Gypsum plaster
Plaster of Paris is a type of building material based on calcium sulphate hemihydrate, nominally CaSO4·1/2H2O. It is created by heating gypsum to about 150 °C.[1]
2 CaSO4·2H2O → 2 CaSO4·0.5H2O + 3 H2O (released as steam).
A large gypsum deposit at Montmartre in Paris is the source of the name.[1][2] When the dry plaster powder is mixed with water, it re-forms into gypsum. Plaster is used as a building material similar to mortar or cement. Like those materials plaster starts as a dry powder that is mixed with water to form a paste which liberates heat and then hardens. Unlike mortar and cement, plaster remains quite soft after drying, and can be easily manipulated with metal tools or even sandpaper. These characteristics make plaster suitable for a finishing, rather than a load-bearing material.
One of the skills used in movie and theatrical sets is that of "plasterer", gypsum plaster often being used to simulate the appearance of surfaces of wood, stone, or metal. Nowadays, plasterers are just as likely to use expanded polystyrene, although the job title remains unchanged.
Lime plaster
Main article: Lime plaster
Lime plaster is a mixture of calcium hydroxide and sand (or other inert fillers). Carbon dioxide in the atmosphere causes the plaster to set by transforming the calcium hydroxide into calcium carbonate (limestone). Whitewash is based on the same chemistry.
To make lime plaster, limestone (calcium carbonate) is heated to produce quicklime (calcium oxide). Water is then added to produce slaked lime (calcium hydroxide), which is sold as a white powder. Additional water is added to form a paste prior to use. The paste may be stored in air-tight containers. Once exposed to the atmosphere, the calcium hydroxide turns back into limestone, causing the plaster to set.
Lime plaster was a common building material for wall surfaces in a process known as lath and plaster, whereby a series of wooden strips on a studwork frame was covered with a semi-dry plaster that hardened into a surface. The plaster used in most lath and plaster construction was mainly lime plaster, with a cure time of about a month. To stabilize the lime plaster during curing, small amounts of Plaster of Paris were incorporated into the mix. Because Plaster of Paris sets quickly, "retardants" were used to slow setting time enough to allow workers to mix large working quantities of lime putty plaster. A modern form of this method uses expanded metal mesh over wood or metal structures, which allows a great freedom of design as it is adaptable to both simple and compound curves. Today this building method has been partly replaced with drywall, also composed mostly of gypsum plaster. In both these methods a primary advantage of the material is that it is resistant to a fire within a room and so can assist in reducing or eliminating structural damage or destruction provided the fire is promptly extinguished.
Lime plaster is used for true frescoes. Pigments, diluted in water, are applied to the still wet plaster.
Cement plaster
See also: Cement render
Cement plaster is a mixture of suitable plaster, sand, portland cement and water which is normally applied to masonry interiors and exteriors to achieve a smooth surface. Interior surfaces sometimes receive a final layer of gypsum plaster. Walls constructed with stock bricks are normally plastered while face brick walls are not plastered. Various cement-based plasters are also used as proprietary spray fireproofing products. These usually use vermiculite as lightweight aggregate. Heavy versions of such plasters are also in use for exterior fireproofing, to protect LPG vessels, pipe bridges and vessel skirts.
Sunday, April 25, 2010
History
The earliest operations on the pericardium (the sac that surrounds the heart) took place in the 19th century and were performed by, Francisco Romero[1] Dominique Jean Larrey, Henry Dalton, and Daniel Hale Williams. The first surgery on the heart itself was performed by Norwegian surgeon Axel Cappelen on the 4th of September 1895 at Rikshospitalet in Kristiania, now Oslo. He ligated a bleeding coronary artery in a 24 year old man who had been stabbed in the left axillae and was in deep shock upon arrival. Access was through a left thoracotomy. The patient awoke and seemed fine for 24hrs, but became ill with increasing temperature and he ultimately died from what the post mortem proved to be mediastinitis on the 3rd postoperative day[2][3]. The first successful surgery of the heart, performed without any complications, was by Dr. Ludwig Rehn of Frankfurt, Germany, who repaired a stab wound to the right ventricle on September 7, 1896.
Surgery on great vessels (aortic coarctation repair, Blalock-Taussig shunt creation, closure of patent ductus arteriosus), became common after the turn of the century and falls in the domain of cardiac surgery, but technically cannot be considered heart surgery.
Heart Malformations – Early Approaches
In 1925 operations on the valves of the heart were unknown. Henry Souttar operated successfully on a young woman with mitral stenosis. He made an opening in the appendage of the left atrium and inserted a finger into this chamber in order to palpate and explore the damaged mitral valve. The patient survived for several years[4] but Souttar’s physician colleagues at that time decided the procedure was not justified and he could not continue[5][6].
Cardiac surgery changed significantly after World War II. In 1948 four surgeons carried out successful operations for mitral stenosis resulting from rheumatic fever. Horace Smithy (1914-1948) of Charlotte, revived an operation due to Dr Dwight Harken of the Peter Bent Brigham Hospital using a punch to remove a portion of the mitral valve. Charles Bailey (1910-1993) at the Hahnemann Hospital, Philadelphia, Dwight Harken in Boston and Russell Brock at Guy’s Hospital all adopted Souttar’s method. All these men started work independently of each other, within a few months. This time Souttar’s technique was widely adopted although there were modifications[5][6].
In 1947 Thomas Holmes Sellors (1902-1987) of the Middlesex Hospital operated on a Fallot’s Tetralogy patient with pulmonary stenosis and successfully divided the stenosed pulmonary valve. In 1948, Russell Brock, probably unaware of Sellor’s work, used a specially designed dilator in three cases of pulmonary stenosis. Later in 1948 he designed a punch to resect the infundibular muscle stenosis which is often associated with Fallot’s Tetralogy. Many thousands of these “blind” operations were performed until the introduction of heart bypass made direct surgery on valves possible[5].
Open heart surgery
This is a surgery in which the patient's chest is opened and surgery is performed on the heart. The term "open" refers to the chest, not to the heart itself. The heart may or may not be opened depending on the particular type of surgery.
It was soon discovered by Dr. Wilfred G. Bigelow of the University of Toronto that the repair of intracardiac pathologies was better done with a bloodless and motionless environment, which means that the heart should be stopped and drained of blood. The first successful intracardiac correction of a congenital heart defect using hypothermia was performed by Dr. C. Walton Lillehei and Dr. F. John Lewis at the University of Minnesota on September 2, 1952. The following year, Soviet surgeon Aleksandr Aleksandrovich Vishnevskiy conducted the first cardiac surgery under local anesthesia.
Surgeons realized the limitations of hypothermia - complex intracardiac repairs take more time and the patient needs blood flow to the body (and particularly the brain); the patient needs the function of the heart and lungs provided by an artificial method, hence the term cardiopulmonary bypass. Dr. John Heysham Gibbon at Jefferson Medical School in Philadelphia reported in 1953 the first successful use of extracorporeal circulation by means of an oxygenator, but he abandoned the method, disappointed by subsequent failures. In 1954 Dr. Lillehei realized a successful series of operations with the controlled cross-circulation technique in which the patient's mother or father was used as a 'heart-lung machine'. Dr. John W. Kirklin at the Mayo Clinic in Rochester, Minnesota started using a Gibbon type pump-oxygenator in a series of successful operations, and was soon followed by surgeons in various parts of the world.
Dr. Nazih Zuhdi worked for four years under Drs. Clarence Dennis, Karl Karlson, and Charles Fries, who built an early pump-oxygenator. Zuhdi and Fries worked on several designs and re-designs of Dennis' earlier model from 1952-1956 at the Brooklyn Center. Zuhdi then went to work with Dr. C. Walton Lillehei at the University of Minnesota. Lillehei had designed his own version of a cross-circulation machine, which came to become known as the DeWall-Lillehei heart-lung machine. Zuhdi worked on perfusion and blood flow trying to solve the problem of air bubbles while bypassing the heart so the heart could be stopped for the operation. Zuhdi moved to Oklahoma City, OK, in 1957, and began working at the Oklahoma University College. Zuhdi, the heart surgeon, teamed up with Dr. Allen Greer, a lung surgeon and Dr. John Carey, forming a three man open heart surgery team. With the advent of Dr. Zuhdi's heart-lung machine which was modified in size, being much smaller than the DeWall-Lillehei heart-lung machine, and with other modifications, reduced the need for blood down to a minimal amount, and the cost of the equipment down to $500.00 and also reduced the prep time from two hours to 20 minutes. Dr. Zuhdi performed the first Total Intentional Hemodilution open heart surgery on Terry Gene Nix, age 7, on February 25, 1960, at Mercy Hospital, Oklahoma City, OK. The operation was a success; however, Nix died three years later in 1963.[7] In March, 1961, Zuhdi, Carey, and Greer, performed open heart surgery on a child, age 3 1/2, using the Total Intentional Hemodilution machine, with success. That patient is still alive.[8]
In 1985 Dr. Zuhdi performed Oklahoma's first successful heart transplant on Nancy Rogers at Baptist Hospital. The transplant was successful, but Rogers, a cancer sufferer, died from an infection 54 days after surgery.[9]
modern beating-heart surgery
Since the 1990s, surgeons have begun to perform "off-pump bypass surgery" - coronary artery bypass surgery without the aforementioned cardiopulmonary bypass. In these operations, the heart is beating during surgery, but is stabilized to provide an almost still work area. Some researchers believe this approach results in fewer post-operative complications (such as postperfusion syndrome) and better overall results (study results are controversial as of 2007, the surgeon's preference and hospital results still play a major role).
Minimally invasive surgery
A new form of heart surgery that has grown in popularity is robot-assisted heart surgery. This is where a machine is used to perform surgery while being controlled by the heart surgeon. The main advantage to this is the size of the incision made in the patient. Instead of an incision being at least big enough for the surgeon to put his hands inside, it does not have to be bigger than 3 small holes for the robot's much smaller hands to get through. Also, a major advantage to the robot is the recovery time of the patient, instead of months of recovery time, some patients have recovered and resumed playing athletics in a matter of weeks.[citation needed]
Surgery on great vessels (aortic coarctation repair, Blalock-Taussig shunt creation, closure of patent ductus arteriosus), became common after the turn of the century and falls in the domain of cardiac surgery, but technically cannot be considered heart surgery.
Heart Malformations – Early Approaches
In 1925 operations on the valves of the heart were unknown. Henry Souttar operated successfully on a young woman with mitral stenosis. He made an opening in the appendage of the left atrium and inserted a finger into this chamber in order to palpate and explore the damaged mitral valve. The patient survived for several years[4] but Souttar’s physician colleagues at that time decided the procedure was not justified and he could not continue[5][6].
Cardiac surgery changed significantly after World War II. In 1948 four surgeons carried out successful operations for mitral stenosis resulting from rheumatic fever. Horace Smithy (1914-1948) of Charlotte, revived an operation due to Dr Dwight Harken of the Peter Bent Brigham Hospital using a punch to remove a portion of the mitral valve. Charles Bailey (1910-1993) at the Hahnemann Hospital, Philadelphia, Dwight Harken in Boston and Russell Brock at Guy’s Hospital all adopted Souttar’s method. All these men started work independently of each other, within a few months. This time Souttar’s technique was widely adopted although there were modifications[5][6].
In 1947 Thomas Holmes Sellors (1902-1987) of the Middlesex Hospital operated on a Fallot’s Tetralogy patient with pulmonary stenosis and successfully divided the stenosed pulmonary valve. In 1948, Russell Brock, probably unaware of Sellor’s work, used a specially designed dilator in three cases of pulmonary stenosis. Later in 1948 he designed a punch to resect the infundibular muscle stenosis which is often associated with Fallot’s Tetralogy. Many thousands of these “blind” operations were performed until the introduction of heart bypass made direct surgery on valves possible[5].
Open heart surgery
This is a surgery in which the patient's chest is opened and surgery is performed on the heart. The term "open" refers to the chest, not to the heart itself. The heart may or may not be opened depending on the particular type of surgery.
It was soon discovered by Dr. Wilfred G. Bigelow of the University of Toronto that the repair of intracardiac pathologies was better done with a bloodless and motionless environment, which means that the heart should be stopped and drained of blood. The first successful intracardiac correction of a congenital heart defect using hypothermia was performed by Dr. C. Walton Lillehei and Dr. F. John Lewis at the University of Minnesota on September 2, 1952. The following year, Soviet surgeon Aleksandr Aleksandrovich Vishnevskiy conducted the first cardiac surgery under local anesthesia.
Surgeons realized the limitations of hypothermia - complex intracardiac repairs take more time and the patient needs blood flow to the body (and particularly the brain); the patient needs the function of the heart and lungs provided by an artificial method, hence the term cardiopulmonary bypass. Dr. John Heysham Gibbon at Jefferson Medical School in Philadelphia reported in 1953 the first successful use of extracorporeal circulation by means of an oxygenator, but he abandoned the method, disappointed by subsequent failures. In 1954 Dr. Lillehei realized a successful series of operations with the controlled cross-circulation technique in which the patient's mother or father was used as a 'heart-lung machine'. Dr. John W. Kirklin at the Mayo Clinic in Rochester, Minnesota started using a Gibbon type pump-oxygenator in a series of successful operations, and was soon followed by surgeons in various parts of the world.
Dr. Nazih Zuhdi worked for four years under Drs. Clarence Dennis, Karl Karlson, and Charles Fries, who built an early pump-oxygenator. Zuhdi and Fries worked on several designs and re-designs of Dennis' earlier model from 1952-1956 at the Brooklyn Center. Zuhdi then went to work with Dr. C. Walton Lillehei at the University of Minnesota. Lillehei had designed his own version of a cross-circulation machine, which came to become known as the DeWall-Lillehei heart-lung machine. Zuhdi worked on perfusion and blood flow trying to solve the problem of air bubbles while bypassing the heart so the heart could be stopped for the operation. Zuhdi moved to Oklahoma City, OK, in 1957, and began working at the Oklahoma University College. Zuhdi, the heart surgeon, teamed up with Dr. Allen Greer, a lung surgeon and Dr. John Carey, forming a three man open heart surgery team. With the advent of Dr. Zuhdi's heart-lung machine which was modified in size, being much smaller than the DeWall-Lillehei heart-lung machine, and with other modifications, reduced the need for blood down to a minimal amount, and the cost of the equipment down to $500.00 and also reduced the prep time from two hours to 20 minutes. Dr. Zuhdi performed the first Total Intentional Hemodilution open heart surgery on Terry Gene Nix, age 7, on February 25, 1960, at Mercy Hospital, Oklahoma City, OK. The operation was a success; however, Nix died three years later in 1963.[7] In March, 1961, Zuhdi, Carey, and Greer, performed open heart surgery on a child, age 3 1/2, using the Total Intentional Hemodilution machine, with success. That patient is still alive.[8]
In 1985 Dr. Zuhdi performed Oklahoma's first successful heart transplant on Nancy Rogers at Baptist Hospital. The transplant was successful, but Rogers, a cancer sufferer, died from an infection 54 days after surgery.[9]
modern beating-heart surgery
Since the 1990s, surgeons have begun to perform "off-pump bypass surgery" - coronary artery bypass surgery without the aforementioned cardiopulmonary bypass. In these operations, the heart is beating during surgery, but is stabilized to provide an almost still work area. Some researchers believe this approach results in fewer post-operative complications (such as postperfusion syndrome) and better overall results (study results are controversial as of 2007, the surgeon's preference and hospital results still play a major role).
Minimally invasive surgery
A new form of heart surgery that has grown in popularity is robot-assisted heart surgery. This is where a machine is used to perform surgery while being controlled by the heart surgeon. The main advantage to this is the size of the incision made in the patient. Instead of an incision being at least big enough for the surgeon to put his hands inside, it does not have to be bigger than 3 small holes for the robot's much smaller hands to get through. Also, a major advantage to the robot is the recovery time of the patient, instead of months of recovery time, some patients have recovered and resumed playing athletics in a matter of weeks.[citation needed]
Asphalt
Asphalt (specifically, asphalt concrete) has been widely used since 1920-1930. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue from repeated loading over time is the most common failure mechanism. Most asphalt surfaces are built on a gravel base, which is generally at least as thick as the asphalt layer, although some 'full depth' asphalt surfaces are built directly on the native subgrade. In areas with very soft or expansive subgrades such as clay or peat, thick gravel bases or stabilization of the subgrade with Portland cement or lime may be required. Polypropylene and polyester materials have also been used for this purpose[5] and in some countries, a foundation of polystyrene blocks has used, which has the added advantage of providing a frost proof base.[6] The actual material used in paving is termed HMA (Hot Mix Asphalt), and it is usually applied using a free floating screed.
An asphalt concrete surface will generally be constructed for high volume primary highways having an Average Annual Daily Traffic load higher than 1200 vehicles per day.[7] Advantages of asphalt roadways include relatively low noise, relatively low cost compared with other paving methods, and perceived ease of repair. Disadvantages include less durability than other paving methods, less tensile strength than concrete, the tendency to become slick and soft in hot weather and a certain amount of hydrocarbon pollution to soil and groundwater or waterways.
In the 1960s, rubberized asphalt was used for the first time, mixing crumb rubber from used tires with asphalt. In addition to using tires that would otherwise fill landfills and present a fire hazard, rubberized asphalt is more durable and provides a 7-12 decibel noise reduction over conventional asphalt. However, application of rubberized asphalt is more temperature-sensitive, and in many locations can only be applied at certain times of the year.
An asphalt concrete surface will generally be constructed for high volume primary highways having an Average Annual Daily Traffic load higher than 1200 vehicles per day.[7] Advantages of asphalt roadways include relatively low noise, relatively low cost compared with other paving methods, and perceived ease of repair. Disadvantages include less durability than other paving methods, less tensile strength than concrete, the tendency to become slick and soft in hot weather and a certain amount of hydrocarbon pollution to soil and groundwater or waterways.
In the 1960s, rubberized asphalt was used for the first time, mixing crumb rubber from used tires with asphalt. In addition to using tires that would otherwise fill landfills and present a fire hazard, rubberized asphalt is more durable and provides a 7-12 decibel noise reduction over conventional asphalt. However, application of rubberized asphalt is more temperature-sensitive, and in many locations can only be applied at certain times of the year.
Mid-engine V6/V8
- The Dino was the first mid-engined Ferrari. This layout would go on to be used in most Ferraris of the 1980s and 1990s. V6 and V8 Ferrari models make up well over half of the marque's total production.
1968-1974 Dino
1968-1969 Dino 206 GT
1969-1974 246GT Berlinetta, or Coupe
1972-1974 246GTS (targa top) Spider
1975-1989 208/308/328 GTB/GTS
1975-1977 308 GTB (GRP)
1977-1979 308 GTB and GTS
1980-1981 208 GTB & GTS
1980-1981 308 GTBi & GTSi
1982-1985 208 GTB/GTS Turbo
1982-1985 308 GTB/GTS Quattrovalvole
1986-1989 328 GTB & GTS
1986 208 GTB/GTS Turbo
1989-1994 348
1989-1993 348 TB & TS
1993-1994 348 GTB, GTS & Spider
1994-1999 F355
1994-1999 F355 Berlinetta & GTS
1995-1999 F355 Spider
1995 F355 Challenge
1998-1999 355 F1
1999-2004 360
1999-2004 360 Modena & Spider
2003-2004 360 Challenge Stradale
2005 F430
2005 F430 & F430 Spider
2007 430 Scuderia
2009 Scuderia Spider 16M
2010 458 (announced)
TBA Ferrari 458 Italia
Saturday, April 24, 2010
Floor tiles
- These are commonly made of ceramic, porcelain, or stone, although recent technological advances have resulted in rubber or glass tiles for floors as well. Ceramic tiles may be painted and glazed. Small mosaic tiles may b
e laid in various patterns. Floor tiles are typically set into mortar consisting of sand, cement and often a latex additive for extra adhesion. The spaces between the tiles are nowadays filled with sanded or unsanded floor grout, but traditionally mortar was used.
Natural stone tiles can be beautiful but as a natural product they are less uniform in color and pattern, and require more planning for use and install
ation. Mass produced stone tiles are uniform in width and length. Granite or marble tiles are sawn on both sides and then polished or finished on the facing up side, so that they have a uniform thickness. Other natural stone tiles such as slate are typically "riven" (split) on the facing up side so that the thickness of the tile varies slightly from one spot on the tile to another and from one tile to another. Variations in tile thickness can be handled by adjusting the amount of mortar under each part of the tile, by using wide grout lines that "ramp" between different thicknesses, or by using a cold chisel to knock off high spots.
Some stone tiles such as polished granite, marble, and traverti
ne are very slippery when wet. Stone tiles with a riven (split) surface such as slate or with a sawn and then sandblasted or honed surface will be more slip resistant. Ceramic tile for use in wet areas can be made more slip resistant either by using very small tiles so that the grout lines acts as grooves or by imprinting a contour pattern onto the face of the tile.
The hardness of natural stone tiles varies such that some of the softer stone (e.g. limestone) tiles are not suitable for very heavy traffic floor areas. On the other hand, ceramic tiles typically have a glazed upper surface and when that becomes scratched or pitted the floor looks worn, whereas the same amount of wear on natural stone tiles won't show, or will be less noticeable.
Natural stone tiles can be stained by spilled liquids; they must be sealed and periodically resealed with a sealant in contrast to ceramic tiles which only need their grout lines sealed. However, because of the complex, non repeating patterns in natural stone, small amounts of dirt on many natural stone floor tiles do not show.
Most vendors of stone tiles emphasize that there will be variation in color and pattern from one batch of tiles to another of the same description and variation within the same batch.
Stone floor tiles tend to be heavier than ceramic tiles and somewhat more prone to breakage during shipment.
Rubber floor tiles have a variety of uses, both in residential and commercial settings. They are especially useful in situations where it is desired to have high-traction floors or protection for an easily breakable floor. Some common uses include flooring of garage, workshops, patios, swimming pool decks, sport courts, gyms, and dance floors.
Plastic floor tiles including interlocking floor tiles that can be installed without adhesive or glue are a recent innovation and are suitable for areas subject to heavy traffic, wet areas and floors that are subject to movement, damp or contamination from oil, grease or other substances that may prevent adhesion to the substrate. Common uses include old factory floors, garages, gyms and sports complexes, schools and shops.
Medieval letter tiles were used to create Christian inscriptions on church floors
Manufacturing process and uses
- After the fusion of a mixture of natural sand and recycled glass at 1,450 °C, the glass that is produced is converted into fibres. The cohesion and mechanical strength of the product is obtained by the presence of a binder that “cements” the fibres together. Ideally, a drop of bonder is placed at each fibre intersection. This fiber mat is then heated to around 200 °C to polymerize the resin and is calendered to give it strength and st
ability. The final stage involves cutting the wool and packing it in rolls or panels under very high pressure before palletizing the finished product in order to facilitate transport and storage. Glass wool having better advantages compair to other insulation materials.But it is hazardous due to its
duct & very small glass particles which can travel into the human body during inhalation. web:http://www.glass-wool-insulation-china.com
USE
- Glass wool is a thermal insulation that consists of intertwined and flexible glass fibres, which causes it to "package" air, resulting in a low density that can be varied through compression and binder content. It can be a loose fill material, blown into attics, or, together with an active binder sprayed on the underside of structures, sheets and panels that can be used to insulate flat surfaces such as cavity wall insulation, ceiling tiles, curtain walls as well as ducting. It is also used to insulate piping and for soundproofing.
web:http://www.glass-wool-insulation-china.com/
Concrete block
- Blocks of cinder concrete (cinder blocks or breezeblocks), ordinary concrete (concrete blocks), or hollow tile are generically known as Concrete Masonry Units (CMU)s. They usually are much larger th
an ordinary bricks and so are much faster to lay for a wall of a given size. Furthermore, cinder and concrete blocks typically have much lower water absorption rates than brick. They often are used as the structural core for veneered brick masonry, or are used alone for the walls of factories, garages and other industrial style buildings where such appearance is acceptable or desirable. Such blocks often receive a stucco surface for decoration. Surface-bonding cement, which contains synthetic fibers for reinforcement, is sometimes used in this application and can impart extra strength to a block wall. Surface-bonding cement is often pre-coloured and can be stained or painted thus resulting in a finished stucco-like surface.
The primary structural advantage of concrete blocks in comparison to smaller clay-based bricks is that a CMU wall can be reinforced by filling the block voids with concrete with or without steel rebar. Generally, certain voids are designated for filling and reinforcement, particularly at corners, wall-ends, and openings while other voids are left empty. This increases wall strength and stability more economically than filling and reinforcing all voids. Typically, structures made of CMUs will have the top course of blocks in the walls filled with concrete and tied together with steel reinforcement to form a bond beam. Bond beams are often a requirement of modern building codes and controls . Another type of steel reinforcement, referred to as ladder-reinforcement, can also be embedded in horizontal mortar joints of concrete block walls. The introduction of steel reinforcement generally results in a CMU wall having much greater lateral and tensile strength than unreinforced walls.
CMUs can be manufactured to provide a variety of surface appearances. They can be colored during manufacturing or stained or painted after installation. They can be split as part of the manufacturing process, giving the blocks a rough face replicating the appearance of natural stone, such as brownstone. CMUs may also be scored, ribbed, sandblasted, polished, striated (raked or brushed), include decorative aggregates, be allowed to slump in a controlled fashion during curing, or include several of these techniques in their manufacture to provide a decorative appearance. [1]
"Glazed concrete masonry units are manufactured by bonding a permanent colored facing (typically composed of polyester resins, silica sand and various other chemicals) to a concrete masonry unit, providing a smooth impervious surface." [2]
Glass block or glass brick are blocks made from glass and provide a translucent to clear vision through the block.
Biosynthesis cocain
- The first synthesis and elucidation of the cocaine molecule was by Richard Willstätter in 1898.[24] Willstätter's synthesis derived cocaine from tropinone. Since then, Robert Robinson and Edward Leete have made significant contributions to the mechanism of the synthesis.
Biosynthesis of N-methyl-pyrrolinium cation
Biosynthesis of N-methyl-pyrrolinium cation
The biosynthesis begins with L-Glutamine, which is derived to L-ornithine in plants. The major contribution of L-ornithine and L-arginine as a precursor to the tropane ring was confirmed by Edward Leete.[25] Ornithine then undergoes a Pyridoxal phosphate-dependent decarboxylation to form putrescine. In animals, however, the urea cycle derives putrescine from ornithine. L-ornithine is converted to L-arginine,[26] which is then decarboxylated via PLP to form agmatine. Hydrolysis of the imine derives N-carbamoylputrescine followed with hydrolysis of the urea to form putrescine. T
he separate pathways of converting ornithine to putrescine in plants and animals have converged. A SAM-dependent N-methylation of putrescine gives the N-methylputrescine product, which then undergoes oxidative deamination by the action of diamine oxidase to yield the aminoaldehyde. Schiff base formation confirms the biosynthesis of the N-methyl-Δ1-pyrrolinium cation.
Biosynthesis of cocaine
The additional carbon atoms required for the synthesis of cocaine are derived from acetyl-CoA, by addition of two acetyl-CoA units to the N-methyl-Δ1-pyrrolinium cation.[27] The first addition is a Mannich-like reaction with the enolate anion from acetyl-CoA acting as a nucleophile towards the pyrrolinium cation. The second addition occurs through a Claisen condensation. This produces a racemic mixture of the 2-substituted pyrrolidine, with the retention of the thioester from the Claisen condensation. In formation of tropinone from racemic ethyl [2,3-13C2]4(Nmethyl- 2-pyrroli
dinyl)-3-oxobutanoate there is no preference for either stereoisomer.[28] In the biosynthesis of cocaine, however, only the (S)-enantiomer can cyclize to form the tropane ring system of cocaine. The stereoselectivity of this reaction was further investigated through study of prochiral methylene hydrogen discrimination.[29] This is due to the extra chiral center at C-2.[30] This process occurs through an oxidation, which regenerates the pyrrolinium cation and formation of an enolate anion, and an intramolecular Mannich reaction. The tropane ring system undergoes hydrolysis, SAM-dependent methylation, and reduction via NADPH for the formation of methylecgonine. The benzoyl moiety required for the formation of the cocaine diester is synthesized from phenylalanine via cinnamic acid.[31] Benzoyl-CoA then combines the two units to form cocaine.
Robert Robinson's acetonedicarboxylate
Robinson biosynthesis of tropane
The biosynthesis of the tropane alkaloid, however, is still uncertain. Hemscheidt proposes that Robinson's acetonedicarboxylate emerges as a potential intermediate for this reaction.[32] Condensation of N-methylpyrrolinium and acetonedicarboxylate would generate the oxobutyrate. Decarboxylation leads to tropane alkaloid formation.
Reduction of tropinone
The reduction of tropinone is mediated by NADPH-dependent reductase enzymes, which have been characterized in multiple plant species.[33] These plant species all contain two types of the reductase enzymes, tropinone reductase I and tropinone reductase II. TRI produces tropine and TRII produces pseudotropine. Due to differing kinetic and pH/activity characteristics of the enzymes and by the 25-fold higher activity of TRI over TRII, the majority of the tropinone reduction is from TRI to form tropine.[34]
United States Bridges
- Aerial Lift Bridge - An automobile bridge in Duluth, Minnesota which began life as an aerial transfer or ferry bridge.
Arthur Kill Vertical Lift Bridge - Connecting Elizabeth, New Jersey, and Staten Island, New York; at 170 m span, the longest in the world.
ASB Bridge - A bridge that handled both trains and cars on two decks over the Missouri River in Kansas City, Missouri.
Broadway Bridge a bridge built which spans the Harlem River carrying both traffic from Broadway but also that of the no 1 Train of the New York City Subway .
Burlington-Bristol Bridge - A two-lane bridge over the Delaware River, joining Bristol, Pennsylvania with Burlington, New Jersey between Philadelphia and New York City.
Canal Street railroad bridge - Chicago, IL 1914
Cape Cod Canal Railroad Bridge - A single-track railroad bridge over the Cape Cod Canal in Bourne, Massachusetts.
Cape Fear Memorial Bridge - A four-lane bridge over the Cape Fear River that joins Wilmington and Brunswick County, North Carolina.
Chesapeake & Delaware Canal Lift Bridge - A single-track railroad bridge over the Chesapeake and Delaware Canal in Delaware that was built in 1966 for the Pennsylvania Railroad and replaced an earlier structure when the U.S. Army Corps of Engineers widened the canal in the mid-1960s. It is the only bridge of its type along the canal, with earlier highway lift or swing bridges being replaced by high-level crossings.
Claiborne Avenue Bridge - A four lane bridge over the ICWW carrying LA 39 in New Orleans
Conrail Bridge - A single track railroad bridge over the mouth of the Cuyahoga River in Cleveland, one of nine railroad and automobile lift bridges, and three bascule bridges, allowing ore boats to service the Flats.
Danziger Bridge - The world's widest vertical lift movable bridge, at seven lanes, over the ICWW in New Orleans
Fourteenth Street Bridge (Ohio River) - A single-track railroad bridge over the Ohio River at its widest point, Louisville, Kentucky.
Green Island Bridge - Opened in 1981, its span is a simply supported plate girder bridge supported by a cross member
Hastings Rail Bridge - A single track railroad bridge at Hastings, Minnesota over the Mississippi River
Hawthorne Bridge - A four lane bridge over the Willamette River in Portland, Oregon. Opened in 1910, it is the oldest operating vertical lift bridge in the United States.[6]
Interstate Bridge - Carries Interstate 5 traffic over the Columbia River between Vancouver, Washington, and Portland, Oregon.
Main Street Bridge - A four-lane bridge over the St. Johns River in downtown Jacksonville, Florida.
Marine Parkway-Gil Hodges Memorial Bridge - Crosses Rockaway Inlet between Brooklyn and Queens, New York; designed in 1937 by David Steinman.
Murray Morgan Bridge - Steel lift bridge in Tacoma, Washington. Notable for its height above water, sloping span and overhead span to carry a water pipe. Closed October 23rd, 2007.
Park Avenue Bridge - New York City bridge with a 160-metre (520 ft) span, which replaced a swing bridge in 1960.
Portage Lake Lift Bridge - A bridge which connects the Michigan cities of Hancock and Houghton
Sarah Mildred Long Bridge and Memorial Bridge - Two lift bridges (out of 3 bridges) over the Piscataqua River between Portsmouth, New Hampshire and Kittery, Maine.
Stillwater Bridge - A highway bridge that joins Stillwater, Minnesota with Houlton, Wisconsin over the St. Croix River.
St. Paul Union Pacific Vertical-lift Rail Bridge - A single-track railroad bridge in downtown St. Paul, Minnesota over the Mississippi River.
Steel Bridge - A double-lift bridge in Portland, Oregon over the Willamette River. Its bottom deck carries railroad tracks and a bike lane and can be lifted independently of the upper deck with a road and light rail tracks. It is the only double-deck bridge with independent lifts in the world.[7]
Tower Bridge - A four-lane bridge over the Sacramento River connecting Sacramento and West Sacramento, California.
Torrence Avenue (Chicago, IL) & 4 Railroad bridges along Calumet Shipping Canal
Alaska Building
The Alaska Building is a 14-floor building in Seattle. It was built in 1904 to designs by St. Louis architects Eames and Young. It is currently being converted into a hotel by American Life. At the time of its completion, it was the tallest building in Seattle.
Statement of Significance, credited to Mildred Andrews, Ph.D. of Andrews History Group.
The fourteen-story Alaska Building was completed in 1904, following eleven months of construction. It was designed by Eames and Young, a St. Louis architectural firm, under the supervision of local architects, Saunders and Lawton. The contractor was James Black Masonry Construction.
The history behind the building's construction is of note. In 1897 when Alaskan prospectors came ashore at a Seattle wharf with a "ton of gold," the city marketed itself as the "Gateway to the Klondike." The successful promotional capaign sparked a period of explosive economic and population growth that spurred development of the city's infrastructure, transforming it from a town into a metropolis. In 1903, Seattle's Scandinavian-American Bank, directed by Jafet Lindeberg, J.E. Chillberg and others, purchased the southeast corner of Second Avenue and Cherry Street from the Amos Brown estate with the intention of erecting a new bank building. Shortly after the land purchase, J.C. Marmaduke of St. Louis proposed a partnership to construct the more ambitious Alaska Building. Caught up in the boomtown spirit of the Gold Rush years, the bank's shareholders readily endorsed the project, which was intended to promote business ventures between Alaska and the Pacific Northwest.
As the first steel-frame strucutre of any height in the Northwest, the Alaska Building was Seattle's first "skyscraper" and its tallest building - a distinction that it held until 1911. In addition to its height, it is notable for its Beaux Arts ornamentation, which is a rarity in Seattle. When the building opened, the Alaska Club, a prominent commercial organization of residents and entrepreneurs, convened in the penthouse, and maintained a reading room that featured Alaska newspapers and mineral exhibits; the Scandinavian-American banking hall occupied the main floor. The Alaska Biulding heralded the development of other imposing structures on what soon became the city's major commercial strip, popularly known as the Second Avenue canyon.
In their book, Hard Drive to the Klondike, Lisa Mighetto and Marcia Babcock Montgomery make the following observation, regarding the Alaska Building. "This fourteen-story structure symbolized the significance of the gold rush in Seattle. The porthole windows along the top floor looked out over the waterfront, providing a view of the shipbuilding, shipping and rail industries that the gold rush encouraged. For many years a gold nugget embedded in the building's front door reminded visitors of the stampede and the city's connection to the Far North."
Today, the Alaska Building remains a dominant structure on th enorthern cusp of the Pioneer Square Historic District, which was created by a City of Seattle ordinance in 19070, and which was listed on the National Register of Historic Places the same year as the Pioneer Square Skid Road National Historic District. The Alaska Biulding was rehabilitated by the architects Stickney/Murphy in 1908.
Statement of Significance, credited to Mildred Andrews, Ph.D. of Andrews History Group.
The fourteen-story Alaska Building was completed in 1904, following eleven months of construction. It was designed by Eames and Young, a St. Louis architectural firm, under the supervision of local architects, Saunders and Lawton. The contractor was James Black Masonry Construction.
The history behind the building's construction is of note. In 1897 when Alaskan prospectors came ashore at a Seattle wharf with a "ton of gold," the city marketed itself as the "Gateway to the Klondike." The successful promotional capaign sparked a period of explosive economic and population growth that spurred development of the city's infrastructure, transforming it from a town into a metropolis. In 1903, Seattle's Scandinavian-American Bank, directed by Jafet Lindeberg, J.E. Chillberg and others, purchased the southeast corner of Second Avenue and Cherry Street from the Amos Brown estate with the intention of erecting a new bank building. Shortly after the land purchase, J.C. Marmaduke of St. Louis proposed a partnership to construct the more ambitious Alaska Building. Caught up in the boomtown spirit of the Gold Rush years, the bank's shareholders readily endorsed the project, which was intended to promote business ventures between Alaska and the Pacific Northwest.
As the first steel-frame strucutre of any height in the Northwest, the Alaska Building was Seattle's first "skyscraper" and its tallest building - a distinction that it held until 1911. In addition to its height, it is notable for its Beaux Arts ornamentation, which is a rarity in Seattle. When the building opened, the Alaska Club, a prominent commercial organization of residents and entrepreneurs, convened in the penthouse, and maintained a reading room that featured Alaska newspapers and mineral exhibits; the Scandinavian-American banking hall occupied the main floor. The Alaska Biulding heralded the development of other imposing structures on what soon became the city's major commercial strip, popularly known as the Second Avenue canyon.
In their book, Hard Drive to the Klondike, Lisa Mighetto and Marcia Babcock Montgomery make the following observation, regarding the Alaska Building. "This fourteen-story structure symbolized the significance of the gold rush in Seattle. The porthole windows along the top floor looked out over the waterfront, providing a view of the shipbuilding, shipping and rail industries that the gold rush encouraged. For many years a gold nugget embedded in the building's front door reminded visitors of the stampede and the city's connection to the Far North."
Today, the Alaska Building remains a dominant structure on th enorthern cusp of the Pioneer Square Historic District, which was created by a City of Seattle ordinance in 19070, and which was listed on the National Register of Historic Places the same year as the Pioneer Square Skid Road National Historic District. The Alaska Biulding was rehabilitated by the architects Stickney/Murphy in 1908.
Thursday, April 22, 2010
General use
Aluminium is the most widely used non-ferrous metal.[32] Global production of aluminium in 2005 was 31.9 million tonnes. It exceeded that of any other metal except iron (837.5 million tonnes).[33] Forecast for 2012 is 42–45 million tons, driven by rising Chinese output.[34] Relatively pure aluminium is encountered only when corrosion resistance and/or workability is more important than strength or hardness. A thin layer of aluminium can be deposited onto a flat surface by physical vapour deposition or (very infrequently) chemical vapour deposition or other chemical means to form optical coatings and mirrors. When so deposited, a fresh, pure aluminium film serves as a good reflector (approximately 92%) of visible light and an excellent reflector (as much as 98%) of medium and far infrared radiation.
Pure aluminium has a low tensile strength, but when combined with thermo-mechanical processing, aluminium alloys display a marked improvement in mechanical properties, especially when tempered. Aluminium alloys form vital components of aircraft and rockets as a result of their high strength-to-weight ratio. Aluminium readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon (e.g., duralumin). Today, almost all bulk metal materials that are referred to loosely as "aluminium", are actually alloys. For example, the common aluminium foils are alloys of 92% to 99% aluminium.[35]
Household aluminium foil
Aluminium-bodied Austin "A40 Sports" (circa 1951)
Aluminium slabs being transported from the smelters
Some of the many uses for aluminium metal are in:
Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles etc.) as sheet, tube, castings etc.
Packaging (cans, foil, etc.)
Construction (windows, doors, siding, building wire, etc.)
A wide range of household items, from cooking utensils to baseball bats, watches.[36]
Street lighting poles, sailing ship masts, walking poles etc.
Outer shells of consumer electronics, also cases for equipment e.g. photographic equipment.
Electrical transmission lines for power distribution
MKM steel and Alnico magnets
Super purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs.
Heat sinks for electronic appliances such as transistors and CPUs.
Substrate material of metal-core copper clad laminates used in high brightness LED lighting.
Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.
Aluminium can be reacted with hydrochloric acid to form hydrogen gas.
Pure aluminium has a low tensile strength, but when combined with thermo-mechanical processing, aluminium alloys display a marked improvement in mechanical properties, especially when tempered. Aluminium alloys form vital components of aircraft and rockets as a result of their high strength-to-weight ratio. Aluminium readily forms alloys with many elements such as copper, zinc, magnesium, manganese and silicon (e.g., duralumin). Today, almost all bulk metal materials that are referred to loosely as "aluminium", are actually alloys. For example, the common aluminium foils are alloys of 92% to 99% aluminium.[35]
Household aluminium foil
Aluminium-bodied Austin "A40 Sports" (circa 1951)
Aluminium slabs being transported from the smelters
Some of the many uses for aluminium metal are in:
Transportation (automobiles, aircraft, trucks, railway cars, marine vessels, bicycles etc.) as sheet, tube, castings etc.
Packaging (cans, foil, etc.)
Construction (windows, doors, siding, building wire, etc.)
A wide range of household items, from cooking utensils to baseball bats, watches.[36]
Street lighting poles, sailing ship masts, walking poles etc.
Outer shells of consumer electronics, also cases for equipment e.g. photographic equipment.
Electrical transmission lines for power distribution
MKM steel and Alnico magnets
Super purity aluminium (SPA, 99.980% to 99.999% Al), used in electronics and CDs.
Heat sinks for electronic appliances such as transistors and CPUs.
Substrate material of metal-core copper clad laminates used in high brightness LED lighting.
Powdered aluminium is used in paint, and in pyrotechnics such as solid rocket fuels and thermite.
Aluminium can be reacted with hydrochloric acid to form hydrogen gas.
Methods of manufacture
Bricks may be made from clay, shale, soft slate, calcium silicate, concrete, or shaped from quarried stone.
Clay is the most common material, with modern clay bricks formed in one of three processes - soft mud, dry press, or extruded.
In 2007 a new type of brick was invented, based on fly ash, a by-product of coal power plants.
Brick making at the beginning of the 20th century.
Clay is the most common material, with modern clay bricks formed in one of three processes - soft mud, dry press, or extruded.
In 2007 a new type of brick was invented, based on fly ash, a by-product of coal power plants.
Brick making at the beginning of the 20th century.
[edit] Optimal dimensions, characteristics, and strength
For efficient handling and laying bricks must be small enough and light enough to be picked up by the bricklayer using one hand (leaving the other hand free for the trowel). Bricks are usually laid flat and as a result the effective limit on the width of a brick is set by the distance which can conveniently be spanned between the thumb and fingers of one hand, normally about four inches (about 100 mm). In most cases, the length of a brick is about twice its width, about eight inches (about 200 mm) or slightly more. This allows bricks to be laid bonded in a structure to increase its stability and strength (for an example of this, see the illustration of bricks laid in English bond, at the head of this article). The wall is built using alternating courses of stretchers, bricks laid longways and headers, bricks laid crossways. The headers tie the wall together over its width.
A bigger brick makes for a thicker (and thus more insulating) wall. Historically, this meant that bigger bricks were necessary in colder climates (see for instance the slightly larger size of the Russian brick in table below), while a smaller brick was adequate, and more economical, in warmer regions. A notable illustration of this correlation is the Green Gate in Gdansk; built in 1571 of imported Dutch brick, too small for the colder climate of Gdansk, it was notorious for being a chilly and drafty residence. Nowadays this is no longer an issue, as modern walls typically incorporate specialized insulation materials.
The correct brick for a job can be picked from a choice of colour, surface texture, density, weight, absorption and pore structure, thermal characteristics, thermal and moisture movement, and fire resistance.
Face brick ("house brick") sizes,[12] from small to large
Standard
Imperial
Metric
India
9 × 4¼ × 2¾ inches
228 × 107 × 69 mm
United States
8 × 4 × 2¼ inches
203 × 102 × 57 mm
United Kingdom
8½ × 4 × 2½ inches
215 × 102.5 × 65 mm
South Africa
8¾ × 4 × 3 inches
222 × 106 × 73 mm
Australia
9 × 4⅓ × 3 inches
230 × 110 × 76 mm
Sweden
250 × 120 × 62 mm
Russia
250 × 120 × 65 mm
In England, the length and the width of the common brick has remained fairly constant over the centuries, but the depth has varied from about two inches (about 51 mm) or smaller in earlier times to about two and a half inches (about 64 mm) more recently. In the United States, modern bricks are usually about 8 × 4 × 2.25 inches (203 × 102 × 57 mm). In the United Kingdom, the usual ("work") size of a modern brick is 215 × 102.5 × 65 mm (about 8.5 × 4 × 2.5 inches), which, with a nominal 10 mm mortar joint, forms a "coordinating" or fitted size of 225 × 112.5 × 75 mm, for a ratio of 6:3:2.
Some brickmakers create innovative sizes and shapes for bricks used for plastering (and therefore not visible) where their inherent mechanical properties are more important than the visual ones.[13] These bricks are usually slightly larger, but not as large as blocks and offer the following advantages:
a slightly larger brick requires less mortar and handling (fewer bricks) which reduces cost
ribbed exterior aids plastering
more complex interior cavities allow improved insulation, while maintaining strength.
Blocks have a much greater range of sizes. Standard coordinating sizes in length and height (in mm) include 400×200, 450×150, 450×200, 450×225, 450×300, 600×150, 600×200, and 600×225; depths (work size, mm) include 60, 75, 90, 100, 115, 140, 150, 190, 200, 225, and 250. They are usable across this range as they are lighter than clay bricks. The density of solid clay bricks is around 2,000 kg/m³: this is reduced by frogging, hollow bricks, etc.; but aerated autoclaved concrete, even as a solid brick, can have densities in the range of 450–850 kg/m³.
Bricks may also be classified as solid (less than 25% perforations by volume, although the brick may be "frogged," having indentations on one of the longer faces), perforated (containing a pattern of small holes through the brick removing no more than 25% of the volume), cellular (containing a pattern of holes removing more than 20% of the volume, but closed on one face), or hollow (containing a pattern of large holes removing more than 25% of the brick's volume). Blocks may be solid, cellular or hollow
The term "melfrog" for the indentation on one bed of the brick is a word that often excites curiosity as to its origin. The most likely explanation is that brickmakers also call the block that is placed in the mould to form the indentation a frog. Modern brickmakers usually use plastic frogs but in the past they were made of wood. When these are wet and have clay on them they resemble the amphibious kind of frog and this is where they got their name. Over time this term also came to refer to the indentation left by them.[Matthews 2006]
A bigger brick makes for a thicker (and thus more insulating) wall. Historically, this meant that bigger bricks were necessary in colder climates (see for instance the slightly larger size of the Russian brick in table below), while a smaller brick was adequate, and more economical, in warmer regions. A notable illustration of this correlation is the Green Gate in Gdansk; built in 1571 of imported Dutch brick, too small for the colder climate of Gdansk, it was notorious for being a chilly and drafty residence. Nowadays this is no longer an issue, as modern walls typically incorporate specialized insulation materials.
The correct brick for a job can be picked from a choice of colour, surface texture, density, weight, absorption and pore structure, thermal characteristics, thermal and moisture movement, and fire resistance.
Face brick ("house brick") sizes,[12] from small to large
Standard
Imperial
Metric
India
9 × 4¼ × 2¾ inches
228 × 107 × 69 mm
United States
8 × 4 × 2¼ inches
203 × 102 × 57 mm
United Kingdom
8½ × 4 × 2½ inches
215 × 102.5 × 65 mm
South Africa
8¾ × 4 × 3 inches
222 × 106 × 73 mm
Australia
9 × 4⅓ × 3 inches
230 × 110 × 76 mm
Sweden
250 × 120 × 62 mm
Russia
250 × 120 × 65 mm
In England, the length and the width of the common brick has remained fairly constant over the centuries, but the depth has varied from about two inches (about 51 mm) or smaller in earlier times to about two and a half inches (about 64 mm) more recently. In the United States, modern bricks are usually about 8 × 4 × 2.25 inches (203 × 102 × 57 mm). In the United Kingdom, the usual ("work") size of a modern brick is 215 × 102.5 × 65 mm (about 8.5 × 4 × 2.5 inches), which, with a nominal 10 mm mortar joint, forms a "coordinating" or fitted size of 225 × 112.5 × 75 mm, for a ratio of 6:3:2.
Some brickmakers create innovative sizes and shapes for bricks used for plastering (and therefore not visible) where their inherent mechanical properties are more important than the visual ones.[13] These bricks are usually slightly larger, but not as large as blocks and offer the following advantages:
a slightly larger brick requires less mortar and handling (fewer bricks) which reduces cost
ribbed exterior aids plastering
more complex interior cavities allow improved insulation, while maintaining strength.
Blocks have a much greater range of sizes. Standard coordinating sizes in length and height (in mm) include 400×200, 450×150, 450×200, 450×225, 450×300, 600×150, 600×200, and 600×225; depths (work size, mm) include 60, 75, 90, 100, 115, 140, 150, 190, 200, 225, and 250. They are usable across this range as they are lighter than clay bricks. The density of solid clay bricks is around 2,000 kg/m³: this is reduced by frogging, hollow bricks, etc.; but aerated autoclaved concrete, even as a solid brick, can have densities in the range of 450–850 kg/m³.
Bricks may also be classified as solid (less than 25% perforations by volume, although the brick may be "frogged," having indentations on one of the longer faces), perforated (containing a pattern of small holes through the brick removing no more than 25% of the volume), cellular (containing a pattern of holes removing more than 20% of the volume, but closed on one face), or hollow (containing a pattern of large holes removing more than 25% of the brick's volume). Blocks may be solid, cellular or hollow
The term "melfrog" for the indentation on one bed of the brick is a word that often excites curiosity as to its origin. The most likely explanation is that brickmakers also call the block that is placed in the mould to form the indentation a frog. Modern brickmakers usually use plastic frogs but in the past they were made of wood. When these are wet and have clay on them they resemble the amphibious kind of frog and this is where they got their name. Over time this term also came to refer to the indentation left by them.[Matthews 2006]
