, and ⁴⁰K activity concentrations, have confirmed the dilution effect attributable to the mixing water, including the water that binds to the hydration products formed (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
). Radionuclide activity concentrations are normally determined with gamma spectrometry on ground samples (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
, 6666. Alonso, M.M.; Suárez-Navarro, J.A.; Pérez-Sanz, R.; Gascó, C.; Moreno de los Reyes, A.M.; Lanzón, M.; Blanco-Varela, M.T.; Puertas, F. (2020) Data in Brief. 33, 106488. https://doi.org/10.1016/j.dib.2020.106488.
). The concentrations in hydrated cement pastes bearing different types of SCMs are listed in Table 10. The dilution effect associated with water (water/cement ratio used in the mixes) on the radionuclide concentrations and the ACI for different pastes can be deduced from a comparison of the data in Table 10 to the values in Tables 8 and 9.

The authors of this review recently proposed a new method for determining radionuclide concentration and ACI on hardened but unground Portland cement paste as part of Spanish Ministry of Science and Innovation-funded project BIA2016-77252-P. The method was developed on cubic specimens of 5 cm on a side of hardened and unadditioned Portland cement paste (5252. Suárez-Navarro, J.A.; Moreno-Reyes, A.M.; Gascó, C.; Alonso, M.M.; Puertas, F. (2020) Gamma spectrometry and LabSOCS-calculated efficiency in the radiological characterisation of quadrangular and cubic specimens of hardened portland cement paste. Rad. Phys. Chem. 171, 108709. https://doi.org/10.1016/j.radphyschem.2020.108709.
).

Table 10.  Radionuclide concentration in hydrated cements bearing different types of SCMs (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
), determined on ground powdered samples.

Cement paste	Radionuclide concentration (Bq kg-1)
	226Ra	232Th	40K	ACI
OPC	7.86 ± 0.60	13.83 ± 0.60	166.7 ± 6.7	0.1428 ± 0.0041
White Cement	26.96 ± 0.73	3.42 ± 0.16	59.0 ± 3.2	0.1271 ± 0.0038
CAC	28.6 ± 1	98.9 ± 1.8	17.2 ± 3.4	0.535 ± 0.011
OPC+ 10 % SF	6.97 ± 0.59	13.31 ± 0.58	165.1 ± 6.8	0.1384 ± 0.0057
OPC+ 50 % FA	49.1 ± 1.3	62.2 ± 1.1	211.6 ± 8.0	0.5097 ± 0.0099
OPC+50 % S	41.5 ± 1.1	22.76 ± 0.69	114.1 ± 5.4	0.2914 ± 0.0069
OPC+50 % L	9.35 ± 0.33	7.09 ± 0.48	7.09 ± 0.48	0.0928 ± 0.0044

OPC: CEM 52.5R; SF: silica Fume; FA: fly ash; S: ground blast furnace slag; L: limestone; CAC: calcium aluminium cement
Reproduced with kind permission of Elsevier

That new methodology was developed on 48 h and 64 d cubic (5 cm on side) specimens of hardened portland cement paste. The pastes were prepared with a number of gamma radiation ‘cocktails’ (²¹⁰Pb, ²⁴¹Am, ¹³⁷Cs, ⁶⁰Co, ⁴⁰K and ²²⁶Ra) with known activity concentrations and emission energy values ranging from 46.54 keV to 1332.5 keV. The gamma cocktails were carefully blended with the water and cement to ensure a uniform mix. Gamma spectrometry was conducted on 48 hours and 64 days compact solid samples. The solid cubic specimens were measured at different heights on a LabSOCS-calibrated ultrapure germanium (HPGe) detector (5252. Suárez-Navarro, J.A.; Moreno-Reyes, A.M.; Gascó, C.; Alonso, M.M.; Puertas, F. (2020) Gamma spectrometry and LabSOCS-calculated efficiency in the radiological characterisation of quadrangular and cubic specimens of hardened portland cement paste. Rad. Phys. Chem. 171, 108709. https://doi.org/10.1016/j.radphyschem.2020.108709.
). The same pastes were ground and re-measured to validate the results for the cubic monolithic specimens (5 cm on side). The specimens tested are depicted in Figure 5.

Figure 5.  Quadrangular prismatic cement paste specimens 1 cm to 5 cm high (5252. Suárez-Navarro, J.A.; Moreno-Reyes, A.M.; Gascó, C.; Alonso, M.M.; Puertas, F. (2020) Gamma spectrometry and LabSOCS-calculated efficiency in the radiological characterisation of quadrangular and cubic specimens of hardened portland cement paste. Rad. Phys. Chem. 171, 108709. https://doi.org/10.1016/j.radphyschem.2020.108709.
). Reproduced with kind permission of Elsevier.

The findings showed that i) the experimentally tested activities found for both plastic cylindrical containers and cubic cement pastes using LabSOCS-calculated efficiency proved to be statistically comparable, ii) the variation in efficiency with quadratic specimen height satisfactorily corrected the gamma photon attenuation induced by the photoelectric and Compton effects in the energy range studied (46.54 keV to 1332.5 keV) as well as changes in the solid angle of the detector, iii) as the activity found on the six sides of the cubic cement specimen were statistically indistinguishable, activity may be determined by measuring just one side and iv) the accuracy and precision observed for the two counting geometries met the standard acceptability criteria applied in environmental radioactivity laboratories. Although no significant differences were found between 48 hours and 64 days cubic cement paste activity, analyses should preferably be conducted after the hydration reactions have run full course to avoid possible distortions in the ²²⁶Ra activity values calculated from ²²²Rn progeny. Figure 6 graphs the variation in method efficiency with specimen height in the energy range studied. This new measuring methodology is currently being validated for cement pastes bearing NORM waste and hybrid alkali-activated cement pastes.

Figure 6.  Variation in efficiency with the height of quadrangular specimens in the range of energies studied, 46.54 keV (²¹⁰Pb) to 1332.5 keV (⁶⁰Co) (5252. Suárez-Navarro, J.A.; Moreno-Reyes, A.M.; Gascó, C.; Alonso, M.M.; Puertas, F. (2020) Gamma spectrometry and LabSOCS-calculated efficiency in the radiological characterisation of quadrangular and cubic specimens of hardened portland cement paste. Rad. Phys. Chem. 171, 108709. https://doi.org/10.1016/j.radphyschem.2020.108709.
).

Radiological studies have likewise been conducted on Portland cement concretes (1010. Labrincha, J.; Puertas, F.; Schroeyers, W.; Kovler, K.; Pontikes, Y.; Nuccetelli, C.; Krivenko, P.V.; Kovalchuk, O.; Petropavlovsky, O.; Komljenovic, M.; Fidanchevski, E.; Wiegers, R.; Volceanov. E.; Gunay, E.; Sanjuán, M. A.; Ducman, V.; Angjusheva, B.; Bajare, D.; Kovacs, T.; Bator, G.; Schreurs, S.; Aguiar, J.; Provis, J.L. (2017) From NORM by-products to building materials. In Naturally Ocurring Radiactive Materials in Construction. Chapter 7. Ed. W. Schroeyers. Elservier, 183-252, https://doi.org/10.1016/B978-0-08-102009-8.00007-4.
). Trevisi et al. (105105. Trevisi, R.; Risica, S.; D’Alessandro, M.; Paradiso, D.; Nuccetelli. C. (2012) Natural radioactivity in building materials in the European Union: a database and an estimate of radiological significance. J. Env. Rad. 105, 11-20. https://doi.org/10.1016/j.jenvrad.2011.10.001.
) ran an extensive study of the radiological data for a number of building materials, concretes among them. The concentration activities for concretes from different countries drawn from that paper are reproduced in Table 11.

The value given for each concrete as a whole includes the radionuclide content in its main components: cement, water, aggregates, admixtures and mineral additions, all of which must be borne in mind in radiological assessments, given concrete heterogeneity.

The concentration activities of standardised and other conventional cements are tabled in earlier sections of this review. Aggregates, which account for 50 % to 75 % of the total weight, play a significant part in concrete properties and behaviour. Several authors have studied the radiological behaviour of different types of natural aggregates (6464. Piedecausa, B.; Chinchón-Payá, S.; Morales, M.A.; Sanjuán, M.A. (2011) Radioactividad natural de los materiales de construcción. Aplicación al hormigón. Parte 1. Radiación externa: índice de riesgo radiactivo. Cem. Horm. 945, 40-65.
, 7474. Turhan, Ş. (2008) Assessment of the natural radioactivity and radiological hazards in Turkish cement and its raw materials. J. Env. Rad. 99 [2], 404-414. https://doi.org/10.1016/j.jenvrad.2007.11.001.
, 9292. Turhan, Ş.; Gürbüz, G. (2008) Radiological significance of cement used in building construction in Turkey. Rad. Protec. Dos. 129 [4], 391-396. https://doi.org/10.1093/rpd/ncm454.
, 9990 Espinosa, S.; Golzarri, J.I.; Gamboa, I.; Jacobsen, I. (1986) Natural radioactivity in Mexican building Materials by SSNT. Nuclear Tracks Rad. Meassu. 12, [1-6], 767-770.
, 108108. Raghu, Y.; Ravisankar, R.; Chandrasekaran, A.; Vijayagopal, P.; Venkatraman, B. (2018) Assessment of natural radioactivity and radiological hazards in building materials used in the Tiruvannamalai District, Tamilnadu, India, using a statistical approach. J. Taibah Univ. Sci. 11 [4], 523-533. https://doi.org/10.1016/j.jtusci.2015.08.004.
).

Table 11.  ²²⁶Ra, ²³²Th and ⁴⁰K activity concentration in 2727 concrete samples (105105. Trevisi, R.; Risica, S.; D’Alessandro, M.; Paradiso, D.; Nuccetelli. C. (2012) Natural radioactivity in building materials in the European Union: a database and an estimate of radiological significance. J. Env. Rad. 105, 11-20. https://doi.org/10.1016/j.jenvrad.2011.10.001.
).

Country	N of samples	226Ra (Bq kg-1)			232Th (Bq kg-1)			40K (Bq kg-1)
		Average	Min	Max	Average	Min	Max	Average	Min	Max
Austria	1	15	7	21	14	3	57	164	16	382
Belgium	37	17	5	42	16	5	42	247	85	490
Bulgaria	2	25	19	30	24	17	30	450	200	700
Czech Republic	491	33			24			495
Denmark	121	152	15	670	27	10	53	620	280	1190
Finland	294	42	33	53	37	34	39	740	359	964
France	16	44	8	126	40	4	106	88	58	118
Germany	75	54	30	100	57	23	100	629	400	1100
Greece	64	40	22	85	6	3	17	101	7	383
Hungary	97	16	13	18	22	11	33	356	204	437
Ireland	8	29	18	68	12	3	13	217	16	1100
Italy	20	19	13	23	18	12	24	329	230	457
Lithuania	1	32			17			426
Luxembourg	2	93	88	98	92	90	93	110	73	146
The Netherlands	55	35	10	115	30	6	132	263	140	870
Poland	678	115	65	200	72	36	127	666	492	1005
Portugal	38	61	1	167	50	1	152	747	11	1450
Romania	133	65	17	114	64	16	115	425	163	918
Slovakia	41	34	11	45	27	7	40	402	251	664
Slovenia	3	117	20	309	20	10	40	218	105	406
Spain	24	30			32			204
Sweden	509	242	42	1300	70	31	100	627	276	819
United Kingdom	17	61	18	89	30	13	42	493	370	650
Overall average		60			35			392
CV (%) Overall range			1	1300	1	152			7	1450

The nature of the fine (sand) and coarse aggregates used in concrete manufacture determines their contribution to the overall radionuclide concentration activity in concrete, although it varies widely. According to Raghu et al. (105105. Trevisi, R.; Risica, S.; D’Alessandro, M.; Paradiso, D.; Nuccetelli. C. (2012) Natural radioactivity in building materials in the European Union: a database and an estimate of radiological significance. J. Env. Rad. 105, 11-20. https://doi.org/10.1016/j.jenvrad.2011.10.001.
), in India the contribution of the sand to ²²⁶Ra activity may range from 90 Bq kg^-1 to 554 Bq kg^-1; in ²³²Th from 101 Bq kg^-1 to 358 Bq kg^-1 and in ⁴⁰K from 280-633 Bq kg^-1. Figure 7 compares the mean radium equivalent activity of sand to the activity of other Tiruvannamalai building materials (108108. Raghu, Y.; Ravisankar, R.; Chandrasekaran, A.; Vijayagopal, P.; Venkatraman, B. (2018) Assessment of natural radioactivity and radiological hazards in building materials used in the Tiruvannamalai District, Tamilnadu, India, using a statistical approach. J. Taibah Univ. Sci. 11 [4], 523-533. https://doi.org/10.1016/j.jtusci.2015.08.004.
).

Figure 7.  Mean radium equivalent activity in Tiruvannamalai building materials (108108. Raghu, Y.; Ravisankar, R.; Chandrasekaran, A.; Vijayagopal, P.; Venkatraman, B. (2018) Assessment of natural radioactivity and radiological hazards in building materials used in the Tiruvannamalai District, Tamilnadu, India, using a statistical approach. J. Taibah Univ. Sci. 11 [4], 523-533. https://doi.org/10.1016/j.jtusci.2015.08.004.
). Reproduced with kind permission of Elsevier.

Kovler et al. (6363. Kovler, K.; Haquin, G.; Manasherov, V.; Ne´eman, E.; Lavi, N. (2002) Natural radionuclides in building materials available in Israel. Build. Environ. 37 [5], 531-537. https://doi.org/10.1016/S0360-1323(01)00048-8.
) studied radionuclide concentrations in Israeli building materials and compared the values for different types of standard weight and lightweight aggregates. Their findings are reproduced in Table 12.

Table 12.  Specific radioactivity (Bq kg^-1) of ²²⁶Ra, ²³²Th and ⁴⁰K in natural aggregates available in Israel (6363. Kovler, K.; Haquin, G.; Manasherov, V.; Ne´eman, E.; Lavi, N. (2002) Natural radionuclides in building materials available in Israel. Build. Environ. 37 [5], 531-537. https://doi.org/10.1016/S0360-1323(01)00048-8.
).

Normal weight aggregate	Radionuclide concentration (Bq·kg-1)
	226Ra	232Th	40K
Basalt coarse	12.0	13.7	308.5
Dolomite coarse	28.0	3.1	33.6
Limestone coarse	18.3	7.4	77.1
Gravel	15.0	3.0	50.4
Limestone sand	12.1	4.1	51.1
Quartz sand	3.1	3.7	90.9
Lightweight aggregate
LECA (Norwegian weight product, made of expanded clay)	66.1	58.3	1149.0
Pumice aggregate (Greek product)	53.2	65.9	1155.0
Experimental aggregate (Israeli product, made of coal fly ash)	61.2	55.1	1015.0
Tuff	33.1	41.1	534.3

Reproduced with kind permission of Elsevier

As the data in Table 12 show, the lightweight aggregate exhibited higher values in all natural radionuclides, ⁴⁰K in particular.

The activity concentrations of the natural uranium, thorium, actinium series and ⁴⁰K are known to be high in granite, where the thorium (Th)/uranium (U) mass ratio ranges from 2.25 to 4.67 (1717. Condomines, M.; Hemond, C.; Allègre, C. (1988) UThRa radioactive disequilibria and magmatic processes. Earth Planet. Sci. Lett. 90 [3], 243-262.
, 109109. Allard, B.; Olofsson, U.; Torstenfelt, B. (1984) Environmental actinide chemistry. Inor. Chimi. Acta. 94 [4], 205-221.
, 110110. Plant, J.A.; Saunders, A.D. (1966) The Radioactive Earth. Radia. Protec. Dosi. 68 [1-2], 25-36. https://doi.org/10.1093/oxfordjournals.rpd.a031847.
). Granite is a mineral that can be used as a building material in its own right or as fine aggregate in portland cement mortars and concretes. The authors of this review recently studied (under aforementioned project BIA2016-77252-R) the effect of particle size distribution and mineralogical composition of granite from the Spanish region of Galicia on the radiological behaviour of cement mortars (1919. Suárez-Navarro, J.A.; Alonso, M.M.; Gascó, C.; Pachón, A.; Carmona-Quiroga, P.M.; Argiz, C.; Sanjuán, M.A.; Puertas, F. (accepted 2021) Effect of particle size and composition of granitic sands on the radiological behavior of mortars. Bol. Soc. Esp. Cer. Vid. Available online 2 June 2021. https://doi.org/10.1016/j.bsecv.2021.05.001.
, 111111. Sanjuan, M.A.; Argiz, C.; Alonso, M.M.; Suarez-Navarro, J.A.; Gascó, C.; Puertas, F. (2019) Natural radioactivity of Portland cement mortars made with granite sand. 15^th International Congress on Chemistry of Cement (Prague).
). According to the findings, granite particle size distribution and mineralogical composition affect radionuclide activity concentration, as may be inferred from Table 13 and Figure 8 (111111. Sanjuan, M.A.; Argiz, C.; Alonso, M.M.; Suarez-Navarro, J.A.; Gascó, C.; Puertas, F. (2019) Natural radioactivity of Portland cement mortars made with granite sand. 15^th International Congress on Chemistry of Cement (Prague).
). The activity concentrations of the thorium and uranium natural decay series were highest in the finest fractions. A correlation was observed between thorium and the MgO and Fe₂O₃ normally present in mica group phyllosilicates. ACI values were higher in granite aggregate than quartz sand mortars (Figure 9) (1919. Suárez-Navarro, J.A.; Alonso, M.M.; Gascó, C.; Pachón, A.; Carmona-Quiroga, P.M.; Argiz, C.; Sanjuán, M.A.; Puertas, F. (accepted 2021) Effect of particle size and composition of granitic sands on the radiological behavior of mortars. Bol. Soc. Esp. Cer. Vid. Available online 2 June 2021. https://doi.org/10.1016/j.bsecv.2021.05.001.
).

Table 13.  Activity concentration of radioisotopes ⁴⁰K, ²¹⁴Pb and ²¹²Pb for three types of granite aggregates, standard aggregate and cement (111111. Sanjuan, M.A.; Argiz, C.; Alonso, M.M.; Suarez-Navarro, J.A.; Gascó, C.; Puertas, F. (2019) Natural radioactivity of Portland cement mortars made with granite sand. 15^th International Congress on Chemistry of Cement (Prague).
).

Material (Spanish Region)		Size	Activity concentration (Bq kg-1)
			40K	214Pb(226Ra)	212Pb(232Th)
Granite aggregate	Coruña	230 µm	1015 ± 43	200 ± 30	70.5 ± 5.7
		0-2 mm	1030 ± 44	207 ± 31	72 ± 12
		0-4 mm	1081 ± 92	180 ± 27	65 ± 11
		5-8 mm	1206 ± 104	148 ± 22	63 ± 11
		9-20 mm	1201 ± 88	172 ± 26	95 ± 16
	Vigo	230 µm	945 ± 81	135 ± 20	99 ± 16
		0-2 mm	875 ± 75	128 ± 19	90 ± 15
		0-4 mm	841 ± 72	115 ± 17	86 ± 14
		5-8 mm	1244 ± 106	99 ± 15	88 ± 14
		9-20 mm	1191 ± 103	120 ± 18	120 ± 20
	Lugo	230 µm	1032 ± 88	114 ± 17	161 ± 26
		0-2 mm	933 ± 80	96 ± 15	148 ± 24
		0-4 mm	1050 ± 90	90 ± 14	139 ± 23
		5-8 mm	1347 ± 115	111 ± 17	152 ± 33
		9-20 mm	1073 ± 92	90 ± 14	79 ± 13
Standard siliceous aggregate		0 - 2 mm	147 ± 13	4.2 ± 0.71	7.2 ± 1.2
Cement			205 ± 18	32.0 ± 4.9	15.0 ± 2.4

Figure 8.  Variation in the activity concentration index with particle size in three types of granite aggregates (111111. Sanjuan, M.A.; Argiz, C.; Alonso, M.M.; Suarez-Navarro, J.A.; Gascó, C.; Puertas, F. (2019) Natural radioactivity of Portland cement mortars made with granite sand. 15^th International Congress on Chemistry of Cement (Prague).
). Reproduced with kind permission of Elsevier.

Figure 9.  Activity concentration index, ACI, for mortars prepared with standardised (AN) or (Coruña, Vigo or Lugo) granite aggregates with particle sizes 0 mm to 2 mm and 0 mm to 4 mm (111111. Sanjuan, M.A.; Argiz, C.; Alonso, M.M.; Suarez-Navarro, J.A.; Gascó, C.; Puertas, F. (2019) Natural radioactivity of Portland cement mortars made with granite sand. 15^th International Congress on Chemistry of Cement (Prague).
). Reproduced with kind permission of Elsevier.

Very few studies have been conducted on the contribution of concrete admixtures to overall concrete radiological behaviour. The authors of this article, under project BIA2016-77252-R, explored the behaviour of several organic and inorganic admixtures used as pigments or water repellents in concretes and mortars (4848. Suarez-Navarro, J.A.; Lanzón, M.; Moreno-Reyes, A.M.; Gascó, C.; Alonso, M.M.; Blanco-Varela, M.T.; Puertas, F. (2019). Radiological behaviour of pigments and water repellents in cement-based mortars. Construc. Build. Mat. 225, 879-885. https://doi.org/10.1016/j.conbuildmat.2019.07.271.
). Low radionuclide concentrations were observed except in natural pigments, which raised the ²³⁸U series concentration. Those low levels were attributable to the raw material used, namely the red mud generated in aluminium production. The radiological risk for the general public and for workers due to exposure to pigment-modified construction materials was consequently assessed. The doses received by those two communities were neither significant nor constituted any perceptible hazard, essentially in light of the small amounts of pigment used to prepare mortars.

4.5.2. Alkali-activated cements and concretes. Geopolymers

 ⌅

Alkali-activated materials (AAMs) are the product of the reaction between a (solid or dissolved) alkaline metal and a solid silicoaluminate powder (binder or precursor). The precursor may be metakaolin, steel or ion mill slag, a natural pozzolan or fly or bottom ash. The alkalinity required is sourced from alkaline hydroxides, silicates, carbonates, sulfates, aluminates or oxides. As many of the precursors and some activators may carry NORM waste, the radionuclide concentration of these alternative cements and mortars should be determined (1010. Labrincha, J.; Puertas, F.; Schroeyers, W.; Kovler, K.; Pontikes, Y.; Nuccetelli, C.; Krivenko, P.V.; Kovalchuk, O.; Petropavlovsky, O.; Komljenovic, M.; Fidanchevski, E.; Wiegers, R.; Volceanov. E.; Gunay, E.; Sanjuán, M. A.; Ducman, V.; Angjusheva, B.; Bajare, D.; Kovacs, T.; Bator, G.; Schreurs, S.; Aguiar, J.; Provis, J.L. (2017) From NORM by-products to building materials. In Naturally Ocurring Radiactive Materials in Construction. Chapter 7. Ed. W. Schroeyers. Elservier, 183-252, https://doi.org/10.1016/B978-0-08-102009-8.00007-4.
).

The radiological behaviour of alkali-activated slag and fly ash cement pastes was first studied by Puertas et al. (6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
) in vitreous blast furnace slag (BFS) activated with waterglass (AAS) (SiO₂/Na₂O ratio of 0.86) and the same precursor activated with NaOH pre-treated waste glass (waste glass-AAS) at the same SiO₂/Na₂O ratio. The fly ash(FA) precursor, in turn, was activated with an 8 M NaOH solution containing 15 % waterglass (N/15Wg-AAFA) as well as with waste glass (waste glass-AAFA). Their findings are summarised in Table 14.

Table 14.  Post-alkaline activation activity concentrations (Bq kg^-1) in raw materials (fly ash, BFS and waste glass) and cements (uncertainty, k=2) (1010. Labrincha, J.; Puertas, F.; Schroeyers, W.; Kovler, K.; Pontikes, Y.; Nuccetelli, C.; Krivenko, P.V.; Kovalchuk, O.; Petropavlovsky, O.; Komljenovic, M.; Fidanchevski, E.; Wiegers, R.; Volceanov. E.; Gunay, E.; Sanjuán, M. A.; Ducman, V.; Angjusheva, B.; Bajare, D.; Kovacs, T.; Bator, G.; Schreurs, S.; Aguiar, J.; Provis, J.L. (2017) From NORM by-products to building materials. In Naturally Ocurring Radiactive Materials in Construction. Chapter 7. Ed. W. Schroeyers. Elservier, 183-252, https://doi.org/10.1016/B978-0-08-102009-8.00007-4.
, 6565. Puertas, F.; Alonso, M.M.; Torres-Carrasco, M.; Rivilla, P.; Gasco, C.; Yagüe, L.; Suárez, J. A.; Navarro, N. (2015) Radiological characterization of anhydrous/hydrated cements and geopolymers. Construc. Build. Mat. 101 [1], 1105-1112. https://doi.org/10.1016/j.conbuildmat.2015.10.074.
).

Series	238U		232Th			40K	ACIa
Material	234Th	214Pb	228Ac	212Pb	208Tl
Fly ash	130 ± 7.1	127.4 ± 1.3	130.3 ± 1.5	133.8 ± 1.3	41.33 ± 0.57	316.4 ± 5.9	1.1815 ± 0.0089
BFS	156.4 ± 6.8	147.2 ± 1.4	45.7 ± 0.86	42.9 ± 1.2	14.71 ± 0.30	76.3 ± 2.7	0.7448 ± 0.0065
Waste glass	11.4 ± 1.1	8.73 ± 0.19	5.83 ± 0.22	6.28 ± 0.12	1.867 ± 0.075	226.8 ± 4.4	0.1338 ± 0.0020
Wg-AAS	91.5 ± 5.6	48.7 ± 1.1	22.84 ± 0.71	23.3 ± 0.69	7.7 ± 0.39	77.0 ± 5.0	0.3022 ± 0.0054
Waste glass-AAS	94.4 ± 6.7	54.5 ± 1.4	23.78 ± 0.81	24.99 ± 0.83	8.04 ± 0.41	89.2 ± 4.8	0.3303 ± 0.0064
N/15Wg-AAFA	56.4 ± 5.7	36.44 ± 0.97	67.8 ± 1.4	75.1 ± 1.8	21.57 ± 0.59	578 ± 15	0.6531 ± 0.0092
Waste glass-AAFA	57.4 ± 3.2	37.9 ± 1.1	62.2 ± 1.2	75.1 ± 1.2	22.62 ± 0.63	550 ± 14	0.6207 ± 0.0084

The overall ACI values were higher for fly ash than for vitreous slag and the former were much higher than observed for ordinary Portland cement. Nonetheless, as the values recorded for these geopolymers were consistently lower than 1, they would be fully compliant with the existing legislation.

A more recent study conducted by Nuccetelli et al. (7575. Nuccetelli, C.; Trevisi, R.; Ignjatović, I.; Dragaš, J. (2017) Alkali-activated concrete with Serbian fly ash and its radiological impact. J. Env. Rad. 168, 30-37. https://doi.org/10.1016/j.jenvrad.2016.09.002.
) of the radiological behaviour of concretes manufactured with fly ash from five coal-fired power plants in Serbia yielded the results given in Table 15. Their findings also showed ACI values consistently under 1 in all the alkaline concretes analysed.

Table 15.  Natural radionuclide activity concentration in alkali-activated fly ash concretes (7575. Nuccetelli, C.; Trevisi, R.; Ignjatović, I.; Dragaš, J. (2017) Alkali-activated concrete with Serbian fly ash and its radiological impact. J. Env. Rad. 168, 30-37. https://doi.org/10.1016/j.jenvrad.2016.09.002.
).

AAFASC samples	232Th	226Ra	40K	ACI
	(Bq kg-1)
C_FA-1	18.4 ± 0.4	28.5 ± 1.5	232 ± 4	0.26 ± 0.1
C_FA-2	18.6 ± 0.4	28.8 ± 1.3	225 ± 4	0.26 ± 0.1
C_FA-3	12.5 ± 0.2	21.2 ± 0.9	196 ± 3	0.20 ± 0.1
C_FA-4	14.9 ± 0.3	27.7 ± 1.7	218 ± 3	0.24 ± 0.1
C_FA-5	16.1 ± 0.3	28.3 ± 1.2	197 ± 3	0.24 ± 0.1

Other authors report that alkali-activated metakaolin materials are also free of radiological risk (8888. Ivanović, M.; Kljajević, Lj.; Nenadović, M.; Bundaleski, N.; Vukanac, I.; Todorović, B.; Nenadović, S. (2018) Physicochemical and radiological characterization of kaolin and its polymerization products. Mater. Construcc. 68 [330], e155 https://doi.org/10.3989/mc.2018.00517.
). That paper also specifies the absorbed dose rate (DR) and the annual effective dose rate (EDR), calculated as recommended in the UNSCEAR 2000 report. The authors note that the specific activity of the natural radionuclides in metakaolin resulting from pre-heating kaolin at 750 °C was 1.6, while the geopolymer exhibited the lowest specific activities.

The present authors, again under the umbrella of project BIA2016-77252-R, explored the compositions of a number of geopolymer pastes, including hybrid systems (blends of OPC and an activated precursor traditionally used in geopolymers). The precursors included coal fly ash, glassy blast furnace slag and red mud (9090. Skaropoulou, A.; Tsivilis, S.; Kakali, G.; Sharp, J. H.; Swamy, R. N. (2009) Long term behavior of Portland limestone cement mortars exposed to magnesium sulfate attack. Cem. Concr. Comp. 31 [9], 628-636 https://doi.org/10.1016/j.cemconcomp.2009.06.003.
). The radiological findings graphed in Figure 10 show that when red mud accounts for ≥60 % of a cement or geopolymer, the ACI values exceed 1. At lower values the waste is Euratom directive-compliant. Croymans et al. (112112. Croymans, T.; Schroeyers, W.; Krivenko, P.; Kovalchuk, O.; Pasko, A.; Hult, M.; Marissens, G.; Lutter, G.; Schreurs, S. (2017) Radiological characterization and evaluation of high volume bauxite residue alkali activated concretes. J. Env. Rad. 168, 21-29. https://doi.org/10.1016/j.jenvrad.2016.08.013.
) contend that to ensure workers receive lower than the safe occupational dose stipulated in Radiation Protection (RP) 122 (0.3 mSv/a), building materials should contain less than 75 wt% of Ukrainian bauxite waste. Applying that same criterion, however, no constraint on the use of Ukrainian bauxite waste would be necessary in road construction.

Figure 10.  Activity concentration index (I) for the pastes studied (9494. Alonso, M.M.; Pasko, A.; Gascó, C.; Suarez, J.A.; Kovalchuk, O.; Krivenko, P.; Puertas, F. (2018) Radioactivity and Pb and Ni immobilization in SCM-bearing alkali-activated matrices. Construc. Build. Mat. 159, 745-754. https://doi.org/10.1016/j.conbuildmat.2017.11.119.
).