Phase Assemblage Research Articles

Thermodynamic mechanisms on the effects of mix proportion, and type and dosage of chemical modifier on phase assemblage of magnesium oxysulfate cement

The effects of the type of raw material, mix proportion, and chemical modifier on the mechanical properties and water resistance of magnesium oxysulfate cement (MOS) have been extensively studied. However, the formation mechanism of hydration products remains obscure. This study aims to clarify the hydration mechanism of MOS through a thermodynamic modeling approach and to explore the effects of mix proportion and type and dosage of modifier on the phase assemblage as well as the mechanical properties of hardened paste. The volume fraction of 5Mg(OH)2⋅MgSO4⋅7H2O (5-1-7) is used as a key parameter to establish the relationship between the mix proportion and the compressive strength of the MOS system. The results demonstrate that the thermodynamic modeling method can predict the phase evolution of MOS with various mix proportions. As the molar ratio of reactive-MgO (α-MgO) to MgSO4 increases, both the 5-1-7 volume fraction and compressive strength of hardened paste initially increase and then decrease, while decreasing as water dosage increases. The volume fraction of 5-1-7 is proportional to the compressive strength of MOS. Compressive strength is greatest at molar ratio of nMgO:nMgSO4 = 4–9 and nH2O:nMgSO4 = 9–20. The efficiency of modifiers is: citric acid (CA) > tartaric acid > EDTA > phosphoric acid > acetic acid. The modifying mechanism of CA involves the initial formation of 3Mg(OH)2⋅MgSO4⋅8H2O(3-1-8), followed by its transformation into 5-1-7.

Insights on the effects of carbonates and phosphates on the hydration of magnesia (alumino-)silicate cements

Cements based on magnesium oxide (MgO) and reactive (alumino-)silicates (xSiO2-yAl2O3) have drawn increasing attention owing to their potential to be produced using raw materials with low CO2 emissions. This study examines how the phase assemblages and compressive strengths of magnesia (alumino-)silicate cements are influenced by the addition of sodium hexametaphosphate (NaHMP) and sodium carbonate (Na2CO3). Cement paste samples with a Mg/Si molar ratio of 1.5 and Al/Si molar ratios of 0 and 1.0 were prepared using microsilica (SF) and metakaolin (MK), respectively, and investigated using SEM, TGA, XRD, and 29Si, 27Al, 31P, and 13C MAS NMR. The results showed that the addition of NaHMP and sodium carbonate enhanced the reactivity of the raw materials in the Al-free MgO-SF systems, with magnesium silicate hydrate (M-S-H) being the primary hydrated phase. After 91 days, the degrees of reaction of microsilica were ∼86% and 96% for systems containing 0 and 2.5 wt % Na2CO3, respectively. In contrast, the reactivity of metakaolin in the Al-containing MgO-MK systems was limited to ∼53%, irrespective of Na2CO3 addition, likely due to the excess sodium hexametaphosphate covering the surface of MK. Here, the main reaction products were magnesium aluminosilicate hydrate (M-A-S-H) and hydrotalcite (Mg6Al2CO3(OH)16·4(H2O))-like phases. Despite the MgO-SF systems displaying higher degree of reaction than the MgO-MK systems, the latter exhibited higher compressive strength. Sodium carbonate increased the compressive strength of the MgO-SF systems but decreased that of the MgO-MK systems. Thermodynamic modelling was also carried out and the results generally agreed with the phase formation observed with XRD and solid-state NMR.

An investigation of the source of calcium carbonate from the carbonated Portland cement: Based on the transformation of hydrates

In this work, two PC pastes were used to carry out accelerated carbonation experiments, and phase assemblages of paste samples collected at different sampling depths were analyzed. The source of CaCO3 originating from the carbonation reaction of hydrates in cement was quantitatively determined by a novel method based on the transformation of hydrates. Experimental results indicated that the phase assemblages in the carbonated zone of two PC pastes showed minor differences. C(A)SH, ettringite, AFm-CO3, and unhydrated cement particles in the complete carbonation zone of two cement pastes were carbonated and transformed into other phases. For the surface of two PC pastes (0–3 mm), calculations showed that the CaCO3 originating from the carbonation of calcium hydroxide and C(A)SH accounted for 75.3% and 72.6% of the total CaCO3, respectively. A concentration of 20% CO2 was not beneficial for the diffusion of CO2 and the subsequent precipitation of CaCO3 at the later period of carbonation.

Fabrication of Si3N4 ceramics with adjustable microstructure and mechanical properties via Y2O3 contents in ZrN–AlN–Y2O3 ternary sintering additives

To adapt to the different application environments, Si3N4 ceramics are required to have different mechanical properties. Therefore, in this study, Si3N4 ceramics with adjustable mechanical properties were fabricated via using ZrN–AlN–Y2O3 ternary sintering additives and hot-pressing at 1650 °C for 30 min. Subsequently, the effect of the Y2O3 concentration on the phase assemblage, microstructure, mechanical properties, and crack propagation of Si3N4 ceramics was systematically investigated. The results demonstrated that Si3N4 ceramics presented adjustable microstructure and mechanical properties with the Y2O3 contents added in the range of 0∼8 wt%. With the increase of Y2O3 contents, the average aspect ratio of Si3N4 grains had an increase of 61.77%, increasing from 3.95 to 6.39. Besides, the Si3N4 grains and the formed YAG intergranular phase exhibited a fairly good combination at the nano-scale. Si3N4 grains and intergranular phase were the main influence factors on the mechanical properties of Si3N4 ceramics. As a result, the bending strength was from 700.99 ± 38.72 to 961.13 ± 36.84 MPa. The fracture toughness exhibited a range of 4.87 ± 0.11 to 6.10 ± 0.23 MPa⋅m1/2, while Vickers hardness achieved a high level of 16.09 ± 0.16 to 19.98 ± 0.39 GPa.

Recent University Research, Implementation and Education in Support of Pyrometallurgical Lead Processing

The increasing chemical complexity of lead process streams encountered in industrial high temperature processing operations, as the result of declining primary resources, increased metal recycling and increased overall range of metals in modern devices has highlighted the urgent need for new predictive tools, fundamental phase equilibria and thermodynamic information and thermodynamic models to characterise the chemical behaviour of these systems. The paper examines recent progress in experimental and thermodynamic modelling research on process fundamentals, the availability of advanced, predictive computer-based tools and the implementation of the research outcomes into industrial practice. A wide range of chemical systems and phase assemblages have been studied. Some examples are taken from the current research program at PYROSEARCH, which involves the characterisation of multi-component, multi-phase gas-slag-matte-speiss-metal-solids systems with the PbO-ZnO-“Cu2O”-FeO-Fe2O3-CaO-Al2O3-MgO-SiO2-S as major and As-Sn-Sb-Bi-Ag-Au-Ni-Co-Cr-Na as minor elements with focus on systems directly relevant to lead primary and recycling pyrometallurgical processes. Examples of the application of advanced analytical techniques to fundamental and applied industrial research are also given. The implementation of new research outcomes into industrial practice depends critically on commitments by research staff as well as industry management and the availability of well-trained metallurgical engineers. We examine the current status of research implementation, university research, metallurgical engineering education and the availability of suitable educational pathways and initiatives that can be taken to increase undergraduate enrolments. Active engagement and support by industry is critical in ensuring the continuation of academic programs and advanced technical skills required by the industry.

Multiscale computational modelling of nano-silica reinforced cement paste: Bridging microstructure and mechanical performance

This study presents a systematic model to optimise nano-silica utilisation in cement paste and predict its nonlinear behaviour. The model integrates a hydration model, which calculates the dissolution rate of each clinker mineral, with a thermodynamic model that simulates the hydration reaction and interaction between hydrates and nano-silica. The investigation considered different replacement levels of nano-silica (2 and 4% by weight of cement) to analyse the phase assemblages and porosity of nano-silica reinforced cement paste. The reaction between nano-silica and the hydrate (portlandite) was meticulously accounted for by incorporating the formation of calcium-silica-hydrate (C-S-H) with a realistic transition from jennite-type C-S-H (Si/Ca ratio of 0.58) to tobermorite C-S-H (Si/Ca ratio of 0.67). The coupled model was validated against the experimental results obtained from thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy, ensuring its reliability. Subsequently, the model was used to compute the volume fractions of various phases including hydrates, unhydrated clinkers, pores, and unreacted nano-silica. A representative volume element (RVE) was formulated for the cement pastes with and without nano-silica using MATLAB. The RVE was further evaluated through finite element analysis using COMSOL Multiphysics, enabling the computation of homogenised material properties such as compressive strength, and this aligned well with experimental findings. In summary, the proposed systematic model provides a realistic prediction of the nonlinear behaviour of cement pastes with different nano-silica replacement levels. Its applicability extends to the optimisation of cement-based composites for diverse engineering applications.

Natural carbonation of portland cement with synthetic zeolite Y as a supplementary cementitious material

Risks associated with carbonation are a key limitation to greater replacement levels of ordinary portland cement (OPC) by supplementary cementitious materials (SCMs). The addition of pozzolanic SCMs in OPC alters the hydrate assemblage by forming phases like calcium-(alumina)-silicate-hydrate (C-(A)-S-H). The objective of the present study was to elucidate how such changes in hydrate assemblage influence the chemical mechanisms of carbonation in a realistic OPC system. Here, we show that synthetic zeolite Y (faujasite) is a highly reactive pozzolan in OPC that reduces the calcium content of hydration products via prompt consumption of calcium hydroxide from the evolving phase assemblage prior to CO2 exposure. Suppression of portlandite at moderate to high zeolite Y content led to a more damaging mechanism of carbonation by disrupting the formation of a passivating carbonate layer. Without this layer, carbonation depth and CO2 uptake are increased. Binders containing 12–18% zeolite Y by volume consumed all the calcium hydroxide from OPC during hydration and reduced the Ca/(Si+Al) ratio of the amorphous products to near 0.67. In these cases, higher carbonation depths were observed after exposure to ambient air with decalcification of C-(A)-S-H as the main source of CO2 buffering. Binders with either 0% or 4% zeolite Y contained calcium hydroxide in the hydrated microstructure, had higher Ca/(Si+Al) ratios, and formed a calcite-rich passivation layer that halted deep carbonation. Although the carbonated layer in the samples with 12% and 18% zeolite Y contained 70% and 76% less calcite than the OPC respectively, their higher carbonation depths resulted in total CO2 uptakes that were 12x greater than the OPC sample. Passivation layer formation in samples with calcium hydroxide explains this finding and was further supported by thermodynamic modeling. High Si/Al zeolite additives to OPC should be balanced with the calcium content for optimal carbonation resistance.

Efflorescence of fly ash-based geopolymer mortars under quasinatural conditions: The relationship between curing temperature, ion transport, and compressive strength

This investigation reports the effect of curing temperatures ranging from 20 °C to 80 °C on the efflorescence of fly ash-based geopolymer mortars under quasinatural conditions. The microstructures of the geopolymers before and after efflorescence were characterized by SEM and MIP, respectively. These characterizations are adopted to further explain the change in compressive strength. The micromorphology and phase assemblage of the efflorescence products were identified by SEMEDS and XRD, respectively, indicating that the significant ions involved in the efflorescence include Ca2+, Na+, and CO32-; then, the concentrations of those ions in the leachate were detected by ICP, AAS, and acidbase neutralization titration, respectively. The results show that low curing temperatures (≤ 50 °C) promote the diffusion of ions into the leachate, while high curing temperatures (> 50 °C) contribute to the transportation of ions towards the drying part for the formation of hollow structured Na2CO3·7 H2O. Although the increase in the compressive strength of the geopolymers resulting from efflorescence decreased with increasing curing temperature, the 50 °C-cured geopolymer exhibited the highest compressive strength during efflorescence. This study provides a reference for mitigating efflorescence and improving practicability in the hydraulic engineering of geopolymers.

Synthesis, solubility and thermodynamic properties of N-A-S-H gels with various target Si/Al ratios

The synthesis of N-A-S-H gel with high Si/Al ratios (>2) has been rarely reported in the literature, leaving the establishment of a reliable synthesis route as an open challenge. This paper aims to synthesize N-A-S-H gels with Si/Al ratios ranging from 1 to 3 and establish their thermodynamic database. The effects of reaction temperature, reaction time, initial Si/Al, concentration of reactants and pH of the matrix on the Si/Al ratios of the synthesized N-A-S-H gel were investigated. Results showed that N-A-S-H gels with target Si/Al ratios can be synthesized by controlling the concentration of reactants, pH and initial Si/Al ratios. The solubility products of the obtained N-A-S-H gels were determined via dissolution tests at different temperatures, to determine thermodynamic data. The development of this experimentally derived thermodynamic database of N-A-S-H gels constitutes a crucial step in the advancement of thermodynamic modeling of geopolymer, providing valuable insight into geopolymer reactions and phase assemblages.

Unified hydration model for multi-blend fly ash cementitious systems of wide-range replacement rates

Developments of binary, ternary, and even quaternary cementitious binder materials have been widely recognised in research and practices to elevate the sustainability of modern construction industry. To this end, a robust method to predict the hydration of novel binder systems is essential to facilitate informed material designs, yet extremely lacking. In this study, focusing on fly ash cement binders, a unified hydration model, applicable to multi-blend systems that further incorporate hydrated lime and/or nano silica, is freshly established. The proposed method features kinetic models to predict reaction degree for each binder component that are further coupled with a thermodynamic model to evaluate phase assemblage during hydration. The proposed model is carefully calibrated and verified against separate sets of experimental data. It is demonstrated to be applicable to binders incorporating up to 80 % of total cement replacement, and capable of robustly assessing the influence of multi-blend compositions on the hydrating systems.

Encapsulation of iodine-loaded adsorbents in blended Portland cement and geopolymer wasteforms

Capture of radioiodine by solid adsorbents and subsequent cementation is a promising solution to achieve “Near Zero” emissions from nuclear fuel cycles. We investigate cementation of iodine-loaded silica adsorbents in blast furnace slag blended Portland cement (BFS:PC) and metakaolin-based geopolymers, and subsequent leaching in deionised water. Adsorbent encapsulation retarded BFS:PC hydration, but not geopolymer reaction. Phase assemblage was unaffected by adsorbent encapsulation for both BFS:PC and geopolymers, which comprised calcium aluminosilicate hydrate and potassium aluminosilicate hydrate gels, respectively. Adsorbents were encapsulated intact within BFS:PC, whereas adsorbents dissolved in the high pH of fresh geopolymers. BFS:PC exhibited low leaching stability and an alteration layer, however minimal iodine leaching occurred due to intact absorbents. Geopolymers showed high leaching stability, however adsorbent degradation resulted in significant iodine leaching. This evidences potential for cementation of radioiodine-loaded adsorbents under mild conditions, and highlights the importance of synergy when designing adsorbents and wasteforms for radioiodine abatement.

The role of supplementary cementitious materials and fiber reinforcements in enhancing the sulfate attack resistance of SCC/ECC composite systems

The purpose of this study is to investigate the effects of sulfate exposure on the mechanical behavior of fresh-to-fresh composite systems (CS), incorporating self-compacting concrete (SCC) in compression and engineered cementitious composites (ECC) in tension. ECCs were designed based on various supplementary cementitious materials (SCM) such as low and high calcium fly ash, slag and reinforcing fibers such as PVA and steel fibers. Repeated cycles of immersion in concentrated sodium sulfate solution were followed by drying at high temperatures (80 °C). After 90 and 180 days of cyclic exposure, the mechanical properties including flexural, compressive and tensile bond strength and mass change were evaluated. To investigate microstructural deterioration and reaction product concentration, SEM-EDS and backscattered electron imaging were used to examine sulfate profiles at the interfacial zone between SCC and ECC. Composite samples demonstrated excellent physico-mechanical resilience. The incorporation of low calcium fly ash and slag was observed to have a beneficial impact on residual mechanical properties in long-term exposures, along with the de-passivation capacity of the reinforcing fibers. No physical de-bonding was observed in any CS, however phase assemblages revealed high concentrations of reaction products in the SCC layers near the interfacial bond with the ECC layers.

Durability and heavy metals leaching behavior of cemented paste backfill using chemical activated binary slag as binder under sulfate attack

The present study conducted an extensive investigation into the durability of Na2SO4-activated binary slag cementitious materials for use in cemented paste backfill (CPB) under sulfate attack conditions. The primary objectives were to assess the feasibility of employing a cost-effective and environmentally friendly binder in CPB applications. Samples were subjected to exposure to Na2SO4 and MgSO4 solutions for a duration of 30 weeks, and multiple aspects including dimension stability, micro and macro mechanical strength evolution, changes in phase assemblage, microstructure following sulfate attack, and heavy metals leaching were examined. The study revealed that Na2SO4-activated binary slag (OPC-slag/S) exhibited superior resistance to sulfate attack, demonstrating enhanced dimension stability. Notably, sample OPC-slag/S displayed an increase in compressive strength, even after prolonged exposure to sulfate solutions for 30 weeks. This increase amounted to approximately 10.76% and 4.81% following exposure to Na2SO4 and MgSO4 solutions, respectively. The heightened resistance of binder OPC-slag/S to sulfate attack can be attributed to its low portlandite content and the early consumption of aluminates, primarily due to the formation of ettringite. This phenomenon effectively prevents the formation of detrimental and expansive products within the cement matrix during sulfate attack. On the other hand, CPB samples with binder OPC-slag/S showed the best performance in heavy metals immobilizaton capacity due to the high resistance to sulfate attack. In conclusion, this study underscores the potential of utilizing OPC-slag/S as a cost-effective and environmentally friendly binder for CPB applications in sulfate-rich environments.

Investigation on chloride migration behavior of metakaolin-quartz-limestone blended cementitious materials with electrochemical impedance spectroscopy method

Calcined clay and limestone powder composites offer a viable solution for reducing carbon emissions in building materials by allowing significant cement replacement. However, there is a need for further investigation into their impact on durability, especially for low-grade clays. In this study, different ratios of metakaolin and quartz powder are utilized to simulate various grades of calcined clay, while limestone powder is incorporated as a partial cement substitute. Initially, the influence of metakaolin content on rapid chloride migration was analyzed. Subsequently, various analytical techniques such as free water content, Mercury Intrusion Porosimetry (MIP), X-ray diffraction (XRD)/Rietveld method, and electrochemical impedance spectroscopy (EIS) test were employed to investigate the effects of metakaolin contents on the pore structure, phase assemblage, and electrochemical parameters of the blended cementitious system. The relationship between chloride migration coefficient and free water content, critical pore size, and impedance parameters was established to determine the key indicators for chloride migration. The study revealed that systems with partial metakaolin content demonstrate improved chloride resistance in the blended system, which could be predicted using Rct1 from the EIS test. Furthermore, the inclusion of metakaolin and limestone powder facilitated the formation of Monocarboaluminate (Mc) and Hemicarboaluminate (Hc), leading to the refinement of the pore structure and inhibition of chloride transport within the blended material. This study indicates the potential of low-grade calcined clay to enhance the overall durability of the blended cementitious system while contributing to carbon emissions reduction.

Sulfate resistance of carbonated basic oxygen furnace slag-metakaolin-Portland cement blends

Basic oxygen furnace slag (SS) is prone to carbonation due to its alkaline properties. The combined use of carbonated basic oxygen furnace slag (CSS) with metakaolin (MK) as a composite supplementary cementitious material (CSS-MK) can improve the reactivity of CSS and significantly lower the overall embodied CO2 emission. However, the impact of CSS-MK on the resistance of external sulfate attack (ESA) of cement remains unclear. This study aims to clarify the influence of CSS-MK on the resistance of cement to ESA. Compressive strength, water absorption, and electrical flux before ESA, and macro-scale expansion, microstructure, and evolution of phase assemblage during ESA were investigated. Results indicate that CSS-MK exhibits higher strength reactivity compared to SS-MK, enabling a 30% cement replacement level without compromising compressive strength after 7 days. CSS-MK reduces water absorption by 37.9% and electrical flux by 67.6%, enhancing transport property and reducing sulfate ion intrusion into the cement paste. The carbonation treatment transforms calcium silicate in SS into CaCO3, decreasing soluble calcium content, and creating a CaCO3-based passivation layer that inhibits sulfate ion corrosion. Meanwhile, the reaction in CSS-MK blends between the CaCO3 in CSS and MK consumes Ca(OH)2, forms ettringite and thermodynamically more stable carboaluminate, and results in the absence of monosulfate prior to ESA and the presence of carboaluminate during ESA, which consequently decreases ettringite content by 40% in paste after 240 days of ESA. Furthermore, at the macroscopic level, the expansion decreased by 85.2% after 360 days of ESA, effectively mitigating specimen cracking and damage.

Ebnerite and epiebnerite: NH4ZnPO4 dimorphs with zeolite-type frameworks from the Rowley mine, Arizona, USA

Abstract Ebnerite and epiebnerite, both with the ideal formula NH4ZnPO4, are new mineral species from the Rowley mine, Maricopa County, Arizona, USA. They occur in an unusual bat-guano-related, post-mining assemblage of phases. Epiebnerite grows epitactically on ebnerite and replaces it. Ebnerite and epiebnerite are found in intimate association with alunite, halite, mimetite, newberyite, sampleite, struvite and wulfenite on hematite-rich quartz–baryte matrix. Crystals of ebnerite are colourless narrow prisms up to ~0.3 mm in length. The streak is white, lustre is vitreous, Mohs hardness is ~2, tenacity is brittle and fracture is splintery. The density is 2.78(2) g⋅cm–3. Ebnerite is optically uniaxial (–) with ω = 1.585(2) and ɛ = 1.575(2). Epiebnerite occurs as colourless prisms or blades, up to about 10 × 3 × 2 μm, in parallel growth forming ribs with serrated edges epitactic on ebnerite prisms. The streak is white, lustre is vitreous, Mohs hardness is probably ~2, tenacity is brittle. The calculated density is 2.851 g⋅cm–3. Epiebnerite is optically biaxial with all indices of refraction near 1.580. Electron microprobe analysis gave the empirical formula [(NH4)0.89K0.06]Σ0.95(Zn0.96Cu0.07)Σ1.03[(P0.97Si0.03)Σ1.00O4] for ebnerite and [(NH4)0.67K0.28]Σ0.95(Zn0.99Cu0.02)Σ1.02(P1.00O4) for epiebnerite. Ebnerite is hexagonal, P63, with a = 10.67051(16), c = 8.7140(2) Å, V = 859.25(3) Å3 and Z = 8. Epiebnerite is monoclinic, P21, with a = 8.796(16), b = 5.457(16), c = 8.960(16) Å, β = 90.34(6)°, V = 430.1(17) Å3 and Z = 4. The structures of ebnerite (R1 = 0.0372 for 1168 Io > 2σI reflections) and epiebnerite (known from synthetic monoclinic NH4ZnPO4) are zeolite-like frameworks based upon corner-sharing linkages between alternating ZnO4 and PO4 tetrahedra with channels in the frameworks hosting the NH4 groups. The two structures are topologically distinct. Ebnerite belongs to the family of ‘stuffed derivatives’ of tridymite, whereas epiebnerite possesses an ABW-type zeolite structure.

Compressive strength development and microstructure evolution of mortars prepared using reactivated cementitious materials under carbonation curing

The effect of carbonation curing on depth-wise carbonation gradient and compressive strength development of RCM was evaluated. The RCM mortars were carbonated for seven curing periods, complemented by a thorough investigation of carbonation degree, phase assemblage, and microstructural at varying depths. Results showed a significant increase in compressive strength, from 3.3 MPa on the first day to 51.7 MPa after seven days and 63.5 MPa after 28 days of carbonation curing. A notable gradient in CaCO3 concentration was observed, decreasing from 41.4% at the surface to 16.8% at 25 mm depths. Additionally, the formation of CaCO3 polymorphs and Ca-modified silica gel in the surface layers was found to enhance microstructural density and impede CO2 penetration, while a higher prevalence of micropores was noted in the inner regions. These findings highlight the potential of optimizing the carbonation regime or employing internal carbonation methods to achieve a more homogeneous microstructure.

A Machine Learning-Based Thermobarometer for Magmatic Liquids

Abstract Experimentally calibrated models to recover pressures and temperatures of magmas are widely used in igneous petrology. However, large errors, especially in barometry, limit the capacity of these models to resolve the architecture of crustal igneous systems. Here, we apply machine learning to a large experimental database to calibrate new regression models that recover P–T of magmas based on melt composition plus associated phase assemblage. The method is applicable to compositions from basalt to rhyolite, pressures from 0.2 to 15 kbar, and temperatures of 675°C to 1400°C. Testing and optimisation of the model with a filter that removes estimates with standard deviation above the 50th percentile show that pressures can be recovered with root-mean-square-error (RMSE) of 1.1 to 1.3 kbar and errors on temperature estimates of 21°C. Our findings demonstrate that, given constraints on the coexisting mineral assemblage, melt chemistry is a reliable recorder of magmatic variables. This is a consequence of the relatively low thermodynamic variance of natural magma compositions despite their relatively large number of constituent oxide components. We apply our model to two contrasting cases with well-constrained geophysical information: Mount St. Helens volcano (USA), and Askja caldera in Iceland. Dacite whole-rocks from Mount St Helens erupted 1980 to 1986, inferred to represent liquids extracted from cpx–hbl–opx–plag–mt–ilm mush, yield melt extraction source pressures of 5.1 to 6.7 kbar in excellent agreement with geophysical constraints. Melt inclusions and matrix glasses record lower pressures (0.7–3.8 kbar), consistent with magma crystallisation within the upper reaches of the imaged geophysical anomaly and during ascent. Magma reservoir depth estimates for historical eruptions from Askja match the location of seismic wave speed anomalies. Vp/Vs anomalies at 5 to 10 km depth correspond to hot (~990°C) rhyolite source regions, while basaltic magmas (~1120°C) were stored at 7 to 17 km depth under the caldera. These examples illustrate how our model can link petrology and geophysics to better constrain the architecture of volcanic feeding systems. Our model (MagMaTaB) is accessible through a user-friendly web application (https://igdrasil.shinyapps.io/MagmaTaBv4/).

Quantitative characterization of recycled cementitious materials before and after carbonation curing: Carbonation kinetics, phase assemblage, and microstructure

Carbonation curing for cement-based materials is one of the effective means to achieve carbon neutrality in the construction industry. The pure cement clinker was hydrated for 90 d to simulate recycled cementitious materials (RCMs) to further investigate the carbonation reaction kinetics, phase assemblage and microstructure. The results revealed that the carbonation rates of cement clinker’s main components, i.e. C3S, C2S, C3A, and C4AF were 100%, 63.24%, 28.92%, and 14.93%, respectively. As the carbonation reaction proceeded, the calcium hydroxide (CH) would be fully consumed, while C-S-H began to become the main reactant, generating low-Ca C-S-H and even fully polymerized Ca-modified silica gel. At the same time, the unhydrated C3S and C2S were carbonized, forming carbonation products, i.e. CaCO3 and xCaO·SiO2·nH2O. Interestingly, the amount of poorly-crystalline CaCO3 was initially decreased and then increased, possibly attributed to the partial transformation into well-crystalline CaCO3 at an early stage, whereas the remaining amount was produced through the reaction of C-S-H at a later stage. Finally, the carbonation reaction was further explained through two models, the early stage was described by a chemical reaction model while the later stage was represented by a product-layer diffusion model.

Effects of C-S-H seeding dosages on the calorimetry and phase assemblage of cement hydration

Effects of C-S-H seeding dosages on the calorimetry and phase assemblage of cement hydration