Slow Reactivity Research Articles

Sustainable enhancement of fly ash-based geopolymers: Impact of Alkali thermal activation and particle size on green production

Addressing the challenges posed by the slow reactivity of fly ash (FA) with alkali at ambient temperatures, this study delves into the enhancement of FA-based geopolymers through alkali thermal activation (ATA). The ATA process, conducted at 550°C for 1 h, significantly increases the availability of reactive silica and alumina, which are essential for geopolymerization. A critical focus of the research is the influence of FA particle size on ATA’s efficacy and the resultant mechanical properties of the geopolymers. Findings reveal that the ATA process facilitates the rapid dissolution of the vitreous phase in FA. This leads to a sequential release of silica and alumina, which is pivotal for the geopolymer’s matrix development. Notably, geopolymers synthesized from finely milled FA, post-ATA, demonstrate a marked increase in compressive strength, escalating from 30.51 MPa to an impressive 38.46 MPa. The study meticulously delineates geopolymerization into four distinct stages—initial dissolution, depolymerization, geopolycondensation and gelation, and final diffusion, with the initial dissolution and final diffusion stages being paramount in defining the reaction kinetics and the ultimate strength of the geopolymer. This enhanced understanding paves the way for optimizing FA utilization in geopolymers, promising a more sustainable and efficient pathway for producing construction materials with superior mechanical properties.

Ultrasmall VOx nanoparticle as low-cost photothermal nanoprobe for enzyme-based biodetection

Low-cost photothermal probes facilitate the practical application of photothermal detection. However, current photothermal nanoprobes are generally larger in size and thus have slower reactivity with analytes, which is not conducive to rapid testing. Therefore, ultra-small photothermal nanoprobes would be preferred but have not been reported. Here, the ultrasmall VOx nanoparticle is constructed as low-cost photothermal nanoprobe, which is more reactive to H2O2 and thus has reduced response time. In cooperation with enzymes, this nanoprobe can be used for photothermal detection of other biomolecules, such as glucose and uric acid. Compare with the standard colorimetric method, the photothermal method with ultrasmall VOx nanoparticle has high similarity and low analytical error of less than 5 %, which is sufficient for actual practice.

Oxidation of Microcystis aeruginosa and Microcystins with Peracetic Acid.

Peracetic acid (PAA) shows potential for use in drinking water treatment as an alternative to prechlorination, such as for mussel control and disinfection by-product precursor destruction, though its impact as a preoxidant during cyanobacterial blooms remains underexplored. Here, Microcystis aeruginosa inactivation and microcystin-LR and -RR release and degradation using PAA were explored. The toxin degradation rates were found to be higher in alkaline conditions than in neutral and acidic conditions. However, all rates were significantly smaller than comparable rates when using free chlorine. The inactivation of M. aeruginosa cells using PAA was faster at acidic pH, showing immediate cell damage and subsequent cell death after 15-60 min of exposure to 10 mg/L PAA. In neutral and alkaline conditions, cell death occurred after a longer lag phase (3-6 h). During cell inactivation, microcystin-LR was released slowly, with <35% of the initial intracellular toxins measured in solution after 12 h of exposure to 10 mg/L PAA. Overall, PAA appears impractically slow for M. aeruginosa cell inactivation or microcystin-LR and -RR destruction in drinking water treatment, but this slow reactivity may also allow it to continue to be applied as a preoxidant for other purposes during cyanobacterial blooms without the risk of toxin release.

Kinetics of Alkali-Silica Reaction: Application to Sandstone.

Despite extensive research, the relationship between the progression of the alkali-silica reaction (ASR) and the expansion of concrete due to ASR, particularly for the heterogeneous aggregate with slow reactivity, is not thoroughly understood. In this paper, the dissolution kinetics of reactive silica present in sandstone when exposed to NaOH solutions, alongside the expansion characteristics of rock prisms under ASR conditions, were studied. The experimental results indicate that ASR behaves as a first-order reaction, accompanied by an exponential decrease in the concentration of OH- over time, and the dissolution rate of silica is predominantly governed by diffusion dynamics. Notably, increasing the temperature accelerates ASR, which augments the expansive pressure in a confined and limited space, leading to more significant aggregate expansion. Conversely, higher temperatures also result in a diminished retention of ASR gels within the aggregate, leading to the mitigation of ASR expansion. Our findings underscore that larger aggregates retain a greater quantity of gels, resulting in more pronounced expansion. To establish an ASR prediction model based on the relationship of the ASR expansion of concrete to high and low temperatures, the parameters such as the range of curing temperatures and the grading size of aggregates should be carefully considered for the experiments.

Efectos olvidados: herramienta de análisis en la producción de PYMES Industriales de Cuenca

Small and medium-sized enterprises (SMEs) are the support for the promotion of development through the production and sale of their products. The aspect to be studied is the decrease in production, a consequence of the slow economic reactivation of these firms since the events related to the pandemic in the year 2020. The research seeks to recognize the measures and consequences in order to address and solve the identified problem. This will be achieved through the application of the Theory of Neglected Effects (TEO), which are not always captured by the scholars of the subject, to reduce hesitations and decide in a more accurate way. Methodologically, the research has a mixed descriptive approach, where the synthetic analytical method is implemented. Surveys were applied to subjects with production expertise, using the endecadary scale and fuzzy logic to develop a square matrix of forgotten effects, thus identifying the underlying variable. The results reveal changes in the form of behavior from synergy, which positively impacts increased productivity by decreasing costs. Finally, by applying the guidelines of the scholars and obtaining a matrix that relates qualitative variables, based on cause and effect links, a criterion is obtained that facilitates decisions and the possibility for companies to arrange production increases for the fortune of the company.

Impact of Low-Reactivity Calcined Clay on the Performance of Fly Ash-Based Geopolymer Mortar

Availability of aluminosiliceous materials is essential for the production and promotion of geopolymer concrete. Unlike fly ash, which can only be found in industrial regions, clays are available almost everywhere but have not received sufficient attention to their potential use as a precursor for geopolymer synthesis. This study investigates the effectiveness of calcined clay as a sole and binary precursor (with fly ash) for the preparation of geopolymer mortar. Fly ash-based geopolymer containing between 0 and 100% low-grade calcined clay was prepared to investigate the effect of calcined clay replacement on the geopolymerization process and resultant mortar, using a constant liquid/solid ratio. Reagent-grade sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) were mixed and used for the alkali solution preparation. Six different mortar mixes were formulated using sand and the geopolymer binder, comprising varying fly ash-to-calcined clay ratios. The combined effect of the two source materials on compressive strength, setting time, autogenous shrinkage, and porosity was studied. The source materials were characterized using XRD, SEM, FTIR, and XRF techniques. Isothermal calorimetry was used to characterize the effect of low-grade calcined clay on the geopolymerization process. The addition of calcined clay reduced the surface interaction between the dissolved particles in the alkali solution, leading to slow initial reactivity. Geopolymer mortar containing 20% calcined clay outperformed the reference geopolymer mortar by 5.6%, 17%, and 18.5% at 7, 28, and 91 days, respectively. The MIP analysis revealed that refinement of the pore structure of geopolymer specimens containing calcined clay resulted in the release of tensional forces within the pore fluid. Optimum replacement was found to be 20%. From this study, the mutual reliance on the physical and inherent properties of the two precursors to produce geopolymer mortar with desirable properties has been shown. The findings strongly suggest that clay containing low content of kaolinite can be calcined and added to fly ash, together with appropriate alkali activators, to produce a suitable geopolymer binder for construction applications.

Future ready limes for the AAC industry

AbstractLime is an essential raw material for the production of Autoclaved Aerated Concrete (AAC). Its functionality is triple in this application: The mineral phase giving rise to the mechanical strength of AAC (tobermorite) is formed by the reaction of quicklime (calcium oxide, CaO) with silica (silicon dioxide, SiO2) under hydrothermal curing. Lime is also providing the alkaline conditions required for the formation of the hydrogen bubbles structuring the mineral foam. Finally, the exothermic hydration (“slaking”) reaction with water is providing the required energy input in the system. Lime is produced by the calcination of limestone (CaCO3) releasing carbon dioxide (CO2). Today's limes appreciated for the production of AAC are showing slow reactivity, with t60 values typically higher than 8 and up to 16 min and more. Those limes are obtained by severe calcination, so‐called “hardburning,” which requires a higher amount of energy compared to standard high reactive limes, releasing more CO2 accordingly. Seeking for improving the carbon footprint of its product portfolio, Lhoist investigates different pathways to produce limes suitable for the production of AAC. This paper presents new lime qualities under development, their slaking behavior, and impact on the typical AAC process steps. The new limes show smooth while modified slaking profiles. The use of such lime qualities will allow for a progressive shift from today's formulation technologies towards formulations with highly improved environmental profile.

Human 2'-Deoxynucleoside 5'-Phosphate N-Hydrolase 1: Mechanism of 2'-Deoxyuridine 5'-Monophosphate Hydrolysis.

The enzyme 2'-deoxynucleoside 5'-phosphate N-hydrolase 1 (DNPH1) catalyzes the N-ribosidic bond cleavage of 5-hydroxymethyl-2'-deoxyuridine 5'-monophosphate to generate 2-deoxyribose 5-phosphate and 5-hydroxymethyluracil. DNPH1 accepts other 2'-deoxynucleoside 5'-monophosphates as slow-reacting substrates. DNPH1 inhibition is a promising strategy to overcome resistance to and potentiate anticancer poly(ADP-ribose) polymerase inhibitors. We solved the crystal structure of unliganded human DNPH1 and took advantage of the slow reactivity of 2'-deoxyuridine 5'-monophosphate (dUMP) as a substrate to obtain a crystal structure of the DNPH1:dUMP Michaelis complex. In both structures, the carboxylate group of the catalytic Glu residue, proposed to act as a nucleophile in covalent catalysis, forms an apparent low-barrier hydrogen bond with the hydroxyl group of a conserved Tyr residue. The crystal structures are supported by functional data, with liquid chromatography-mass spectrometry analysis showing that DNPH1 incubation with dUMP leads to slow yet complete hydrolysis of the substrate. A direct UV-vis absorbance-based assay allowed characterization of DNPH1 kinetics at low dUMP concentrations. A bell-shaped pH-rate profile indicated that acid-base catalysis is operational and that for maximum kcat/KM, two groups with an average pKa of 6.4 must be deprotonated, while two groups with an average pKa of 8.2 must be protonated. A modestly inverse solvent viscosity effect rules out diffusional processes involved in dUMP binding to and possibly uracil release from the enzyme as rate limiting to kcat/KM. Solvent deuterium isotope effects on kcat/KM and kcat were inverse and unity, respectively. A reaction mechanism for dUMP hydrolysis is proposed.

Automated microarray platform for single-cell sorting and collection of lymphocytes following HIV reactivation.

A promising strategy to cure HIV-infected individuals is to use latency reversing agents (LRAs) to reactivate latent viruses, followed by host clearance of infected reservoir cells. However, reactivation of latent proviruses within infected cells is heterogeneous and often incomplete. This fact limits strategies to cure HIV which may require complete elimination of viable virus from all cellular reservoirs. For this reason, understanding the mechanism(s) of reactivation of HIV within cellular reservoirs is critical to achieve therapeutic success. Methodologies enabling temporal tracking of single cells as they reactivate followed by sorting and molecular analysis of those cells are urgently needed. To this end, microraft arrays were adapted to image T-lymphocytes expressing mCherry under the control of the HIV long terminal repeat (LTR) promoter, in response to the application of LRAs (prostratin, iBET151, and SAHA). In response to prostratin, iBET151, and SAHA, 30.5%, 11.2%, and 12.1% percentage of cells, respectively. The arrays enabled large numbers of single cells (>25,000) to be imaged over time. mCherry fluorescence quantification identified cell subpopulations with differing reactivation kinetics. Significant heterogeneity was observed at the single-cell level between different LRAs in terms of time to reactivation, rate of mCherry fluorescence increase upon reactivation, and peak fluorescence attained. In response to prostratin, subpopulations of T lymphocytes with slow and fast reactivation kinetics were identified. Single T-lymphocytes that were either fast or slow reactivators were sorted, and single-cell RNA-sequencing was performed. Different genes associated with inflammation, immune activation, and cellular and viral transcription factors were found.

Reactivity of Unconventional Fly Ashes, SCMs, and Fillers: Effects of Sulfates, Carbonates, and Temperature

Abstract Reactivity information for a range of unconventional fly ashes is unavailable in literature. The objective of this study is to quantify the reactivity of numerous unconventional fly ashes using the R3 test (ASTM C1897-20, Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements) and the modified R3 test and to determine how sulfates, carbonates, and temperature affect the measured reactivity. A small set of other supplementary cementitious materials and fillers was used to benchmark the fly ash results. Heat release, calcium hydroxide consumption, and bound water were measured for the different materials. For siliceous materials with relatively low calcium oxide (CaO) + aluminum oxide (Al2O3) contents, temperature had a dominant effect on the heat release. On the other hand, for materials with higher CaO + Al2O3 contents, the effects of sulfates and carbonates dominated the effect of temperature. The slow but sustained reactivity of Class F fly ashes highlighted the importance of kinetic corrections or extrapolations to the reactivity measured in the R3 test. However, when testing at 50°C, the heat release curves of all tested materials plateaued at the end of 10 days, indicating that kinetic corrections were not required. Correlations between reactivity and early- and later-age paste properties are discussed.

Effect of Steam Curing Condition on Strength and Water Absorption Properties of High Strength Green Concrete

The high-strength concrete could be achieved by using the clinker with the incorporation of cementitious material such as GGBS. However, the use of GGBS as a partial replacement for OPC could retard the strength performances at an early age due to the slow reactivity of slag. In the precast industry, the minimal initial strength of concrete is the most important factor for the demolding of concrete elements. Thus, the improvement on the early strength could be made by using the thermal treatment (steam curing) and a combination of GGBS with highly reactive material such as RHA. In the present study, the performance of pozzolanic and cementitious products was evaluated through the compressive strength and water absorption rate. The results show that the mixture which consists of 40 wt.% cement used with blended GGBS and RHA at ratios of 50, and 10 wt.%, respectively, performed better under the steam curing regimes. The inclusion of RHA-GGBS as a partial replacement for cement could provide a synergic effect by improving the compressive strength value and giving a low water absorption rate of the high-strength concrete.

Development and dual validation on a transient inspired by KRUSTY of the sNDM diffusion method for easy, MC-based, core analysis

Successfully validated on a typical CANDU LOCA and fruitfully applied to safety assessment studies of high conversion water-cooled cores, the Nodal Drift Method (NDM) has recently been generalized. The so-called “super NDM” (sNDM) methodological product offers an even simpler way to core analysis, basically by feeding the diffusion approximation with specific adjustments from Monte Carlo calculations. The test case chosen for validation has been inspired by the KRUSTY experiment of a fast small UMo core driven by its radial BeO reflector, and is defined by a MCNP model of a few cells. The selected heat-up transient consists in a slow reactivity insertion, from nominal steady-state, of 120 pcm in 600 s. Fuel power and average temperature increase from about 2200 W and 1000 K up to 2500 W and 1100 K at the new equilibrium reached one hour later. Using an axisymmetric structured mesh, large nodal volumes and appropriate MCNP tallies, sNDM manages to reproduce the exact same initial equilibrium as its Monte Carlo reference. Lightly completed for reactivity insertion and thermal feedback, sNDM is doubly validated by comparison to both known-valid point kinetics over the whole transient and MCNP neutron balance for two remarkable states. Such a simplifying and promising approach, making full use of MC-based diffusion, is methodologically discussed. Further development effort and small core design applications are finally proposed.

Effects of form, fineness and placement of lime with and without soil tillage on barley and canola growth and development

No-tillage systems and slow movement of surface-applied limestone can lead to stratification of soil acidity. Incorporation of lime by tilling soil is not preferred by producers following conservation agriculture practices. There is limited research on ways to facilitate lime movement without soil disturbance. This study aimed to determine the effects of form, fineness and calcium carbonate equivalent (CCE) of calcitic lime on its movement in soil with or without different soil disturbance actions and consequent effects on productivity of barley (Hordeum vulgare L.) and canola (Brassica napus L.). A field trial was established in the Western Cape province, South Africa. Ten treatments included a control, lime with different forms and fineness, and tillage practices. Due to the slow movement and reactivity of lime in soil, it was unlikely that growth responses from barley or canola would be detected within the first two years following liming. A once-off strategic tillage action promoted crop growth. This was attributed to deeper redistribution of lime in the soil (15–30 cm depth), among secondary agronomic responses to tillage. Strategic once-off tillage may address the stratification of both soil acidity and nutrients, such as calcium (Ca) and magnesium (Mg), and could be considered as an option to incorporate into management of no-tillage production systems.

Dissolution of β-C2S Cement Clinker: Part 1 Molecular Dynamics (MD) Approach for Different Crystal Facets.

A major concern in the modern cement industry is considering how to minimize the CO2 footprint. Thus, cements based on belite, an impure clinker mineral (CaO)2SiO2 (C2S in cement chemistry notation), which forms at lower temperatures, is a promising solution to develop eco-efficient and sustainable cement-based materials, used in enormous quantities. The slow reactivity of belite plays a critical role, but the dissolution mechanisms and kinetic rates at the atomistic scale are not known completely yet. This work aims to understand the dissolution behavior of different facets of β-C2S providing missing input data and an upscaling modeling approach to connect the atomistic scale to the sub-micro scale. First, a combined ReaxFF and metadynamics-based molecular dynamic approach are applied to compute the atomistic forward reaction rates (RD) of calcium (Ca) and silicate species of (100) facet of β-C2S considering the influence of crystal facets and crystal defects. To minimize the huge number of atomistic events possibilities, a generalized approach is proposed, based on the systematic removal of nearest neighbors’ crystal sites. This enables us to tabulate data on the forward reaction rates of most important atomistic scenarios, which are needed as input parameters to implement the Kinetic Monte Carlo (KMC) computational upscaling approach. The reason for the higher reactivity of the (100) facet compared to the (010) is explained.

Enhancing the hardened properties of blended cement paste cured at 0 °C by using alkali-treated ground granulated blast furnace slag

The use of high-volume ground granulated blast furnace slag (GGBFS) in cement-based materials significantly reduces CO2 emissions. Nevertheless, low curing temperatures are barriers to using environmentally friendly materials in winter construction works. This is mainly attributed to slow GGBFS's reactivity and blends' strength development due to the low alkalinity offered by the slow hydration rate of Portland cement (PC) at low temperatures. In this study, sodium hydroxide was employed to produce dry reactive pre-alkali-activated GGBFS (A-GGBFS), with an intention to increase the system's alkalinity and reactivity. The blended cement paste was prepared with 50% PC replacement with untreated and treated GGBFS, and cured constantly at 0 °C for 28 days. The A-GGBFS accelerated the hydration rate and enhanced the precipitation of hydration products. By adding an optimal NaOH content during the pre-alkali-activation process, the 3 and 28 days compressive strengths of paste increased by 41% and 37%, respectively, gaining a comparable 28 days compressive strength to that measured in a 100% PC-based binder. The microstructural assessments are consistent with compressive strength measurements.

Sustainable utilization of pre-treated and nano fly ash powder for the development of durable geopolymer mortars

Developments in geopolymer construction are gaining more interest nowadays due to the elimination of cement and the consequent effects such as carbon dioxide emission, greenhouse effect, etc. Although the use of fly ash as a binder in the geopolymer system acts as a key solution for the major hazardous effects like land dumping, soil contamination, groundwater pollution, and respiratory diseases, the slow reactivity of the fly ash resulted in the considerable reduction in the strength. In this paper, a novel pretreatment method was employed on the fly ash binder in terms of thermal and mechanical means. Also, a cost-effective nano fly ash powder was synthesized and used as filler material on the geopolymer system. The efficiency of the fabricated geopolymer mortar was assessed by examining the workability, compressive strength, and resistance against chloride ion penetration. The geopolymer mortars with pre-treated fly ash exhibited a highly workable mix of 130% improved flow rate without adding any superplasticizer. Further, the addition of 1% nano fly ash, exhibited the highest compressive strength of 71.22 MPa, confirmed almost nil chloride ion permeability, and sustained 90% residual strength after immersing in the brine solution for 60 days which explored the development of sustainable and cost-effective geopolymer construction in the marine environment.

Electron Trap Dynamics in Polymer Light‐Emitting Diodes

AbstractSemiconducting polymers are being studied intensively for optoelectronic device applications, including solution‐processed light‐emitting diodes (PLEDs). Charge traps in polymers limit the charge transport and thus the PLED efficiency. It is firmly established that electron transport is hindered by the presence of the universal electron trap density, whereas hole trap formation governs the long‐term degradation of PLEDs. Here, the response of PLEDs to electrical driving and breaks covering the timescale from microseconds to (a few) hours is studied, thus focusing on electron traps. As reference polymer, a phenyl‐substituted poly(para‐phenylene vinylene) (PPV) copolymer termed super yellow (SY) is used. Three different traps with depths between ≈0.4 and 0.7 eV, and a total trap site density of ≈2 × 1017 cm−3 are identified. Surprisingly, filling of deep traps takes minutes to hours, at odds with the common notion that charge trapping is complete after a few hundred microseconds. The slow trap filling feature for PLEDs is confirmed using poly(2‐methoxy‐5‐(2‐ethylhexyloxy)‐1,4‐phenylene vinylene (MEH‐PPV) and poly(3‐hexylthiophene) (P3HT) as active materials. This unusual phenomenon is explained with trap deactivation upon detrapping and slow trap reactivation. The results provide useful insight to pinpoint the chemical nature of the universal electron traps in semiconducting polymers.

High-Fidelity Steady-State and Transient Simulations of an MTR Research Reactor Using Serpent2/Subchanflow

In order to join efforts to develop high-fidelity multi-physics tools for research reactor analysis, the KIT is conducting studies to modify the coupled multi-physics codes developed for power reactors. The coupled system uses the Monte Carlo Serpent 2 code for neutron analysis and the Subchanflow code for thermo-hydraulic analysis. Serpent treats temperature dependence using the target motion sampling method and Subchanflow was previously extended and validated with experimental data for plate-type reactor analysis. This work present for the first time the steady-state and transient neutron and thermo-hydraulic analysis of an MTR core defined in the IAEA 10 MW benchmark using Serpent2/Subchanflow. Important global and local parameters for nominal steady-state conditions were obtained, e.g., the lowest and highest core plate/channel power/temperature, the radial and axial core power profile at the plate level, and the core coolant temperature distribution at the subchannel level. The capabilities of Serpent2/Subchanflow to perform transient analysis with on-the-fly motion of the control plates were tested, namely with fast and slow reactivity insertion. Based on the unique results obtained for the first time at the subchannel and plate level, it can be stated that the coupled Serpent2/Subchanflow code is a very promising tool for research reactor safety-related investigations.

Discovery of C5H+ and detection of C3H+ in TMC-1 with the QUIJOTE line survey

We report the discovery of the C5H+ cation toward TMC-1 with the QUIJOTE line survey. Four lines from J = 7 − 6 up to J = 10 − 9 have been identified in perfect harmonic frequency relation that can be fit with B = 2411.94397 ± 0.00055 MHz and D = 138 ± 3 Hz. The standard deviation of the fit is 4.4 kHz. After discarding potential candidates, C5H− among them, we conclude that the carrier is C5H+, for which accurate ab initio calculations provide B = 2410.3 MHz. We also report for the first time in a cold starless core the detection of the C3H+ cation. The column densities we derive for C5H+ and C3H+ are (8.8 ± 0.5)×1010 cm−2 and (2.4 ± 0.2)×1010 cm−2, respectively. Hence, the C5H+/C3H+ abundance ratio is 3.7 ± 0.5. The fact that C5H+ is more abundant than C3H+ is well explained by dedicated chemical models and is due to the slow reactivity of C5H+ with H2, while C3H+ reacts with H2.

Slow pyrolysis and gasification reactivity of thermally treated spent coffee grounds pre-treated by wet oxidation

Slow pyrolysis and gasification reactivity of thermally treated spent coffee grounds pre-treated by wet oxidation