Investigation of the dispersed composition of dust of inert materials exposed to overload in the manufacture of building materials

At enterprises for the manufacture of building materials, when pouring bulk components, there is an intense emission of dust into the air of the working area of the room. The article presents the results of the dispersed analysis of dust when pouring cement, crushed stone, silicate bricks and chalk, and the integral functions of the distribution of dust particles by diameter are constructed. According to the criteria of Lyashchenko and Reynolds, the results of the sedimentation rate of dust particles were theoretically obtained. Measures are given to reduce the dust content of the air in the working area of the shop.

Dust Emission from Gobi under Different Dust Content Conditions: A Wind Tunnel Study atop the Mogao Grottoes

Dust emission from the Gobi desert is one of the major sources of global atmospheric aerosols. However, the main factors affecting dust emission from Gobi remain poorly understood. In this paper, field wind tunnel experiments were performed atop the Mogao Grottoes to determine the variation characteristics of the vertical dust flux (F) of particulate matter less than 10 μm (PM10) for Gobi surfaces with different dust content and wind speeds under external sand supply. The results demonstrate that F obeyed a power function with increasing friction velocity (U∗), and increased exponentially with the increasing surface dust content (C). The index of n-value in the formula F∝U∗n is taken in the range of 2.02–2.63 under the surface of 27.3–47.3% dust content (<100 µm), and the dust emission rate was significantly enhanced when the surface dust content exceeded approximately 37%. This study indicates that wind force is the primary dynamic condition affecting Gobi dust emission, and that surface dust content is a significant factor in determining the quantity of dust emission. Furthermore, the contribution of wind force to PM10 emission is greater than the surface dust content, and the higher the height, the greater the weight of friction velocity.

Utilization of Quarry Dust as a Partial Replacement of Sand in Concrete Making

The use of crushed quarry dust as a partial replacement of river sand in concrete production was investigated in this study. This is expedient as quarry dust can be available at some locations with insufficient river sand for construction purposes. The use of quarry dust is also in concrete is also a measure necessary for improvement of concrete strength. River sand was replaced with quarry dust for different mix designs of concrete for 0% to 25% replacement levels with 5% intervals. The physical properties of river sand and quarry dust were tested and reported and the workability as well as compressive strengths of the concrete mixtures were also tested. It was observed that the slump values increased with increase in percentage replacement of sand with quarry dust. The compressive strength of cubes at 28 day curing for control mixture of 1:3:6 at 0% partial replacement of river sand with quarry dust was 12.6N/mm2 but compressive strengths of 21.5 N/mm2 and 26.0 N/mm2 were gotten for 1:2:4 concrete and 1:1.5:3 concrete respectively. As the quarry dust content increased to 25%, the 28day compressive strength increased to 13.58 N/mm2 and 21.57 N/mm2 for the 1:3:6 and 1:2:4 mixes respectively. Compressive strength values decreased to a value of 25.72N/mm2 for the 1:1.5:3 concrete mix. The maximum compressive strength values were reached at 20% quarry dust content at the age of 28 days for the three concrete grades investigated. The increase in compressive strength with inclusion of quarry dust was attributed to the higher specific gravity of quarry dust above river sand. The compressive strength of quarry dust concrete continued to increase with age for all the percentages of quarry dust contents. Quarry dust was recommended as a suitable partial replacement for river bed sand in concrete production.

Research and Analysis of the Sources of Emission of Respirable Fraction of Dust at the Coal Mines

At the deposits of the Krasnoyarsk Territory, the actual concentration of the suspended dust is 60–83 mg/m3. The search for efficient ways of reducing dust emission and dust suppression remains an urgent task, since fine dust has a negative effect on the health of enterprise employees and on mining equipment reducing its service life. Full-scale measurements were conducted related to the dust content and dispersed composition of the aerosols. The dust content was measured by counting method with the use of CEM DT-9880 dust particle counter. The measurements were conducted at the points located at different distances from the road of the section. The content of the most dangerous fraction PM2.5 was 48 % of the total amount of fine dust or 30–40 mg/m3, while the maximum permissible concentration for this fraction is 0.16 mg/m3. The employees who constantly work near the automotive haul roads and the ruins of an exploded rock mass are exposed to the strongest effects of dust emissions on the respiratory organs. To reduce the dust load on the employees of the mining enterprise, it is most appropriate to deal primarily with the dust emitted from the open pit roads, since this will help to reduce the dust load by 30–40 %. The permissible length of service for the operator of the loading equipment of one of the open-pit mines of the Krasnoyarsk Territory was calculated: it will be 9 years, and not 17, as was obtained earlier — without considering the actual content of the respirable dust. With the most rational parameters of drilling and blasting operations and using all methods to reduce dust formation, it is possible to reduce the dust emission by 15–20 %.

THE USE OF QUARRY DUST FOR PARTIAL REPLACEMENT OF CEMENT IN CEMENT-SAND MORTAR

This research was carried out to investigate the effect of partially replacing cement with quarry dust in cement-sand mortar. Tests including setting times, water absorption, compressive strength and density test were carried out on mortar with cement partially replaced with 0%, 5%, 10%, 15%, 20%, 25% and 30% quarry dust and presented. Experimental results show that replacement of quarry dust as partial replacement of cement in cement-sand mortar decrease the initial and final setting times of cement paste and increase the water absorption of the mortar. The partial replacement shows an improvement of compressive strength at 5% quarry dust content after which there is a decrease with increase in quarry dust content at all the ages. The increase in compressive strength at 5% indicates possible pozzalanic activity at that level. Thus quarry dust can be utilized as cement replacement material at 5% dust content. Above this it can be utilized as fine aggregate replacement for use in low-strength mortar applications

The Cold Dust Content of the Nearby Galaxies IC 5325, NGC 7496, NGC 7590, and NGC 7599

Star-forming galaxies are rich reservoirs of dust, both warm and cold. But the cold dust emission is faint alongside the relatively bright and ubiquitous warm dust emission. Recently, evidence for a very cold dust component has also been revealed via millimeter/submillimeter photometry of some galaxies. This component, despite being the most massive of the three dust components in star-forming galaxies, is by virtue of its very low temperature, faint and hard to detect together with the relatively bright emission from warmer dust. Here we analyze the dust content of a carefully selected sample of four galaxies detected by IRAS, WISE, and SPT, whose spectral energy distributions (SEDs) were modeled to constrain their potential cold dust content. Low-frequency radio observations using the GMRT were carried out to segregate cold dust emission from non-thermal emission in millimeter/submillimeter wavebands. We also carried out AstroSat/UVIT observations for some galaxies to constrain their SED at shorter wavelengths so as to enforce energy balance for the SED modeling. We constructed their SEDs across a vast wavelength range (extending from ultraviolet to radio frequencies) by assembling global photometry from GALEX FUV+NUV, UVIT, Johnson BRI, 2MASS, WISE, IRAC, IRAS, AKARI, ISOPHOT, Planck HFI, SPT, and GMRT. The SEDs were modeled with CIGALE to estimate their basic properties, in particular to constrain the masses of their total and very cold dust components. Although the galaxies’ dust masses are dominated by warmer dust, there are hints of very cold dust in two of the targets, NGC 7496 and NGC 7590.

Characterizing the dust content of disk substructures in TW Hydrae

Context. A key piece of information to understand the origin and role of protoplanetary disk substructures is their dust content. In particular, disk substructures associated with gas pressure bumps can work as dust traps, accumulating grains and reaching the necessary conditions to trigger the streaming instability. Aims. In order to shed some light on the origin and role that disk substructures play in planet formation, we aim to characterize the dust content of substructures in the disk of TW Hya. Methods. We present Atacama Large Millimeter Array (ALMA) observations of TW Hya at 3.1 mm with ~50 milliarcsecond resolution. These new data were combined with archival high angular resolution ALMA observations at 0.87, 1.3, and 2.1 mm. We analyze these multiwavelength data to infer a disk radial profile of the dust surface density, maximum particle size, and slope of the particle size distribution. Results. Most previously known annular substructures in the disk of TW Hya are resolved at the four wavelengths. Inside the inner 3 au cavity, the 2.1 and 3.1 mm images show a compact source of free–free emission, likely associated with an ionized jet. Our multiwavelength analysis of the dust emission shows that the maximum particle size in the disk of TW Hya is >1 mm. The inner 20 au are completely optically thick at all four bands, which results in the data tracing different disk heights at different wavelengths. Coupled with the effects of dust settling, this prevents the derivation of accurate density and grain size estimates in these regions. At r > 20 au, we find evidence of the accumulation of large dust particles at the position of the bright rings, indicating that these are working as dust traps. The total dust mass in the disk is between 250 and 330 M⊕, which represents a gas-to-dust mass ratio between 50 and 70. Our mass measurement is a factor of 4.5–5.9 higher than the mass that one would estimate using the typical assumptions of large demographic surveys. Conclusions. Our results indicate that the ring substructures in TW Hya are ideal locations to trigger the streaming instability and form new generations of planetesimals.