Analitic Investigation of the Regularities of Changing Dust Concentration During the Abrasive Decrease of Stone Structures

In the process of repair or restoration of building structures, it is often necessary to strengthen building structures from limestone-shell rock, concrete, reinforced concrete, hard materials-granite, basalt, etc. by cutting or making cuts of the required size with detachable circles of synthetic diamond and cubic boron nitride (CA and CBN)The cutting process is accompanied by considerable dust formation, which can be both harmful and dangerous factor in the work.The aim of the work is studying the process of dust sedimentation and the regularity of the change in dust concentration during the abrasive cutting of concrete and stone materials.Mathematical models have been developed – dust emission from under the wheel, speed of sedimentation of dust particles depending on their material, size and shape, and also depending on temperature, pressure and humidity, the concentration of dust in the working space and the concentration change during the cutting cycle are calculated.It is shown that the velocity of the sedimentation of particles depends significantly on the shape. The higher the sphericity, the higher the sedimentation rate. The ambient temperature has little effect on the sedimentation rate, in the temperature range (-20 → + 40 °C) at which the operation takes place.The sedimentation rate of dust particles generated by cutting the most common building stone materials also differs slightly. Almost the same sedimentation rate has dust particles obtained by cutting basalt and concrete. A bit higher is the sedimentation rate of particles from granite.The sedimentation rate of particles of generated dust is about 600-700 cm/h or 10-11 cm/min for particles measuring 6 μm. This means that at a production height of about 2 m (200 cm) during the operating cycle (about 3 min), the dust will remain at an altitude of about 1.5 m, i.е. practically remains in the working area. This gives grounds to assert about a high concentration of dust during the cutting cycle (about 4.8 108/m3)

Investigation of the Formation Process of Hazardous and Harmful Production Factors When Cutting a Stone for Construction Works

Stone cutting for construction work is carried out by disk diamond wheels the rotation speed of which, and, consequently, the cutting speed is 35-50 m/s. In view of the high intensity of the cutting process and intensive microchip formation, the process of stone cutting is accompanied by considerable dust formation, which can be both harmful and dangerous in the work.The greatest danger is represented by dust particles, which dimensions are 5 μm or less. These particles have the greatest pathogenic effect on the respiratory system of the human body. In addition, the settling time of these particles is measured in hours. Thus, even after the termination of work, the risk of dust exposure to the human body remains. Insignificant time of inhalation of these particles can lead a person to disability and death. Insurance payments in case of disability and compensation in case of death of an employee for these reasons all over the world amount to multibillion sums, which, even for this reason, makes the issue of combating this phenomenon very urgent.In this paper, the process of generation of hazardous and harmful production factors arising as a result of dust formation during the stone cutting, the regularity of dust distribution by fractions, quantitative indicators of the process for improving equipment, as well as individual and collective means of personnel protection are determined. The shape and dimensions of the cutting grains of the cutting discs are studied in the paper, depending on the grain material and the grain size of the cutting disc. Thecurvature radii of the cutting grains depend on the grain material and the grain size of the cutting disc. The actual number of grains participating in cutting and, consequently, in dust formation is shown.The dimensions of the dust particles depend on the graininess of the cutting discs and the processing regimes. Using the law of normal particle size distribution, the percentage of dust particles is determined depending on processing conditions. The rate of particle settling depends on their size and mass. The formation of a dust-air mixture and its probable concentration and chemical composition of dust depend on the chemical composition of the cutting materials.Regularities are obtained, which can give an opportunity to improve the individual and collective protection of workers from this harmful production factor

A new shock tube configuration for studying dust-lifting during the initiation of a coal dust explosion

The traditional defence against propagating coal dust explosions is the application of dry stone dust. This proven and effective safety measure is strictly regulated based on extensive international experience. While new products, such as foamed stone dust, offer significant practical benefits, no benchmark tests currently exist to certify their dust lifting performance in comparison to dry stone dust. This paper reviews the coal dust explosion mechanism, and argues that benchmark testing should focus on dust lifting during the initial development of the explosion, prior to arrival of the flame. In a practical context, this requires the generation of shock waves with Mach numbers ranging from 1.05 to 1.4, and test times of the order of 10’s to 100’s of milliseconds. These proposed test times are significantly longer than previous laboratory studies, however, for certification purposes, it is argued that the dust lifting behaviour should be examined over the full timescales of an actual explosion scenario. These conditions can be accurately targeted using a shock tube at length scales of approximately 50 m. It is further proposed that useful test time can be maximised if an appropriately sized orifice plate is fitted to the tube exit, an arrangement which also offers practical advantages for testing. The paper demonstrates this operating capability with proof-of-concept experiments using The University of Queensland’s X3 impulse facility

THE PERFORMANCE EVALUATION OF HOT ROLLED ASPHALT MIXED WITH SAWDUST ASH AS A FILLER1

ABSTRACT There are two methods of mixing hot asphalt (Hotmix) applied in Indonesia; those are AAHSTO (American Method) using Asphalt Concrete (AC) system and British Standard (British Method) using Hot Rolled Asphalt (HRA) system. Some p;roblems appeared when both methods are implemented in Indonesia. The problems of Asphalt Concrete System are cracking and brittle while HRA system bleeding are often happened. HRA asphalting system is also often called as gap gradation asphalting which relies on the strength and adhesiveness of fine aggregate. Filler is one of the important fine aggregate components. The materials of filler can be cement, refined stone (ash of stone), slag etc. However, this kind of filler has higher economical value and is very limited in quantity. Therefore, innovations and research in needed to find the economical filler material. The research is aimed to study and evaluate the performance of mixture of HRA and sawdust filler and compare to the mixture with standard filler (stone ash). In this research, the composition of each filler used in the mixture are 100% of stone dust, 50% of stone dust – 50% of sawdust, and 100% of sawdust. The research indicated that the mixture of asphalt and filler of 100% sawdust really has the worst mixing characteristics value, while the mixture of asphalt and filler of stone dust and sawdust with the content of each 50% - 50% can give characteristics value approaching to the mixture of asphalt and 100% stone dust filler, even though it has more content of asphalt. Is is also indicated that in the optimum content of asphalt to all mixtures of asphalt is the same as the optimum asphalt content of 100% stone dust as much as 6.65%, so to the mixture of asphalt by using sawdust filler either part of it (50%) or the whole (100%), the characteristics with the one using 100% stone dust filler is still better. The mixture using 100% sawdust filler is not recommended for heavy traffic, because it may be bleeding will be experienced, while the mixture using filler of 50% stone dust – 50% sawdust have to be further studied to find the best composition, since its structural values obtained nearly approaches the standard mixture (filler of 100% stone dust). Further test have to be concerned and especially its durability and permeabilit

Designing and Validating The Persian Version of a Questionnaire for Estimating Exposure to Occupational Dust among Stone Carving and Stone Cutting Workers

Introduction: The accurate amount of stone carvers' exposure to dust cannot be always measured with dust measuring devices. In this study, the researchers tried to estimate long term exposure of stone carving workers to dust by using a researcher- made questionnaire. Methods: Stone carving workshops in Kerman, Iran were visited and after obtaining informed consent, the researcher-made questionnaire was completed for each worker. The questionnaire included 46 questions in 4 sections. Experts from Iran and abroad cooperated in confirming the face and content validity and according to their comments the questionnaire was validated in two stages. In order to prove the construct validity of the questionnaire, the scores of dust exposure and respiratory symptoms were compared. The reliability was determined by test-retest and calculating R-Cronbach. Results: Finally, 27 questions were approved for the final questionnaire. The reliability of the questionnaire was r=0.954, P<0.001 according to test retest and 0.80 according to Kappa. Internal reliability of the questionnaire was 0.86. Construct validity was confirmed and those who had higher exposure to dust showed significantly more respiratory symptoms. Conclusion: With regard to the acceptable reliability and validity, this questionnaire can be used to estimate the amount of exposure to dust in stone carving workers

Dust crystallinity in protoplanetary disks: the effect of diffusion/viscosity ratio

The process of turbulent radial mixing in protoplanetary disks has strong relevance to the analysis of the spatial distribution of crystalline dust species in disks around young stars and to studies of the composition of meteorites and comets in our own solar system. A debate has gone on in the recent literature on the ratio of the effective viscosity coefficient $\nu$ (responsible for accretion) to the turbulent diffusion coefficient $D$ (responsible for mixing). Numerical magneto-hydrodynamic simulations have yielded values between $\nu/D\simeq 10$ (Carballido, Stone & Pringle, 2005) and $\nu/D\simeq 0.85$ (Johansen & Klahr, 2005}). Here we present two analytic arguments for the ratio $\nu/D=1/3$ which are based on elegant, though strongly simplified assumptions. We argue that whichever of these numbers comes closest to reality may be determined {\em observationally} by using spatially resolved mid-infrared measurements of protoplanetary disks around Herbig stars. If meridional flows are present in the disk, then we expect less abundance of crystalline dust in the surface layers, a prediction which can likewise be observationally tested with mid-infrared interferometers.Comment: 9 pages, 5 figures, accepted for publication in A&

A comparison of the results from intra-pleural and intra-peritoneal studies with those from inhalation and intratracheal tests for the assessment of pulmonary responses to inhalable dusts and fibres.

The aim of this paper is to compare results from inhalation studies with those from intraperitoneal and intrapleural tests, where available, for a number of fibrous and particulate test materials. The objective is to determine how well intraperitoneal/intrapleural studies predict the pathological responses observed in more standard in vivo studies of pulmonary toxicity, with a particular focus on carcinogenicity. Published toxicity data was obtained for a number of materials including asbestos, wollastonite, MMVFs (including glass fibres, stone wools and RCF), silicon carbide whiskers, potassium octatitanate, quartz, kevlar, polypropylene and titanium dioxide. For some of the fibrous material reviewed, there is conformity between the results of intraperitoneal and inhalation tests such that they are either consistently positive or consistently negative. For the remaining fibrous materials reviewed, intraperitoneal and inhalation tests give different results, with positive results in the intraperitoneal test not being reflected by positive inhalation results. It is suggested that the intraperitoneal test can be used to exonerate a dust or fibre (because if negative in the intraperitoneal test it is extremely unlikely to be positive in either inhalation or intratracheal tests) but should not be used to positively determine that a dust or fibre is carcinogenic by inhalation. We would argue against the use of intraperitoneal tests for human health risk assessment except perhaps for the purpose of exoneration of a material from classification as a carcinogen.Peer reviewedFinal Accepted Versio

Can dust coagulation trigger streaming instability?

Streaming instability can be a very efficient way of overcoming growth and drift barriers to planetesimal formation. However, it was shown that strong clumping, which leads to planetesimal formation, requires a considerable number of large grains. State-of-the-art streaming instability models do not take into account realistic size distributions resulting from the collisional evolution of dust. We investigate whether a sufficient quantity of large aggregates can be produced by sticking and what the interplay of dust coagulation and planetesimal formation is. We develop a semi-analytical prescription of planetesimal formation by streaming instability and implement it in our dust coagulation code based on the Monte Carlo algorithm with the representative particles approach. We find that planetesimal formation by streaming instability may preferentially work outside the snow line, where sticky icy aggregates are present. The efficiency of the process depends strongly on local dust abundance and radial pressure gradient, and requires a super-solar metallicity. If planetesimal formation is possible, the dust coagulation and settling typically need ~100 orbits to produce sufficiently large and settled grains and planetesimal formation lasts another ~1000 orbits. We present a simple analytical model that computes the amount of dust that can be turned into planetesimals given the parameters of the disk model.Comment: 12 pages, 6 figures, 1 table, accepted for publication in A&A (minor corrections with respect to v1