The influence of calcium sulfate content on the hydration of belite-calcium sulfoaluminate cements with different clinker phase compositions

The influence of different amounts of gypsum on the hydration of a belite-rich and a ye'elimite-rich belite-calcium sulfoaluminate clinker (BCSA) was investigated. The hydration kinetics, phase assemblages and compressive strength development of cements prepared using ye’elimite/ calcium sulfate molar ratios of 1, 1.5 and 2 were studied. Besides ettringite and monosulfate, aluminium hydroxide, strätlingite, C−S−H, iron-containing siliceous hydrogarnet and hydrotalcite were present as hydration products. Increasing the amount of gypsum increased the ratio of ettringite to monosulfate formed in the cement paste, lowered the amount of pore solution, delayed the dissolution of belite and ferrite, decreased the formation of strätlingite and, in the case of the ye’elimite-rich BCSA, led to an increase in compressive strength. Increased amounts of belite in the clinker led to the formation of higher quantities of C–S–H, at the expense of strätlingite and a lower compressive strength, as belite has a lower degree of reaction than ye’elimite and due to the formation of more C–S–H and strätlingite compared to the more space-filling ettringite. The thermodynamic model established for BCSA cement hydration agrees well with the experimental data. Compressive strength directly correlated with bound water from thermogravimetric analyses and inversely correlated with the porosity calculated from thermodynamic modelling.

Dynamic Character of Thermal Analysis Where Thermal Inertia Is a Real and Not Negligible Effect Influencing the Evaluation of Non-Isothermal Kinetics: A Review

The development of instrumentation has allowed thermal analysis to become a widely used method not only in calorimetry but also in the field of non-isothermal kinetics that, however, provides a simplified philosophy of measurements. From the beginning, a methodology is used describing the course of reaction in a simplified temperature regime measured in an inert sample. In a most common case of DTA, the degree of reaction is subtracted from the partial areas of the as-cast peak in the unified mode of the peak linear background. Usually, the effect of thermal inertia, resulting from the reality of heat transfer and changing the peak background to a non-linear s-shaped form, is not incorporated. Therefore, the question of whether or not to include this effect of thermal inertia has become a current underlying problem of thermo-analytical kinetics. The analysis of the rectangular input heat pulses and their DTA responding fundamentally point to the need to include it thus becoming essential and not negligible. In the case of parallel evaluations, the effect of inertia can be partially compensated for each other such as in the Kissinger evaluation method. The study presents a broad overview of the thermo-analytical methodology used and points to the often-neglected literature. However, standard mainstream kinetics procedures need be fixed, and an improved solution found to account for the effect of heat transfer and dissipation, which is becoming the focus of thermal analysis methods of future and also the intention of this review.

Production Rate of SiO Gas from Industrial Quartz and Silicon

The production rate of SiO gas from industrial quartz and silicon has been investigated by isothermal heat treatment experiments. Mixtures of silicon and different quartz samples have been heated to temperatures ranging from 1650 °C to 1950 °C and held for 30 to 120 minutes before cooling. The weight loss of each sample has been correlated to degree of reaction and a model for the reaction rate of Si + SiO2 has been developed based on these values. Five different types of industrial quartz were used in the experiments. No significant difference was found in their reaction rate, even though there are large variations in impurity content, melting rate, decrepitation, and phase transformation rate of each sample. Further on, it is shown that the reaction rate of silicon mixed with various types of quartz can be described by an Arrhenius equation: $${{\rm {d}}\alpha /{\rm {d}}t = k_0 \, A \, {\rm {exp}} (- Q / RT)}$$ d α / d t = k 0 A exp ( - Q / R T ) . A reaction constant (k0) equal to $${6.25 \, 10^8 {\rm {g}}\, {\rm {s}}^{-1}\, {\rm{m^{-2}}}}$$ 6.25 10 8 g s - 1 m - 2 and an activation energy (Q) equal to $${557\, {\rm {kJ \, mol^{-1}}}}$$ 557 kJ mol - 1 were obtained by linear regression. The degree of reaction ($${\alpha }$$ α ) is shown to be increasing with available reaction area, temperature, and time.

Classification and Milling Increase Fly Ash Pozzolanic Reactivity

Upcycling and reclaiming of low quality or stored coal combustion fly ashes could enable to tap into a voluminous resource of supplementary cementitious materials (SCMs) for low-carbon blended cements. Low reactivity fly ashes are usually either too crystalline or too coarse. Beneficiation treatments for coarse fly ashes comprise size classification or milling processes to extract or produce fine size fractions of higher pozzolanic reactivity. This article compares the effect of size classification and milling treatments on the reactivity of a siliceous fly ash (FA). The intrinsic chemical reactivity is assessed using the R3 heat release test method. The results showed significant increases of 57 and 40% for fine classified and milled fly ash compared to the initial fly ash, respectively. In addition heat release and portlandite consumption were measured for blended cements with 30 wt.% Portland cement replacement by the fly ashes. Both test results are combined to calculate the degree of reaction of the fly ashes over time in blended cement. The results demonstrate a strong effect of particle size on fly ash reactivity and degree of reaction. It is shown that increasing the inherent reactivity of fly ashes is an effective way of both accelerating compressive strength gain and enhancing late age strength with fine classified fly ashes reaching equivalent strength as neat Portland cement by 28 days and attaining a strength activity index of 137% by 90 days.

Effects of Al Particle Size on the Impact Energy Release of Al-Rich PTFE/Al Composites under Different Strain Rates

Polytetrafluoroethylene (PTFE)/Al reactive material with different aluminum particle sizes were prepared by molding and sintering, and the effect of aluminum particle size on the impact behavior of PTFE/Al reactive material with a mass ratio of 50:50 was investigated. The results show that aluminum particle size has significant effects on the shock-reduced reaction diffusion, reaction speed, and degree of reaction of the PTFE/Al reactive material. At a moderate strain rate, the reaction delay of PTFE/Al increased, and the reaction duration and degree decreased, with the increase of aluminum particle size. Under the strong impact of explosive loading, aluminum particle size has little effect on the reaction delay, which maintains at about 1.5 μs–2.5 μs, but the reaction durability and degree of reaction of PTFE/Al decrease with increasing aluminum particle size. There is also a strain rate threshold for the shock-induced reaction of PTFE/Al reactive material, which is closely related to aluminum particle size. The shock-induced reaction occurs when the strain rate threshold is exceeded.

Study on the Impact-Induced Energy Release Characteristics of Zr68.5Cu12Ni12Al7.5 Amorphous Alloy

As a new kind of multifunctional energetic structural material (MESM), amorphous alloy will undergo a chemical reaction and release energy under impact load. In this paper, an analysis method for the impact-induced reaction parameters of solid materials was derived based on a three-term equation of state and Avrami–Erofeev equation. The relation between the degree of reaction, pressure, and temperature of Zr68.5Cu12Ni12Al7.5 amorphous alloy was obtained. The influence of participation of an oxidizing reaction on the material energy release efficiency was analyzed. The relation between the energy release efficiency and impact velocity was achieved by an experiment in which Zr68.5Cu12Ni12Al7.5 amorphous alloy fragments impact a steel plate. The variations of pressure and temperature during the impact process were obtained. In the end, a reaction kinetic model was modified, and the kinetic parameters for the impact-induced reaction of materials in an air environment were obtained.

Enzyme kinetics of CRISPR molecular diagnostics

CRISPR diagnostic assays have gained significant interest in the last few years. This interest has grown rapidly during the current COVID-19 pandemic where CRISPR diagnostics have been frontline contenders for rapid testing solutions. This surge in CRISPR diagnostics research prompts the following question: What exactly are the achievable limits of detection and associated assay times enabled by the kinetics of Cas12 and Cas13 enzymes? To address this question, we here present a model based on Michaelis-Menten enzyme kinetics theory applied to Cas enzymes. We use the model to develop analytical solutions for reaction kinetics and develop back-of-the­ envelope criteria to validate and check for consistency in reported enzyme kinetics parameters. We applied our analyses to all studies known to us which report Michaelis-Menten-type kinetics data for CRISPR associated enzymes. These studies include all subtypes of Cas12 and Cas13 and orthologs. We found all studies but one clearly violate at least two of our three rules of consistency. We further use our model to explore ranges of reaction time scales and degree of reaction completion for practically relevant target concentrations applicable to CRISPR-diagnostic assays.

Quantitative Correlation between the Degree of Reaction and Compressive Strength of Metakaolin-Based Geopolymers

For geopolymers (usually composed of unreacted precursor and gel), the compressive strength is controlled by two factors. The first is the degree of reaction, or, equivalently, the amount of gel formed, including any calcium silicate hydrate gel in calcium-containing mixtures. The second factor is the gel composition, generally given by the Si/Al ratio. These two parameters are interrelated for typical silicate-activated metakaolin geopolymers. By separating out effects of Si/Al ratio and degree of reaction, this study quantitatively correlates the degree of reaction with the compressive strength of metakaolin-based geopolymers with and without calcium. Solid-state 29Si nuclear magnetic resonance (NMR) aided with chemical extractions was used to determine gel amounts and composition for several geopolymer mixtures. The compressive strength was also measured for each mixture at 7 days. Both the increase of Na/Al ratio in mixtures without calcium and addition of external calcium increased the degree of reaction, and compressive strength correlated linearly (R2 > 0.88) with the degree of reaction.

Usage of supplementary cementitious materials: advantages and limitations

It is well known that cement production is not neutral for natural environment among others due to high CO2 emission. Different strategies of mitigation of negative environmental impact of its production are developed. One of the ways is utilization of supplementary cementitious materials (SCMs) in the manufacture of cement and concrete. Introduction of aluminosilicate SCMs into binding mixture makes that more amount of so-called C–A–S–H phase appears in hydration products, affecting microstructure and properties of final hardened composite. The aim of this work is to discuss the possibilities of utilization of selected SCMs in different binding mixtures including some advantages and limitations. Literature review on the subject was carried out. Some of our own research results were also presented. In the Part I of this review, some information about history of ancient binding materials and the possibilities of inspiring modern engineers with ancient constructions in the aspect of using SCMs in modern concrete were presented. Using pozzolanic aluminosilicate SCMs in relation to their influence on formed products, microstructure and mechanical properties of hardened material were discussed. Some problems with possibilities of study of SCMs reaction degree were identified. Emphasis was put on the usefulness of isothermal calorimetry and thermal analysis for investigations of hydration process and identification of hydrated products as well as evaluation of degree of reaction of SCMs.

Electromechanical Activity of the Heart and Intracardiac Hemodynamics in Patients With Different Forms of Acute and Recurrent Bronchial Pathology

The article presents an analysis of indicators of Electromechanical activity of the heart and intracardiac hemodynamics in children of the first three years of life, patients with acute and recurrent bronchopulmonary diseases. The direction and degree of reaction of rhythmic activity, repolarization, morphometric and volemic parameters depending on the form of lung pathology were determined.