Paste Composition Research Articles

Estimation of cement paste stiffness and UHPC elastic modulus through measured phase-property upscaling

The elastic stiffness of bulk concrete materials results from the complex interaction of aggregates, voids, and hydrated cement (which can have multiple hardened phases at multiple length scales). Given the complexities associated with understanding the arrangement of these particles within bulk concrete volumes, estimations for elastic modulus often rely on empirical correlations with unit weight and compressive strength. Such estimations are inherently scale-dependent and fail to capture variability in mix designs, particularly the variability found in specialty concrete mixes. To develop a scale-independent method for estimating elastic modulus from mix-design volume fraction information, this study explores a novel bottom-up approach using cement paste phase stiffness values determined through micro-mechanical experimentation and randomized Monte-Carlo spring arrangement simulations. Statistical representations of cement paste phase stiffness distributions and bulk volume fraction data are combined to provide estimations for elastic stiffness in both the composite cement paste and bulk concrete containing fine aggregate and fibers. Resulting a priori estimations of UHPC cement paste stiffness from the micro-mechanical upscaling simulations were within 4% of measured values (based on mix-design and void volume fraction information alone) for a selected sample of mix proportions. When applied to the two UHPC mixes containing fibers and fine aggregate, upscaling simulations consistently overpredicted the measured elastic modulus, likely due to the aggregate-cement interfacial transition zone (ITZ) properties that were not captured in the micro-mechanical testing.

Impact of Ground Granulated Blast Furnace Slag on Calcium Leaching of Low-Heat Portland Cement Paste.

Low-heat Portland cement and ground granulated blast furnace slag are widely used for the preparation of hydraulic concrete. Nevertheless, the effect and mechanism of corrosion on low-heat Portland cement paste mixed with ground granulated blast furnace slag need to be further explored. This paper investigated the impact of ground granulated blast furnace slag on the calcium leaching of low-heat Portland cement paste by evaluating its mass loss, porosity, leaching depth, compressive strength, and Vickers hardness, and comparing it with the leaching performance of ordinary Portland cement paste. Furthermore, the phase composition and morphology of low-heat Portland cement paste containing ground granulated blast furnace slag were analyzed by X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The results indicate that, after 180 days of soaking in ammonium chloride solution, the mass loss rate, growth rate of porosity, leaching depth, and compressive strength loss rate of low-heat Portland cement paste were 8.0%, 43.6%, 9.1 mm, and 27.7%, respectively, while those of ordinary Portland cement paste were 7.4%, 37.8%, 8.4 mm, and 30.1%, indicating that low-heat Portland cement paste is slightly more damaging than ordinary Portland cement. The addition of ground granulated blast furnace slag could significantly improve the leaching resistance of low-heat Portland cement. For instance, after adding 20% ground granulated blast furnace slag, the above test values were 2.4%, 28.5%, 5.6 mm, and 20.8%, respectively. The reason for this is that ground granulated blast furnace slag has the potential to reduce the porosity of low-heat Portland cement paste, and it can also undergo the secondary hydration reaction with its hydration product Ca(OH)2 to enhance the paste structure. Considering the cost performance, the suitable dosage of low-heat Portland cement paste for satisfactory leaching resistance is about 20%.

Development of a highly loaded zirconium carbide paste for material extrusion additive manufacturing

A highly loaded, aqueous-based zirconium carbide (ZrC) paste was developed for ceramic on-demand extrusion (CODE). Commercial ZrC powder was ball milled to reduce the particle size to ∼1 μm. Paste composition was determined by rheological characterization and observation of printing behavior; the final paste consisted of 46–47 vol% ZrC, 43.5 vol% distilled water, 8.1 vol% dispersant, and 1.6 vol% binder. Rheological characterization of the paste showed a yield stress of ∼8 Pa and shear thinning behavior (ΔG′/Δσ* = −55). The paste was printed using a 610 μm nozzle; a test print showed shape fidelity using the developed paste. A pressureless sintering study was performed; a sintering temperature of 2000°C with a 2-hour hold produced samples of 90 % relative density with 3.8 μm grains, which was consistent with literature. The developed paste, in combination with the pressureless densification results, adds a new, ultra-high temperature material to ceramic extrusion additive manufacturing.

Optimization of Awaze paste formulations: The effects of using spices through a mixture design approach

Previous studies have revealed the microbial quality of Awaze paste. However, limited reports describe the effect of individual spices on Awaze paste quality. A mixture design approach was used to determine the appropriate proportions, with 15 experimental points for independent variables including RP (60–90 %), GA (10–30 %), RO (5–20 %), and GI (5–10 %). The techno-functional properties, particle size, antioxidant activity (DDPH radical assay), proximate composition, iron (Fe), zinc (Zn) content, viscosity, hardness, and microbiological quality of Awaze paste were assessed. The prepared Awaze paste showed a range of characteristics, with antioxidant activity (DDPH radical assay) ranging from 11.86 % to 62.5 %, crude protein content from 6.18 % to 16.22 %, crude fat from 5.7 % to 12.6 %, crude fiber from 16.86 % to 29.06 %, total ash content from 6.32 % to 9.94 %, total carbohydrate from 41.79 % to 60.61 %, energy from 264.3 to 329.2 k cal. , iron (Fe) content from 35.59 to 108.82 mg/100g, zinc (Zn) content from 1.72 to 26.93 mg/100g, viscosity from 65.5 to 125.5 cps, hardness from 8.48 to 55.09 g, yeast and mold count from 0.83 to 2.04 log cfu/g, and total bacterial count from 1.53 to 2.61 log cfu/g. Significant differences (p < 0.05) were observed in proximate composition, techno-functional properties, particle size, antioxidant activity, physicochemical properties, and microbiological characteristics among the formulations of Awaze paste. The selected formula showed a statistically significant difference (p < 0.05) compared to the control sample. The formulation containing 74.79 % RP, 10 % GA, 10.2 % RO, and 5.0 % GI was determined to be the optimal formula with a desirability of 0.73, based on the evaluated parameters. This preferred Awaze paste had a porosity of 28.12 %, particle size of 16.49 μm, antioxidant activity of 63.63 %, crude protein content of 17.28 %, iron (Fe) content of 98.06 mg/100g, and zinc (Zn) content of 15.04 mg/100g. Therefore, this optimal blend of ingredients could be used to produce a consumer accepted Awaze paste.

Large variability and 2H-depletion of Middle Miocene to Pleistocene alkenone hydrogen isotopes in the Equatorial Pacific reflect subsurface, low light haptophyte growth

Hydrogen isotope ratios of haptophyte derived long-chain alkenones (δ2HC37:2) have shown to be a useful tool for reconstructing past isotopic compositions of surface seawater (δ2HSSW). The δ2HSSW is related to global ice volume, sea surface salinity and the local hydrological cycle. Here, we present a hydrogen isotope record of alkenones spanning the last 14.5 Ma from IODP site U1338 in the east equatorial Pacific. The alkenone-based reconstructed δ2HSSW is substantially more negative and variable than reconstructed δ2HSSW based on published oxygen isotopes of coccolith carbonates. This suggests that factors other than the isotopic composition of seawater affect the hydrogen isotopic composition of alkenones. The relatively negative and highly variable δ2HC37:2 values are in line with published modern observations on alkenones from suspended particulate matter in the equatorial and north Pacific, with the highest values at relatively high light conditions at the surface and the lowest values at higher water depth and relatively low light conditions. This suggests that the relatively negative and highly variable δ2HC37:2 values in these Middle Miocene to Pleistocene sediments are likely derived from haptophytes growing below the sea surface under variable low light conditions. In regions where the contribution of alkenones from subsurface production, due to high subsurface nutrients, at low light intensities to the sediment is relatively high the δ2HC37:2 has to be interpreted with care as a proxy for δ2HSSW.

Enhanced carbon-based back contact electrodes for perovskite solar cells: Effect of carbon paste composition on performance and stability

To address the issue of cost and instability in perovskite solar cells (PSCs), it is promising to substitute the regular hole collecting electrode i.e., spiro-OMeTAD/Au with inorganic hole transport layer (HTL)/carbon electrode. In this study, three carbon pastes were investigated with different binders: polymethyl methacrylate (PMMA), styrene-butadiene-styrene (SBS) and ethyl cellulose (EC). Carbon layers were compared in terms of mechanical stability, conductivity and performance as back contact electrodes in PSCs with an inorganic HTM composed of CuInS2 nanoparticles. To assess mechanical properties of the carbon pastes, adhesion tests by using tape, ultrasonication in the media of deionized water and acidic deionized water, and also flexibility test were performed. The carbon layer based on SBS carbon paste (SBS-CP) was intact after adhesion tests and over 1017 cycles of flexibility test. The one based on PMMA carbon paste (PMMA-CP) didn't tolerate all mechanical tests and disintegrated. The carbon layer based on EC carbon paste (EC-CP) partly damaged after adhesion tests and didn't pass the flexibility test. The best efficiency of 18.6 % was obtained for a device based on SBS-CP and significant shelf-life stability over 172 days stored in relative humidity of 40 % and dark.

Insight into the performance of composite binder with high-volume steel slag, blast furnace slag and desulfurization gypsum

The performance of composite binders with high-volume steel slag (SS), granulated blast furnace slag (GBFS) and desulfurization gypsum (DG) were systematically investigated. The results show that the synergistic effects of high volume (40–60%) of SS with GBFS and less than 15% of DG could perform adequate setting time, higher strength, well volume stability and soundness as well as dense microstructure. The higher compressive strengths exceeding 70 MPa at 28 days and up to 80 MPa at 90 days could be obtained for composite pastes with high-volume SS, which exhibit tight relationships with [CaO]·[SO3]/[Al2O3]·[SiO2] and [CaO]·[Al2O3]/[SO3]2 molar ratios. More (15–19%) AFt and less (about 1%) portlandite produced during the hydration of composite binders. C–S–H gels and calcite crystals were formed. The composite binder possesses lower energy consumption, high carbon reduction and low cost compared with Portland cement in favor of the low-carbon cementitious material production and effective utilization of SS.

Early hydration of hot-stuffy steel slag-cement composite pastes: isothermal calorimetry and phase evolution

Hot stuffy self-disintegration has become an advanced and popular steel slag treatment method in recent years, presenting numerous advantages. Hot-stuffy steel slag (HSS) obtained by self-disintegration treatment technology with waste heat has different compositions and properties compared with ordinary steel slag (OSS). Although the properties of OSS as a mineral admixture have been reported by numerous articles, few researches focus on HSS, especially its effect on early cement hydration. In this paper, the early hydration of HSS-cement composite pastes is investigated from the insights of isothermal calorimetry and phase evolution. Effects of HSS on the setting time, hydration heat, reaction product, reaction degree, microstructure, and pore solution were systematically studied and compared with those of OSS. Results show that, unlike OSS, HSS hardly ever retards the early hydration of cement. This is caused by the differences in the composition of HSS and OSS due to the diversity in their production treatment processes. During the hot stuffy self-disintegration, the key retarding component in OSS, such as C12A7, reacts with water and their contents in HSS are reduced. It is found that hot stuffy self-disintegration is an effective method to mitigate the retardation effect of steel slag on the early hydration of cement. This study provides a better understanding of HSS, which is crucial for its utilization in cementitious materials.

Mechanical Properties and Durability of Composite Cement Pastes Containing Phase-Change Materials and Nanosilica.

Escalating global surface temperatures are highlighting the urgent need for energy-saving solutions. Phase-change materials (PCMs) have emerged as a promising avenue for enhancing thermal comfort in the construction sector. This study assessed the impact of incorporating PCMs ranging from 1% to 10% by mass into composite Portland cement partially replaced by fly ash (FA) and nanosilica particles (NS). Mechanical and electrochemical techniques were utilized to evaluate composite cements. The results indicate that the presence of PCMs delayed cement hydration, acting as a filler without chemically interacting within the composite. The combination of FA and PCMs reduced compressive strength at early ages, while thermal conductivity decreased after 90 days due to the melting point and the latent heat of PCMs. Samples with FA and NS showed a significant reduction in the CO2 penetration, attributed to their pozzolanic and microfiller effects, as well as reduced water absorption due to the non-absorptive nature of PCMs. Nitrogen physisorption confirmed structural changes in the cement matrix. Additionally, electrical resistivity and thermal behavior assessments revealed that PCM-containing samples could reduce temperatures by an average of 4 °C. This suggested that PCMs could be a viable alternative for materials with thermal insulation capacity, thereby contributing to energy efficiency in the construction sector.

Evaluation of Antimicrobial Efficiency, Shear Bond Strength, and Adhesive Remnant Index of TiO2 Infiltrated Orthodontic Adhesive - An In Vitro Study.

Enamel demineralization is an unavoidable adverse effect encountered with bonding brackets in orthodontic therapy. Introducing nanoparticles into the composite adhesive paste can prevent enamel demineralization. Titanium dioxide (TiO2) is known to exhibit direct antimicrobial efficiency. This study aimed to assess the antibacterial efficiency and shear bond strength (SBS) of an orthodontic bonding composite infiltrated with TiO2 nanoparticles. This in vitro study evaluated the efficiency of TiO2 nanoparticle-incorporated light-curing orthodontic composite paste (ENLIGHT, ORMCO). Twenty extracted premolars were randomly and equally allocated to the two study groups, N = 10. While a conventional composite was utilized for the bonding brackets in Group I, a TiO2-incorporated composite was used in Group 2. The adhesive remnant index (ARI) scores given by Artun and Bergland et al. and SBS were determined. Furthermore, the antimicrobial efficiency was estimated using the minimum inhibitory concentration (MIC)/minimum bactericidal concentration (MBC) and agar well diffusion assay for six composite disc specimens. The results were statistically analyzed using the chi-square test and Student's t test, at P < 0.05. After 24 h of curing, no statistical mean difference was observed between the two groups in terms of ARI or SBS scores (P > 0.05). However, there was a significant increase in the antimicrobial efficiency of Group II when compared with Group I (P < 0.05). TiO2 nanoparticle-incorporated orthodontic composites improve the antimicrobial efficiency with no significant change in the SBS. The ARI scores indicate the presence of 50% remnant orthodontic composite on the tooth enamel surface post debonding.

Ultrasensitive tadalafil detection with eco-friendly CeO2/Al-pillared clay incorporated pencil graphite paste electrode

In this study, we have constructed a novel voltammetric sensor based on montmorillonite clay (MMT) incorporated with CeO2 nanoparticles using a composite graphite paste electrode as a cross linker (MMT-CeO2NPs/GPG-PE) for the trace determination of tadalafil (TAD) drug. The characterization of CeO2 nanoparticles has been conducted using various analytical techniques, including X-ray diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. The morphology of the composite of CPG and MMT-CeO2NPs/CPG was elucidated through scanning electron microscopy (SEM). The newly developed sensor (MMT-CeO2NPs/CPG-PE) exhibited remarkable efficiency towards TAD oxidation using adsorptive stripping square-wave voltammetry (AdS-SWV) in Mcllvaine buffer solution (pH 8.0). A highly selective and sensitive method for TAD detection has been successfully applied based on MMT-CeO2NPs/CPG-PE, showing two different linear concentration ranges of 0.005−0.1 and 0.1–9.9 µM. The LOD and LOQ were determined to be 1.97 × 10−10 and 6.57 × 10−10 M, respectively, with a sensitivity of 3916 µA µM−1 cm−2. Interestingly, the sensing electrode exhibited excellent reproducibility, reusability, and stability even after 30 days. Moreover, the newly developed nano-sensor (MMT-CeO2NPs/CPG-PE) has been effectively utilized for the accurate detection of TAD in pharmaceutical formulations and spiked human blood serum and urine samples, demonstrating no interference from other substances.

Assessing the performance of short 18S rDNA markers for environmental DNA metabarcoding of marine protists

AbstractMarine protists are globally distributed and sensitive to environmental conditions, which makes them a focal group when studying the effects of climate change on biodiversity and ocean health. However, they are a highly diverse group with varying evolutionary histories and morphologies and widely variable preservation potential in the fossil record. Thus, their past diversity and composition are poorly known. Paleogenetics, which relies, among other approaches, on DNA metabarcoding of sedimentary ancient DNA (sedaDNA), provides a promising avenue to explore the past history and responses of marine protists to global change. Choosing the right marker for sedaDNA studies is critical, striking a balance between marker length and taxonomic resolution. While marker guides exist for modern environmental DNA surveys, a thorough assessment of existing short markers for sedaDNA studies targeting protists is lacking. In this study, we report on a comparison of in silico PCR for eight short 18S rDNA markers, including one from the Tara Oceans initiative and a longer marker commonly used in modern marine eDNA studies. We analyze their taxonomic coverage and resolution, taxonomic overlap and uniqueness between markers, co‐amplification of non‐protist taxa, and amplicon size differences across taxonomic groups. Additionally, we provide a detailed analysis of diatoms, dinoflagellates, haptophytes, and chlorophytes. Our study is aimed at supporting project‐specific marker choices for characterizing protist composition and diversity. While we focus on marine protists, our results are applicable to other aquatic and terrestrial environments.

Revisiting the Correlation Between the Valdivia and San Pedro Ceramic Complexes (Based on Technological Characteristics)

This article presents the results of a study of ceramics associated with the Valdivia and San Pedro complexes at the Real Alto site, southwestern Ecuador. The test sample, studied in 2022, includes fragments of vessels from two morphological and functional groups, relating to the first two phases of the Valdivia culture (bowls and pots) and those representing the San Pedro complex (vessels with necks and a bowl). A comparative analysis was based on identified technological indicators marking various stages of pottery manufacture. Certain differences are seen in the composition of paste and in the hand-shaping of the vessels. Significant differences were revealed in surface treatment and decoration. This is evidenced by the use of colored and plain coating, high-quality solid or matte striped polishing, and complexity of decoration. Distinctive features of firing include the use of different kilns and various atmospheric modes. Parallels include broadly similar firing temperatures. The technological difference between the two morphological and functional groups of the Valdivia complex is that bowls were manufactured with more complex and labor-consuming techniques, whereas pots are technologically somewhat similar to those from San Pedro. Radiocarbon dates (4640–4450 BP) suggest that the two traditions coexisted. Differences may reflect their cultural distinctness.

Isocyanate microcapsules recovering automatically impermeability of cement paste through self-hydrophobic broken panels

Cracks are inevitable in the use of cement-based materials. It takes a lot of resources to repair these cracks and prolong the service life of cement-based materials. Self-healing cement-based materials that can automatically repair cracks and improve the self-healing ability of cement-based materials have become the focus of current research. The current self-healing systems achieve impermeability recovery of matrix by the filling cracks. Few scholars have paid attention to the impermeability recovery through self-hydrophobic broken panels. In this paper, SEM, FTIR, core content titration, water flux test and contact angle test were carried out. The morphology, composition, core content and impermeability recovery effect of self-healing cement paste were prepared and characterized. Carbon nanotubes are used to improve the water resistance of isocyanate microcapsules, which possess a diameter of 237.6 ± 59.1 μm, distinct core-shell structure, and good dispersibility. The residual core fraction is 58.2 % after 21 days in Ca(OH)2 aqueous solutions. The microcapsules maintain integrity without breakage when mixed with fresh cement paste and have good bonding compatibility with cement matrix. When microcapsules are embedded into cement paste, the cracks could break the microcapsules releasing isocyanate to wet the broken panels. The isocyanates react with the moisture with the formation of polyurea, changing the contact angle of broken panels from near 0° to 118.4 ± 0.1°. The hydrophobic panels could retard the water penetration and recover the impermeability of cement paste. Based on this, a new self-healing mechanism of self-hydrophobic fracture surface to realize self-healing of impermeability of cement matrix is proposed.

Лабораторные испытания притирочной пасты НАА ЛМ

The article is devoted to the development of the composition of lapping paste. Various compositions of pastes are considered. Laboratory tests of lapping pastes have been carried out. The following criteria were analyzed: the physical properties of the formulations, the quality of lapping, and the time to perform the operation. The best of the developed formulations has been selected. Keywords: ABRASIVE, OPERATION TIME, CYLINDER HEAD, LAPPING QUALITY, LABORATORY TESTS, LAPPING PASTE, VALVE LAPPING, REPAIR, COMPOSITION, COUPLING

Hydration kinetics and apparent activation energy of cement pastes containing high silica fume content at lower curing temperature

To promote the application of silica fume (SF) in civil engineering in cold regions, relative influences from SF content and low temperature environment on the early hydration kinetics of composite cement pastes were evaluated based on the isothermal calorimetric method. The effect of high SF content on the apparent activation energy (Ea) of Portland cement and the filler effect (via the index of area multiplier) of SF on the hydration parameters was also analyzed. The results showed that the intensity of the shoulder peak (Al peak) of the hydration kinetic curve (heat flow curve) gradually grew as the SF content increased, and the double-peak phenomenon was gradually clear. The heat flow peak is delayed and lowered with the decreasing curing temperature, while the final time of the induction stage and the duration of the acceleration stage are delayed. Moreover, the duration of the acceleration stage was slightly extended with the increase of SF content. The full-width at half-maximum (FWHM) value of the heat flow curves dropped as the SF content and curing temperature increased. The low temperature environment and the inclusion of SF inhibited the growth in early hydration degree. The higher SF content mitigated the impact of low temperature on the hydration time parameter τ. The apparent Ea results also indicated that the SF reduced the temperature sensitivity of the hydration process of the composite cement pastes, which might contribute to the development of the hydration reaction at low temperatures. The AM (Area Multiplier) factor increased approximately linearly with increasing SF replacement levels. Apparent Ea decreased linearly with increasing AM, which may be attributed to a further reduction in the diffusion-controlled hydration rate of composite cement pastes with larger AM.

Enhanced Cadmium Sensing in Fertilizer Samples using Zeolite-modified Graphite Electrode

The presence of heavy metals in fertilizers poses significant environmental and health risks, necessitating robust detection methods to ensure agricultural sustainability and food safety. This study focuses on synthesizing Na-P1 zeolite from coal fly ash and fumed silica wastes, employing it as a potent modifier in graphite electrodes to enhance the electrochemical detection of cadmium (II) in fertilizer samples. Through meticulous assessment using cyclic voltammetry (CV) in a potential window of −1.2 V to 0.5 V, square wave voltammetry (SWV) in a potential region of −1 V to 0.5 V, and electrochemical impedance spectroscopy (EIS) in a frequency ranging from 100 kHz to 10 mHz under open circuit potential polarization, the electrochemical performance of the zeolite-modified graphite electrode (ZGE) was evaluated. The optimization process involved fine-tuning various parameters such as paste composition, solution pH, scan rate, and analyte concentration. Real sample analysis confirmed the applicability of the method in fertilizer samples. Notably, in an HCl medium (pH = 1.0), the SWV oxidation peak of Cd(II) was observed at −0.56 V (vs SCE) with a deposition time of 20 s and a scan rate of 75 mV∙s−1. The ZGE exhibited a remarkable detection limit of 1 μM, a quantification limit of 5 μM, and a high sensitivity of 6.581 μA/μM.cm2 within a linear detection range of 10−3–10−6 M. These findings highlight the potential utility of Na-P1 zeolite in handheld analytic device manufacturing, offering promising applications in environmental monitoring, resource management, and water and soil resource remediation.

Aquatic moss δ18O as a proxy for seasonally resolved lake water δ18O, northwest Greenland

Reconstructing past climate seasonality is fundamental to understanding the nature of past climate changes. This is especially true in the Arctic, where climate is intensely seasonal and proxies that can distinguish climate conditions of multiple seasons in a single year are relatively rare. We propose that submerged aquatic mosses, which are abundant subfossils in some Arctic lake sediments and have distinctive seasonal growth morphologies, can be used to estimate past lake water oxygen isotope composition (δ18Olw) across multiple seasons. Aquatic mosses are abundant, well preserved, and grow continuously in Arctic lakes whenever light is available, with some species displaying unique seasonal morphologies influenced by water temperature. Although Greenland paleorecords suggest that aquatic moss oxygen isotope values (δ18Oom) reflect the δ18O values of lake water, no modern calibration between δ18Oom and δ18Olw exists in Greenland. We present a modern δ18Oom vs. δ18Olw calibration using multiple moss species or morphotypes from eight lakes and ponds near Pituffik (Thule), northwest Greenland. We find strong linear relationships (r2 = 0.76-0.85) between the δ18Oom and δ18Olw values of multiple species or morphotypes across the range of relatively low δ18Olw values at Pituffik, and our results indicate isotopic fractionations are similar to those found previously at lower latitudes. To assess the potential of mosses as archives of seasonal δ18Olw values, we analyzed δ18Oom in season-specific segments of moss strands, with seasons identified based upon growth morphology. Moss inferred lake water δ18O values (δ18Olwom) are higher in autumn than spring or summer, likely due to increasing contributions of 18O enriched precipitation and the cumulative effects of lake water evaporation throughout the ice-free season. For moss subsampled throughout summer, δ18Olwom values generally increased through the season in parallel with observed δ18Olw values. Potential temperature dependent fractionation effects during biosynthesis, however, remain unconstrained and should be further addressed with future research. Overall, these findings suggest that aquatic mosses from lake sediments could be used to directly resolve climate seasonality of the past.

Carbonation model of alkali-activated slag-metakaolin composite pastes based on pore structure parameters

The carbonation behavior of alkali-activated materials (AAMs) over time is crucial for structural durability. In this study, accelerated carbonation tests were conducted on alkali-activated slag-metakaolin (AASM) composite pastes. The effects of various slag content at 0%, 20%, and 40%, and Na2O content at 15%, 17%, 19%, 21%, and 23% on the pore structure, carbonation depth, and material alkalinity of AASM composite pastes were studied. The research results indicated that with the increase in slag content and Na2O content, the pore structure of AASM composite pastes tended to become denser. The influence of slag content and Na2O content on the early carbonation depth was significant. In the 0% slag content group, the carbonation depth at 3d of accelerated carbonation decreased by 61.4% when the Na2O content increased from 15% to 23%. With the increase in slag content, the effect of Na2O content on carbonation depth tended to weaken. In the 40% slag content group, the carbonation depth at 3d of accelerated carbonation remained below 10 mm. As accelerated carbonation progressed, the measured pH value rapidly decreased before 7d of accelerated carbonation and gradually stabilized thereafter. Based on pore structure parameters, predictive models for carbonation depth and material alkalinity of AASM composite pastes were constructed. The results of the accelerated carbonation test were used to validate the model calculations. The results show that the model based on pore structure parameters can effectively predict the carbonation depth and material alkalinity of AASM composite pastes.

Study on triaxial compression performance and damage characteristics of fiber-reinforced ecological matrix cementing gangue gypsum fill material.

Polypropylene fiber was equally mixed into alkali-activated slag fly ash geopolymer in order to ensure the filling effect of mine goaf and improve the stability of cemented gangue paste filling material with ecological matrix. Triaxial compression tests were then conducted under various conditions. The mechanical properties and damage characteristics of composite paste filling materials are studied, and the damage evolution model of paste filling materials under triaxial compression is established, based on the deviatoric stress-strain curve generated by the progressive failure behavior of samples. Internal physical and chemical mechanisms of the evolution of structure and characteristics are elucidated and comprehended via the use of SEM-EDS and XRD micro-techniques. The results show that the fiber can effectively improve the ultimate strength and the corresponding effective stress strength index of the sample within the scope of the experimental study. The best strengthening effect is achieved when the amount of NaOH is 3% of the mass of the solid material, the amount of fiber is 5‰ of the mass of the solid material, and the length of the fiber is about 12 mm. The action mode of the fiber in the sample is mainly divided into single-grip anchoring and three-dimensional mesh traction. As the crack initiates and develops, connection occurs in the matrix, where the fiber has an obvious interference and retardation effect on the crack propagation, thereby transforming the brittle failure into a ductile failure and consequently improving the fracture properties of the ecological cementitious coal gangue matrix. The theoretical damage evolution model of a segmented filling body is constructed by taking the initial compaction stage end point as the critical point, and the curve of the damage evolution model of the specimen under different conditions is obtained. The theoretical model is verified by the results from the triaxial compression test. We concluded that the experimental curve is in good agreement with the theoretical curve. Therefore, the established theoretical model has a certain reference value for the analysis and evaluation of the mechanical properties of paste filling materials. The research results can improve the utilization rate of solid waste resources.