Papers by Keyword: Granulometry

Abstract: Plastic waste is an ever-growing concern, causing harm to many ecological and human health aspects, one of the major contributors to this problem being packaging. Mycelium composites (MC) are ecologically safe materials, well suited for the short-life usage as packaging materials. In our study we made MC using fine and coarse granulometry hemp shives applying them in 3 substrate variants – with added bran, with added bran and birch bark, and as the sole substrate. We assessed material's water absorption and mechanical properties, chemical decomposition, biodegradability, mold resistance and fungal biomass. Granulometric effect was observed only when using shives as the sole substrate, where larger particle size gave poorer results. Bran did not significantly improve mechanical properties or water uptake. Bark reduced water uptake by ~200 %, but lowered mechanical properties, and provided no benefits to mold resistance which was low for all specimens. Overall, hemp MC showed complete biodegradability after 12 weeks, mechanical properties up to 0,235 MPa, compatible with expanded polystyrene, but very high water uptake of up to 1000 %. Future studies are needed to reduce water absorption and improve mold resistance, as well as invent consensus methodology for better cross-study comparison.

Abstract: Silicate micro- and nano-additives are multifunctional in relation to cement systems. Their application can solve a wide range of technological problems while maintaining the economic efficiency of technical solutions. The effect of silicate additives and fillers is determined by their level of dispersion, due to which the technologies for producing nano- and submicro-sized dispersed materials are being developed. The combination of mechanochemical synthesis of modified calcium hydrosilicates with subsequent thermolysis makes it possible to produce calcium silicate dispersions (SCD), which differ in polymodality of the fractional composition including submicro (10^–7–10^–6 m) and microdimensional (≥10^–6 m) modes. The main element of the technology is the use of modifying carbohydrate, which acts as a stabilizer of hydrated phases of silicates. A comparative study of SCD produced using sucrose (sSCD) and lactose (lSCD) revealed the effect of these carbohydrates on the properties of sSCD and lSCD, as well as their effectiveness as a component of cementitious composite binder. It was found that the level of adsorption of modifying carbohydrate determines the physical properties of SCD (granulometry, specific surface area). The relatively high residual content of free sucrose (0.24%) in the composition of sSCD prevents the consolidation of silicates nanoparticles formed during the thermolysis, causes a high content of submicro sized fractions and a high specific surface area with sSCD (26.3 ± 0.7 m²/g). Lactose is absorbed by the silicate phase; the residual content of free lactose does not exceed 0.028% of lSCD. The low content of stabilizing carbohydrate contributes to the development of nanoparticle consolidation, a decrease in the specific surface area of lSCD to 13.0 ± 0.2 m²/g and content of submicrosized fractions. The residual content of free carbohydrates and particle size characteristics of sSCD and lSCD determine the nature of their influence on Cement-SCD-based concrete setting and hardening. The presence of residual sucrose in the composition of sSCD and fine fractions determines the competitive nature of the processes of retardation of hardening and acceleration of hardening of the cement system due to the nucleation effect, as a result of which the curve of the setting time is extreme. In addition, the inhibitory effect of sucrose reduces the strength of concrete on the 7^th day. By the 28^th day, the inhibitory effect of sucrose has been overcome, and concrete samples demonstrate an 18% increase in compressive strength with a sSCD content of 30%. The low content of residual free lactose in the composition of lSCD causes the nucleation effect. As a result, there is a monotonous reduction in the setting time of concrete mix with an increase in the content of lSCD in the composition of HF, as well as a significant increase in concrete strength (up to 127%) on the 7^th day. At the same time, on the 28th day the strength of concrete increases slightly

Abstract: Cement production belongs to the most important branch of industry. It is marked out by processing of great quantity of natural raw materials and of considerable energetic demand. Not only the intensification of the contemporary production processes is the permanent effort of the cement industry, but also the search for new energy less demanding methods. The paper is focused on one of the most important components of the intensification of cement production – on the preparation of raw meal. It mainly deals with the influence of granulometry and microhomogeneity of the input raw materials on the quality and economy of the process of production and on the final product. The study was carried out mainly by methods of optical microscopy and the determination of technological parameters of cements. It has been found that a change in granulometry of raw meal has a significant impact on the formation rate of the clinker phases. Subsequently, the grindability of the clinker and the strength of the cement are influenced, especially in the short-term hydration. Change of granulometry and homogeneity of raw meal can greatly optimize the quality and economy of the cement production process.

Abstract: This document deals with study of nanoand micro particles of artificial corundum in cement mixtures. This inert material with high hardness is usually used as fine-grained additions of concrete mixture. The most important characteristic of corundum is very high hardness (number 9 on Mohr scale). That is the reason, why is mostly added to the cement mixture primary intended for high load flooring. In this paper were studied several type of recycled corundum classified due to its origin. Because it is a recycled material, it was necessary to first examined basic physical properties such as chemical composition or granulometry. We have applied this fine grain material to cement mixes and compared their mechanical properties. For comparison measurement were used a mixture without this admixture and mixture with a corundum with similar granulometry but non-recycled origin.

Abstract: The main aim of this paper is determined of properties, especially granulometry, of recycled silicon carbide waste and its possibility of using in new cementitious recipes. Paper is focused on importance of creation of grain curves and on relationship between silicon carbide and compounds in concrete matrix. Purpose of this research is using waste material and therefore minimalizes of its production and reduces ecological effect on environment by its recycling. Set of granulometry measurements of each recycled materials were done as well as its grain characteristic. The End of work includes the evaluation of the possible use of SiC waste for cement mixtures.

Abstract: The by-products of energy industry are nowadays often affected by new limits governing the production of harmful gases discharged into the air. These stricter and stricter criteria are often met by electricity producers by changing the combustion process in thermal power plants itself. Nowadays, the SNCR (selective non-catalytic reduction) application is quite common in the combustion process in order to help reduce the nitrogen oxide emission. This article deals with the primary measures of thermal power plants, which in particular consist of a modified treatment of raw materials (coal) entering the combustion process. These primary measures then often cause the formation of fly ash with unsuitable fineness for the use in concrete according to EN 450. The paper presents the comparison of the physico-mechanical parameters of several fly ashes with a different fineness values. The primary task is to assess the impact of non-suitable granulometry in terms of EN 450 on the other physico-mechanical parameters of fly ashes sampled within the same thermal power plant. Several fly ashes produced in the Czech Republic and surrounding countries were evaluated in this way.

Abstract: At the beginning of 2016, the legislation for regulating and reducing the emission of exhaust gases with regard to reducing nitrogen oxides came into force. The articles published to date point to the possibility of increased ammonium salt content in fly ash that has undergone a selective non-catalytic reduction process. This paper addresses other possible negative impacts of the reduction process for nitrogen oxide on the physico-mechanical properties of high-temperature fly ash, especially the morphology of its grains and its impact on the rheology of the composite and the impact on the efficiency index.

Abstract: This project had as objective to evaluate the influence of the content and particle size of the calcite in the filtration properties of clay dispersions. For that, it was realized the characterization of a bentonite clay sample using X-Ray Fluorescence and X-Ray Diffraction. In addition, two samples of calcite (CaCO₃) were granulometrically analyzed by Laser Diffraction. The dispersions were prepared with fixed concentration of clay (10g) and different concentrations of carboxymethylcellulose of low viscosity (0 to 2g), and calcite (0 to 20g). After 24 hours of repose, it were determined the filtration properties (filtrate volume (FV), mudcake thickness (h), and mudcake permeability (k)). It was observed that the lowest filtrate volume was acquired using CaCO₃ sample with the lowest average diameter, and, also, a bigger concentration of calcite was not able to promote a considerable reduction of the filtrate.

Abstract: The high temperature firing to process clay ceramics requires some kind of fuel, which is associated with cost and embodied energy of the final product. Saving in fuel by introducing substances with heating power represents both economical and energetical advantages. The incorporation of a fuel containing waste into the precursor clay body constitutes also an environmentally correct solution for the destination of the waste. A typical fuel-containing waste, generated in large scale, is the residual coal, which falls to the harbor yard during transfer from the cargo ship. This coal can no longer be embarked and is usually discarded in the environment. Its addition into ceramic clay is the most viable solution. Therefore, the objective of the present work is to characterize a residual coal in terms of its chemical constituents, heat power and granulometric distribution. The results indicate that the residual coal presents toxic compounds in amounts below the limits established by the environmental legislation. Its fine granulometry favors the addition to clay ceramics.

Abstract: This work aims to investigate the infiltration of a CaCO₃ filled resin using experiments and the PAM-RTM software. A preform of glass fiber mat, with dimensions 320 x 150 x 3.6 mm, has been used for experiments conducted at room temperature, with injection pressure of 0.25bar. The resin contained 10 and 40% CaCO₃ content with particle size 38μm. The numerical results were evaluated by direct comparison with experimental data. The flat flow-front profile of the rectilinear flow was reached approximately halfway the length of the mold. It was observed, that the speed of the filling decreases with increasing CaCO₃ content and,the higher the amount of CaCO₃ in the resin, the lower the permeability of the reinforcement that is found. The reduction in permeability is due to the presence of calcium carbonate particles between the fibers, hindering the resin flow in the fibrous media. The computational fluid flow analysis with the PAM-RTM proved to be an accurate tool study for the processing of composite materials.