The effect of dispersants on the properties of low-cement concrete for the furnace of smelting of jewelry waste

Melting in ceramic crucible is one of the stages of recycling jewelry production. Conceptivity of concrete mass plays an important role in molding a large-scale refractory crucible to vibration. The impact of a number of commercially available dispersants (CASTAment FS 10, MELFLUX 1641 F, peramin al 200, FF7 SPEZIAL and PC-1701) on the rheology of the low-cement concrete mass of corundo-mullite-zirconium composition and the physico-mechanical properties of the material are considered. The best results were obtained using the PC-1701 dispersant.

Assessment of Thermally Stressed State of Concrete Massif

The paper describes a technique for assessing the thermally stressed state of a concrete massif of a foundation slab made of a self-compacting concrete mixture. The proposed method consists in a preliminary calculation of temperature fields in hardening concrete. The objects of research have been self-compacting concrete mix and structural concrete in the structure mass. The choice of materials for the preparation of a concrete mixture is given and substantiated. The composition of self-compacting concrete has been used to assess the thermally stressed state. A binder with a reduced exotherm has been used in order to reduce the self-heating of concrete. Studies have been carried out to assess the specific heat release of the recommended cement depending on the initial water-cement ratio. The effect of a chemical additive on the rate and magnitude of the specific heat release of cement has been studied. The paper presents the main theoretical provisions and an algorithm for calculating the thermal stress state of a concrete massif. The finite difference method has been used to calculate the expected temperatures and their distribution in the structure mass, and the temperature stresses in the sections of the concrete mass have been calculated to assess the thermally stressed state. The performed calculations of the temperature fields have made it possible to estimate the maximum possible temperatures and temperature differences over the sections of the concrete massif depending on the initial temperature of the concrete mixture and the average daily temperature of the outside air. Analysis of the temperature distribution has revealed the most dangerous sections of the concrete mass. An assessment of the thermal stress state of the concrete mass has been made on the basis of the results pertaining to calculation of temperature fields. The calculation of temperature stresses in the most dangerous sections of the concrete massif has been performed. It is shown that the calculated value of the temperature stress can serve as a characteristic of the thermally stressed state of the concrete mass. The formation of temperature cracks in a concrete mass is possible when the calculated value of the temperature stress exceeds the actual tensile strength of concrete. Comparison of the calculated and actual values of temperatures in the sections of the foundation slab has made it possible to conclude that the calculations of the temperature fields and, as a consequence, possible temperature deformations are correct.

QUALITY CONTROL OF SPRACONCRETE AND POSSIBLE PROBLEMS DURING SHOTCRETING

Shotcrete is a modern technology for protecting the excavations in solid rock masses and it is a process where the concrete mass is applied to the surface by means of high pressure. The installation of sprayed concrete requires special equipment, also a lot of attention and well-trained workers. For that purpose, quality controls are performed during each installation of the shotcrete. In order to ensure that the requirements are met, there is: small, normal and more extensive quality control. The frequency of the tests is determined depending on the concrete, the difficulties of installation, the type of the object, etc. Quality control is done before and after the installation of sprayed concrete. Thus, the test for the temperature of the concrete is done in every 100 m³, the thickness of the torque and the compressive strength are measured every 250 m³ of built-in sprayed concrete. However, the conditions prescribed by the project are not always met. Therefore, problems are possible when using this modern technology for protection of excavations. Such problems can occur in various stages, such as: during the preparation, during the installation and after the installation, as well as possible problems caused by the equipment and workers. To eliminate them or minimize them, attention should be paid to several key things, including the period of incorporation of the wet mixture. If the shotcreting is not completed within 2 hours, the hydration process begins, which complicates the work.

Экстрактовые масла Acacia dealbata Link. для элитной парфюмерной продукции

The aim of this survey was to find the best way for the extraction of essential oils from the Acacia dealbata Link. floral raw materials, as well as discover samples of elite perfumery products of various brands that use this aroma in perfumery compositions. Two methods of extraction with a volatile hydrocarbon solvent were used, namely, 1) Soxhlet extraction; 2) extraction of raw materials by the method of triple infusion in a solvent at a low positive temperature (+ 3 °C). To obtain absolute, concrete was extracted in a classical manner. In the first variant, the yield of concrete was 1.46 % of the weight of raw materials; in the second – 1.18 % but its aroma was more delicate. The content of absolute in the samples was 28.4 % and 24.6 % of the concrete mass, respectively. Famous brands using mimosa fragrance are L`Artisan Parfumeur (Mimosa Pour Moi), Jo Malone (Mimosa & Cardamom), Dolce & Gabbana (Velvet Mimosa Bloom), Calvin Klein (Eternity Summer), Kenzo (Summer by Kenzo), etc.

The increase in turnover of steel-teeming ladles with a combined lining at the steelmaking production in OJSC «BSW – Management Company of Holding «BMC»

Currently, there is a need to increase the turnover of steel-teeming ladles ESPC-1,2, in connection with which the actual question was to reduce the duration of preparation of steel ladles to work. On steel ladles with a combined lining, one of the solution to this problem is to reduce the duration of drying and heating of the concrete working lining, but there is a risk of «undermining» the concrete mass due to the rapid warming of temperature. During the tests of the concrete mass from the manufacturer «A» for the period 2016–2018 the duration of drying and heating was reduced from 52 to 37 hours. Average overhaul life and durability of the concrete lining has increased by 37% and amounted to 96 meltings.

Knitted Meshes for Reinforcing Building Composites

Modern technical textiles, including knitted fabrics, are widely used in the construction industry. Regarding textiles in concrete reinforcement, methods based on shredded fibres, meshes, reinforcing mats, woven textiles and knitted DOStapes are frequently used as underlays of concrete constructions. Textiles are also used in the reinforcement of fibrous FRP composites. The research presented focused on producing composites made of MapeiMapefill concrete mass with reinforcement in the form of three variants of knitted meshes made of 228 tex polyamide threads, polypropylene threads of 6.3 tex and 203 tex glass threads, as well as identification of their mechanical properties. The mesh variant made of glass fibre is especially noteworthy, as its strength is more than three times higher than that of polyamide meshes. At the same time, a very small relative elongation of 3% is observed for this variant of knitted fabric, which is a desired property regarding the comparatively low stretching extension of concrete. In the process of making the composites, the adhesion of the concrete mass to the surface of the threads was analyzed. For this purpose, a "Sopro HE449" type agent was used. Composite beams were subjected to a three-point bending strength analysis on a testing machine. The results of strength measurements of the composites obtained prove that those with glass fibres demonstrate a threefold increase in strength compared to the original concrete beam.

Influence factors on the temperature field in a mass concrete

In construction practice of concrete mass needs a large amount of concrete. Due to the small surface area to volume ratio, the concrete mass is often happening thermal cracking caused by the release of heat during the hydration of the cement. The causes of thermal cracking in concrete mass are complex but the main reason is the increase in temperature in the concrete structure. Provide measures to control the maximum temperature concrete mass is very absolutely necessary. A finite element model of the concrete mass was established by the software Midas civil, the temperature field in the concrete mass has been determined and a mathematical model was created that adequately describes the influence factors on the temperature field in a concrete mass such as unit cement content, cement maximum heat released, the placing temperature of concrete and the water temperature in order to determine the optimal parameters.