INTRODUCTION
Nowadays Silica Fume is Broadly Employed for Generating Substantial Strong concrete for structures Especially Subjected To someggressive environments, For Example marine structures.
It is Coupled with Ordinary Portland Cement OPC (or portland cement Sort I In accordance ASTM C150) Like a substitution for sulfate resistance cement (cement Sort V In accordance ASTM C150) in Generating sulfate resistance concrete.
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* Routes of Exposure
Exposure to welding fumes can occur through inhalation and eye contact.
* Summary of toxicology
1. Effects on Animals: Welding fumes can cause non-specific changes in the lungs; in addition, there is limited evidence for genotoxicity in in vitro test systems. Rats exposed by inhalation or intratracheal instillation of welding fumes from mild-steel welding showed non- specific pulmonary changes with no signs of fibrosis over a period of 450 days [IARC 1990]. The primary effects observed included particle- laden macrophage aggregates, and alveolar epithelial thickening with proliferation of granular pneumocytes [IARC 1990]. Similar changes were observed in the lungs of rats exposed to 1,000 mg/m(3) for 1 hour or to 400 mg/m(3) for 30 minutes/day, six days/week over a two-week period [IARC 1990]. Welding fumes were not associated with an increased incidence of genotoxicity in 11 of 15 in vitro assays, and in all three in vivo tests performed for genotoxicity [IARC 1990].
2. Effects on Humans: Exposure to welding fumes from mild steel is associated with the development of a benign pneumoconiosis, "arc welder's siderosis". This condition is a reversible pneumoconiosis and no associated respiratory signs may be present at the time the pneumoconiosis is discovered [Rom 1992]. Respiratory impairment has been observed in workers exposed to mild steel welding fumes, but these impairments may be the result of exposure to other toxicants in the working environment, such as crystalline silica [Rom 1992]. Exposure to welding fumes can result in metal fume fever; this condition resembles influenza and is characterized by fever, chills, headache, nausea, shortness of breath, muscle pain, and a metallic taste in the mouth [Rom 1992]. The respiratory effects appear to be potentiated by smoking. There is an excess of infertility among welders that led to studies on sperm quality and welding exposures. There appears to be an increased frequency of abnormalities in semen quality associated with duration of exposure. Abnormalities were highest among stainless steel welders. While hypotheses exist, the mechanism of action resulting in infertility is not known [Rom 1992; IARC 1990]. IARC concluded that there is limited evidence in humans for the carcinogenicity of welding fumes and gases [IARC 1990]. This conclusion was based primarily on a review of 11 cohort studies and 12 case-control studies on lung cancer; only three of these studies (all cohort studies) specifically examined manual metal arc welding of iron, mild steel, or aluminum. Two of the cohort studies found no association between welding fumes and cancer. The remaining cohort studies showed an increased risk for lung cancer, which in some may have been inflated due to selection bias. Ten out of twelve case- control studies showed an association between lung cancer and exposure or employment as a welder. Two of the studies found no risk [IARC 1990]. IARC's final conclusion was that welding fumes are possibly carcinogenic to humans [IARC 1990].
* Signs and symptoms of exposure
1. Acute exposure: Acute exposure to welding fumes can result eye, nose, and throat irritation, fever, chills, headache, nausea, shortness of breath, muscle pain, and a metallic taste in the mouth.
2. Chronic exposure: Chronic exposure to welding fumes can result in respiratory effects including coughing, wheezing, and decreased pulmonary function.
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ALUMINUM
CASRN: 7429-90-5
http://toxnet.nlm.nih.gov/cgi-bin/sis/se…
Human Health Effects:
Toxicity Summary:
IDENTIFICATION: Aluminum is a silvery-white, ductile and malleable metal. It is released to the environment both by natural processes and from anthropogenic sources. It is highly concentrated in soil-derived dusts from such activities as mining and agriculture, and in particulate matter from coal combustion. Aluminum occurs ubiquitously in the environment in the form of silicates, oxides and hydroxides, combined with other elements such as sodium and fluorine and as complexes with organic matter. It is not found as a free metal because of its reactivity. Aluminum metal has a wide variety of uses, including structural materials in construction, automobiles and aircraft, and the production of metal alloys. Aluminum compounds and materials also have a wide variety of uses, including production of glass, ceramics, rubber, wood preservatives, pharmaceuticals and waterproofing textiles. Natural aluminum minerals, especially bentonite and zeolite, are used in water purification, sugar refining, brewing and paper industries. HUMAN EXPOSURE: Non-occupational human exposure to aluminum in the environment is primarily through ingestion of food and water. No acute pathogenic effects in the general population have been described after exposure to aluminum. Although it has been hypothesized that aluminum is a risk factor for Alzheimer's disease, present epidemiological evidence does not support a causal association between Alzheimer's disease and aluminum in drinking-water. Neurological syndromes including impairment of cognitive function, motor dysfunction and peripheral neuropathy have been reported in limited studies of workers exposed to aluminum fume. Iatrogenic exposure in patients with chronic renal failure, exposed to aluminum-containing dialysis fluids and pharmaceutical products, may cause encephalopathy, vitamin-D-resistant osteomalacia and microcytic anemia. Premature infants may develop increased tissue loading of aluminum, particularly in bone, when exposed to iatrogenic sources of aluminum. Although human exposure to aluminum is widespread, in only a few cases has hypersensitivity been reported following exposure to some aluminum compounds after dermal application or parenteral administration. There is insufficient information to allow for classification of the cancer risk from human exposures to aluminum and its compounds. Aluminum and its compounds appear to be poorly absorbed in humans. The mechanism of gastrointestinal absorption of aluminum has not yet been fully elucidated. The highest levels of aluminum may be found in the lungs, where it may be present as inhaled insoluble particles. The urine is the most important route of aluminum excretion. ANIMAL STUDIES: The acute toxicity of metallic aluminum and aluminum compounds is low. In short-term studies using rats, mice or dogs to various aluminum compounds in the diet or drinking-water, only minimal effects were observed at the highest administered doses. Adequate inhalation studies were not identified. Following intratracheal administration of aluminum oxide, particle-associated fibrosis was observed. No overt fetotoxicity was noted, nore were general reproductive parameters noted after gavage treatment of rats. There is no indication that aluminum is carcinogenic. It can form complexes with DNA and cross-link chromosomal proteins and DNA, but it has not been shown to be mutagenic in bacteria or induce mutation or transformation in mammalian cells in vitro. Chromosomal aberrations have been observed in bone marrow cells of exposed mice and rats. There is considerable evidence that aluminum is neurotoxic in experimental animals, although there is considerable variation among species. In susceptible species, toxicity following parenteral administration is characterized by progressive neurological impairment, resulting in death with status epilepticus. Osteomalacia, as it presents in man, is observed consistently in larger species (e.g. dogs and pigs) exposed to aluminum; a similar condition is observed in rodents. Absorption via the gastrointestinal tract is usually less than one percent. Aluminum is distributed in most organs within the body with accumulation occurring mainly in bone at high dose levels. To a limited extent, aluminum passes the blood-brain barrier and is also distributed to the fetus. Aluminum is eliminated effectively by urine.
[World Health Organization/International Programme on Chemical Safety. Environmental Health Criteria 194. Aluminium. pp. 1-13 (1997)]**PEER REVIEWED**
Human Toxicity Excerpts:
PRODUCTION PROCESS
Silica Fume Is Truly a by Merchandise Belonging For the silicone and ferro silicone industry.
It Final results From your Decline of quartize to silicone Generating use of Decent Big Excellent charcoal In then Electrical arc furnace.
Furnaces rotate Gradually Circular carbon electrodes. These Generate Electrical arcs deep While in the furnace and Therefore the Substantial Temperatures Necessary to Generate molten silicon.
The Away gLike Along with Oxygen drawn in Covering the furnace is exhausted by Big fans For the baghouse. The Silica Fume Lower into filter bIn thelong with are conveyed to silos.
Silica fume particles Common Dimension is 0.1 micron. These particles are Therefore 100 Instances finer than a grain of cement.
By blowing Oxygen Covering the Silica Fume While in the silo, the particles will touch other particles Along with adhere For them by Surface Region forces. This can be Basic principle of densification for Generating Densified Silica Fume, A Great deal A Whole lot more Sensible and Quick To make use of in concrete.
SPECIFICATIONS FOR Generating use of IN Substantial Strong CONCRETE:
The Specifications for Utilized in concrete are Often Offered When it Arrives to:
SiO2 content: Minimal specified of 85%
SiO3 content: Optimum of 1%
Loss on Ignition: Optimum of 6%
Moisture Content: Optimum of 3%
The SiO2 Minimal Articles will Restrict the Volume of impurities and contaminants While in the Silica Fume. The SiO3 is Limited to Restrict the expansion Anticipated For the Creation of ettringite. Moisture Articles of Silica Fume Residing the furnace is Often negligible. The 3% Restrict is generous And is also Most likely Being exceed with Bad storage. The Common Specification for Use in Hydraulic Cement Concrete Is Truly aSTM C1240.
MAIn theDVANTAGES OF USE FOR CONSTRUCTION
The Substance Continues to be Applied all Covering the earth For a Great deal of Many years While in the Region In which Substantial Durability and Strong concrete Have been required.
A Specific know-how is Necessary for Generating Decent concrete. Simply state, the Refreshing concrete Should Possess a consistency This kind of Which it Might be transported, Positioned and compacted With Out there Website Gear With no segregation. The use in Mixture with superplasticiser (for Enhance the dispersion of cement and Therefore Significantly Decrease the Drinking water demand) Continues to be specified Around the world for Generating Decent Big Excellent concrete. This Aid To Even more Enhance the Features of The two Refreshing and Difficult concrete.
