Inert Admixtures Research Articles

Exploring synergistic effects and hydration mechanisms in metakaolin-blended cement system with varying metakaolin and wollastonite content

The quest for sustainable construction practices has led to a growing interest in reducing cement consumption, with supplementary cementitious materials emerging as a promising solution. While reactive admixtures have been extensively studied, there is a noticeable research gap regarding inert admixtures, a critical component of cementitious systems. This paper introduces a novel metakaolin-blended cement system, optimizing the metakaolin, wollastonite, and ground quartz ratios to enhance microstructure and performance. Within this complex quaternary system, we conduct a comprehensive investigation, including assessments of compressive strength, setting times, heat release during hydration, R3 test. Furthermore, we explore hydration products and microstructure through thermogravimetric analysis, X-ray diffraction, backscattered electron imaging, and mercury intrusion porosimetry. The results indicate the influence of wollastonite on clinker reactions and hydration. Although wollastonite slightly increases meso-scale pores, its fibrous shape enhances the overall microstructure. Substituting 50% of metakaolin with wollastonite not only enhances the pozzolanic reactivity but also leads to improved long-term strength. Moreover, the synergistic effect of wollastonite and metakaolin allows for precise tailoring setting times and modulate hydration kinetics, thereby enhancing the overall performance of the cementitious system.

Determining basic characteristics of stabilizer micro torch burners for the combustion of ballasted fuel gases

This paper reports an experimental study into the combustion of alternative gases in the form of a mixture of propane-butane with air and carbon dioxide after a stabilizing flat module whose both sides are flown around with an airflow. The ballasted fuel was fed by jets into the airflow from the holes located on the side walls of the stabilizer. In this case, the fuel and air were partially premixed. It was established that when ballasting fuel with inert admixtures, the length of the torch and the maximum temperature gradually decreased while nitrogen oxide emissions decreased. With an increase in the content of ballast in fuel, combustion breaks. The dependence of torch stability on the relative consumption of ballast has been established. To stabilize the combustion, highly reactive fuel is supplied to the recirculation zone after a stabilizer from a separate collector. Ballasted fuel passes through the next torches of high-temperature fuel; the all fuel combustion process takes place. The combined scheme of mixture formation makes it possible to adjust fuel consumption in the zones and thus maintain a stable burner power. In the case of supplying all fuel to the recirculation zone after the stabilizer, a so-called "rich" detachment is possible when the torch is detached from the stabilizer. When working under such modes, highly reactive fuel is supplied from the holes on the side walls of the stabilizer, which are placed closer to its detachment edges than the holes for the supply of ballasted fuel. At the same time, the jets of ballasted fuel also pass between the torches of highly reactive fuel so there is joint combustion of all fuel

Action Time-Effect and Mechanism of Low-Calcium Fly Ash in Cement-Based Composites

This study was conducted in order to investigate when low-calcium fly ash plays a physical or chemical effect and what is the chemical effect proportion of low-calcium fly ash. Two types of low-calcium fly ash and quartz powder, with similar fineness as active and inert admixtures, were used as materials in this study. Under different water/binder ratios and hydration ages, the effects of the different types of admixtures and their dosages on the flexural and compressive strength of the composites were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption methods, in addition to an assessment of the degree of hydration of the fly ash, were employed to observe the hydration products at different ages, the microstructures of the hydration products, as well as their surface areas and pore size distributions. The results show that during the hydration period of 28 days, the low-calcium fly ash has a micro-aggregate filling physical effect. However, after 56 days, the hydration degree of fly ash begins to exceed 1%. This illustrates that the low-calcium fly ash has both the pozzolanic activity effect and micro-aggregate filling effect. In contrast, the low-calcium fly ash hydrated for 90 days is still dominated by the physical filling effect.

Adsorption of active trace gases by ensemble of ultrafine porous particles with impermeable cores

In the present study, we analyze the combined influence of several factors on the rate of atmospheric trace gas adsorption by an ensemble of porous aerosol particles. The factors include the presence of a non-porous non-adsorbing inner core, kinetic effects, non-uniform distribution of concentration of adsorbed gas inside particles, inert admixtures in the atmosphere, radioactive decay, and particle number density. The particles size has the same order of magnitude as a free path length of molecules in air. The evolution of concentration of adsorbed active trace gas in solid porous particles is described by an integral equation, while the evolution of active trace radioactive gas in a gaseous phase is determined by an integro-differential equation. Numerical calculations are performed to investigate the adsorption of different isotopes of Radon and Iodine by porous particles. The comparison of rates of gas adsorption for radioactive isotopes of Iodine with a stable isotope I-127 shows that radioactive decay alters the scenario of the gas adsorption process by porous particles. The accuracy of the developed model of radioactive gas adsorption by porous particles is validated by available experimental data.

Effect of SRA on the Course of Hydration of Cement Composites

Cement hydration is a chemical reaction that is associated with the development of hydration heat and changes in the volume of input components that transit from the solid and liquid phase to one homogeneous whole. In order to eliminate the volume changes already occurring during the hydration process, several principles can be applied, such as the use of active or inert admixtures as partial cement substitute or special shrinkage reducing additives. The experiment verifies the effect of anti-shrinkage additives on the course of hydration of cement pastes in terms of the development of hydration temperatures and elimination of volume changes of cement pastes. Volume changes will be monitored for the first 30 hours of cement mixing with water, i.e. in the time when the major changes occur due to this chemical reaction. Due to the expected hydration deceleration of the binder component by the effect of SRA, the impact of the use of these additives on the curing time of the composite and consequently on the mechanical parameters of the concrete will be verified.

Initiation of explosion-induced transformations in energy-saturated materials with nanoadmixtures by a high-voltage electric discharge

We have reported on the results of an experimental investigation of the effect of inert admixtures on the threshold characteristics of the breakdown (initiation) voltage in energy-saturated materials. A physicomathematical model that describes the experimental results has been proposed.

Dependence of the flammability of hydrogen-air mixtures on the chemical and physical properties of admixtures

The effect of chemically reactive and inert admixtures is studied to determine the concentration limits for the flame propagation of hydrogen-air mixtures at atmospheric pressure. The dependence of the effect additives have on their reactivity and mechanism of combustion is discussed. It is shown that the inhibition of combustion is a clear indicator of the unreality of the one-step reaction model at the heart of the theory of thermal combustion.

Initiation of detonation by a high-voltage discharge in powdered explosives with nanosize inert admixtures

It is shown that admixtures of a copper nanopowder in a high-disperse low-sensitivity explosive of the FOX-7 type sharply increase the sensitivity of the mixture to the action of a high-voltage electric discharge and facilitate detonation. The percolation model of propagation of the electric breakdown over a powdered mixture with nanosize admixtures and the model of initiation of detonation by a high-voltage discharge in the mixture of a brisant explosive with an inert admixture are developed. These models are in qualitative and quantitative agreement with experimental data.

Cell model of in-cloud scavenging of highly soluble gases

We investigate mass transfer during absorption of highly soluble gases such as HNO3, H2O2 by stagnant cloud droplets in the presence of inert admixtures. Thermophysical properties of the gases and liquids are assumed to be constant. Diffusion interactions between droplets, caused by the overlap of depleted of soluble gas regions around the neighboring droplets, are taken into account in the approximation of a cellular model of a gas–droplet suspension whereby a suspension is viewed as a periodic structure consisting of the identical spherical cells with periodic boundary conditions at the cell boundary. Using this model we determined temporal and spatial dependencies of the concentration of the soluble trace gas in a gaseous phase and in a droplet and calculated the dependence of the scavenging coefficient on time. We found that scavenging coefficient for gas absorption by cloud droplets remains constant and sharply decreases only at the final stage of absorption. In the calculations we employed a Monte Carlo method and assumed gamma size distribution of cloud droplets. It is shown that despite of the comparable values of Henry's law constants for the hydrogen peroxide (H2O2) and the nitric acid (HNO3), the nitric acid is scavenged more effectively by cloud droplets than the hydrogen peroxide due to a major affect of the dissociation reaction on HNO3 scavenging. It is demonstrated that scavenging of highly soluble gases by cloud droplets leads to strong decrease of soluble trace gas concentration in the interstitial air. We obtained also analytical expressions for the “equilibrium values” of concentration of the soluble trace gas in a gaseous phase and for concentration of the dissolved gas in a liquid phase for the case of hydrogen peroxide and nitric acid absorption by cloud droplets.

Effect of inert and reactive admixtures on the initiation and propagation of laminar spherical flames

The initial stage of the propagation of discharge-initiated laminar spherical flame in stoichiometric natural gas- and isobutylene-oxygen mixtures containing krypton or carbon dioxide and in the hydrogen-air mixture at atmospheric pressure in a constant-volume bomb has been investigated by high-speed color cinematography. Dilution of the combustible mixtures with the admixtures increases the steady-state flame front formation time by a factor larger than 10. The phlegmatizing effect of carbon dioxide on hydrocarbon combustion is stronger than that of krypton. For given combustible mixtures, the ratio of steady-state flame front formation times is inversely proportional to the ratio of the temperature rise values for the flames. The introduction of a minor amount of a reactive admixture (1.2% isobutylene) into the stoichiometric hydrogen-air mixture greatly increases the steady-state flame front formation time.

Evaporation and Condensation of Large Droplets in the Presence of Inert Admixtures Containing Soluble Gas

AbstractIn this study the mutual influence of heat and mass transfer during gas absorption and evaporation or condensation on the surface of a stagnant droplet in the presence of inert admixtures containing noncondensable soluble gas is investigated numerically. The performed analysis is pertinent to slow droplet evaporation or condensation. The system of transient conjugate nonlinear energy and mass conservation equations was solved using anelastic approximation. Using the material balance at the droplet surface the authors obtained equations for Stefan velocity and the rate of change of the droplet radius taking into account the effect of soluble gas absorption at the gas–liquid interface. The authors also derived boundary conditions at gas–liquid interface taking into account the effect of nonisothermal gas absorption. It is demonstrated that the average concentration of the dissolved species in a droplet strongly depends on the relative humidity (RH) for highly soluble and for slightly soluble gaseous atmospheric pollutants. Therewith the difference between the average concentration of the dissolved species in water droplets attains tens of percent for different values of RH.

Influence of inert admixtures on diffusion-controlled collapse of a rising bubble

In this study we considered mass transfer in a system comprising a rising gas bubble composed of a solvable and inert gases and liquid. In the analysis the resistance to mass transfer in both phases is taken into account. It is assumed that the bulk of a bubble, beyond the diffusion boundary layer, is completely mixed, and concentration of absorbate is homogeneous and time-dependent in the bulk. The thermodynamic parameters of a system are considered constant, and the bubble shape is assumed to be spherical. The moving boundary problem is solved in the approximations of thin concentration boundary layers in the gaseous and liquid phases and infinite dilution of an absorbate in the absorbent. The partial parabolic differential equations of mass conservation for gaseous and liquid phases with time-dependent velocity components and time-dependent boundary conditions are solved by combining generalized similarity transformation method with Duhamel's theorem, and the solution is obtained in the form of integral equation. The asymptotic behavior of the obtained solutions is discussed.

Coupled heat and mass transfer during nonisothermal absorption by falling droplet with internal circulation

We considered mass and heat transfer during nonisothermal absorption of a gas by a falling droplet with internal circulation. Gas phase is assumed to be free of inert admixtures and mass transfer is liquid phase controlled. Mass flux is directed from a gaseous phase to a droplet, and the interfacial shear stress causes a fluid flow inside the droplet. Droplet deformation under the influence of interface shear stress is neglected. Absorbate accumulation and temperature increase in the bulk of liquid phase are taken into account. The problem is solved in the approximations of a thin concentration and temperature boundary layers in the liquid phase. The thermodynamic parameters of the system are assumed constant. The system of transient partial parabolic differential equations of convective diffusion and energy balance with time-dependent boundary conditions is solved by combining the similarity transformation method with Duhamel's theorem, and the solution is obtained in a form of Volterra integral equation of the second kind which is solved numerically. Theoretical results are compared with available experimental data for water vapor absorption by falling droplets of aqueous solution of LiBr.

Influence of inert admixtures on the rate of mass transfer during bubble collapse in an alternating electric field

In this study, we consider mass transfer under the influence of an alternating electric field in a system comprising liquid dielectric medium and stationary dielectric gas bubble composed of a solvable and inert gases. Resistance to mass transfer in both phases is taken into account. The applied electric field causes Taylor circulation around the bubble. Bubble deformation under the influence of the electric field is neglected. The bulk of a bubble beyond the diffusion boundary layer is completely mixed, and the concentration of an absorbate is homogeneous and time-dependent in the bulk. The thermodynamic parameters of a system are assumed constant. The moving boundary problem is solved in the approximations of a thin concentration boundary layers in the gaseous and liquid phases and infinite dilution of an absorbate in the absorbent. The partial parabolic differential equations of mass conservation for gaseous and liquid phases with time-dependent velocity components and time-dependent boundary conditions are solved by combining generalized similarity transformation method with Duhamel's theorem, and the solution is obtained in the form of Volterra's integral equation of the second kind for all the frequencies of the applied electric field. The asymptotic behavior of the obtained solutions is discussed. Numerical calculations are performed for different values of distribution coefficient.

Mass Transfer during gas absorption from a linear cluster of slugs in the presence of inert gases

A model of mass transfer during isothermal gas absorption in the presence of inert gas from a slug rising in a channel filled with liquid is suggested. The work studies the case of a small amount of soluble gas inside a slug and employs the approximation of a thin concentration boundary layer. Theoretical results of mass transfer analysis for a single gas slug are applied for determination of mass transfer rate in gas liquid slug flow. In the assumption of a perfect mixing of the dissolved gas in liquid plugs, recurrent relations for the dissolved gas concentration in the n-th liquid plug and mass flux from the n-th gas slug are derived. The mass transfer coefficient in gas-liquid slug flow is determined. In the limiting case the derived formulas for mass transfer in the presence of inert admixtures recover the obtained expressions for mass transfer during absorption of a pure gas. Theoretical results are compared with available experimental data.

Heat and mass transfer during gas hydrate formation at the surface of rising slugs with small admixtures of inert gases

A model of gas hydrate formation on the surface of a slug of forming hydrate gas with inert gas admixture rising in a channel filled with liquid is suggested. Detailed analysis of the case of small concentrations of the inert admixtures in the gaseous phase is presented. Effect of heat released during gas hydrate formation on the rate of gas hydrate formation is investigated. Analytical formula for the rate of gas hydrate formation as a function of the concentration of the inert admixtures in the gaseous phase is derived. It is shown that an isothermal model of gas hydrate formation in the presence of inert gases underestimates a rate of gas hydrate formation in comparison with the nonisothermal model.

Percolation phenomena in explosive mechanochemical synthesis of some metal chalcogenides

Percolation phenomena are observed during the transition from an explosive to nonexplosive mechanochemical synthesis in Met-Met-Halc systems. The transition occurs under the effect of inert additives. In the systems investigated the inert admixtures are unreacted metals and metal chalcogenides synthesized nonexplosively. Two explosive synthesis mechanochemical reactions and two critical volumes x c 1 and x c 2 for the transition from an explosive to a nonexplosive mechanochemical reaction, respectively, correspond to the Met-Met-Halc system. Depending on the x c 1 and x c 2 values, three possible cases, considered in the percolation theory, are observed. It is shown that the final product synthesized in a nonexplosive mechanochemical way plays the role of an inert impurity. On this basis, a mechanism is proposed which explains the existence of a series of mechanochemical, in principle, nonexplosive reactions.

Nonstationary combustion regimes of gasless condensed substances periodically diluted by inert admixtures

Nonstationary combustion regimes of gasless condensed substances periodically diluted by inert admixtures