## 2 Materials and Methods
### Environmental Study
#### 2.5.2 Radiological Study  
Radioactive nuclides are found in varying amounts in traditional building materials and wastes [43]. Natural building materials and wastes contain various amounts of natural radioactive nuclides [43]. Many wastes could be considered NORM (naturally occurring radioactive material) [44], and their use is subject to the legal restrictions of international radiation protection safety standards, such as the European Directive 2013/59 [45]. These standards establish several parameters to characterize the final construction material containing wastes: activity concentration index (I), the absorbed dose (D, Gy/h), radium activity (Ra\({}_{\text{eq}}\)), and effective dose (E, Sv/y). All these parameters are obtained by their activity concentration (in Bq/kg) of \({}^{232}\)Th and \({}^{238}\)U series radionuclides, and \({}^{40}\)K, which can be determined by gamma-ray spectrometry [8]. Two samples were tested for each composition. Cylinder specimens were positioned directly at the top of the detector endcap. A Canberra low-background high-purity germanium GR-6022 reverse electrode coaxial (XtRa) detector (60% relative efficiency) shielded by a 10 cm-thick high-purity lead served as the primary detector. The detector was connected to a DSA-1000 digital spectrum analyzer. The spectra were analyzed using Canberra Genie 2000 gamma software (version 3.2). All the samples were related to one day of sampling. The activity concentrations of the different gamma emitters were determined through the energies of \({}^{232}\)Th (911.2 keV of \({}^{228}\)Ac), \({}^{238}\)U (or its daughter \({}^{226}\)Ra via 351 keV emissions of \({}^{214}\)Pb), and \({}^{40}\)K (1460 keV). Additionally, a Low Energy Germanium (LEGe) GL-2020 detector was used for checking performance at low and moderate energies because it was fabricated with a thin side and front contact affording a better resolution than any other detector. The LEGe detector had an active area of 2000 mm\({}^{2}\) and thickness of 20 mm, and a 0.6 mm carbon epoxy window that improves ruggedness while maintaining good low-energy transmission was used. The detectors' absolute efficiencies were calculated using Canberra LabSOCS software, which is based on the MCNP Monte Carlo code, considering the self-absorption of low-energy gamma rays within the sample [46]. The minimum detectable activity (MDA) and the decision level of both detectors for \({}^{40}\)K, \({}^{210}\)Pb, \({}^{238}\)U, and \({}^{232}\)Th were calculated according to ISO 11929-4 [47]. Additionally, an alternative geometry was checked by placing a cylinder specimen viewed from the side (see Figure 2). The MDA values for this measuring geometry were compared with the geometry of a cylinder specimen viewed from the top. Finally, the gamma-ray spectrometry analyses were validated based on several inter-comparison programs [46; 48]. The gamma radiation dose was calculated to assess the radiological hazard of the proposed hydraulic binders. Activity concentrations of \({}^{226}\)Ra, \({}^{232}\)Th, and \({}^{40}\)K were converted into the absorbed gamma dose rate (D) using the conversion factors presented in the literature [49] at 1 m above ground (in mGy/h by Bq/kg):  
\[D\left(\frac{nG}{h}\right)=0.462\cdot a_{Ra-226}+0.604\cdot a_{Th-232}+0.147 \cdot a_{k-40} \tag{2}\]  
Then, D can be converted into the annual effective dose indoors (E) according to Equation (3):  
\[E\left(\frac{mSv}{y}\right)=0.8\cdot 10^{-6}\cdot Q\cdot D\cdot T \tag{3}\]  
Figure 2: Gamma-ray spectrometry setup showing the measuring geometries with a cylinder specimen viewed from the top (**left**), and a cylinder specimen viewed from the side (**right**). where (1) Q is a converting value of 0.7 Sv/Gy for gamma-ray environmental exposure; (2) the indoor occupancy factor of 0.8 indicates that 80% of the time was spent indoors; and (3) T is the time, equal to 1 year (8760 h.) [49].