Phase Assemblage Research Articles

Assessment of waste eggshell powder as a limestone alternative in portland cement

The decarbonization of the concrete industry is an ongoing pursuit. One solution towards this goal is the use of limestone powder in portland cement. Waste eggshell has tremendous potential as an alternative calcite filler in cement due to its similarities with limestone. In this research, the feasibility of adding 15% and 35% ground eggshell in portland cement to make cement mortars was investigated. The hydration mechanism of eggshell and limestone blended cements was compared through the heat of hydration, phase assemblage, electrical resistivity, compressive strength, and shrinkage measurements. The experimental results showed that cement mortars with ground eggshell attained similar compressive strength as that with limestone. However, eggshell mixtures demand more mixing water to compensate the hydrophobicity of the eggshell membrane. The high calcite content in both eggshell and limestone accelerates the hydration of cement at 15% replacement, but ground eggshell retards cement hydration at 35% replacement due to the dominant influence of the membrane. Overall, eggshell waste is a feasible sustainable alternative to limestone powder at up to 15% portland cement replacement levels. Lifecycle assessment and cost analysis showed that adding 15% ground eggshell in cement concrete further reduces its embodied carbon and energy and cost compared to cement concrete containing limestone powder.

A Review of Principles, Analytical Methods, and Applications of SEM‐EDS in Cementitious Materials Characterization

AbstractScanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM‐EDS) is an indispensable and versatile technique that provides detailed 2D spatial insights into the microstructure of heterogenous cementitious systems. To foster clear and systematic understanding of SEM‐EDS analysis in advancing research on cementitious materials, the state‐of‐the‐art principles, analytical approaches, and applications of SEM‐EDS analysis in cementitious systems are reviewed. This review aims to assist researchers in selecting the most appropriate strategy for SEM‐EDS analysis to quantify phase assemblage, elucidate environmental interactions, and investigate microstructure evolution in cementitious systems. The fundamental concepts related to equipment, signal generation, acquisition of diverse EDS data are first presented. Subsequently, various analysis approaches, including point analysis, grid analysis, and mapping analysis are discussed. This review then emphasizes the practical significance and potential value of SEM‐EDS analysis in addressing phase quantification challenges pertaining to cementitious systems. It is posited that the SEM‐EDS analysis holds the promise of becoming the characterization backbone for quantitative research on cementitious systems.

Belite–ye’elimite–ferrite cements produced from London Clay

London Clay (LC) is generated in significant quantities from major infrastructure development projects within and around London, UK. Excavated LC spoils are typically landfilled or used for landscaping purposes with minimal value. This study investigates the feasibility of producing belite–ye’elimite–ferrite (BYF) cements using LC in combination with kaolin or low-grade bauxite. Six cement clinkers with varying compositions were synthesised at 1300°C. The phase composition of the synthesised clinkers was quantified using X-ray diffraction analysis (XRD) coupled with Rietveld refinement. The hydration behaviour, phase assemblage evolution and mechanical performance of the cements were examined using isothermal calorimetry, XRD, thermogravimetric analysis and compressive strength testing, respectively, up to 90 days of curing. It is demonstrated that LC can be used either on its own or with kaolin or low-grade bauxite to produce BYF cements with a wide range of composition: 31 to 64 wt% belite, 9.3 to 27 wt% ye’elimite and 2.1 to 31 wt% ferrite. The use of LC as the sole alumina source resulted in low compressive strength at early stages. Nevertheless, the strength developed over time, reaching 27.8 MPa at 90 days (0.5 w/b). Possible approaches to develop LC further for producing viable BYF cements are discussed.

Utilization of pretreated green liquor dregs as an activator for blast furnace slag: Effect on hydration, phase assemblage, and rheology

This study explores the utilization of calcium- and magnesium-rich pulp mill residues, i.e., green liquor dregs (GLDs), as an activator for ground granulated blast furnace slag (BFS). The aim of this study is to examine the potential of this unutilized residue when used as a part of alkali-activated materials (AAMs) and in this way enhance the exploitation of GLD. This study focuses on the fresh- and hardened-state properties of the produced paste and mortar samples, where 70% of BFS and 30% of GLD have been incorporated. Two different-sourced and thermally pretreated (105 °C, 300 °C, and 525 °C) GLDs have been used. The effect of thermal treatment on the utilization possibility of GLDs with respect to viscosity, setting times, reactivity, mineralogy, and microstructure is analyzed using the paste samples, while its effect on workability, and strength gain is measured using the mortar samples. Results show that both GLDs enhance the hydration of BFS and that the early-age hydration and strength increase when the GLDs have undergone pretreatment at the highest temperature (525 °C). However, at the later age (28 days), the samples activated with the GLDs treated at 300 °C achieve the highest strength. The addition of both GLDs treated at any temperature increases the viscosity of the composite samples and reduces their workability; however, it should be noted that optimization of water to binder ratio was not the objective of this study. The results of this study show that GLD, previously considered unreactive, can potentially become a reactive component of AAMs.

Elucidating factors on the strength of carbonated compacts: Insights from the carbonation of γ-C2S, β-C2S and C3S

Accelerated carbonation presents a promising approach for enhancing the early strength of cement-based materials while simultaneously sequestering CO₂. This study examines the carbonation of γ-C₂S, β-C₂S, and C₃S compacts to identify the critical factors influencing strength development over extended curing periods. Analysis of the evolution of mechanical properties, microstructure, and phase assemblages reveals three key factors: 1) Degree of carbonation, which directly correlates with the density of the compacts; 2) Crystalline form and crystal size of calcium carbonate, influencing the strength of the crystal interface; and 3) Silica gels, which act as a phase boundary, with hydration products forming in the later stages of β-C₂S carbonation potentially affecting strength. The findings indicate that calcite promotes rapid strength gain in the early stages, while aragonite contributes to long-term performance. The presence of hydration products within the silica gel phase boundary may explain the observed strength reduction in β-C₂S compacts during extended carbonation. These insights provide valuable guidance for optimizing the design and application of carbonated cement-based materials for sustainable construction.

Experimental petrology constraints on kamafugitic magmas

Abstract. Kamafugites are rare volcanic igneous rocks, characterized by the presence of kalsilite and variable amounts of leucite, nepheline, melilite, clinopyroxene, olivine and phlogopite, which may not necessarily be present all together. Kamafugites are silica-poor (moderately ultrabasic to basic), CaO- and alkali-rich (mostly ultrapotassic) lithologies, generated from strongly metasomatized and heterogeneous mantle sources, with abundant phlogopite and little or no orthopyroxene. Melting of phlogopite- and carbonate-bearing veins is often invoked as being responsible for the ultrapotassic and ultracalcic signatures observed in many kamafugites. Nevertheless, many questions still persist about their mantle sources, such as the paragenesis of the metasomatic veins within the lithospheric mantle and the degree of interaction between the initial melts and the peridotite matrix. We experimentally investigated four natural kamafugite samples to determine the mantle assemblages that were in equilibrium with these melts at the onset of partial melting and their genesis. The kamafugites were collected from the three known areas where they occur: Uganda, Italy and Brazil. Near-liquidus experiments were carried out at 1 to 2 GPa and temperatures from 1250 to 1380 °C. These experiments provide information on the mineralogy of the potential mantle sources in each of the volcanic provinces, also allowing a comparison among them. The experiments confirm the common presence of clinopyroxene and phlogopite as the main near-liquidus phases, with olivine joining the near-liquidus phase assemblage in one Italian sample (San Venanzo) and in the Brazilian kamafugite. Other minor phases (apatite and Fe–Ti oxides) also crystallized in near-liquidus conditions, highlighting their importance for at least the Ugandan and Brazilian kamafugites. Our results demonstrate that various amounts of clinopyroxene (∼40 % in Italy and 50 %–60 % in Uganda and Brazil), phlogopite (∼20 %–30 % in Brazil, ∼40 % in Uganda and ∼60 % in Italy) and accessory phases (up to 4 % titanite in Uganda, up to 3 % apatite in Uganda and up to 5 % oxides in Uganda and Brazil) are required for the formation of kamafugite melts. The contribution of olivine differs among the four samples, being negligible for the Ugandan kamafugites and in one of the Italian kamafugites but up to 5 % in the second Italian kamafugite and 10 % in Brazil.

Microstructure and mechanical properties of 3D‐printed zirconia bone scaffold: Experimental and computational analysis

AbstractMicroextrusion‐based additive manufacturing of zirconia‐based bioceramics is capable of fabricating design‐specific architectures with high mechanical strength properties and relative density. We developed a novel organic residue‐free binder system for zirconia paste printing (ZP2) with the shear‐thinning properties apropos to microextrusion‐based 3D printing. Based on thermogravimetric analysis, debinding protocol was established followed by high‐temperature heat treatment under four sintering conditions. Quantitative linear shrinkage (32.3%–42.7% ranging from in‐plane to vertical direction), density (83.3%–87.5%), and surface roughness (7.7–13.8 µm from the parallel to the perpendicular to the infill direction) as a factor of sintering conditions (1400°C–1500°C for 3–4 h) were analyzed. Whereas qualitative phase assemblage demonstrated “sintering condition independent” phase stability; grain growth and reduction in porosity were observed in the microstructure with increment in sintering temperature and hold time. Interestingly, at higher temperature and hold time, the compressive (46–72.4 MPa) and tensile strength (16.2–23.1 MPa) properties experienced a trade‐off between grain growth and reduction in porosity. The ZP2 scaffolds sintered at lower temperature and hold time qualified for the bone scaffold applications having interconnected porosities, biologically relevant surface roughness, and human bone mimicking mechanical properties. With a unique finite element analysis recipe, the mechanical behavior of the “life‐like” reconstructed computer aided design (CAD) geometries identical to real 3D‐printed‐sintered ZP2 scaffolds was quantitatively predicted.

Fracture characteristics and microscopic mechanism of slag-based marine geopolymer mortar prepared with seawater and sea-sand

This study utilized seawater, sea sand, and ternary solid waste to produce marine geopolymer mortar (MGM). 23 groups of MGM samples with varying alkali content and basalt fiber (BF) and polypropylene fiber (PPF) volume fractions, as well as marine cement mortar (MCM), were tested for fracture characteristics. Three initial crack length ratios (a0/h) (0.2, 0.3, and 0.4) were designed. The analysis included load-crack mouth opening displacement (P-CMOD) curves for all specimens, focusing on critical crack length (ac), critical crack tip opening displacement (CTODc), fracture toughness (KSIC), fracture energy (GF), and facture brittleness index (FBI). Results indicated that increasing alkali content enhanced strength and elastic modulus, peak fracture load, critical crack extension length (Δac), and CTODc, while decreasing final CMOD. This was attributed to the increased alkali content, which enhanced the mortar’s density. However, excessive alkali content also led to increased shrinkage damage within the matrix, making it prone to stress concentrations and resulting in brittle failure. Based on the research, it is recommended that the alkali content be controlled within the range of 4–5 %. Hybrid fibers showed superior overall toughness enhancement, increasing KSIC, GF, and FBI by 54.3 %, 95.6 %, and 427.4 %, respectively. This improvement was due to the synergistic effect of BF and PPF, which increased the specimen’s elastic modulus, reduced crack propagation speed, and sustained load-bearing capacity during the later stages of crack development. The fracture toughness of conventional geopolymer mortar was positively correlated with the Ca/Si ratio and was lower than that of MGM. In contrast, MGM’s Ca/Si ratio showed an inverse correlation with KSIC, indicating that phase assemblage governs the fracture resistance of MGM. This is because Cl- in seawater intensified geopolymerization reactions. Interwoven gel structures in MGM, with surface depositions like magnesium aluminosilicate hydrate (M-A-S-H), magnesium silicate hydrate (M-S-H), and silica gel, filled pores, and improved homogeneity, resulting in its superior fracture toughness over conventional geopolymer mortar.

Performances enhancing of supersulfated cement (SSC) using waste alkaline activators: Red mud and carbide slag

Supersulfated cement (SSC), since its invention, showed lower early-age strength gain, which has limited its practical applications. The urgent issue is how to regulate and enhance its early-age performance. In this context, solid waste materials such as bauxite residue-red mud (RM) and carbide slag residue (CS) from acetylene production by calcium carbide hydrolysis were used to improve the hydration and performance of SSC. By utilizing a range of analytical techniques such as isothermal calorimetry (IC), X-ray diffraction (XRD), backscatter scanning electron images (BSE), and thermogravimetric analysis (TGA), the hydration process, phase assemblages and microstructure of CS/RM-modified SSC were systematically investigated. It’s found that CS, as a calcareous alkaline activator, act as a regulator for adjusting the two main hydration reactions of C-A-S-H deposition and ettringite formation in SSC. The alkaline activator induces the hydration of slag and promotes the formation of hydration products. However, an excessively high dosage of carbide slag delays the primary ettringite formation reaction because it inhibits the dissolution of slag and promotes the formation of outer products. It leads to a looser and more porous paste matrix, resulting in higher expansion strain and poor strength gain at full curing ages. In contrast, red mud improves the hydration rate and enhances the hydration degree of SSC within the studied content (up to 30 wt%). With addition of red mud, SSC hydration is significantly advanced and deepened, resulting in more hydrates, particularly inner products. Red mud facilitates the depolymerization of the slag glass network and promotes the forming of nuclei and growth of hydration products. However, an excessively high red mud content would lead to a looser and more porous paste matrix due to the characteristics of red mud particle itself. An optimal red mud content has been identified as 20 wt%.

Uncovering the mechanism controlling strength and microstructural evolution of belite-rich cement-based materials at different temperatures

The effect of temperature on the properties of belite-rich cement-based (BRC) materials is different from that on Portland cement (PC). This study provides a comprehensive understanding of the mechanisms controlling strength and microstructural evolution at different temperatures, especially C-S-H characteristics, of BRC materials. Phase assemblage, pore structure, and microscopic morphology of BRC paste, as well as phase composition and structure, chemically bound water, and bulk density of C-S-H were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), 1H and 29Si nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS). The strength of BRC mortar increased with temperature is because of the higher hydration degree of β-C2S, lower porosity (except for 60 °C), and increased main chain length (MCL) of C-S-H. Hydration degrees of 28-d β-C2S and C3S increased by 202.5% and 16.3%, respectively, while MCL increased by 39.4% from 5 to 60 °C. The higher temperature sensitivity of β-C2S is due to its activation energy being 12.4% greater than that of C3S in BRC paste. Additionally, gel porosity decreased with temperature due to decreased bound water content and increased 16.7% bulk density of C-S-H from 5 to 60 °C. Finally, the CaO/SiO2 was inversely proportional to MCL and bulk density, but positively to H2O/SiO2. The findings deepen the mechanistic understandings of the hydration kinetics and microstructural evolution for temperature-affected BRC material.

Chrome incorporation in high-pressure Fe–Mg oxides

Abstract. The occurrence of Cr-bearing oxide phases as inclusions in diamonds and in extraterrestrial materials has the potential to serve as an indicator of formation conditions. However, such an application requires detailed knowledge of phase stabilities and the influence that Cr may have on its stability. To this end, the incorporation of Cr in high-pressure post-spinel Fe–Mg oxide phases was experimentally investigated at pressures of 14–22 GPa and temperatures between 1100 and 1600 °C using a multi-anvil press. We find that neither the Fe3Cr2O6 nor the Mg3Cr2O6 endmember composition is stable over the expected range of pressure and temperature where Fe5O6 itself is known to be stable. Further experiments along the Fe32+Fe23+O6–Fe32+Cr2O6 binary indicate only small amounts of Cr substitution are possible: ∼ 0.12 cations Cr per formula unit or ∼ 6 mol % Fe32+Cr2O6 component. In contrast, complete solid solution is apparent across both the Fe22+(Cr,Fe3+)2O5 and the Mg2(Cr,Fe3+)2O5 binaries, and there are indications of complete solution in the entire (Mg,Fe2+)2(Cr,Fe3+)2O5 quaternary system. The O5-structured phase usually coexists with (Fe,Mg)O. At 16–20 GPa, a post-spinel phase with O4 stoichiometry was occasionally encountered, having either a modified Ca-ferrite- (mCF-FeCr2O4) or a Ca-titanate-type (CT-MgCr2O4) structure. In one high-temperature experiment at 1600 °C, an unquenchable Mg-rich phase with a reconstructed Mg4Fe23+O7 stoichiometry occurred together with Mg2(Cr,Fe3+)2O5. In one experiment at 1100 °C and 16 GPa with a bulk composition of Mg2(Cr0.6,Fe0.43+)2O5, an assemblage of O5 phase + eskolaite–hematite solid solution + periclase was obtained together with minor amounts of the CT-type phase and a β-(Cr,Fe)OOH phase. The occurrence of these two minor phases in this low-temperature experiment is an indicator of variable reaction kinetics amongst the starting materials, which caused chemical heterogeneities to develop at the onset of the experiment. The structural systematics of Fe22+(Cr,Fe3+)2O5 and (Fe2+,Mg)2(Cr,Fe3+)2O5 solid solutions were investigated. It is notable that the Fe3+ and Cr endmembers have somewhat different crystal structures, belonging to space groups Cmcm (no. 63) and Pbam (no. 55), respectively. The phase transition occurs around the midpoint of the Fe3+–Cr joins. In spite of complexities in the behavior of the unit-cell parameters, the variation in molar volume with composition deviates only slightly from linearity. Wüstite and periclase coexisting in our experiments reveal the incorporation of up to 9 wt % and 25 wt % Cr2O3, respectively. This is consistent with the minor Cr contents reported for some ferropericlase inclusions in natural diamond. The limited solubility of other cations in Fe5O6 limits the likelihood of it being an accessory phase in the Earth's deep upper mantle and transition zone, except in Fe-rich environments. In contrast, the O5 phase appears to be more flexible in accommodating a range of divalent and trivalent cations, suggesting that this phase is more likely to be stabilized, potentially where redox reactions related to diamond formation occur.

Paleoproterozoic ultrahigh-temperature metamorphism in the Helanshan Complex, North China Craton: New constraints from chloritized sapphirine-bearing pelitic granulites

Identifying ultrahigh-temperature (UHT) metamorphism in granulite-facies metamorphic terrains and determining its pressure-temperature-time (P-T-t) paths are crucial steps toward elucidating the anomalously hot geodynamic evolution process. This study presents the inaugural identification of chloritized sapphirine-bearing granulites in the Helanshan Complex, located in the western segment of the Khondalite Belt, North China Craton. Three stages of metamorphic evolution were identified based on petrographic analyses, mineral chemistry, and phase equilibrium modelling: the pre-Tmax stage involves the presence of rutile-stable phase assemblage, wherein rutile is partially substituted by ilmenite; the Tmax stage involves the assemblage of garnet + plagioclase + K-feldspar + sillimanite + spinel ± sapphirine + quartz + ilmenite + melt, as evidenced by microscale (<5 μm) blebs of variably chloritized sapphirine within spinel; and the retrograde cooling stage features the solidus assemblage of garnet + plagioclase + biotite + K-feldspar + sillimanite + cordierite + quartz + ilmenite + melt. Phase equilibrium modelling indicates Tmax conditions of 958–1055 °C and 6.4–7.8 kbar, suggesting UHT conditions accompanied by a high geothermal gradient of approximately 150 °C/kbar. Furthermore, a clockwise P-T trajectory was established, involving pre-Tmax decompression and post-Tmax near-isobaric cooling. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon and monazite U-Pb dating of UHT pelitic granulites produced ages clustering around 1.91 Ga, marking the era of UHT metamorphism within the Helanshan Complex. This discovery broadens the scope of UHT metamorphism and indicates that the entire Khondalite Belt experienced a regional UHT metamorphic event during 1.93–1.91 Ga, which was likely induced by an initial radiogenic heating synergy followed by an augmented mantle heat flux.

Impact of calcination technology on properties of calcined clays

Calcined kaolinitic clays are known to be very reactive pozzolans, and combined with limestone can enable significant clinker substitution in cementitious systems. Thermal activation of kaolinitic clays takes place when the hydroxyl groups are removed, leading to formation of an amorphous reactive structure. There are several technologies for clay activation, but the most used at industrial scale are flash and stationary calcination. The objective of this paper is to investigate the impact of the calcination regime on the properties of the calcined product. It presents the results of an experimental program carried out with a kaolinitic clay calcined at a flash calciner and at a laboratory furnace. Calcination brings about a drop in specific surface, and an increase of average diameter due to agglomeration, an effect more pronounced in stationary calcination. No major differences were found at the heat of hydration, CH consumption and phase assemblage for the fully dehydroxylated material. The flash calcined material had slightly better results mainly due to a finer PSD compared with the one stationary calcined. No major difference was found in water demand and compressive strength for both regimes. As expected, the main impact of the calcination regime is the agglomeration.

Resistance to acid, alkali, chloride, and carbonation in ternary blended high-volume mineral admixed concrete

The World Bank study predicts that 4 °C warming will bring high temperatures, sea-level rise, and saltwater intrusion to coastal areas, damaging coastal concrete structures. Increased CO2 from industrialization exacerbates this, necessitating durable, low-carbon concrete. Combined use of fly ash (FA) and ground granulated blast furnace slag (GGBFS) as high-volume OPC replacements boosts performance while reducing concrete’s carbon footprint. In this perspective current study examines the durability of concrete against aggressive agents (H2SO4, MgSO4, NaCl, and CO2) causing premature deterioration of concrete structures. Initially, three cost-effective sustainable concrete mix designs were developed, incorporating 50% replacement of OPC with locally available supplementary cementitious materials, specifically FA and GGBFS. These mixes were then evaluated for their mechanical and durability performances. The impact of aggressive ions (SO4 2−, Cl−, and CO3 2−) was studied by examining the changes in mechanical performance and phase assemblages. Thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) techniques were used to estimate the phase compositions. Ternary blended concrete having 50% OPC+ 30% GGBFS + 20% FA exhibited optimal synergistic performance, enhancing pozzolanic and hydraulic reactions for better resistance to harmful ions. The sorptivity test confirmed that as the GGBFS content increased, the sorption rate decreased, indicating the higher reactive nature of GGBFS to that of FA. Deleterious compounds formed due to the action of SO4 2-, Cl-, and CO3 2- were identified to be ettringite (Ca6Al2(SO4)3(OH)12.32H2O, AFt) and gypsum (CaSO4.2H2O, Gy), Friedel’s salt (Ca4Al2(OH)12Cl2.4H2O, Fs) and polymorphs of calcium carbonate (CaCO3), respectively through TG mass loss curve. These results were corroborated by FTIR analysis, which showed predominant characteristic bands at 662 cm−1 for SO4 2−, 459 cm−1 for Mg–O stretching, 790 cm−1 for Al–OH bending, and 1431-1443 cm−1 for C–O, confirming the presence of the deleterious compounds.

MgO activated calcined marine clay and its carbonation

Marine clay, a common waste product abundantly available in coastal regions, can serve as an alternative silica source after activation due to its pozzolanic reactivity. In this study, a binder comprising reactive MgO cement and thermally activated marine clay (AMC) was developed. It was found that the developed MgO-AMC binder with a mass ratio of MgO to AMC of 0.4 to 0.6 achieved a 28-day compressive strength of 20.4 MPa under ambient curing. Through accelerated carbonation curing, the highest 28-day compressive strength increased by 45%, and the highest carbon sequestration ratio reached 11.8%. The phase evolution and microstructural development of hydrated/carbonated binder were comprehensively investigated by TG-IR, XRD, NMR, and SEM-EDS. In addition, thermodynamic modelling was performed to further understand the phase assemblage of the hydrated binder, and indicated that M-A-S-H phase was thermodynamically more stable in the developed binder.

Alkali activated steel slag – oil composites: Towards resource efficiency and CO2 neutrality

This study describes advances in high-performance construction material development using a minimum of primary resources while enabling simultaneous CO2 sequestration capacities. Two so far unutilized Austrian steel slags were combined with metakaolin and vegetable oil to produce alkali-activated materials exhibiting high compressive and flexural strength of up to 94 MPa and 13 MPa, respectively. This approach enabled a reduction in primary mineral resources of up to 82 wt%, with an average reduction in global warming potential (GWP) of 52 % compared to a traditional high-performance Portland cement material. Oil addition led to the formation of mainly water unsolvable metal soap phases precipitating within the pore spaces without significantly altering the phase assemblage and chemistry of the binder matrix, but further reducing the GWP by 74 %. The (heavy metal) leaching behavior coincides with that of traditional concrete materials and was even further reduced by the addition of oil.

Magma storage conditions of Lascar andesites, central volcanic zone, Chile

Abstract. Lascar volcano, located in northern Chile, is among the most active volcanoes of the Andean Central Volcanic Zone (CVZ). Its activity culminated in the last major explosive eruption in April 1993. Lascar andesites which erupted in April 1993 have a phase assemblage composed of plagioclase, clinopyroxene, orthopyroxene, Fe–Ti oxides, and rhyolitic glass. To better constrain storage conditions and mechanisms of magmatic differentiation for andesitic magmas in a thick continental crust, crystallization experiments were performed in internally heated pressure vessels at 300 and 500 MPa, in the temperature (T) range of 900–1050 °C, at various water activities (aH2O) and oxygen fugacities (logfO2 between QFM+1.5 and QFM+3.3 at aH2O =1; QFM is quartz–fayalite–magnetite oxygen buffer). The comparison of experimental products with natural phase assemblages, phase compositions, and whole-rock compositions was used to estimate magma storage conditions and to reconstruct the magma plumbing system. We estimate that Lascar two-pyroxene andesitic magmas were stored at 975±25 °C, 300±50 MPa, and logfO2 of QFM+1.5±0.5, under H2O-undersaturated conditions with 2.5 wt % to 4.5 wt % H2O in the melt. The geochemical characteristics of the entire suite of Lascar volcanics indicates that a fractionating magmatic system located at a depth of 10–13 km is periodically replenished with less evolved magma. Some eruptive stages were dominated by volcanic products resulting most probably from the mixing of a mafic andesitic magma with a felsic component, whereas compositional variations in other eruptive stages are better explained by crystal fractionation processes. The relative importance of these two mechanisms (mixing vs. crystal fractionation) may be related to the amount and frequency of magma recharge in the reservoir.

Effect of glass content on the phase assemblage and processing requirements of zirconolite glass-ceramics for actinide immobilisation

Zirconolite is a candidate wasteform for actinides (U/Pu/Th), and glass incorporation to form glass-ceramics provides flexibility to accommodate heterogeneous wastes while simplifying processing requirements; however, the glass content required to optimise these benefits remains unestablished. This systematic study investigated the effect of glass content on zirconolite crystallisation, phase assemblage, phase composition, cerium valence states and partitioning. Cerium-bearing zirconolite glass-ceramics were fabricated by targeting zirconolite (Ca0.8Ce0.2ZrTi1.6Al0.4O7; Ce as actinide surrogate) with varying amounts (0–100 vol%) of glass addition (NaAl1.5B0.5Ca0.7Ti0.2Si2O8.6). Differential scanning calorimetry data revealed that glass addition lowered the zirconolite crystallisation temperature (1283°C to 1200°C). X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy analyses showed that glass addition lowered the temperature (1320°C to 1270°C) required to fabricate phase-pure zirconolite glass-ceramics and minimise CeO2/ZrO2 phases, with > 90 % of cerium preferentially partitioned into zirconolite. X-ray absorption near edge spectroscopy data showed predominantly Ce4+ within zirconolite as targeted.

Phase evolution and performance of sodium sulfate-activated slag cement pastes

This study evaluates the reaction kinetics, phase assemblage, and microstructure evolution of Na2SO4-activated slag cements produced with three commercial slags. The main reaction products identified are ettringite and calcium aluminosilicate hydrates, alongside a poorly crystalline SO42- intercalated Mg-Al-layered double hydroxide (LDH) phase. Results revealed that the Al2O3 slag content alone does not correlate with the cement performance. While pastes made with a higher Al2O3 content slag exhibit faster reaction kinetics, those made with a slag with a higher Mg/Al ratio developed superior compressive strength and reduced porosity over extended curing periods. Thermodynamic modelling simulations indicate that sulfate consumption occurs via ettringite and LDH phase formation, influencing the slag reaction degree, pH value, and porosity reduction in these cements. This research highlights the critical role of slag composition in controlling microstructure and, consequently, performance of sodium sulfate activated slag cement pastes.

First widespread occurrence of rare phosphate chladniite in a meteorite, winonaite Graves Nunataks (GRA) 12510: Implications for phosphide–phosphate redox buffered genesis in meteorites

Abstract The first widespread occurrence of rare Na-, Ca-, and Mg, Mn, Fe-bearing phosphate chladniite was observed in meteorite Graves Nunataks (GRA) 12510, which is a primitive achondrite that sits within the winonaite class. Numerous 1–500 µm chladniite grains were found, often on the margins between silicate clasts and the kamacite portions of the large metal veins that permeated through the sample. The largest chladniite grains are associated with merrillite, kamacite, taenite, troilite, albite, forsterite, diopside, and enstatite, with a few tiny chladniite grains and an apatite grain enclosed within merrillite. GRA 12510s average chladniite composition is Na2.7Ca1.25(Mg10.02Mn0.69Fe0.20)Σ10.91(PO4)9. Electron backscattered diffraction (EBSD) patterns indicate varying degrees of nucleation and growth of chladniite grains. Additionally, the first pure Raman spectrum of chladniite is described here, revealing primary ν1 bands at 954, 974, and especially 984 cm–1. The co-occurrence and close association of merrillite, apatite, chladniite, and P-bearing metallic phases within GRA 12510 suggests that the fO2 of IW-2 to IW-4 is an intrinsic property of the precursor chondritic material, and the phosphate-phosphide reaction may have buffered the final winonaite and IAB iron meteorite phase assemblages. Altogether, chladniite appears to form alongside other phosphates, with their chemistries reflecting the diverse environment of their formation. Meteoritic chladniite likely formed through subsolidus oxidation of schreibersite, scavenging Na from albite, Ca from diopside, Mg from enstatite/forsterite, Fe from kamacite/taenite, and Mn from alabandite/chromite when available. A P0-P5+ redox-buffered environment also has implications for thermometry and fast cooling rates, although more experiments are needed to extrapolate powder reaction rates to those of larger crystals. Furthermore, phosphide-phosphate buffered experiments may aid in investigating equilibrium chemistry at fO2 values between IW-2 and IW-4, which have been challenging to explore experimentally due to the limited availability of solid metal-metal oxide buffers between IW (Fe-FeO) and IW-5 (Cr-Cr2O3) at temperatures and pressures relevant to planetary interiors. Future investigations of phosphide-phosphate redox-buffered genesis at fO2 values between IW-2 and IW-4 have important implications for primitive meteorite constituents (e.g., CAI values), partially differentiated planetesimals and planets, including Mercury and core formation on Earth.