Cement board is composed of aggregated portland cement with a glass-fiber mesh on the surfaces. This 5/16 inch (7.9 mm) thick cement board is designed as an underlayment for tile floors. These are 3 by 5 foot (91 by 152 cm) sheets manufactured by the United States Gypsum Company under the DUROCK brand name. In Europe, the board is manufactured by Etex group and has the Hydropanel brand name - www.hydropanel.com
A cement board is a combination of cement and glass fibers formed into 4 foot by 8 foot sheets, 1/4 to 1/2 inch thick that are typically used as a tile backing board. Cement board can be nailed or screwed to wood or steel studs to create a substrate for vertical tile and attached horizontally to plywood for tile floors, kitchen counters and backsplashes. It can be used on the exterior of buildings as a base for exterior plaster (stucco) systems and sometimes as the finish system itself.
Cement board offers an extremely stable, strong bond for most tile mortars and any materials that use cement based materials to create a finish bond. Cement board also adds impact resistance and strength to the wall surface as compared to water resistant gypsum boards. Cement board is also fabricated in thin sheets with polymer modified cements to allow bending for curved surfaces.
As a tile backing board, cement board has better long-term performance than paper-faced gypsum core products because it will not mold, mildew or physically break down in the continued presence of moisture or leaks. Cement board is not actually waterproof, but it is highly resistant to absorbing moisture and has excellent drying properties. In areas continually exposed to water spray (i.e showers) a waterproofing barrier is usually recommended behind the boards or as a trowel-applied product to the face of the boards behind the finish system.
One major disadvantage of cement board is the weight per square foot. It is approximately twice that of gypsum board, making handling by one person difficult. Cutting of cement board must also be done with carbide-tipped tools and saw blades. Due to its hardness, pre-drilling of fasteners is often recommended. Finally, cement board is initially more expensive than water resistant gypsum board but may provide better long term value.
Cement board is hung with corrosion resistant screws or ring-shank nails. Cement board has very little movement under thermal stress, but the boards are usually installed with a slight gap at joints in shower pans, bathtubs, and each other. These joints are then filled with silicone sealant or the manufacturer's taping compounds before applying a finish. The filled joints are taped like conventional gypsum board, but with fiberglass tapes that provide additional water resistance. Combined with a water impermeable finish, cement board is a stable, durable backing board.
The category of construction material know as cement board includes both water resistant and waterproof board. Each has its own best use.
Typically water resistant cement board is composed of a treated gypsum core with a non organic fiber reinforced covering, either on one or both faces. This type of board requires fastidious sealing of all cut edges and penetrations to maintain the manufacturer's warranty for wet area installations. Gyspum core "cement" board panels are ideal for moist but not truly wet installations of tile and/or stone walls.
There is a class of cement board strictly constructed of a Portland cement based core with glass fiber matt reinforcing at both faces. This type board is truly waterproof. These panels can be immersed in water without any degradation, (excluding freeze thaw cycles). These panels do not require the sealing of edges and penetrations to maintain their structural integrity. These Portland cement based products are smaller in size compared with the gypsum core based products. Typically they range in size from 30" x 48" to 36" x 60". They are, as one would expect, considerably heavier than the gypsum core type panels.
Portland cement based panels are ideal for truly wet locations like shower surrounds and for locations where a Portland cement based thin-set material is used for bonding tile and stone surfaces to a substrate. They are also ideal for floor tile and stone installations over a structural subfloor.
Minggu, 31 Mei 2009
History of Cement
In the 18th century a big effort started in Europe to understand why some limes possess hydraulic properties. John Smeaton often referred to as "father of civil engineering in England" concentrated his work in this field. The French Engineer Louis Vicat, inspired by the work of Smeaton and Parker, began a study of hydraulic limes in 1812 (published in 1818 as "Recherches experimentales sur les chaux de construction". He reported that in the absence of naturally occurring argillaceous components in limestone, quality hydraulic limes could be prepared by the calcination of fixed ratios of clay proportioned with quicklime. In 1818 an English patent was granted to Maurice Leger for "Improvement method of making lime" (Leger used Vicat's method). In 1822, the production of "British Cement" had been started by James Frost at Swanscombe based on a patent for "a new cement or artificial stone". The invention of Portland Cement is generally credited to Joseph Aspedin, an English Bricklayer in 1824. It involves a double kilning such as was described by Vicat. In 1838 a young chemical engineer, Isaac Johnson, burned the cement raw material at high temperature until the mass was nearly vitrified producing the modern Portland Cement. The German Chemist Wilhelm Michaelis proposed the establishment of cement standards in 1875. The earliest kiln is one of William Aspedin's bottle kilns from Robins & Aspedin factory at Northfleet. The earliest bottle or dome kilns were open kilns with tapered chimney to increase the draft. They were burned in a batch rather than in a continuous fashion and were charged with alternating layers of raw feed and solid fuel. The chamber kiln was an improved design developed and patented by Mr. Johnson. The combustion gases from the kiln dried the raw material so that when the kiln was burned out a new charge of dried material is immediately ready for use. The time and heat losses resulting from drawing the clinker, recharging the kiln, and then heating it again led to the design of shaft kiln with continuous burning of the materials, one of the main problem of the new kiln operation was the difficulty of obtaining an even clinker burning, as some of the product would be greatly under-burnt and others be much more heavily clinkered. In 1898 Atlas Portland cement company according to Lewis improved the design by using what is called a rotary kiln, this improvement was a big revolution in the cement industry because the new kiln could produce 200 cement barrels per day compared to a shaft kiln which produced only 40 to max 80 barrels per day; in addition to quick improvement in this new design regarding the mixing, grinding equipments for raw material, grinding equipments for coal, belt conveyor using mix kind of fuel such as natural gas (1904, Iola Portland cement, Iola Kansas). In practice, the operation with the first generation of rotary kiln (Ransone kiln) was very difficult due to problem of maintaining a sufficient and uniform kiln temperature with excessive balling of raw feed and sticking on the Frederick lining. In 1899 Atlas Cement Company improved the technology of the rotary kiln and fuel economy by replacing fuel oil with powdered coal dust. Furthermore, modifications to the kiln were made by addition of two auxiliary clinker coolers, in which the first hot discharged clinker was received as it fell from the kiln and air flowing over it was heated and helped to ignite the coal dust in the rotary kiln. The new clinker produced from the new kiln technology was different than the old clinker especially from the setting time (much faster setting time). The French chemist Pierre Giron solved this problem by adding gypsum to the cement in order to control the setting time. After 1900 there was rapid growth in both rotary kiln and auxiliary equipment technology in the United States. Coal grinding mills were developed and coal burning in cement kilns became the predominant combustion process in the industry. All the equipments related to cement production crusher, raw mill, belt conveyors, bucked elevators were improved. Improvement in the following fields pertaining to cement manufacturing from material science technology has been an ongoing process for 200 years.
Jumat, 29 Mei 2009
Process Making Fiber Cement old type and improvement
Asbestos fiber cement techhology about 120 years ago, Ludwig Hatschek made the first asbestos reinforced cement products, using a paper-making sieve cylinder machine on which a very dilute slurry of asbestos fibers (up to about 10% by weight of solids) and ordinary Portland cement (about 90% or more) was dewatered, in films of about 0.3 mm, which were then wound up to a desired thickness (typically 6 mm) on a roll, and the resultant cylindrical sheet was cut and flattened to form a flat laminated sheet, which was cut into rectangular pieces of the desired size. Sekitar 120 tahun yang lalu, Ludwig Hatschek membuat pertama kali asbes semen produk, menggunakan mesin kertas silinder dan membuat mesin yang sangat membuat slurry dari serat asbes (hingga sekitar 10% oleh berat solids) dan Portland semen biasa (sekitar 90 % atau lebih) di dewatered, dalam lapisan sekitar 0,3 mm, yang kemudian di buat sampai ketebalan yang dikehendaki (biasanya 6 mm) pada roll, dan lembar yang dihasilkan silinder dan di potong dan flattened untuk membentuk flat sheet yg berlapis-lapis, yang merupakan potong menjadi segi empat lembar ukuran yang dikehendaki. These products were then air-cured in the normal cement curing method for about 28 days. Produk-produk ini adalah pengeringan udara biasa dengan normal pengeringan 28 hari.
For over 100 years, this form of fiber cement found extensive use for roofing products, pipe products, and walling products, both external siding (planks and panels), and wet-area lining boards. Selama lebih dari 100 tahun, ini berupa fiber semen ditemukan luas untuk menggunakan produk atap, pipa produk, dan produk Walling, baik eksternal papan (papan dan panel), dan basah-daerah lining boards. Asbestos cement was also used in many applications requiring high fire resistance due to the great thermal stability of asbestos. Asbes semen juga digunakan dalam berbagai aplikasi yang memerlukan daya tahan tinggi api yang besar karena panas stabilitas asbes. The great advantage of all these products was that they were relative lightweight and that water affected them relatively little, since the high-density asbestos/cement composite is of low porosity and Keuntungan yang besar dari semua produk ini adalah mereka yang relatif ringan dan air dipengaruhi mereka relatif sedikit, karena kepadatan tinggi asbes / semen komposit adalah yang rendah dan kerenikan permeability. permeabilitas. The disadvantage of these products was that the high-density matrix did not allow nailing, and methods of fixing involved pre-drilled holes. Yang merugikan dari produk ini adalah bahwa kepadatan tinggi matriks tidak baik, dan pada pemasangan lubang lubang kecil.
Although the original Hatschek process (a modified sieve cylinder paper making machine) dominated the bulk of asbestos cement products made, other processes were also used to make specialty products, such as thick sheets (say greater than about 10 mm which required about 30 films). Walaupun proses Hatschek asli (yang dimodifikasi saringan silinder mesin pembuatan kertas) didominasi massal asbes semen produk yang dibuat, proses lainnya yang juga digunakan untuk membuat produk-produk khusus, seperti lembaran tebal (katakanlah lebih besar dari sekitar 10 mm yang diperlukan sekitar 30 film) . These used the same mixture of asbestos fibers and cement as with the Hatschek process, although sometimes some process aid additives are used for other processes. Yang sama ini digunakan campuran serat asbes dan semen dengan Hatschek sebagai proses, walaupun terkadang beberapa proses bantuan tambahan ini digunakan untuk proses lainnya. For example, fiber cement composites have been made by extrusion, injection molding, and filter press or flow-on machines. Misalnya, serat semen composites yang telah dibuat oleh pengusiran, injection molding, dan penyaring tekan atau pada aliran-mesin.
Two developments occurred around the middle of the last century that had high significance to modern replacements of asbestos based cement composites. Dua perkembangan yang terjadi di sekitar tengah-tengah abad yang tinggi untuk kepentingan replacements modern yang berbasis asbes semen composites. The first was that some manufacturers realized that the curing cycle could be considerably reduced, and cost could be lowered, by autoclaving the products. Yang pertama adalah bahwa beberapa produsen menyadari bahwa siklus pengeringan dapat sangat dikurangi, dan dapat menurunkan biaya, oleh autoclaving produk. This allowed the replacement of much of the cement with fine ground silica, which reacted at autoclave temperatures with the excess lime in the cement to produce calcium silica hydrates similar to the normal cement matrix. Ini diizinkan penggantian banyak semen dengan tanah halus silika yang reaksi pada temperatur autoclave dengan kelebihan kapur di semen untuk memproduksi kalsium silika hydrates mirip dengan matriks semen biasa. Since silica, even when ground, is much cheaper than cement, and since the autoclave curing time is much less than the air cured curing time, this became a common, but by no means universal manufacturing method. Sejak silika, bahkan ketika tanah, jauh lebih murah dari semen, dan sejak autoclave pengasapan waktu lebih kurang dari pengeringan udara waktu, ini menjadi umum, namun tidak berarti metode manufaktur universal. A typical formulation would be about 5- 10% asbestos fibers, about J khas formulasi akan sekitar 5 - 10% serat asbes, sekitar 30-50% 30-50% cement, and about 40-60% silica. semen, dan sekitar 40-60% silika.
The second development was to replace some of the asbestos reinforcing fibers with cellulose fibers from wood. Pengembangan yang kedua adalah untuk mengganti beberapa asbes dengan memperkuat serat selulosa dari serat kayu. This was not widely adopted except for siding products and wet-area lining sheets. Ini tidak banyak diadopsi kecuali papan dan produk-daerah basah lining sheet. The great advantage of this development was that cellulose fibers are hollow and soft, and the resultant products could be nailed rather than by fixing through pre-drilled holes. Keuntungan yang besar dari perkembangan ini adalah serat selulosa yang berongga dan lembut, dan produk-produk yang dihasilkan dapat di pasang dengan di lobangkan dulu.. The siding and lining products are used on vertical walls, which is a far less demanding environment than roofing. Lapis dan papan yang digunakan pada produk tembok vertikal, yang merupakan permintaan lingkungan jauh lebih sedikit dari atap. However, cellulose reinforced cement products are more susceptible to water induced changes, compared to asbestos cement composite materials. A typical formulation would be about 3-4% cellulose, about 4-6% asbestos, and either about 90% cement for air cured products, or about 30-50% cement and about 40-60% silica for autoclaved products.
Asbestos fibers had several advantages. Serat asbes telah beberapa keunggulan. The sieve cylinder machines require fibers that form a network to catch the solid cement (or silica) particles, which are much too small to catch on the sieve itself. Asbestos, although it is an inorganic fiber, can be"refined"into Asbes, meskipun merupakan anorganik serat, bisa "disempurnakan" menjadi many small tendrils running off a main fiber. They are stable at high temperatures. Mereka stabil pada suhu tinggi. They are stable against alkali attack under autoclave conditions. Hence, asbestos reinforced fiber cement products are themselves strong, stiff (also brittle), and could be used in many hostile environments, except highly acidic environments where the cement itself is rapidly attacked chemically. The wet/dry cycling that asbestos roofing products were subjected to, often caused a few problems, primarily efflorescence, caused by the dissolution of chemicals inside the products when wet, followed by the deposition of these chemicals on the surfaces of the products when dried. Efflorescence caused aesthetic degradation of roofing products in particular, and many attempts were made to reduce it. Because the matrix of asbestos reinforced roofing products was generally very dense (specific gravity about 1.7), the total amount of water entering the product even when saturated was relatively low, and the products generally had reasonable freeze thaw resistance. If the density was lowered, the products became more workable (for example they could be nailed) but the rate of saturation and the total water absorption increased and the freeze thaw performance decreased.
Alternative Fiber Cement Technologies In the early 1980's, the health hazards associated with mining, or being exposed to and inhaling, asbestos fibers started to become a major health concern. Alternatif Fiber Semen Technologies . Manufacturers of asbestos cement products in the USA, some of Western Europe, and Australia/New Zealand in particular, sought to find a substitute for asbestos fibers for the reinforcement of building and construction products, made on their installed manufacturing base, primarily Hatschek machines. Over a period of twenty years, two viable alternative technologies have emerged, although neither of these has been successful in the full range of asbestos applications.
In Western Europe, the most successful replacement for asbestos has been a combination of PVA fibers (about 2%) and cellulose fibers (about 5%) with primarily cement (about 80%), sometimes with inert fillers such as silica or limestone (about 10- 30%). This product is air-cured, since PVA fibers are, in general, not autoclave stable. It is generally made on a Hatschek machine, followed by a pressing step using a hydraulic press.
This compresses the cellulose fibers, and reduces the porosity of the matrix. Since PVA fibers can't be refined while cellulose can be, in this Western European technology the cellulose fiber functions as a process aid to form the network on the sieve that catches the solid particles in the dewatering step. This product is used primarily for roofing (slates and corrugates). It is usually (but not always) covered with thick organic coatings. The great disadvantage of these products is a very large increase in material and manufacturing process costs. While cellulose is currently a little more expensive than asbestos fibers at $500 a ton, PVA is about $4000 a ton. Thick organic coatings are also expensive, and hydraulic presses are a high cost manufacture step.
For over 100 years, this form of fiber cement found extensive use for roofing products, pipe products, and walling products, both external siding (planks and panels), and wet-area lining boards. Selama lebih dari 100 tahun, ini berupa fiber semen ditemukan luas untuk menggunakan produk atap, pipa produk, dan produk Walling, baik eksternal papan (papan dan panel), dan basah-daerah lining boards. Asbestos cement was also used in many applications requiring high fire resistance due to the great thermal stability of asbestos. Asbes semen juga digunakan dalam berbagai aplikasi yang memerlukan daya tahan tinggi api yang besar karena panas stabilitas asbes. The great advantage of all these products was that they were relative lightweight and that water affected them relatively little, since the high-density asbestos/cement composite is of low porosity and Keuntungan yang besar dari semua produk ini adalah mereka yang relatif ringan dan air dipengaruhi mereka relatif sedikit, karena kepadatan tinggi asbes / semen komposit adalah yang rendah dan kerenikan permeability. permeabilitas. The disadvantage of these products was that the high-density matrix did not allow nailing, and methods of fixing involved pre-drilled holes. Yang merugikan dari produk ini adalah bahwa kepadatan tinggi matriks tidak baik, dan pada pemasangan lubang lubang kecil.
Although the original Hatschek process (a modified sieve cylinder paper making machine) dominated the bulk of asbestos cement products made, other processes were also used to make specialty products, such as thick sheets (say greater than about 10 mm which required about 30 films). Walaupun proses Hatschek asli (yang dimodifikasi saringan silinder mesin pembuatan kertas) didominasi massal asbes semen produk yang dibuat, proses lainnya yang juga digunakan untuk membuat produk-produk khusus, seperti lembaran tebal (katakanlah lebih besar dari sekitar 10 mm yang diperlukan sekitar 30 film) . These used the same mixture of asbestos fibers and cement as with the Hatschek process, although sometimes some process aid additives are used for other processes. Yang sama ini digunakan campuran serat asbes dan semen dengan Hatschek sebagai proses, walaupun terkadang beberapa proses bantuan tambahan ini digunakan untuk proses lainnya. For example, fiber cement composites have been made by extrusion, injection molding, and filter press or flow-on machines. Misalnya, serat semen composites yang telah dibuat oleh pengusiran, injection molding, dan penyaring tekan atau pada aliran-mesin.
Two developments occurred around the middle of the last century that had high significance to modern replacements of asbestos based cement composites. Dua perkembangan yang terjadi di sekitar tengah-tengah abad yang tinggi untuk kepentingan replacements modern yang berbasis asbes semen composites. The first was that some manufacturers realized that the curing cycle could be considerably reduced, and cost could be lowered, by autoclaving the products. Yang pertama adalah bahwa beberapa produsen menyadari bahwa siklus pengeringan dapat sangat dikurangi, dan dapat menurunkan biaya, oleh autoclaving produk. This allowed the replacement of much of the cement with fine ground silica, which reacted at autoclave temperatures with the excess lime in the cement to produce calcium silica hydrates similar to the normal cement matrix. Ini diizinkan penggantian banyak semen dengan tanah halus silika yang reaksi pada temperatur autoclave dengan kelebihan kapur di semen untuk memproduksi kalsium silika hydrates mirip dengan matriks semen biasa. Since silica, even when ground, is much cheaper than cement, and since the autoclave curing time is much less than the air cured curing time, this became a common, but by no means universal manufacturing method. Sejak silika, bahkan ketika tanah, jauh lebih murah dari semen, dan sejak autoclave pengasapan waktu lebih kurang dari pengeringan udara waktu, ini menjadi umum, namun tidak berarti metode manufaktur universal. A typical formulation would be about 5- 10% asbestos fibers, about J khas formulasi akan sekitar 5 - 10% serat asbes, sekitar 30-50% 30-50% cement, and about 40-60% silica. semen, dan sekitar 40-60% silika.
The second development was to replace some of the asbestos reinforcing fibers with cellulose fibers from wood. Pengembangan yang kedua adalah untuk mengganti beberapa asbes dengan memperkuat serat selulosa dari serat kayu. This was not widely adopted except for siding products and wet-area lining sheets. Ini tidak banyak diadopsi kecuali papan dan produk-daerah basah lining sheet. The great advantage of this development was that cellulose fibers are hollow and soft, and the resultant products could be nailed rather than by fixing through pre-drilled holes. Keuntungan yang besar dari perkembangan ini adalah serat selulosa yang berongga dan lembut, dan produk-produk yang dihasilkan dapat di pasang dengan di lobangkan dulu.. The siding and lining products are used on vertical walls, which is a far less demanding environment than roofing. Lapis dan papan yang digunakan pada produk tembok vertikal, yang merupakan permintaan lingkungan jauh lebih sedikit dari atap. However, cellulose reinforced cement products are more susceptible to water induced changes, compared to asbestos cement composite materials. A typical formulation would be about 3-4% cellulose, about 4-6% asbestos, and either about 90% cement for air cured products, or about 30-50% cement and about 40-60% silica for autoclaved products.
Asbestos fibers had several advantages. Serat asbes telah beberapa keunggulan. The sieve cylinder machines require fibers that form a network to catch the solid cement (or silica) particles, which are much too small to catch on the sieve itself. Asbestos, although it is an inorganic fiber, can be"refined"into Asbes, meskipun merupakan anorganik serat, bisa "disempurnakan" menjadi many small tendrils running off a main fiber. They are stable at high temperatures. Mereka stabil pada suhu tinggi. They are stable against alkali attack under autoclave conditions. Hence, asbestos reinforced fiber cement products are themselves strong, stiff (also brittle), and could be used in many hostile environments, except highly acidic environments where the cement itself is rapidly attacked chemically. The wet/dry cycling that asbestos roofing products were subjected to, often caused a few problems, primarily efflorescence, caused by the dissolution of chemicals inside the products when wet, followed by the deposition of these chemicals on the surfaces of the products when dried. Efflorescence caused aesthetic degradation of roofing products in particular, and many attempts were made to reduce it. Because the matrix of asbestos reinforced roofing products was generally very dense (specific gravity about 1.7), the total amount of water entering the product even when saturated was relatively low, and the products generally had reasonable freeze thaw resistance. If the density was lowered, the products became more workable (for example they could be nailed) but the rate of saturation and the total water absorption increased and the freeze thaw performance decreased.
Alternative Fiber Cement Technologies In the early 1980's, the health hazards associated with mining, or being exposed to and inhaling, asbestos fibers started to become a major health concern. Alternatif Fiber Semen Technologies . Manufacturers of asbestos cement products in the USA, some of Western Europe, and Australia/New Zealand in particular, sought to find a substitute for asbestos fibers for the reinforcement of building and construction products, made on their installed manufacturing base, primarily Hatschek machines. Over a period of twenty years, two viable alternative technologies have emerged, although neither of these has been successful in the full range of asbestos applications.
In Western Europe, the most successful replacement for asbestos has been a combination of PVA fibers (about 2%) and cellulose fibers (about 5%) with primarily cement (about 80%), sometimes with inert fillers such as silica or limestone (about 10- 30%). This product is air-cured, since PVA fibers are, in general, not autoclave stable. It is generally made on a Hatschek machine, followed by a pressing step using a hydraulic press.
This compresses the cellulose fibers, and reduces the porosity of the matrix. Since PVA fibers can't be refined while cellulose can be, in this Western European technology the cellulose fiber functions as a process aid to form the network on the sieve that catches the solid particles in the dewatering step. This product is used primarily for roofing (slates and corrugates). It is usually (but not always) covered with thick organic coatings. The great disadvantage of these products is a very large increase in material and manufacturing process costs. While cellulose is currently a little more expensive than asbestos fibers at $500 a ton, PVA is about $4000 a ton. Thick organic coatings are also expensive, and hydraulic presses are a high cost manufacture step.
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