LYCOS RETRIEVER 
Asbestos
built 658 days ago
Asbestos-cement is a composite material that consists of portland cement reinforced with asbestos fibers. Before the combination of asbestos and cement, these constituent materials were utilized independently for commercial use. Asbestos tended to be too coarse and abrasive to be useful by itself, which led to diverse and popular composite mixtures beginning in the 1880s. Many experiments with asbestos fibers resulted in a variety of mixtures; ... the combination of asbestos and cement (typically portland) proved most useful in the building industry. The proportion of cement to asbestos fibers varied over a range of ten to seventy-five percent by weight, depending on the desired characteristic.1 The portland cement matrix ultimately binds the fibers of asbestos into a hard mass, which is a durable material, mechanically and chemically compatible with the fibers.
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Asbestos is a catch-all term for a variety of different minerals which have a wide range of uses. The word "asbestos" is derived from Greek words meaning "not extinguishable"; asbestos is extremely resistant to fire and heat. All forms of asbestos are fibrous, meaning that asbestos strands can be extracted from the rock and woven and spun much like cotton or other conventional fabrics. In addition to being fireproof and weavable into cloth, asbestos is an outstanding insulator, has high tensile strength, and is chemically stable. The combination of these unusual properties led to the use of asbestos in an enormous variety of household and industrial applications from ancient times; asbestos has been in use for more than two thousand years.
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Asbestos has no odor and can not be identified by visual observation. There are some common products that were produced over the years that may contain asbestos (such as 9"x9" floor tile which contains asbestos 95% of the time). Visual inspection can not determine if there are asbestos fibers in it. Asbestos fibers are very small and some times invisible to the human eye. As a result, microscopic analysis is the only way to determine if a product contains or does not contain asbestos. Polarized Light Microscopy (PLM) and Scanning Electron Microscopy (SEM) are the only two approved methods of analysis to determine asbestos content in a material. PLM is the US EPA accepted method.
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Asbestos fibers have special characteristics. Heat or chemicals do not affect them and they do not conduct electricity. Asbestos is ... very strong. Pound for pound, asbestos is stronger than steel. Asbestos fibers are also very flexible, allowing them to be woven into cloth-like materials. This versatility is why industry has mined and widely used asbestos to make many different products.
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Asbestos was mined and used commercially in North America beginning in the late 1800s. Its use increased greatly during World War II (3, 4). Since then, asbestos has been used in many industries. For example, the building and construction industry has used it for strengthening cement and plastics as well as for insulation, roofing, fireproofing, and sound absorption. The shipbuilding industry has used asbestos to insulate boilers, steampipes, and hot water pipes. The automotive industry uses asbestos in vehicle brakeshoes and clutch pads.
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Asbestos-cement siding shingles imitated wood siding shingles in shape and appearance, typically available in sizes of twelve by twenty-four inches. These shingles originally came in nondescript tones like gray-green, gray-pink, and Dover white. Textures such as grooved, wood-grained, or smooth were pressed into the large asbestos-cement sheets, then cut to the profile of the design, such as Tapertex (flat horizontal lines), Thatched, or Waveline. They were usually predrilled for ease of installation with two to three nails on the bottom of each shingle to secure the panels to the sheathing. Installation was executed from the bottom up. As one row of shingles was nailed, the bottom lip would secure the top of the shingle from the row below (Figure 4).14 This construction technique allowed ease in replacing shingles, unlike wood or slate shingles that were secured at the top of each shingle.
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