This study investigates the long-term durability of alkali-activated materials (AAM) under exposure to different cement leachates, with a particular focus on their potential use in radioactive waste containment applications. Three different binders were considered: sodium-based geopolymers (Na-geo), potassium-based geopolymers (Kgeo), and alkali-activated blast furnace slags (BFS). Since these materials may be incorporated into cement-based host structures in deep radioactive waste repositories, their interaction with leachates enriched in cementitious phases was simulated. Exposure conditions included cement pore solution, limewater, carbonated water, as well as endogenous curing in sealed environments. The evolution of porosity was monitored up to 180 days using thermoporometry and nitrogen adsorption-desorption (PSD). Phase changes were identified by X-ray diffraction, 29Si and 27Al MAS NMR, while compressive tests assessed mechanical performance. Porosity analyses confirmed the mesoporous nature of AAM, with geopolymers showing only slight variations under alkaline curing, while BFS exhibited a decrease in porosity over time, consistent with strength development. XRD and MAS NMR further demonstrated the structural stability of these systems, with no significant changes in crystalline or amorphous phases. Overall, the materials maintained high compressive strengths, confirming their chemical, physical, and mechanical durability across different cementitious leachate environments.

Common geopolymers (GPs) are activated by alkaline solutions of potassium (K) or sodium (Na). Although both properties have been extensively investigated, comparative studies on their fire resistance are still lacking. In this research, Na/K-based GPs were applied as fire-protective steel coatings. Their fire protection was evaluated by a fire test named "burn-through". When the Aluminum/Silicon (Al/Si) molar ratio equaled 0, both GPs showed intumescence (expansion upon heating) during the fire test. The final maximum temperatures of the protected steel plate (TS) were as low as 309/335 degrees C for Na/K-GP. However, with Al/Si = 0.54, K-based GP (TS = 410 degrees C) exhibited intumescence and better fire protection than Na-based GP (TS = 587 degrees C) which even cracked. Physicochemical properties of the GP samples were characterized before and after the fire test, including electron probe micro-analysis, dynamic mechanical analysis, and 29Si solid-state MAS (CP) NMR. Material softening was proved to come from the consumption of Si (Q2) and caused the following intumescence. Such structure was formed in Kbased GP regardless of Al/Si ratio while Si (Q2) atoms were only present in Na-based GP at low Al/Si ratio. It is therefore proven that K-based GP is more appropriate to protect steel than Na-based GP, due to its intumescent property, especially when the Al/Si ratio is high.

This research delves into an in-depth exploration of two distinct approaches to additive manufacturing for creating 3D filters based on sodium geopolymers (GP): direct 3D printing through paste extrusion and reverse 3D printing using sacrificial polymeric templates. The investigation encompasses a comprehensive characterization of GP filters in both their fresh and hardened states. By employing rheology measurements during the fresh state analysis, a clear printability zone for formulations used in direct 3D printing is identified. In both printing methods, an extensive assessment of the structure and porosity of the resultant hardened GP filters is conducted, employing Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM) and 3D X-ray microtomography analyses. This study illuminates the distinct advantages and limitations associated with each manufacturing technique in the context of potential industrial applications of porous filters. Moreover, it underscores the potential for these filters to be further tailored for specific industrial uses through complementary chemical functionalization, thereby paving the way for innovation in the field of advanced filtration and environmental solutions.

Intumescent coatings have the ability to expand during fire and thus provide a significant thermal barrier. They are an asset for the fire protection of steel building structures. In this context, different formulations of intumescent geopolymers (GP) have been proposed in former research. However, the influence of the water content on the fire resistance of GP coated on steel is not well known. This justifies the present study. In the following, GP samples with different water contents are tested and compared using a burn through test set-up, under both undried and dried conditions. Post-mortem analysis via Si-29 solid-state NMR indicates that a higher initial water content leads to a greater degree of geopolymerization. However, this factor does not significantly impact the fire protection of the GP. Conversely, the drying process results in a deterioration of the GP fire performance during the early stages of the fire test, compared to undried samples. Nevertheless, after 30 minutes, by the end of the fire test, the GP temperature becomes stable and no significant difference is observed between dried/undried GP. GP is able to provide the same level of fire protection, even if exposed to a drying environment.

Fire resistance is a key advantage of geopolymer (GP) materials. While most research focuses on alkali-activated GPs, this study examines the fire resistance of phosphoric acid-activated GPs with varying phosphorus-toaluminum (P/Al) molar ratios. By activating metakaolin with different ortho-phosphoric acid (H3PO4) solutions, it was found that GPs with P/Al > 0.59 exhibited intumescence during fire tests, resulting in a 110( degrees)C lower backside temperature (310( degrees)C) compared to non-intumescent GPs (420( degrees)C). Physico-chemical changes were analyzed before and after fire tests using DMA, TGA NMR, EPMA, and XRD. The study revealed dehydration, crystallization, and rheological changes, with NMR showing transitions from Al(VI) to Al(IV), full condensation of phosphorus species, and Si-O-Al to Si-O-Si bonds. Intumescence was linked to GP softening between 100 and 160( degrees)C, achievable only with a P/Al ratio >= 0.74, with no additional benefits from excess phosphorus.

With certain formulations, Geopolymer (GP) exhibits intumescence (expansion upon heating), forming a porous structure, providing a thermal barrier effect. However, there have been no studies demonstrating the mechanism of the intumescence and the corresponding structural changes before and after heating. In this study, GPs are made based on metakaolin and silica fume. Then, GP with two aluminum-to-silicon molar ratio (Al/Si = 0/0.55) are investigated under heating conditions. The GP (Al/Si = 0) exhibits initial softening followed by hardening of the structure (from 50 degrees C to 175 degrees C), with intumescence observed within this temperature range. In contrast, the GP (Al/Si = 0.55) does not exhibit softening or expansion. Solid-state Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) analysis of Si-29 and H-1 were then conducted on both GPs at ambient temperature and after heating at 105/200/300 degrees C for 24 h. Results show that GP softening is due to the transition from Si(Q(2)) to Si(Q(3)) silicate units, while hardening is caused by the transition from Si(Q(3)) to Si(Q(4)) silicate units. Additionally, the proton mobility of GP is higher for lower Al/Si ratios after curing. During heating, the mobility decreases for both GPs due to the removal of free water and the breaking of hydrogen bonds. Our results extend the knowledge of GP intumescence mechanism and call attention to low Al/Si GP for fire/high temperature application.

This research investigates the fire resistance properties of alkali activated Na-based geopolymers (GP), used as steel protective coatings. The effect of different Al/Si molar ratios (0-0.54) is evaluated fire test. When coated on a steel plate, GP having the smaller Al/Si ratio exhibits an intumescent behavior with the highest expansion. When Al/Si = 0, the temperature at the backside of the steel plate is 313 degrees C which is decreased by 347 degrees C compared to an uncoated steel plate (660 degrees C). After fire testing, the GP physico-chemical properties are characterized with optical microscopy, Electron probe micro-analysis, dynamic mechanical analysis. According to stiffness test results, when the temperature approaches 100 degrees C, the GP with a given Al/Si ratio (different from zero) softens and expands (intumescence). The greater the Al/Si ratio in the GP, the more rigid the structure; this phenomenon limits expansion, and hence, lowers the fire protection.

Addressing a critical challenge in the nuclear industry, this study contributes to the effective and sustainable management of radioactive liquid organic waste by studying the effect of the viscosity ratio between the geopolymer grouts and the incorporated organic liquids (OL) on the efficiency of the solidification process. This research provides a practical pathway for industries to manage their liquid organic wastes more effectively, economically, and in alignment with regulatory standards. Three mineral oils are used to simulate OL wastes with an incorporation rate fixed at 30% vol. which represents a considerable proportion from an industrial point of view. To ensure adequate conditioning, the focus of this work is on the effect of the viscosity difference between geopolymer grouts and incorporated OL on the rheological, mechanical, and microstructural properties of geopolymer/OL composites. In total, 9 viscosity ratios, ranging from 0.4 to 430, are tested by varying the viscosity of both the geopolymer grouts and the incorporated OL. First, the results obtained show that OLs with a viscosity higher than 0.05 Pa.s can be efficiently encapsulated in MK-based geopolymer grouts, without requiring any surfactants. This study also confirms that the viscosity ratio is a key factor controlling the formulation and the rheological characteristics of fresh geopolymer/OL emulsions. Accordingly, increasing the geopolymer grout viscosity is an efficient technique for the preparation of geopolymer/OL composites with finely encapsulated OL droplets. In addition, based on the experimental results obtained in this study, a good correlation is established between the rheological parameters of the emulsions and the viscosity of the two phases (geopolymer and OL). This enables the proposition of empirical models that allow estimating the final rheological parameters of the fresh emulsions with an accuracy exceeding 90%. Finally, in terms of mechanical properties, this study confirms that MK-based geopolymers can safely be used for the solidification of a high amount of OL wastes.

This research determines an adequate alkali-activated material (AAM) for the incorporation of huge amounts (20 or 40% vol) of low viscosity organic liquids (LVOL), e.g. for waste stabilization/solidification. The selected AAM are either based on high-Ca content blast furnace slag, or on low Ca-content metakaolin, i.e. on a geopolymer matrix. First, the selection of the AAM is performed to ensure no LVOL leakage and a sufficient compressive strength f c (> 8 MPa). Surfactants are compulsory to allow incorporation. After 90 days curing, for slag pastes, f c ranges between 10 and 20 MPa at 20% vol LVOL, but it is zero at 40% LVOL, whatever the surfactant. For geopolymer pastes, the AAM-LVOL composites have an average f c of 25 MPa at 20% vol LVOL, and of 15 MPa at 40% LVOL. With surfactant, the AAM solid pore structure of slag pastes is denser (with smaller specific surface area and micropore amount); it is unchanged for geopolymer pastes. Whatever the surfactant, air entrained bubbles are present. Their proportion is maximal with Glucopon. Together with LVOL presence, this generally contributes to decreasing f c . The emulsion (entrained air + LVOL droplets) is characterized in hardened AAM by combining 2D Scanning Electron Microscopy and 3D X Ray micro-computed tomography. Surfactants significantly decrease the emulsion droplet size distribution. For geopolymer pastes up to 40% vol LVOL, the most adequate surfactants are Brij O10 and CTAB; for slag paste up to 20% vol LVOL, it is CTAB. Moreover, the setting reactions are not impacted by LVOL or surfactants, and neither are the reaction products. It is concluded that the decrease in mechanical performance of AAM-LVOL composites is only due to physical reasons, particularly the decrease in AAM proportion, the emulsion quality (coalescence, droplet size and shape) and air entrained bubbles.

In this research, novel alkali-activated materials (AAM) are assessed for the conditioning of tritiated or-ganic liquids OL. Their originality is to ensure both the conditioning of radioactive OL waste and the trap-ping of hydrogen or tritium (1 H2 or 3H2). Two types of AAM are compared, either based on metakaolin MK (i.e., on geopolymer GEO solid structure) or on blast furnace slag BFS (i.e., Portland cement solid structure). For the trapping of 1H2 or 3H2, both AAM incorporate a gamma-MnO2/Ag2O getter powder at 10 wt.%.The efficiency of 1H2 trapping in the two AAM is quantified via in situ 1H2 production, using two dis-tinct methods: (1) gamma irradiation (short term 1H2 production) and (2) magnesium metal Mg corrosion (longer term 1H2 production). Complementarily, the 1H2 trapping efficiency of the getter is analyzed in both AAM porewaters.Gamma irradiation with a cumulated dose up to 500 kGy shows that GEO-based AAM added with getter have a H2 trapping efficiency of almost 100% without OL, and 87-92% with OL, when compared to identical materials made with non-trapping gamma-MnO2. BFS-based AAM made with getter have a trapping efficiency of 52-65% without OL and 16-25% with OL.After 443-464 days of Mg corrosion, the cumulated amount of 1H2 trapped in BFS AAM reaches an asymptote of 0.7 mmol/g of getter, but it keeps increasing in GEO AAM. This proves the excellent 1H2 trapping efficiency of getter-functionalized GEO, compared to BFS AAM.Finally, the contact of the getter with the extracted porewaters of the two AAM shows a strong ad-sorption of ions on its surface. In both AAM, this reduces the 1H2 trapping capacity by 50%. When the getter is placed in contact with sulfides, which are present in BFS AAM only, X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) evidence that the structure of the getter is modified. This explains the limited 1 H2 trapping efficiency of the getter in BFS AAM, whereas the getter-functionalized GEO AAM remains efficient.(c) 2023 Elsevier B.V. All rights reserved.

The Boulogne-Sur-Mer area in the North of France is one of the cradles of the French cement industry (the other main one is Grenoble region due to Joseph Vicat's first cement works). From fast setting (Roman) to Portland, those cements were famous in France and have been used throughout the entire country. The main objective of this study is to give a preliminary insight of the type of binders used since there is currently few and scattered data on those specific structures and to assess the efficiency of traditional analytical techniques [X-ray diffraction (XRD), optical (OM) and scanning electron microscopy (SEM) observations, coupled with EDS analysis] used to differentiate natural and artificial cements.

The immobilization of organic liquids in geopolymers – inorganic aluminosilicate cements – has recently been applied efficiently to nuclear waste, where the organic liquid is permanently confined under the form of micrometric droplets. Cutting fluids, a type of nuclear waste, are usually emulsions of organic liquid in water. Eco-friendly cutting fluids are frequently used, composed of vegetable oils. As the immobilization conditions into geopolymers are highly alkaline, saponification reactions are thought to form fatty acid soaps. The latter act as surfactant, thus facilitating the immobilization of the organic liquid by dispersing it in small droplets into the geopolymer matrix. In this contribution, the saponification kinetics in a geopolymer environment are studied by Nuclear Magnetic Resonance (1H NMR) Spectroscopy. Initially, the hydrolysis is performed on sunflower oil (chosen model oil) alone, placed in a typical geopolymer porewater composition. In a second time, this oil is incorporated into a geopolymer, and by grinding the hardened material, and extracting the organic phase, the latter is analysed by NMR. The results indicate that over time the vegetable oil is transformed into fatty acid soaps, by about 40% in 7 days.

This research contributes to nuclear waste management by proposing a simple treatment route for high viscosity (HV) organics (oils and greases). These are currently without an industrial solution, because they are not directly pourable into a cementation matrix. Their solidification/stabilization (S/S) into geopoly-mers (GP) is investigated. Incorporation is achieved by assembling the HV organics (a model oil MO, an industrial oil IO or a grease G) with a low viscosity (LV) solvent, either dodecane (C12) or a mix of tributylphosphate (TBP)/C12, prior to mixing with the fresh GP.First, the minimal solvent amount is determined to achieve sufficient fluidity of the HV oil or grease mix. Two different criteria are used, one for the Newtonian oils and the other for the non-Newtonian grease. Secondly, the immobilization of 20%vol of assembled mix is performed into a GP paste or mortar. The organics bleeding, the GP setting, the rheological properties of the mix, and the mechanical per-formance at 28 days endogenous curing are assessed. The morphology of the oil or grease emulsion inside the hardened GP mortar is determined by 2D SEM observations and 3D quantitative X Ray micro-computed tomography. The efficiency of the immobilization is proven by cross analyzing these properties. In particular, a minimal compressive strength of 25.4 MPa + / - 4.6 is achieved for a GP mortar immobi-lizing 20%vol HVG assembled with TBP/C12; it corresponds to an emulsion made of 12.9%vol droplets in the 10-480 mu m size range, and 7.1%vol smaller than 10 mu m, without organics bleeding.(c) 2022 Elsevier B.V. All rights reserved.

Limestone and clays, or clayey limestones, are the raw materials commonly used for ordinary Portland cement clinker production. For the manufacture of Portland cements, the raw meals were composed on the basis of chemical analysis. In this study, the aims are (1) to investigate local raw meals for clinker manufacturing, from the North of France and (2) to re-discover the adequate mix used in one of the first cement plant in France (Boulogne-sur-Mer). To these purpose, three types of limestones were characterized by X-Ray Fluorescence, X-Ray Powder Diffraction and optical microscopy (OM) to assess their petrography and hence their suitability for clinker production. The limestones to be exploited are located between layers of the Moulin-Wibert limestone cliff (north of Boulogne-sur-Mer) which is the part of the Kimmeridgian stage. Further, different primitive raw meals (BAC1+BAC3 and BAC1+BAC5) were burnt at 1450 °C using modern day technology. Their phase changes and structural evolutions were assessed by X-Ray Powder Diffraction. The final clinker microstructures are observed and analyzed by Scanning Electron Microscopy coupled to Energy Dispersive X-Ray spectroscopy (SEM-EDX).

This study investigates novel Portland cement-based mortars, developed for hydrogen/tritium trapping and radioactive waste immobilization. They incorporate a gamma-MnO2/Ag2O getter powder at 10% wt (i.e. 6.8 to 7.1% vol). Compared to former patented materials, no drying or heat treatment of the materials is needed. Complementarily to X Ray Diffractometry (XRD) and thermo-gravimetry analysis (TGA), 27Al and 29Si Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) evidences that the structure of the Portland cement solids (i.e. the C-A-S-H) is not impacted by the presence of getter, even after several month curing. Yet, Scanning Electron Microscopy coupled to Energy Dispersive Spectroscopy (SEM + EDS) shows that calcium is significantly present at the surface of the getter grains; this could affect trapping efficiency. However, after gamma irradiation with cumulated doses of 491 or 997 kGy (i.e. 23 to 46 days at 900 Gy.h (-1)), all mortars made with getter have a hydrogen trapping efficiency of between 77 and 96%, when compared to the irradiation of mortars made with a non-trapping gamma-MnO2 powder, or to the irradiation of pure water considered alone. This means that the developed mortars display excellent hydrogen trapping efficiency, without any impact on their solid structure. (C) 2022 Elsevier B.V. All rights reserved.