# Effect of Gamma Irradiation on Cementitious Materials Hydration

Rémy Hoarau Belkhiri, Stéphane Poyet, Mejdi Neji, Elisa Leoni, Stéphane Esnouf, Alexandre Dauzères, Thibault Charpentier

► To cite this version:

Rémy Hoarau Belkhiri, Stéphane Poyet, Mejdi Neji, Elisa Leoni, Stéphane Esnouf, et al.. Effect of Gamma Irradiation on Cementitious Materials Hydration. Journal of Advanced Concrete Technology, 2025, 23 (12), pp.546 - 559. 10.3151/jact.23.546. hal-05453418

HAL Id: hal-05453418

https://hal.science/hal-05453418v1

Submitted on 12 Jan 2026

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons CC BY 4.0 - Attribution - International License
# Effect of Gamma Irradiation on Cementitious Materials Hydration

Rémy Hoarau Belkhiri<fnref n="1" />, Stéphane Poyet<fnref n="2" />*, Mejdi Neji<fnref n="3" />, Elisa Leoni<fnref n="4" />, Stéphane Esnouf<fnref n="4" />, Alexandre Dauzères<fnref n="3" /> and Thibault Charpentier<fnref n="5" />

Received 7 July 2025, accepted 1 December 2025

doi: https://doi.org/10.3151/jact.23.546

## Abstract

Cementation is the principal method for long-term conditioning of intermediate- and low-level nuclear waste (ILW/LLW). During hydration, cementitious matrices are exposed to ionizing radiation - primarily gamma rays - raising the question of the potential effect of irradiation on hydration reactions and, ultimately, on material properties. The available literature presents contradictory results, partly attributable to experimental biases related to temperature, drying, and carbonation under irradiation conditions.

This study aims to evaluate the impact of gamma irradiation on the hydration of C₃S, CEM I, CEM III/A, and CEM III/C pastes under controlled experimental conditions (constant temperature, autogenous environment, sealed systems). The mineralogical and microstructural properties of irradiated materials were systematically compared to those of non-irradiated control samples and mature pastes irradiated under analogous conditions. The results show an absence of significant alteration in mineralogy at the mesoscale, and in mechanical properties, with the methodology considered. Only slight modifications in pore size distribution were observed.

These observations indicate the absence of a direct coupling between gamma irradiation and hydration. They confirm that cementitious matrices retain their properties under conditions representative of the immobilization process for ILW/LLW waste packages by cementation. Thus, the assumptions of safety studies, based on data obtained from mature materials, remain fully valid.

## Keywords

Irradiation

Cement

Hydration

Characterization

Radiolysis

## *Corresponding author

Université Paris-Saclay, CEA, Service de Recherche en Corrosion et Comportement des Matériaux, Gif-sur-Yvette, France.

E-mail: stephane.poyet@cea.fr

## 1. Introduction

Cement-based encapsulation is widely implemented for the long-term management of Low- and Intermediate-Level Short-Lived (LILW-SL) and Intermediate-Level Long-Lived (ILW-LL) radioactive waste. Wastes are immobilized within a tailored cementitious matrix, such as grout or mortar, to ensure containment and stability over extended timeframes. A direct consequence of this technique is the exposure of the cementitious matrix to ionizing radiation emitted by the waste, predominantly gamma rays, throughout the hydration process. Depending on the waste configuration, dose rates experienced by these matrices can reach up to 0.2 kGy/h (EDF, 2015).

During hydration, cementitious materials comprise a solid phase (initially anhydrous compounds, subsequently hydrates) and a liquid phase (mixing water, later evolving into pore solution). Under gamma irradiation, previous studies have shown that the solid phase remains largely unaffected by radiation up to very high absorbed doses, exceeding 100 MGy (Baral et al., 2022; Field et al., 2015; Maruyama et al., 2018; Pomaro, 2016). In contrast, the liquid phase is subject to immediate partial chemical dissociation through radiolysis, forming highly reactive radical species (Allen, 1948). For

LILW-SL and ILW-LL, the absorbed dose during early hydration is insufficient to induce significant changes in the solid phase, given the rapid kinetics of matrix hydration. Therefore, the primary anticipated effect of irradiation during hydration is the alteration of the liquid phase composition and the generation of radical species. Due to their extreme reactivity, it is pertinent to investigate whether these irradiation-induced radicals interact with cement hydration reactions. One notable example is the possible formation of calcium peroxide octahydrate (CaO₂·8H₂O) via the reaction between portlandite and hydrogen peroxide (H₂O₂) (Bouniol & Lapuerta-Cochet, 2012):

$$Ca(OH)_2 + H_2O_2 + 6H_2O \rightarrow CaO_2\cdot8H_2O \quad (1)$$

Such radicals could potentially modify the mineralogical assemblage and, thus, the properties and long-term durability of the cementitious material. A key issue is that current safety assessments for radioactive waste conditioning matrices are primarily based on data from non-irradiated or mature-irradiated cementitious materials after completion of hydration. This reliance raises concerns about the representativeness of these assessments, given that the actual matrices may undergo property changes due to irradiation during the initial stages of hydration-changes that are not accounted for in conventional safety case data.

<footnote n="1">¹ Researcher, Autorité de Sûreté Nucléaire et de Radioprotection (ASNR), F-92260, Fontenay-aux-Roses, and Université Paris-Saclay, CEA, Service de Recherche en Corrosion et Comportement des Matériaux, F-91191 Gif Sur Yvette, France.</footnote>

<footnote n="2">² Research Engineer, Université Paris-Saclay, CEA, Service de Recherche en Corrosion et Comportement des Matériaux, F-91191 Gif Sur Yvette, France.</footnote>

<footnote n="3">³ Researcher, Autorité de Sûreté Nucléaire et de Radioprotection (ASNR), F-92260, Fontenay-aux-Roses, France.</footnote>

<footnote n="4">⁴ Researcher, Université Paris-Saclay, CEA, Service de Physico-Chimie, F-91191 Gif Sur Yvette, France.</footnote>

<footnote n="5">⁵ Researcher, Université Paris-Saclay CEA, CNRS, Nanosciences et Innovation pour les Matériaux la Biomedecine et l'Energie (NIMBE), F-91191 Gif-sur-Yvette cedex, France.</footnote>
<caption>**Table 1**</caption>

Summary of available studies on the effects of irradiation on the hydration of cementitious materials.

<table><thead><tr><th rowspan="2">References</th><th colspan="3">Irradiation</th><th colspan="3">Material</th><th rowspan="2">Observed effect</th><th rowspan="2">Potential bias</th></tr><tr><th>Dose rate (Total dose)</th><th>Duration</th><th>Temperature irradiated / Control</th><th>Type</th><th>W/C</th><th>Δt<sub>0</sub></th></tr></thead><tbody><tr><td>Glinicki et al. (2021)</td><td>≈4.6 kGy/h (35 to 39 kGy)</td><td>8 h</td><td>10 to 13 °C / 10 °C, 23 and 40 °C</td><td>Mortar</td><td>0.45</td><td>60 min</td><td>Total porosity decrease. Pore size refinement. Flexural strength increase. Higher hydration rate.</td><td>Temperature effect not considered</td></tr><tr><td>Dąbrowski et al. (2021)</td><td>≈3.5 kGy/h (56 kGy)</td><td>16 h</td><td>15 °C / 15 °C</td><td>Mortar</td><td>0.50</td><td>60 min</td><td>Elastic modulus increase. Higher hydration rate.</td><td>Temperature effect not considered</td></tr><tr><td>Burnham et al. (2016)</td><td>≈4 mGy/h (0.75 Gy)</td><td>168 h</td><td>N.R.</td><td>Mortar</td><td>0.40</td><td>N.R.</td><td>Total porosity decrease. Compressive strength increase. Increase in compressive strength, depending on the absorbed dose.</td><td>Samples irradiated in open air</td></tr><tr><td>Craeye et al. (2015b)</td><td>0.01 to 2 kGy/h (0.04 to 32 kGy)</td><td>24 to 672 h</td><td>N.R.</td><td>Mortar</td><td>0.48 to 0.78</td><td>30 min</td><td>Total porosity decrease. Effect of water-to-cement ratio and slag content. Mass loss measured after irradiation.</td><td>Unclear irradiation conditions</td></tr><tr><td>Khmurovska et al. (2018)</td><td>3.9 - 4.7 kGy/h (2.3 to 2.6 MGy)</td><td>1200 h</td><td>10 to 23°C / 10 to 23°C</td><td>OPC Mortar</td><td>0.38</td><td>8 h</td><td>Pronounced shrinkage in irradiated samples not sealed with Parafilm compared to similar controls, promoting carbonation.</td><td>Unclear irradiation conditions</td></tr><tr><td>Alvares Ferreira et al. (2018)</td><td>N.R. (6 kGy)</td><td>N.R</td><td>N.R.</td><td>OPC Mortar & Paste</td><td>0.50</td><td>7 d</td><td>Increase in total porosity. Higher hydration rate.</td><td>Temperature effect not considered</td></tr><tr><td>Mobasher et al. (2015)</td><td>≈18.6 Gy/h (4.77 MGy)</td><td>256 h</td><td>50°C / 20°C and 50°C</td><td>Paste (CEM I + Slag)</td><td>0.35</td><td>8 d</td><td>Reduction in physically adsorbed water content, inducing microcracking. Total porosity increase. Compressive strength increase.</td><td>Samples irradiated in open air</td></tr></tbody></table>

N.R. = Data not reported in the article

Δt₀ = Time interval between material preparation and the beginning of irradiation

Available studies investigating the effects of radiation on the hydration of cementitious materials are limited and tend to suggest the existence of a measurable effect; however, the experimental results remain contradictory (Table 1). Craeye et al. (2015a) reported an increase in total pore volume, whereas the findings of Alvares Ferreira et al. (2018) and Glinicki et al. (2021) indicate the opposite trend. Regarding mechanical properties, a decrease in the elastic modulus of cement pastes following early-age gamma exposure has been observed (Dąbrowski et al., 2021; Glinicki et al., 2021; Mobasher et al., 2015), yet other studies have contradicted these findings (Craeye et al., 2015b; Khmurovska et al., 2021). Additionally, several investigations have reported a higher hydration rate after gamma irradiation compared to control specimens (Alvares Ferreira et al., 2018; Dąbrowski et al., 2021; Glinicki et al., 2021) but these results are not supported by Mobasher et al. (2015). It is also worth noting that a similar experiment investigating the effect of PuO₂ incorporation at an early age revealed only a limited impact of alpha particles (Kearney et al., 2020).

These results suggest that the observed contradictions may be attributed to significant differences in the experimental methodologies considered (Table 1). During irradiation, a portion of the energy transferred to the material and its surroundings is dissipated as heat, resulting in elevated temperatures in the irradiated material and the ambient air. Temperature is known to exert a substantial influence on cementitious materials hydration. Under endogenous conditions (i.e., without water exchange between the material and its environment), the hydration kinetics increase with temperature (Cong & Kirkpatrick, 1995; Gallucci et al., 2013; Lothenbach et al., 2007). Thus, if control specimens are maintained at a lower temperature than irradiated samples, one might erroneously conclude that irradiation accelerates hydration

and/or enhances mechanical properties. Conversely, under open conditions—where water exchange with the environment is possible— increased temperature can accelerate drying, thereby inhibiting hydration (Patel et al., 1988) and potentially leading to the mistaken conclusion that irradiation slows hydration or causes cracking.

In open systems, the presence of CO₂ can promote carbonation of the material, which may either densify the matrix through CaCO₃ precipitation—thus improving mechanical properties (Ahmed & Benharzallah, 2017; Chang & Chen, 2005; Jerga, 2004), or contribute to cracking and a reduction in mechanical performance (Auroy et al., 2018; Borges et al., 2010; Cui et al., 2020; Wan et al., 2014). During hydration, the phenomena of drying, carbonation, and temperature variation may overlap with the effects of irradiation and be responsible for the experimental results observed. Therefore, it is impossible to conclusively identify a potential effect of irradiation on the hydration of cementitious materials based solely on these existing results.

This study aims to provide a better understanding of the mechanisms induced by gamma irradiation of cementitious materials during their hydration while minimizing biases related to temperature, drying, and carbonation. This is done by conducting irradiation under autogenous conditions and paying attention to submitting the control specimens to a temperature similar to the irradiated ones. To this end, C₃S, CEM I, CEM III/A, and CEM III/C pastes were subjected to gamma irradiation immediately after preparation/mixing, over durations covering part of their hydration. The pastes were irradiated in sealed containers (closed system) to limit or eliminate the effects of drying and carbonation. In parallel, control specimens were stored under the same conditions (closed system) and at the same temperature but without irradiation. The mineralogy, microstructure, and mechanical properties
<caption>**Table 2**</caption>

Mineralogical compositions (from the cements data sheet, wt.%) and verified by XRD quantitative phase analysis.

<table><caption>**Table 3**</caption><thead><tr><th>Cement</th><th>C<sub>3</sub>S</th><th>C<sub>2</sub>S</th><th>C<sub>3</sub>A</th><th>C<sub>4</sub>AF</th><th>Gypsum (C̄SH<sub>2</sub>)</th><th>Anhydrite (C̄S)</th><th>Calcite (C̄C)</th><th>Slag</th></tr></thead><tbody><tr><td>C<sub>3</sub>S/C<sub>2</sub>S</td><td>92.0</td><td>8.0</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>CEM I</td><td>62.7</td><td>9.5</td><td>10.4</td><td>7.6</td><td>5.2</td><td></td><td></td><td></td></tr><tr><td>CEM III/A</td><td>23.2</td><td>3.8</td><td>3.5</td><td>2.8</td><td></td><td>3.9</td><td>3.8</td><td>63.2</td></tr><tr><td>CEM III/C</td><td>10.0</td><td>1.3</td><td>1.4</td><td>1.1</td><td></td><td>4.5</td><td></td><td>81.2</td></tr></tbody></table>

Main properties of the anhydrous reagents used in the study (from the cements data sheet).

<table><thead><tr><th>Cement</th><th>SSA</th><th>ρ</th><th>Strength class</th><th>f<sub>c</sub> at 28 d</th><th>Setting time</th><th>Q(41 h)</th></tr></thead><tbody><tr><td>C<sub>3</sub>S/C<sub>2</sub>S</td><td>N/A</td><td>3.1 g/cm<sup>3</sup></td><td>N/A</td><td>N/A</td><td>N/A</td><td>N/A</td></tr><tr><td>CEM I</td><td>3.8 cm<sup>2</sup>/g</td><td>3.1 g/cm<sup>3</sup></td><td>52.5 N</td><td>63 MPa</td><td>3 h 30 min</td><td>375 J/g</td></tr><tr><td>CEM III/A</td><td>4.2 cm<sup>2</sup>/g</td><td>2.9 g/cm<sup>3</sup></td><td>52.5 L</td><td>64 MPa</td><td>4 h 00 min</td><td>290 J/g</td></tr><tr><td>CEM III/C</td><td>4.6 cm<sup>2</sup>/g</td><td>2.9 g/cm<sup>3</sup></td><td>32.5 N</td><td>44 MPa</td><td>4 h 30 min</td><td>179 J/g</td></tr></tbody></table>

SSA = Specific surface area

ρ = Density

f<sub>c</sub> = Compressive strength according to EN 197-1 (test on mortar)

Q(41 h) = Heat emitted after 41 hours of hydration

N/A = Data not available or not measured

of these samples were analyzed to identify any potential effects of irradiation. Finally, similar experiments were conducted on mature pastes to confirm or refute any possible coupling between irradiation and hydration.

## 2. Material and methods

### 2.1 Samples preparation

The C<sub>3</sub>S pastes were prepared with a water-to-cement ratio (W/C) of 0.5, ensuring good workability (ease of mixing and placing) while avoiding any bleeding (water separation at the surface). The C<sub>3</sub>S used was supplied by the Septodont Company¹ (see Notations) and consists of a mixture primarily composed of C<sub>3</sub>S (92 wt.%) along with C<sub>2</sub>S (8 wt.%). The blend composition was verified using XRD and NMR analyses. All cement pastes were prepared with a W/C ratio of 0.4. The CEM I cement was supplied by the Beffes cement plant (Calcia, France), while the CEM III/A and CEM III/C types were provided by the Rombas cement plant (Calcia, France). The characteristics of the binders are summarized in Tables 2 and 3.

The pastes were prepared in small batches (approximately 200 mL) using a benchtop stirrer (IKA Microstar 15). Ultrapure water (18.2 MΩ·cm) was used, and the mixture was stirred for 5 minutes to achieve the proper consistency for casting: 2 minutes at 250 rpm, followed by 3 minutes at 500 rpm. The mixture was then poured into polystyrene² (see Notations) conical-bottom test tubes (h = 6 cm; Ø = 1.4 cm), which

were vibrated on a vibrating plate for 2 minutes to ensure compaction and remove air bubbles.

For irradiation experiments conducted during hydration, the open test tubes were placed as quickly as possible into sealed vessels (using a silver gasket and bolting the lid with a torque wrench, see Fig. 1) to minimize drying and carbonation during irradiation. No pumping or air replacement was performed in the vessels; thus, they were filled with air at room temperature and pressure. The time interval between paste preparation and the start of irradiation was around 30 minutes.

The pastes were prepared as described above for irradiation tests on mature pastes, and the test tubes were immediately closed and sealed with Parafilm® to maintain endogenous conditions. They were then stored in an inert glove box (nitrogen atmosphere) for one year before irradiation tests were conducted according to the previously described protocol.

### 2.2 Irradiation

The irradiations were carried out in three series of experiments on two different experimental platforms, both equipped with a ⁶⁰Co (gamma radiation) source but with different activities: EPICUR³ and LABRA⁴ (see Notations). The irradiation test conditions (dose rate, material, etc.) are summarized in Table 4. Dose rates were determined in preliminary tests, which replicated the intended irradiation conditions, using alanine dosimeters attached to the test tubes within the vessel.

During the EP22 experiment (EPICUR platform), pastes undergoing hydration (C<sub>3</sub>S and CEM I) were exposed to a dose rate of 2.9 kGy/h

<figure><img src="image_2.png" /><figcaption>**Fig. 1**</figcaption></figure>

(A) Polystyrene molds used for sample casting (h = 6 cm; Ø = 1.4 cm), and (B) Stainless steel vessel (X2 CrNi 19-11; V = 265 cm³).
<table><caption>**Table 4**
Studied pastes and irradiation conditions.</caption><thead><tr><th rowspan="2">Exp. / Platform</th><th rowspan="2">Irradiation</th><th rowspan="2">Binder</th><th rowspan="2">W/C</th><th colspan="2">Dose rate / Dose</th><th rowspan="2">Temperature (°C) Irradiated / Control</th><th rowspan="2">Freeze drying</th></tr><tr><th>Duration</th><th>Dose</th></tr></thead><tbody><tr><td rowspan="2">EP22</td><td rowspan="2">EPICUR</td><td>During hydration</td><td>C<sub>3</sub>S<br>CEM I</td><td>0.50<br>0.40</td><td>14 d at<br>2.9 kGy/h</td><td>1 MGy</td><td>35<br>/ 20 and 35</td><td>Done at 28 d</td></tr><tr><td>C<sub>3</sub>S<br>CEM I</td><td>0.50<br>0.40</td><td>28 d at<br>2.5 kGy/h</td><td>1.7 MGy</td><td>15<br>/ 15</td><td>Done at 28 d</td></tr><tr><td rowspan="2">LA22</td><td rowspan="2">LABRA</td><td>During hydration</td><td>CEM III/A<br>CEM III/C</td><td>0.40<br>0.40</td><td></td><td></td><td></td><td></td></tr><tr><td>C<sub>3</sub>S<br>CEM III/A</td><td>0.50<br>0.40</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td rowspan="2">EP23</td><td rowspan="2">EPICUR</td><td rowspan="2">Mature pastes</td><td>CEM I</td><td>0.40<br>0.40</td><td>10 d at<br>11.6 kGy/h</td><td>2.8 MGy</td><td>55<br>/ 55</td><td>No freeze-drying</td></tr><tr><td>CEM III/A<br>CEM III/C</td><td>0.40<br>0.40</td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

for 2 weeks (346 hours, absorbed dose of 1.0 MGy). The temperature inside the chamber was continuously monitored throughout irradiation. After a few hours, it stabilized and remained constant, with an average value of around 35 °C. The pastes were kept in the irradiator under radiation for 14 days, then removed and stored in a glove box (controlled temperature within the laboratory of 20 ± 3 °C) for additional 14 days before being freeze-dried to limit the effects of residual hydration. To study the effect of temperature induced by radiation, two vessels containing control pastes were kept in two different laboratory ovens: one at 35 °C to replicate the temperature conditions inside the irradiator, and the other at 20 °C to replicate standard ambient conditions.

The EP23 experiment was also conducted on the EPICUR platform but after the replacement of the ⁶⁰Co sources, which significantly increased both the dose rate and the average temperature inside the irradiator, as shown in **Table 4**. This test was performed on mature pastes, and the samples were not freeze-dried at the end of the experiment. The LA22 experiment was carried out on the LABRA platform in a large, ventilated hall, where the recorded average temperature was 15 °C (see **Table 4**). This test was performed on pastes undergoing hydration over a total duration of 28 days. The control pastes were placed in the ventilated hall outside the irradiation chamber. All pastes were freeze-dried immediately after irradiation (at 28 days of hydration). It should be noted that the dose rates used in this study (between 2.5 and 12 kGy/h) are much higher than those to which cementitious immobilization matrices would be exposed under operational conditions in France.

## 2.3 Methods

Microindentation tests were performed on polished sections. The polishing protocol followed the work of (Dewitte et al., 2024), which helps minimize measurement issues related to surface roughness. An Anton Paar NH3 nano-indenter equipped with a Berkovich-type indenter tip was used in this study. Grids of 24 × 24 measurement points with 200 µm spacing were performed. The loading/unloading rates were set at 300 mN/min, and the maximum load was set at 300 mN. Data processing was carried out using the Gaussian mixtures method from the Python sklearn library (Bernachy-Barbe, 2019; Jain et al., 1999). Deconvolution clusters were defined based on Constantinides and Ulm (2004), Vandamme and Ulm (2013) and Velez et al. (2001). Poisson's ratio of 0.24 was chosen, following the protocol used in another study (Dewitte, 2023).

Thermogravimetric analyses (TGA) were performed using a Netzsch STA 409 PC LUXX device. The ground samples (120 mg ± 0.1 mg) were heated from 30 °C to 1150 °C at 10 °C/min under a nitrogen flow (80 mL/min) (Villain et al., 2007). Four analyses were carried out for each sample set. The results were post-processed using the tangential method to evaluate the amount of portlandite, whose decomposition temperature is between 450 and 550 °C (Lothenbach et al., 2017;

Ramachandran et al., 2002).

Nuclear Magnetic Resonance (NMR) spectra with magic-angle spinning (MAS) were acquired on a Bruker Avance IV NEO 500WB spectrometer (11.7 T magnetic field) for the ²⁷Al nucleus and on a Bruker Avance II 300WB spectrometer (7.2 T magnetic field) for ¹H and ²⁹Si nuclei. In these configurations, spectra were acquired using a Bruker CPMAS (Cross-Polarization Magic Angle Spinning) 4 mm probe (powder samples compacted in ZrO₂ rotors, about 100 mg) at a spinning frequency of 12.5 kHz (rotation period 80 µs).

For ²⁹Si, spectra were acquired using a spin echo sequence (90-tau-180-tau-acquisition, with echo delay tau synchronized with spinning, tau = 80 µs), preceded by a presaturation consisting of a train of 90° pulses separated by a 10 ms delay nulling the magnetization, followed by a variable recovery/relaxation period. This recovery time was set at 8 s (after verifying the stability of relative intensities for different recovery times), and 1024 to 4096 scans were accumulated to obtain a satisfactory signal-to-noise ratio. The ¹H proton spectra were acquired with a spin echo synchronized with spinning and presaturation.

The ²⁷Al spectra were recorded with a short single pulse (1 µs, to operate in the linear excitation regime and avoid intensity variations due to quadrupolar interaction effects) to obtain quantitative data (the area of each contribution represents the relative amount of each environment), and with RF decoupling of protons. The recycle delay was set to 1 s, and 4096 scans—or more—were accumulated. Chemical shifts were calibrated using a solid sample of tetrakistrimethylsilane (TKS, ²⁹Si, 9.9 ppm and ¹H, 0.2 ppm) and a 1 M aqueous solution of AlCl₃ (²⁷Al, 0 ppm). A custom-developed software was used for data processing (details are given in Brunet et al. (2010)) as well as a module from the Python nmrglue library (Helmus & Jaroniec, 2013).

X-ray diffractograms were acquired using two different diffractometers from grounded, non-freeze-dried pastes to preserve the structure of ettringite (Zhou & Glasser, 2001). For the EP22 experiments, a PANalytical Aeris Research diffractometer with Cu Kα irradiation (40 kV, 15 mA) was used, with data collected between 20 = 5° and 70° at a step size of 0.011° for a total duration of 2 hours. The other pastes were tested with a Panalytical X'Pert (45 kV, 40 mA), with diffractograms acquired between 5° and 70° at a step size of 0.011° for a total duration of 1 hour. Acquisition durations (1 h and 2 h) were chosen to obtain diffractograms of comparable quality while maximizing the signal-to-noise ratio.

The diffractograms were then used to quantify the mineralogical phases present. This quantification, referred to in this paper as Quantitative Phase Analysis (QPA), was performed using Panalytical HighScore Plus v4.9 software (Degen et al., 2014) using crystallographic data from the Crystallographic Open Database (COD, 2025) and the structural models proposed by Richardson (2014) to describe C-S-H phase, following the recommendations of Snellings (2017). A hydration model was used to evaluate the hydration progress of the C₃S and CEM I pastes to validate the results obtained. The model proposed by Parrott
and Killoh (1984), in its version modified by Lothenbach et al. (2008a, 2008b) using the C18 thermodynamic database (Lothenbach et al., 2019) and the GEMs code (Blaser et al., 2015), was used.

The microstructure was studied by Mercury Intrusion Porosimetry (MIP) using a Micromeritics Autopore IV on a freeze-dried paste section (approximately 0.5 g). A contact angle of 130° and a surface tension of 0.48 N/m, as defined in Kaufmann (2010), were used as parameters for the Washburn equation (Washburn, 1921). Data were collected incrementally up to a maximum pressure of 414 MPa (corresponding to a minimum pore entry diameter of 3 nm), with a minimum reporting pressure of 0.14 MPa (entry diameter of 10 µm). Four analyses were carried out for each sample set.

It is important to note that only a single measurement was performed for both NMR and XRD analyses. These techniques are generally characterized by good repeatability, with the main source of uncertainty arising from sample preparation. This limitation was mitigated through the consistent application of a rigorous and standardized protocol throughout the study. Furthermore, the decision to adopt this approach was driven by the focus on specific hydration times and the use of non-freeze-dried samples for both XRD and NMR analyses, thereby ensuring comparability and preserving practical feasibility.

## 3. Results

### 3.1 Irradiation during hydration

First, examination of the X-ray diffractograms of C₃S and CEM I pastes, both irradiated (Irr.) and non-irradiated (Ctrl.) from the EP22 experiment, clearly shows that the mineralogical assemblage is not altered by irradiation (Fig. 2). The same mineral phases are observed in both the control and irradiated pastes, and no unusual mineral phase potentially formed under irradiation—such as calcium peroxide octahydrate, as mentioned in the introduction—is detected. Nor is there any significant presence of carbonate mineral phases (primarily CaCO₃), indicating that the vessel maintained a satisfactory seal during

the irradiation phase. The diffractograms of the irradiated pastes at 35 °C (C₃S and CEM I) show slight variations in the intensity of the portlandite (CH) peaks, which become evident by simply subtracting the diffractograms ΔC₃S (Ctrl.35-Irr.35) and ΔCEM I (Ctrl.35-Irr.35). These differences are likely attributable to insufficient grinding during sample preparation before analysis leading. Although grain size was not measured in this study—despite its known relevance for accurate QPA—the resulting powder is estimated to have an average particle size of around 100 to 200 µm. Alternatively, they may also stem from preferential orientation effects (Snellings, 2017; Winnefeld et al., 2017).

The diffractograms of C₃S and CEM I pastes stored at 20 °C (Ctrl.20) display marked differences when compared to those stored at 35 °C (Ctrl.35). For the anhydrous phases, the comparison was made on peak intensities: at 20 °C, the main peaks of the unreacted clinker phases, at 20 = 32° and 41°, are more intense than at 35 °C, which indicates a lower consumption of the anhydrous phases at the lower temperature. Conversely, hydration product peaks are less intense at 20 °C than at 35 °C, in line with the reciprocal decrease of anhydrous phases, exemplified by portlandite reflections at 2θ = 18° and 34°. This is further illustrated in the difference plots ΔC₃S (Ctrl.35-Irr.20) and ΔCEM I (Ctrl.35-Irr.20), which clearly evidence a lower degree of hydration at 20 °C.

The diffractograms of the irradiated and non-irradiated pastes from the LA22 experiment (C₃S, CEM I, CEM III/A, and CEM III/C pastes) are presented in Fig. 3. As a reminder, all pastes were subjected to the same temperature (approximately 15 °C) during this test. The diffractograms do not exhibit any significant mineralogical variations in the irradiated pastes (Irr.) compared to their control counterparts (Ctrl.), as indicated by the flat difference curves ΔC₃S (Ctrl.15-Irr.15), ΔCEM I (Ctrl.15-Irr.15), ΔCEM III/A (Ctrl.15-Irr.15), and ΔCEM III/C (Ctrl.15-Irr.15). The lack of significant mineralogical variations—both qualitatively (the mineral phases present) and quantitatively (the associated mass fractions), as shown by the QPA results reported in Table 5—is related to the absence of a temperature difference

<figure><img src="image_3.png" /><figcaption>**Fig. 2**

Diffractograms of pastes from the LA22 irradiation experiment (total dose of 1.7 MGy), showing the influence of irradiation and temperature on hydration. (A) C₃S and CEM I pastes; (B) CEM III/A and CEM III/C pastes.

Anhydrous standing for the unhydrated binder diffractogram; summary of test conducted reported in Table 4.

(* = C-(A-)S-H; CH = Portlandite; AFt = Ettringite; AFm = Hemicarbonate/Monocarboaluminate; D = Dolomite)

(Δ = Difference obtained by subtracting the corresponding diffractograms)</figcaption></figure>
between the control and irradiated pastes.

The TGA measurements on the EP22 cement pastes (Fig. 4) confirm the results observed by XRD. The DTG curves show a greater mass loss between 30 and 300 °C for samples cured at 20 °C (Ctrl.20) compared to those cured at 35 °C (Ctrl.35), due to the dehydration of the AFm, AFt, and C-S-H phases (Lothenbach et al., 2017). Since freeze-drying halted hydration, these mass changes correspond solely to the evaporation of chemically bound water. This temperature effect on C-S-H is well documented (Bentur et al., 1979; Gallucci et al., 2013; Lothenbach et al., 2007; Roosz et al., 2016). In parallel, the TGA measurements do not show any significant effect of irradiation: the irradiated (Irr.35) pastes exhibit mass changes similar to the respective control paste (Ctrl.35), indicating no measurable impact on the

chemically bound water in the cement hydrates. A similar observation can be made for the TGA results obtained on the LA22 cement pastes (not shown here): no significant effect attributable to irradiation was identified. The results obtained by TGA and QPA (Table 5) are consistent with the hydration model, with temperature accelerating the hydration kinetics (Gallucci et al., 2013).

A comparison of the ²⁰Si NMR control pastes stored at 20 °C (Ctrl. 20) and 35 °C (Ctrl. 35) from the EP22 experiment also demonstrates the impact of temperature (Fig. 5). As a reminder, a summary of test conducted is reported in Table 4. The decrease of Q⁰ (–75 to –70 ppm) from 20 °C to 35 °C reflects the reduction in residual anhydrous phases (C₃S and C₂S) with increasing temperature, consistent with the thermally activated hydration process. Additionally, the relative variations in Q¹

<figure><img src="image_4.png" /><figcaption>Fig. 3</figcaption></figure>

Diffractograms of pastes from the LA22 irradiation experiment (total dose of 1.7 MGy), showing the influence of irradiation and temperature on hydration. (A) C₃S and CEM I pastes; (B) CEM III/A and CEM III/C pastes.

Anhydrous standing for the unhydrated binder diffractogram; summary of test conducted reported in Table 4.

(* = C-(A-)S-H; CH = Portlandite; AFt = Ettringite; AFm = Hemicarbonate/Monocarboaluminate; D = Dolomite)

<figure><img src="image_5.png" /><figcaption>Fig. 4</figcaption></figure>

TG and DTG curves of pastes from the EP22 irradiation experiment (total dose of 1.0 MGy). Summary of test conducted reported in Table 4.
<caption>**Table 6**</caption>

Si site contributions from NMR spectral deconvolution for pastes from the EP22 (1.0 MGy) and LA22 (1.7 MGy) experiments. Summary of test conducted reported in Table 4.

<table><thead><tr><th>Exp</th><th>ID</th><th>Q<sup>0</sup> (%)</th><th>Q<sup>1</sup> (%)</th><th>Q<sup>2b</sup> (%)</th><th>Q<sup>2</sup> (%)</th></tr></thead><tbody><tr><td></td><td>δ (ppm)</td><td>-68.9 to -74.8</td><td>-79.1</td><td>-81.6</td><td>-84.5</td></tr><tr><td rowspan="7">EP22</td><td>C<sub>3</sub>S -- Irr.35</td><td>22.6</td><td>52.2</td><td>2.3</td><td>22.9</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.35</td><td>24.6</td><td>51.4</td><td>1.4</td><td>22.6</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.20</td><td>34.0</td><td>50.1</td><td>1.3</td><td>14.7</td></tr><tr><td>CEM I -- Irr.35</td><td>25.1</td><td>32.4</td><td>28.4</td><td>14.2</td></tr><tr><td>CEM I -- Ctrl.35</td><td>25.4</td><td>32.7</td><td>27.2</td><td>14.8</td></tr><tr><td>CEM I -- Ctrl.20</td><td>36.1</td><td>40.8</td><td>11.9</td><td>11.2</td></tr><tr><td rowspan="7">LA22</td><td>C<sub>3</sub>S -- Irr.15</td><td>32.3</td><td>49.4</td><td>4.5</td><td>13.8</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.15</td><td>32.2</td><td>52.3</td><td>2.8</td><td>12.7</td></tr><tr><td>CEM I -- Irr.15</td><td>30.0</td><td>48.0</td><td>8.8</td><td>13.3</td></tr><tr><td>CEM I -- Ctrl.15</td><td>34.1</td><td>46.6</td><td>9.4</td><td>9.9</td></tr><tr><td>CEM III/A -- Irr.15</td><td>27.5</td><td>37.1</td><td>20.6</td><td>14.8</td></tr><tr><td>CEM III/A -- Ctrl.15</td><td>27.6</td><td>33.0</td><td>27.0</td><td>12.4</td></tr></tbody></table>

Based on these results, no alteration in the elastic properties of the pastes after irradiation is to be noted. The effect of temperature on the hardness and elastic modulus of the EP22 samples (Ctrl.35 and Ctrl.20) could not be demonstrated due to the slight temperature difference between the control pastes (Bahafid et al., 2018). Any variations in mechanical properties likely fall within the measurement uncertainty of the technique. No degradation of elastic properties was observed for C<sub>3</sub>S pastes in the LA22 experiment. In the absence of mineralogical changes, which would support the stability of mechanical properties in irradiated materials at early age, any observed degradation may result from uneven polishing prior to analysis rather than irradiation itself. These results are consistent with previous observations.

Mercury intrusion porosimetry results for the EP22 pastes are shown in Fig. 8. The impact of temperature (C<sub>3</sub>S Ctrl.20 vs. C<sub>3</sub>S Ctrl.35) is evident: accessible porosity is lower for the Ctrl.20 sample, with a decrease in pore volume between 120 nm and 1 µm, in agreement with the literature (Bahafid et al., 2018; Bentur et al., 1979; Lothenbach et al., 2007). Irradiated C<sub>3</sub>S pastes show pore refinement compared to the Ctrl. 35 sample for pore entry diameter between 30 and 500 nm, and an increase between 500 nm and 1 µm. For irradiated CEM I pastes, there is an increase in pore volume between 10 and 70 nm. These changes indicate a decreased accessible porosity without creating new pores at the micrometer scale. However, the measured accessible porosity is

lower in the irradiated pastes. The increase in mercury-accessible porosity observed between 100 nm and 1 µm in CEM I controls and between 1 and 2 µm in C<sub>3</sub>S controls is attributed to a freeze-drying artifact (Berodier et al., 2017).

Accessible porosities from the EP22 and LA22 experiments are provided in Table 8. These results indicate a decrease in accessible pore volume after irradiation, except for the CEM III/C pastes. However, the limited magnitude of these changes, combined with a lack of reproducibility—particularly between the C<sub>3</sub>S pastes from EP22 and LA22—makes it difficult to draw definitive conclusions about the impact of early-age irradiation on the microstructure of these materials.

## 3.2 Irradiation of mature pastes

The XRD analyses of mature cement pastes (experiment EP23) are shown in Fig. 9. These diffractograms indicate that irradiation does not affect the mineralogical assemblage, both qualitatively (the mineral phases present) and quantitatively (the associated mass fractions), consistent with previous observations (Section 3.1). It should be noted that the absorbed dose for the mature pastes (2.8 MGy) is higher than that for the pastes during hydration (1.0 to 1.7 MGy).

The evolution of the microstructure in irradiated mature pastes of CEM III/A and CEM III/C is presented in Figs. 10(A) and 10(B), respectively. An apparent decrease in accessible porosity is observed for

<figure><img src="image_6.png" /><figcaption>**Fig. 6**</figcaption></figure>

<sup>27</sup>Al MAS NMR spectra of irradiated and control CEM I pastes: (A) from the EP22 experiment (1.0 MGy) and (B) from the LA22 experiment (1.7 MGy). Summary of test conducted reported in Table 4.
<caption>**Table 7**</caption>

Microindentation results for cement pastes from the EP22 (1.0 MGy) and LA22 (1.7 MGy) experiments. Data for the CEM I Ctrl.20 sample are not available. Summary of test conducted reported in Table 4.

<table><thead><tr><th>Exp.</th><th>ID</th><th>Elastic modulus (GPa)</th><th>Hardness (GPa)</th></tr></thead><tbody><tr><td rowspan="5">EP22</td><td>C<sub>3</sub>S -- Irr.35</td><td>17.8 ± 0.9</td><td>0.45 ± 0.04</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.35</td><td>16.1 ± 0.7</td><td>0.38 ± 0.03</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.20*</td><td>18.2 ± 1.0</td><td>0.52 ± 0.06</td></tr><tr><td>CEM I -- Irr.35</td><td>22.0 ± 0.7</td><td>0.55 ± 0.06</td></tr><tr><td>CEM I -- Ctrl.35</td><td>23.0 ± 0.7</td><td>0.65 ± 0.06</td></tr><tr><td rowspan="6">LA22</td><td>C<sub>3</sub>S -- Irr.15</td><td>10.6 ± 0.5</td><td>0.19 ± 0.03</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.15</td><td>14.1 ± 0.6</td><td>0.23 ± 0.03</td></tr><tr><td>CEM I -- Irr.15</td><td>18.7 ± 0.5</td><td>0.33 ± 0.03</td></tr><tr><td>CEM I -- Ctrl.15</td><td>17.2 ± 0.4</td><td>0.32 ± 0.03</td></tr><tr><td>CEM III/A -- Irr.15</td><td>17.9 ± 0.3</td><td>0.31 ± 0.02</td></tr><tr><td>CEM III/A -- Ctrl.15</td><td>18.4 ± 0.3</td><td>0.33 ± 0.04</td></tr><tr><td rowspan="3"></td><td>CEM III/C -- Irr.15</td><td>12.2 ± 0.2</td><td>0.17 ± 0.01</td></tr><tr><td>CEM III/C -- Ctrl.15</td><td>12.3 ± 0.1</td><td>0.18 ± 0.01</td></tr></tbody></table>

irradiated CEM III/A pastes, while no change is detected in CEM III/C pastes. These results, consistent with those gathered for early-age irradiation experimentations (Table 8), suggest that the observed microstructural changes are unrelated to altered hydration mechanisms under irradiation. Notably, Bouniol (2004, 2021) reported porosity changes in mature C<sub>3</sub>S and CEM I pastes exposed to gamma radiation.

## 4. Discussion

For similar curing temperatures, a comparison of control and irradiated pastes by NMR, TGA, and XRD revealed no significant effects of early-age irradiation on mineralogy: no new phases formed, no carbonation occurred, and hydration rates were unaffected. Thus, literature hypotheses suggesting that irradiation increases the hydration rate were not confirmed (Alvares Ferreira et al., 2018; Dąbrowski et al., 2021; Glinicki et al., 2021). Microindentation measurements also showed no significant changes in mechanical properties, with no apparent decrease (Dąbrowski et al., 2021; Glinicki et al., 2021; Mobasher et al., 2015) or increase (Craceye et al., 2015b; Khmurovska et al., 2021) in elastic modulus after irradiation. Although a slight change in porosity was observed in some irradiated pastes during hydration—consistent with other studies (Burnham et al., 2016; Dąbrowski et al., 2021; Glinicki et al., 2021)—this effect

cannot be attributed to a direct coupling between irradiation and hydration, as it was also seen in mature pastes.

To explain the observed changes in pore size distribution, a dissolution/precipitation process could be considered: irradiation-induced dissolution of one or more mineral phases, followed by reprecipitation after irradiation, independent of the hydration degree. For example, portlandite could dissolve under irradiation in favor of calcium peroxide octahydrate (see introduction), which would then dissolve and reprecipitate portlandite once irradiation stops. However, this remains hypothetical and is not supported by experimental results from this or other studies. In situ monitoring of mineralogy under irradiation would be needed to confirm or refute this hypothesis.

The consumption of free water by radiolysis has been proposed by Baral et al. (2022) to explain some observed effects. The amount of water involved can be estimated with simple assumptions: all mixing water is available for radiolysis, secondary reactions (recycling H<sub>2</sub>) are neglected, and the primary yield of water decomposition, G<sub>H<sub>2</sub>O</sub>, is used. The following applies:

$$ \%_{H_2O \text{ lost}} = \frac{H_2O_{\text{lost}}}{H_2O_{\text{in}}} \Leftrightarrow \%_{H_2O \text{ lost}} = \frac{(m_{H_2O \text{ in.}} \times G_{H_2O} \times DA)}{m_{H_2O \text{ in.}}} \Leftrightarrow = G_{H_2O} \times DA \times M_{H_2O} \quad (2) $$

where %<sub>H<sub>2</sub>O lost</sub> is the fraction of water lost by radiolysis from the initial content, m<sub>H<sub>2</sub>O in</sub> is the initial water mass (in kg), M<sub>H<sub>2</sub>O</sub> the

<figure><img src="image_7.png" /><figcaption>**Fig. 7**</figcaption></figure>

¹H MAS Spectra (echo time: 80 µs) of irradiated and non-irradiated CEM I pastes: (A) freeze-dried (EP22) and (B) non-freeze-dried (LA22). Summary of test conducted reported in Table 4.
<caption>**Table 8**</caption>

Accessible porosity measured by MIP. Summary of test conducted reported in Table 4.

<table><thead><tr><th>Exp.</th><th>ID</th><th>Pore volume (%)</th></tr></thead><tbody><tr><td rowspan="7">EP22</td><td>C<sub>3</sub>S -- Irr.35</td><td>17.6</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.35</td><td>19.9</td></tr><tr><td>C<sub>3</sub>S -- Ctrl.20</td><td>16.1</td></tr><tr><td>CEM I -- Irr.35</td><td>14.7</td></tr><tr><td>CEM I -- Ctrl.35</td><td>16.0</td></tr><tr><td>CEM I -- Ctrl.20</td><td>/</td></tr><tr><td>C<sub>3</sub>S -- Irr.15</td><td>17.6</td></tr><tr><td rowspan="7">LA22</td><td>C<sub>3</sub>S -- Ctrl.15</td><td>17.5</td></tr><tr><td>CEM I -- Irr.15</td><td>14.8</td></tr><tr><td>CEM I -- Ctrl.15</td><td>16.1</td></tr><tr><td>CEM III/A -- Irr.15</td><td>12.3</td></tr><tr><td>CEM III/A -- Ctrl.15</td><td>16.9</td></tr><tr><td>CEM III/C -- Irr.15</td><td>24.9</td></tr><tr><td>CEM III/C -- Ctrl.15</td><td>25.5</td></tr></tbody></table>

molar mass of water, G<sub>-H₂O</sub> is the primary decomposition yield of water [1.1 × 10⁻⁶ mol/J at 20 °C and alkaline, or 10.8 molecules /100 eV (Bouniol, 2004)], and DA is the absorbed dose in Gy (J/kg).

Using the EP23 irradiation conditions (2.8 MGy), calculations estimate that only about 5% of the total water is consumed by radiolysis. In other words, gamma irradiation up to several MGy over 14 days results in only a minor water loss during hydration. For reference, the

dose rates experienced by immobilization matrices in operational contexts are much lower than those studied here (see Section 1). Therefore, radiolysis does not significantly impact hydration through water consumption at the dose rates used in this study. This conclusion is further supported by ¹H MAS NMR data (Fig. 7), which showed no significant change in free water content in irradiated pastes. Thus, the radiolytic decomposition of free water during hydration is not

<figure><img src="image_8.png" /><figcaption>**Fig. 8**</figcaption></figure>

Pore size distribution (right); cumulative accessible pore volume (left). Results for irradiated and control pastes from the EP22 irradiation (1.0 MGy). Data for the CEM I Ctrl.20 sample are not available. Summary of test conducted reported in Table 4.
<figure><img src="image_9.png" /><figcaption>**Fig. 9**

Diffractograms of mature pastes from the EP23 experiment (2.8 MGy). Summary of test conducted reported in Table 4. (* = C-(A-)S-H; CH = Portlandite; AFt = Ettringite; AFm = Hemicarboaluminate/Monocarboaluminate; D = Dolomite)</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. 10**

Pore size distribution (right); cumulative accessible pore volume (left). Results for irradiated and control mature pastes from the EP23 irradiation (2.8 MGy). Summary of test conducted reported in Table 4.</figcaption></figure>
quantitatively significant, confirming that observed variations are not
due to water loss from radiolysis.

Overall, these results show that, under the methodology of this study (gamma irradiation at several kGy/h, autogenous conditions to limit carbonation and drying and similar temperature for irradiated and control specimens), irradiation during hydration has no significant effect on cement matrices. Temperature differences between control and irradiated samples can likely explain contradictory effects reported in the literature. Additionally, irradiation in open systems may cause drying or carbonation during irradiation, affecting test results. In some cases, combined effects of temperature, drying, and carbonation may also play a role (Bahafid et al., 2018; Gallucci et al., 2013; Lothenbach et al., 2007), although this study did not assess the impact of these other mechanisms.

**5. Conclusion**

A literature review shows that irradiation during cement hydration
could have an effect, but published results are contradictory. A
critical examination of the operational conditions reveals
experimental protocols that are sometimes questionable: temperature differences between control samples and irradiated samples and/or irradiation in open systems that can induce drying and carbonation during irradiation. This work, therefore, aimed to determine whether exposure to ionizing radiation during hydration is likely to generate modifications that could impact the properties of cementitious materials, thus constituting a safety issue for the conditioning of radioactive waste. To address potential biases related to temperature, drying, and carbonation, we developed an experimental and analytical methodology using sealed reactors to prevent drying and carbonation. For consistency, the temperature was carefully monitored during gamma irradiation to ensure that the control sample was subjected to a comparable curing temperature.

Our results show that early-age exposure to gamma doses of a few
MGy does not significantly alter the mineralogy of cement pastes: no
new phases formed, no carbonation occurred, and hydration rates were
unaffected. Based on our results, irradiation had only a limited effect on
the development of local elastic mechanical properties. Minor changes
were observed in pore size distribution for both hydrating and mature
irradiated pastes, suggesting no direct coupling between hydration and
irradiation and that any observed effects are due solely to gamma
exposure.

With the methodology used in this study, no impact of gamma
radiation on the hydration of cement pastes was detected. Therefore,
the contradictory results presented in the literature are more than
likely related to experimental biases: temperature differences between
control and irradiated samples and/or drying and carbonation during
irradiation (which can be accelerated by temperature). From an
operational point of view, the properties of cementitious materials are
not altered by radiation, which confirms the integrity of cementitious
encapsulation matrices exposed to gamma radiation during their
hydration. The only observed effects are minor changes in pore size
distribution. Based on current knowledge, the properties of
cementitious materials used in safety assessments for nuclear waste
packages are not affected by gamma irradiation at doses and dose rates
relevant to ILW-LL waste conditioning. Consequently, safety studies
based on mature matrices remain valid, and the conclusions drawn
from these studies are justified.

These results indicate that irradiation does not significantly affect the
durability or long-term performance of packaging matrices, although
this point requires further verification. Radiolysis and the generation of
radical species can modify the redox potential of the pore solution,
which may in turn influence radionuclide retention. This highlights the
need for monitoring redox conditions, for example by analyzing the
oxidation states of relevant species. In addition, a more comprehensive

assessment of long-term behavior under repository conditions should
consider potential interactions between radiolysis and environmental
stresses such as drying, temperature fluctuations, or carbonation.

Notations

1 Septodont Company: https://www.septodont.fr/

2 Polystyrene was chosen for its good radiation tolerance (Albano et al., 2003)

3 EPICUR platform is located at the ASNR site (formerly IRSN) in Cadarache, France, and was initially developed for the study of iodine chemistry in PWR containment buildings under accident conditions (https://www.irsn.fr/recherche/dispositif-dessai-programme-epicur/)

4 LABRA platform is affiliated with CEA and located at the Paris-Saclay center (France), conducting tests for qualification of resistance to ionizing radiation and radio-sterilization operations (https://www.sfen.org/rgn/labra-laboratoire-rayonnements-appliques/)

Acknowledgments

The authors would like to express their thanks to the COSTO funding
program run by the French Alternative Energies and Atomic Energy
Commission (CEA), which made it possible to carry out this research.
The authors also gratefully acknowledge the financial support of the
French Institute for Radiological Protection and Nuclear Safety
(IRSN). Finally, the authors wish to thank Mélanie Moskura (CEA,
CNRS, NIMBE) for her invaluable assistance with NMR data
acquisition.

References

Ahmed, M., & Benharzallah, K. (2017). Effect of the carbonatation and the type of cement (CEM I, CEM II) on the ductility and the compressive strength of concrete. *Construction and Building Materials, 148*, 874-886.
https://doi.org/10.1016/j.conbuildmat.2017.05.098

Albano, C., Reyes, J., Ichazo, M., Gonzaléz, J., Hernández, M., & Rodríguez, M. (2003). Mechanical, thermal and morphological behaviour of the polystyrene/polypropylene (80/20) blend, irradiated with γ-rays at low doses (0-70 kGy). *Polymer Degradation and Stability, 80*(2), 251-261.
https://doi.org/10.1016/S0141-3910(02)00405-6

Allen, A. O. (1948). Radiation chemistry of aqueous solutions. *The Journal of Physical and Colloid Chemistry, 52*(3), 479-490.
https://doi.org/10.1021/j150459a009

Alvares Ferreira, E. G., Yokaichiya, F., Marumo, J. T., Vicente, R., Garcia-
Moreno, F., Kamm, P. H., Klaus, M., Russina, M., Gunther, G., Jimenez, C.
E., & Franco, M. K. K. D. (2018). Influence of the irradiation in cement for
the Brazilian radioactive waste repositories: Characterization via X-ray
diffraction, X-ray tomography and quasielastic neutron scattering. *Physica B:
Condensed Matter, 551*, 256-261.
https://doi.org/10.1016/j.physb.2018.01.018

Auroy, M., Poyet, S., Le Bescop, P., Torrenti, J.-M., Charpentier, T., Moskura, M., & Bourbon, X. (2018). Comparison between natural and accelerated carbonation (3% CO₂): Impact on mineralogy, microstructure, water retention and cracking. *Cement and Concrete Research, 109*, 64-80.
https://doi.org/10.1016/j.cemconres.2018.04.012

Bahafid, S., Ghabezloo, S., Faure, P., Duc, M., & Sulem, J. (2018). Effect of the hydration temperature on the pore structure of cement paste: Experimental investigation and micromechanical modelling. *Cement and Concrete Research, 111*, 1-14.
https://doi.org/10.1016/j.cemconres.2018.06.014

Baral, A., Rodriguez, E. T., Hunnicutt, W. A., Cakmak, E., Sun, H., Ilavsky, J., Le Pape, Y., Rosseel, T. M., & Garg, N. (2022). Ultra-high gamma irradiation of calcium silicate hydrates: Impact on mechanical properties, nanostructure, and atomic environments. *Cement and Concrete Research, 158*, 106855.
https://doi.org/10.1016/j.cemconres.2022.106855

Bentur, A., Berger, R. L., Kung, J. H., Milestone, N. B., & Young, J. F. (1979). Structural properties of calcium silicate pastes: II, Effect of curing temperature. *Journal of the American Ceramic Society, 62*(7-8), 362-366.
https://doi.org/10.1111/j.1151-2916.1979.tb19079.x
Bernachy-Barbe, F. (2019). A data analysis procedure for phase identification in nanoindentation results of cementitious materials. *Materials and Structures*, 52(5), Article No. 95. https://doi.org/10.1617/s11527-019-1397-y

Berodier, E., Bizzozero, J., & Muller, A. C. A. (2017). Mercury intrusion porosimetry. In: *A Practical Guide to Microstructural Analysis of Cementitious Materials*. Boca Raton, Florida: CRC Press, 419-444.
https://doi.org/10.1201/b19074

Blaser, N., Vizcaya, L. S., Estill, J., Zahnd, C., Kalesan, B., Egger, M., Gsponer, T., & Keiser, O. (2015). Gems: An R package for simulating from disease progression models. *Journal of Statistical Software*, 64, 1-22.
https://doi.org/10.18637/jss.v06.i40

Borges, P. H. R., Costa, J. O., Milestone, N. B., Lynsdale, C. J., & Streatfield, R. E. (2010). Carbonation of CH and C-S-H in composite cement pastes containing high amounts of BFS. *Cement and Concrete Research*, 40(2), 284-292.
https://doi.org/10.1016/j.cemconres.2009.10.020

Bouniol, P. (2004). *L'état des connaissances sur la radiolyse de l'eau dans les colis de déchets cimentés et son approche par simulation*. (Report No. CEA-R-6069). Vienna : International Atomic Energy Agency. (in French)

Bouniol, P. (2021). Bétons de radioprotection. In: *Techniques de l'ingénieur Génie Nucléaire: Vol. Base Documentaire TIP180WEB* (Article No. BN3740v2). Gif-sur-Yvette, France : CEA Paris-Saclay. (in French)
https://doi.org/10.51257/a-v2-bn3740

Bouniol, P., & Lapuerta-Cochet, S. (2012). The solubility constant of calcium peroxide octahydrate in relation to temperature; its influence on radiolysis in cement-based materials. *Journal of Nuclear Materials*, 420(1), 16-22.
https://doi.org/10.1016/j.jnucmat.2011.09.009

Brunet, F., Charpentier, T., Chao, C. N., Peycelon, H., & Nonat, A. (2010). Characterization by solid-state NMR and selective dissolution techniques of anhydrous and hydrated CEM V cement pastes. *Cement and Concrete Research*, 40(2), 208-219. https://doi.org/10.1016/j.cemconres.2009.10.005

Burnham, S., Huang, L., & Jevremovic, T. (2016). Examining the effect of gamma radiation exposure in early stage of concrete curing on its strength and long-term durability. In: *24th International Conference on Nuclear Engineering*, Charlotte, North Carolina 26-30 June 2016. New York: American Society of Mechanical Engineers. Volume 5, Paper No. V005T15A068.
https://doi.org/10.1115/ICONE24-60924

Chang, C.-F., & Chen, J.-W. (2005). Strength and elastic modulus of carbonated concrete. *Materials Journal*, 102(5), 315-321.
https://doi.org/10.14359/14710

COD. (2025). *Crystallography open database* [online]. Vilnius, Lithuania, VU University Institute of Biotechnology. Available from: <https://www.crystallography.net/cod/>.

Cong, X., & Kirkpatrick, R. J. (1995). Effects of the temperature and relative humidity on the structure of C-S-H gel. *Cement and Concrete Research*, 25(6), 1237-1245. https://doi.org/10.1016/0008-8846(95)00116-T

Constantinides, G., & Ulm, F.-J. (2004). The effect of two types of C-S-H on the elasticity of cement-based materials: Results from nanoindentation and micromechanical modeling. *Cement and Concrete Research*, 34(1), 67-80.
https://doi.org/10.1016/S0008-8846(03)00230-8

Craeye, B., De Schutter, G., Vuye, C., & Gerardy, I. (2015a). Cement-waste interactions: Hardening self-compacting mortar exposed to gamma radiation. *Progress in Nuclear Energy*, 83, 212-219.
https://doi.org/10.1016/j.pnucene.2015.03.019

Craeye, B., De Schutter, G., Vuye, C., & Gerardy, I. (2015b). Cement-waste interactions: Hardening self-compacting mortar exposed to gamma radiation. *Progress in Nuclear Energy*, 83, 212-219.
https://doi.org/10.1016/j.pnucene.2015.03.019

Cui, D., Zuo, X., Zheng, K., & Talukdar, S. (2020). Tomography-based investigation on the carbonation behavior through the surface-opening cracks of sliced paste specimen. *Materials*, 13(8), Article No. 8.
https://doi.org/10.3390/ma13081804

Dąbrowski, M., Glinicki, M. A., Dziedzic, K., Jóźwiak-Niedźwiedzka, D., Sikorin, S., Fateev, V. S., & Povalansky, E. I. (2021). Early age hardening of concrete with heavy aggregate in gamma radiation source – Impact on the modulus of elasticity and microstructural features. *Journal of Advanced Concrete Technology*, 19(5), 555-570. https://doi.org/10.3151/jact.19.555

Degen, T., Sadki, M., Bron, E., König, U., & Nénert, G. (2014). The HighScore suite. *Powder Diffraction*, 29(S2), S13-S18.
https://doi.org/10.1017/S0885715614000840

Dewitte, C. (2023). *Multiphysics evaluation of low CO₂ and low pH cementitious matrices exposed to Mg-bearing environments*. Thesis (Doctoral). National Institute of Applied Sciences of Toulouse. https://theses.fr/2023ISAT0034

Dewitte, C., Lacarrière, L., Neji, M., Bertron, A., & Dauzères, A. (2024). Chemo-mechanical characterization of a low-pH model cement paste in magnesium bearing environment. *Cement and Concrete Research*, 184, 107598.
https://doi.org/10.1016/j.cemconres.2024.107598

EDF. (2015). *Référentiel de conditionnement des déchets MAVL, Pièce 2*. Paris: Électricité de France (EDF). (in French)

Field, K. G., Remec, I., & Pape, Y. L. (2015). Radiation effects in concrete for nuclear power plants – Part I: Quantification of radiation exposure and radiation effects. *Nuclear Engineering and Design*, 282, 126-143.
https://doi.org/10.1016/j.nucengdes.2014.10.003

Gallucci, E., Zhang, X., & Scrivener, K. L. (2013). Effect of temperature on the microstructure of calcium silicate hydrate (C-S-H). *Cement and Concrete Research*, 53, 185-195. https://doi.org/10.1016/j.cemconres.2013.06.008

Glinicki, M. A., Dąbrowski, M., Antolik, A., Dziedzic, K., Sikorin, S., Fateev, V., & Povolansky, E. (2021). Gamma irradiation sensitivity of early hardening cement mortar. *Cement and Concrete Composites*, 126, 104327.
https://doi.org/10.1016/j.cemconcomp.2021.104327

Helmus, J. J., & Jaroniec, C. P. (2013). Nmrglue: An open source Python package for the analysis of multidimensional NMR data. *Journal of Biomolecular NMR*, 55(4), 355-367.
https://doi.org/10.1007/s10858-013-9718-x

Jain, A. K., Murty, M. N., & Flynn, P. J. (1999). Data clustering: A review. *ACM Computing Surveys*, 31(3), 264-323.
https://doi.org/10.1145/331499.331504

Jerga, J. (2004). Physico-mechanical properties of carbonated concrete. *Construction and Building Materials*, 18(9), 645-652.
https://doi.org/10.1016/j.conbuildmat.2004.04.029

Kaufmann, J. (2010). Pore space analysis of cement-based materials by combined nitrogen sorption – Wood’s metal impregnation and multi-cycle mercury intrusion. *Cement and Concrete Composites*, 32(7), 514-522.
https://doi.org/10.1016/j.cemconcomp.2010.04.003

Kearney, S. A., Stemberk, P., Sikorin, S., Kaladkevich, Y., Pavalanski, E., & Fatseyeu, V. (2018). The effect of gamma-ray irradiation on mechanical properties of early-age cement mortar. *Civil Engineering Journal*, 27(3), 357-363. https://doi.org/10.14311/CEJ.2018.03.0028

Khmurovska, Y., Stemberk, P., Sikorin, S., Němeček, J., Jóźwiak-Niedźwiedzka, D., Doleželová, M., Kaladkevich, Y., Pavalanski, E., & Fatseyeu, V. (2021). Effects of gamma-ray irradiation on hardened cement mortar. *International Journal of Concrete Structures and Materials*, 15(1), Article No. 17. https://doi.org/10.1186/s40069-020-00452-7

Korpa, A., & Trettin, R. (2006). The influence of different drying methods on cement paste microstructures as reflected by gas adsorption: Comparison between freeze-drying (F-drying), D-drying, P-drying and oven-drying methods. *Cement and Concrete Research*, 36(4), 634-649.
https://doi.org/10.1016/j.cemconres.2005.11.021

Lothenbach, B., Durdziński, P., & De Weerdt, K. (2017). Thermogravimetric analysis. In: *A Practical Guide to Microstructural Analysis of Cementitious Materials*. Boca Raton, Florida: CRC Press, 177-212. https://doi.org/10.1201/b19074

Lothenbach, B., Kulik, D. A., Matschei, T., Balonis, M., Baquerizo, L., Dilnesa, B., Miron, G. D., & Myers, R. J. (2019). Cemdata18: A chemical thermodynamic database for hydrated Portland cements and alkali-activated materials. *Cement and Concrete Research*, 115, 472-506.
https://doi.org/10.1016/j.cemconres.2018.04.018

Lothenbach, B., Le Saout, G., Gallucci, E., & Scrivener, K. (2008a). Influence of limestone on the hydration of Portland cements. *Cement and Concrete Research*, 38(6), 848-860. https://doi.org/10.1016/j.cemconres.2008.01.002

Lothenbach, B., Matschei, T., Möschner, G., & Glasser, F. P. (2008b). Thermodynamic modelling of the effect of temperature on the hydration and porosity of Portland cement. *Cement and Concrete Research*, 38(1), 1-18.
https://doi.org/10.1016/j.cemconres.2007.08.017

Lothenbach, B., Winnefeld, F., Alder, C., Wieland, E., & Lunk, P. (2007). Effect of temperature on the pore solution, microstructure and hydration
products of Portland cement pastes. *Cement and Concrete Research*, 37(4), 483-491. https://doi.org/10.1016/j.cemconres.2006.11.016

Maruyama, I., Ishikawa, S., Yasukouchi, J., Sawada, S., Kurihara, R., Takizawa, M., & Kontani, O. (2018). Impact of gamma-ray irradiation on hardened white Portland cement pastes exposed to atmosphere. *Cement and Concrete Research*, 108, 59-71. https://doi.org/10.1016/j.cemconres.2018.03.005

Mobasher, N., Bernal, S. A., Kinoshita, H., Sharrad, C. A., & Provis, J. L. (2015). Gamma irradiation resistance of an early age slag-blended cement matrix for nuclear waste encapsulation. *Journal of Materials Research*, 30(9), 1563-1571. https://doi.org/10.1557/jmr.2014.404

Parrot, L. J., & Killoh, D. C. (1984). Prediction of cement hydration. *British Ceramic Proceedings*, 35, 41-53.

Patel, R. G., Killoh, D. C., Parrott, L. J., & Gutteridge, W. A. (1988). Influence of curing at different relative humidities upon compound reactions and porosity in Portland cement paste. *Materials and Structures*, 21(3), 192-197. https://doi.org/10.1007/BF02473055

Pomaro, B. (2016). A review on radiation damage in concrete for nuclear facilities: From experiments to modeling. *Modelling and Simulation in Engineering*, (2016), 1, 4165746. https://doi.org/10.1155/2016/4165746

Ramachandran, V. S., Paroli, R. M., Beaudoin, J. J., & Delgado, A. H. (2002). *Handbook of thermal analysis of construction materials*. Norwich, New York: William Andrew Publishing.

Richardson, I. G. (2014). Model structures for C-(A)-S-H(I). *Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials*, 70(6), 903-923. https://doi.org/10.1107/S2052520614021982

Roosz, C., Gaboreau, S., Grangeon, S., Prêt, D., Montouillout, V., Maubec, N., Ory, S., Blanc, P., Vieillard, P., & Henocq, P. (2016). Distribution of water in synthetic calcium silicate hydrates. *Langmuir*, 32(27), 6794-6805. https://doi.org/10.1021/acs.langmuir.6b00878

Snellings, R. (2017). X-ray powder diffraction applied to cement. In: *A Practical Guide to Microstructural Analysis of Cementitious Materials*. Boca Raton, Florida: CRC Press, 107-176. https://doi.org/10.1201/b19074

Stephant, S. (2015). *Etude de l'influence de l'hydratation des laitiers sur les propriétés de transfert gazeux dans les matériaux cimentaires*. Thesis (Doctoral). Bourgogne University. (in French)

Vandamme, M., & Ulm, F.-J. (2013). Nanoindentation investigation of creep properties of calcium silicate hydrates. *Cement and Concrete Research*, 52, 38-52. https://doi.org/10.1016/j.cemconres.2013.05.006

Velez, K., Maximilien, S., Damidot, D., Fantozzi, G., & Sorrentino, F. (2001). Determination by nanoindentation of elastic modulus and hardness of pure constituents of Portland cement clinker. *Cement and Concrete Research*, 31(4), 555-561. https://doi.org/10.1016/S0008-8846(00)00505-6

Villain, G., Thiery, M., & Platret, G. (2007). Measurement methods of carbonation profiles in concrete: Thermogravimetry, chemical analysis and gammadensimetry. *Cement and Concrete Research*, 37(8), 1182-1192. https://doi.org/10.1016/j.cemconres.2007.04.015

Wan, K., Xu, Q., Wang, Y., & Pan, G. (2014). 3D spatial distribution of the calcium carbonate caused by carbonation of cement paste. *Cement and Concrete Composites*, 45, 255-263. https://doi.org/10.1016/j.cemconcomp.2013.10.011

Washburn, E. W. (1921). Note on a method of determining the distribution of pore sizes in a porous material. *Proceedings of the National Academy of Sciences of the United States of America*, 7(4), 115-116.

Winnefeld, F., Schöler, A., & Lothenbach, B. (2017). Sample preparation. In: *A Practical Guide to Microstructural Analysis of Cementitious Materials*. Boca Raton, Florida: CRC Press, 1-35. https://doi.org/10.1201/b19074

Zhou, Q., & Glasser, F. P. (2001). Thermal stability and decomposition mechanisms of ettringite at < 120 °C. *Cement and Concrete Research*, 31(9), 1333-1339. https://doi.org/10.1016/S0008-8846(01)00558-0

## Author contributions

Rémy Hoarau Belkhiri: Methodology, Investigation, Validation, Formal analysis, Visualization, Writing – Original Draft, Writing – Revising Draft.

Stéphane Poyet: Conceptualization, Methodology, Supervision, Validation, Data curation, Writing – Revising Draft.

Mejdi Neji: Conceptualization, Methodology, Supervision, Validation, Data curation, Writing – Revising Draft.

Elisa Leoni: Methodology, Conceptualization, Methodology, Supervision, Validation, Data curation, Writing – Revising Draft.

Stéphane Esnouf: Methodology, Supervision, Validation, Data curation, Writing – Revising Draft.

Alexandre Dauzères: Project administration, Funding acquisition, Writing – Revising Draft.

Thibault Charpentier: Investigation, Supervision, Validation, Formal analysis, Formal analysis, Writing – Revising Draft.

## Declaration of competing interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Published under the Creative Commons Attribution 4.0 International License (CC BY 4.0).

<figure><img src="image_11.png" /></figure>