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103-519: Autoclaved aerated concrete ( AAC ) is a lightweight, precast, cellular concrete building material, eco-friendly, suitable for producing concrete-like blocks . It is composed of quartz sand , calcined gypsum , lime , portland cement , water and aluminium powder . AAC products are cured under heat and pressure in an autoclave . Developed in the mid-1920s, AAC provides insulation, fire, and mold -resistance. Forms include blocks, wall panels, floor and roof panels, cladding (façade) panels and lintels. It

206-412: A bitumen binder, which is frequently used for road surfaces , and polymer concretes that use polymers as a binder. Concrete is distinct from mortar . Whereas concrete is itself a building material, mortar is a bonding agent that typically holds bricks , tiles and other masonry units together. Grout is another material associated with concrete and cement. It does not contain coarse aggregates and

309-436: A spindle moulder . For smaller, lighter jobs, the router used in this way can be more convenient than the spindle moulder, with the task of set up being somewhat faster. There is also a much wider range of bit profiles available for the router, although the size is limited. The router table is usually oriented so that the router bit is vertical and the table over which the work is passed is horizontal. Variations on this include

412-433: A French structural and civil engineer . Concrete components or structures are compressed by tendon cables during, or after, their fabrication in order to strengthen them against tensile forces developing when put in service. Freyssinet patented the technique on 2 October 1928. Concrete is an artificial composite material , comprising a matrix of cementitious binder (typically Portland cement paste or asphalt ) and

515-502: A Jet Motor Hand Router. In the 1930s, Stanley Works acquired a line of portable routers from Roy L. Carter, and marketed an 18000 RPM electric hand router similar to modern routers. Further refinement produced the plunge router, invented by ELU (now part of DeWalt ) in Germany around 1949. Modern routers are often used in place of traditional moulding planes or spindle moulder machines for edge decoration (moulding) of timber. Routing

618-399: A base housing a vertically mounted universal electric motor with a collet on the end of its shaft. The bit is height-adjustable to allow protrusion through an opening in a flat sole plate, usually via adjusting the motor-mounting height (the mechanism of adjustment is widely varied among manufacturers). Control of the router is derived from a handle or knob on each side of the device, or by

721-452: A cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and makes it flow more freely. As stated by Abrams' law , a lower water-to-cement ratio yields a stronger, more durable concrete, whereas more water gives a freer-flowing concrete with a higher slump . The hydration of cement involves many concurrent reactions. The process involves polymerization ,

824-400: A concrete component—and become a part of the binder for the aggregate. Fly ash and slag can enhance some properties of concrete such as fresh properties and durability. Alternatively, other materials can also be used as a concrete binder: the most prevalent substitute is asphalt , which is used as the binder in asphalt concrete . Admixtures are added to modify the cure rate or properties of

927-434: A dispersed phase or "filler" of aggregate (typically a rocky material, loose stones, and sand). The binder "glues" the filler together to form a synthetic conglomerate . Many types of concrete are available, determined by the formulations of binders and the types of aggregate used to suit the application of the engineered material. These variables determine strength and density, as well as chemical and thermal resistance of

1030-446: A fine table top, many users prefer a D handle, with variable speed, as it seems to permit better control and burning the wood can be minimized. Routers have many uses. With the help of the multitude of jigs and various bits, they are capable of producing dovetails, mortises, and tenons, moldings of infinite varieties, dados, rabbets/rebates , raised-panel doors and frames, cutting circles, and so much more. The tool usually consists of

1133-452: A greater degree of fracture resistance even in seismically active environments. Roman concrete is significantly more resistant to erosion by seawater than modern concrete; it used pyroclastic materials which react with seawater to form Al- tobermorite crystals over time. The use of hot mixing and the presence of lime clasts are thought to give the concrete a self-healing ability, where cracks that form become filled with calcite that prevents

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1236-546: A key event in the history of architecture termed the Roman architectural revolution , freed Roman construction from the restrictions of stone and brick materials. It enabled revolutionary new designs in terms of both structural complexity and dimension. The Colosseum in Rome was built largely of concrete, and the Pantheon has the world's largest unreinforced concrete dome. Concrete, as

1339-415: A large aggregate that is too large for the size of the formwork, or which has too few smaller aggregate grades to serve to fill the gaps between the larger grades, or using too little or too much sand for the same reason, or using too little water, or too much cement, or even using jagged crushed stone instead of smoother round aggregate such as pebbles. Any combination of these factors and others may result in

1442-461: A large type of industrial facility called a concrete plant , or often a batch plant. The usual method of placement is casting in formwork , which holds the mix in shape until it has set enough to hold its shape unaided. Concrete plants come in two main types, ready-mix plants and central mix plants. A ready-mix plant blends all of the solid ingredients, while a central mix does the same but adds water. A central-mix plant offers more precise control of

1545-546: A major museum with similar roof construction, was ordered permanently closed 21 June 2024 because of severely deteriorated roof panels dating from its opening in 1969. While repair options were proposed, the centre's ultimate owner, the provincial government of Ontario , had previously announced plans to relocate the centre and therefore requested the facility be closed immediately rather than paying for repairs. Approximately 400 other public buildings in Ontario are understood to contain

1648-451: A mix which is too harsh, i.e., which does not flow or spread out smoothly, is difficult to get into the formwork, and which is difficult to surface finish. Wood router There is also a traditional hand tool known as a router plane , a form of hand plane with a broad base and a narrow blade projecting well beyond the base plate. CNC wood routers add the advantages of computer numerical control (CNC). The laminate trimmer

1751-469: A mixture of calcium silicates ( alite , belite ), aluminates and ferrites —compounds, which will react with water. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay or shale (a source of silicon, aluminium and iron) and grinding this product (called clinker ) with a source of sulfate (most commonly gypsum ). Cement kilns are extremely large, complex, and inherently dusty industrial installations. Of

1854-405: A number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted. The size distribution of the aggregate determines how much binder is required. Aggregate with a very even size distribution has the biggest gaps whereas adding aggregate with smaller particles tends to fill these gaps. The binder must fill the gaps between the aggregate as well as paste

1957-639: A polymer-modified stucco or plaster compound, or a covering of siding materials such as natural or manufactured stone, veneer brick , metal or vinyl siding . AAC materials can be routed, sanded, or cut to size on-site using a hand saw and standard power tools with carbon steel cutters. Autoclaved aerated concrete is also known by various other names, including autoclaved cellular concrete (ACC), autoclaved concrete , cellular concrete , porous concrete , Aircrete , Thermalite , Hebel , Aercon , Starken , Gasbeton , Airbeton , Durox , Siporex (silicon pore expansion), Suporex , H+H and Ytong . AAC

2060-576: A roofing collapse, other buildings were found to have issues with their RAAC construction, with some of these only being discovered to have been made from RAAC during the crisis. During the 2023 crisis, it was observed that it was likely for RAAC in other countries to exhibit problems similar to those found in the United Kingdom. The original site of the Ontario Science Centre in Toronto, Canada,

2163-424: A semi-liquid slurry (paste) that can be shaped, typically by pouring it into a form. The concrete solidifies and hardens through a chemical process called hydration . The water reacts with the cement, which bonds the other components together, creating a robust, stone-like material. Other cementitious materials, such as fly ash and slag cement , are sometimes added—either pre-blended with the cement or directly as

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2266-493: A simple, fast way of getting a basic idea of the properties of the finished concrete without having to perform testing in advance. Various governing bodies (such as British Standards ) define nominal mix ratios into a number of grades, usually ranging from lower compressive strength to higher compressive strength. The grades usually indicate the 28-day cure strength. Thorough mixing is essential to produce uniform, high-quality concrete. Separate paste mixing has shown that

2369-461: A small empire in the regions of southern Syria and northern Jordan from the 4th century BC. They discovered the advantages of hydraulic lime , with some self-cementing properties, by 700 BC. They built kilns to supply mortar for the construction of rubble masonry houses, concrete floors, and underground waterproof cisterns . They kept the cisterns secret as these enabled the Nabataeans to thrive in

2472-419: A small router may cut rapidly. Owing to inertia at these high speeds, the normal wood cutting mechanism of Type I chips cannot take place. The cutter edge angle is blunt, approaching 90°, and so a Type III chip forms, with waste material produced as fine dust. This dust is a respiratory hazard, even in benign materials. The forces against the cutter are light, so routers may be hand-held. When milling metals,

2575-484: A three motor drive system utilizing either servo or stepper motors. More advanced routers use a four motor system for added speed and accuracy. A tool similar to a router, but designed to hold smaller cutting bits—thereby making it easier to handle for small jobs—is a laminate trimmer . A related tool, called a spindle moulder (UK) or shaper (North America), is used to hold larger cutter heads and can be used for deeper or larger-diameter cuts. Another related machine

2678-415: A variety of router styles, some are plunge, some are D handled, some are double knob handled. Different manufacturers produce the routers for different wood works, as plunge routers, fixed-base wood routers, combo routers, variable-speed routers, laminate trimmers, CNC wood routers. Nowadays, most better quality routers have variable speed controls and will have plunge bases that can also be locked in place so

2781-409: A variety of tooled processes performed. The hydration process is exothermic , which means ambient temperature plays a significant role in how long it takes concrete to set. Often, additives (such as pozzolans or superplasticizers ) are included in the mixture to improve the physical properties of the wet mix, delay or accelerate the curing time, or otherwise change the finished material. Most concrete

2884-524: Is a concrete-based material used for both exterior and interior construction. One of its advantages is quick and easy installation because the material can be routed , sanded, or cut to size on-site using a hand saw and standard power tools with carbon steel cutters. AAC is well suited for high-rise buildings and those with high temperature variations. Due to its lower density, high-rise buildings constructed using AAC require less steel and concrete for structural members. The mortar needed for laying AAC blocks

2987-534: Is a high speed process of cutting, trimming, and shaping wood, metal, plastic, and a variety of other materials. Routing and milling are conceptually similar, and end mills can be used in routers, but routing wood is different from milling metal in terms of the mechanics. Chip formation is different, so the optimal tool geometry is different. Routing is properly applied to relatively weak and brittle materials, typically wood. As these materials are weak in small sections, routers can run at extremely high speeds, so even

3090-409: Is a smaller, lighter version of the router. Although it is designed for trimming laminates , it can also be used for smaller general routing work. Rotary tools can also be used similarly to routers with the right bits and accessories (such as plastic router bases). Before power routers existed, the router plane was often used for the same purpose. An incremental step toward modern power routers

3193-431: Is also an insulator. AAC products see use in construction, such as industrial buildings, residential houses, apartment buildings, and townhouses. Their applications include exterior and interior walls, firewalls, wet room walls, diffusion-open thermal insulation boards, intermediate floors, upper floors, stairs, opening crossings, beams and pillars. Exterior uses require an applied finish to guard against weathering, such as

Autoclaved aerated concrete - Misplaced Pages Continue

3296-412: Is five times less than the production of other building materials. There is no loss of raw materials in the production process, and all production waste is returned to the production cycle. Production of aerated concrete requires less energy than for all other masonry products, thereby reducing the use of fossil fuels and associated carbon dioxide (CO 2 ) emissions. The curing process also saves energy, as

3399-468: Is flat and had been covered with cement". "The floors were cement, in some places hard, but, by long exposure, broken, and now crumbling under the feet." "But throughout the wall was solid, and consisting of large stones imbedded in mortar, almost as hard as rock." Small-scale production of concrete-like materials was pioneered by the Nabatean traders who occupied and controlled a series of oases and developed

3502-403: Is important to check to verify the switch is in the off position, prior to plugging it in. For safety, larger router cutters can usually only be used in a router that is mounted in a router table. This makes the tool even more versatile and stable. The purpose of multiple handle arrangements depends on the bit. Control is easier with different configurations. For example, when shaping the edge of

3605-406: Is mixed and cast in forms, aluminium powder reacts with calcium hydroxide and water to form hydrogen . The hydrogen gas foams and doubles the volume of the raw mix creating gas bubbles up to 3 millimetres ( 1 ⁄ 8  in) in diameter—it has been described as having bubbles inside like "a chocolate Aero bar ". At the end of the foaming process, the hydrogen escapes into the atmosphere and

3708-404: Is mounted to the underside of the table, with a hole allowing the bit to protrude above the table top. This allows the work to be passed over the router, rather than passing the router over the work. This has benefits when working with smaller objects and makes some router operations safer to execute. A router table may be fitted with a fence , fingerboards and other work-guiding accessories to make

3811-424: Is often caused by RAAC's high susceptibility to water infiltration due to its porous nature, which causes corrosion of internal reinforcements in ways that are hard to detect. This places increased tensile stress on the bond between the reinforcement and concrete, lowering the material's service life. Detailed risk analyses are required on a structure-by-structure basis to identify areas in need of maintenance and lower

3914-425: Is positioned at the finer end of the scale of work done by a molding spindle. That is to say it is able to cut grooves, edge molding, and chamfer or radius the edge of a piece of wood. It is also possible to use it for cutting some joints . The shape of cut that is created is determined by the size and shape of the bit (cutter) held in the collet and the depth by the depth adjustment of the sole plate. There are

4017-566: Is poured with reinforcing materials (such as steel rebar ) embedded to provide tensile strength , yielding reinforced concrete . In the past, lime -based cement binders, such as lime putty, were often used but sometimes with other hydraulic cements , (water resistant) such as a calcium aluminate cement or with Portland cement to form Portland cement concrete (named for its visual resemblance to Portland stone ). Many other non-cementitious types of concrete exist with other methods of binding aggregate together, including asphalt concrete with

4120-427: Is produced using no aggregate larger than sand. Quartz sand (SiO 2 ), calcined gypsum, lime (mineral) and/or cement and water are used as a binding agent. Aluminum powder is used at a rate of 0.05%–0.08% by volume (depending on the pre-specified density). In some countries, like India and China, fly ash generated from coal-fired power plants , and having 50–65% silica content, is used as an aggregate. When AAC

4223-417: Is reduced due to the lower number of joints. Similarly, less material is required for rendering, because AAC can be shaped precisely before installation. Even though regular cement mortar can be used, most buildings that use AAC materials use thin bed mortar in thicknesses around 3.2 millimetres ( 1 ⁄ 8  in), depending on the national building codes. Unlike most other concrete applications, AAC

Autoclaved aerated concrete - Misplaced Pages Continue

4326-611: Is replaced by air, leaving a product as light as 20% of the weight of conventional concrete. When the forms are removed from the material, it is solid but still soft. It is then cut into either blocks or panels and placed in an autoclave chamber for 12 hours. During this steam pressure hardening process, when the temperature reaches 190 °C (374 °F) and the pressure reaches 800 to 1,200 kPa (8.0 to 12.0 bar; 120 to 170 psi), quartz sand reacts with calcium hydroxide to form calcium silicate hydrate , which gives AAC its high strength and other unique properties. Because of

4429-559: Is then blended with aggregates and any remaining batch water and final mixing is completed in conventional concrete mixing equipment. Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (pouring, pumping, spreading, tamping, vibration) and without reducing the concrete's quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration ) and can be modified by adding chemical admixtures, like superplasticizer. Raising

4532-508: Is twice that of steel, wood, plastics, and aluminium combined. When aggregate is mixed with dry Portland cement and water , the mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts with the water through a process called concrete hydration that hardens it over several hours to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. This time allows concrete to not only be cast in forms, but also to have

4635-562: Is usually either pourable or thixotropic , and is used to fill gaps between masonry components or coarse aggregate which has already been put in place. Some methods of concrete manufacture and repair involve pumping grout into the gaps to make up a solid mass in situ . The word concrete comes from the Latin word " concretus " (meaning compact or condensed), the perfect passive participle of " concrescere ", from " con -" (together) and " crescere " (to grow). Concrete floors were found in

4738-711: Is usually more of an improvised expedient than a production process, and is noisy and hard on tools. Routing is usually limited to soft metals (aluminium etc.) and rigid non-metals. Specially designed cutters are used for a variety of patterns, cuts, and edging. Both hand controlled and machine controlled/aided routers are common today. Routing is a shaping process that produces finished edges and shapes. Some materials that are difficult to shape with other processes, such as fiber-glass, Kevlar, and graphite, can be shaped and finished neatly via various routing techniques. Apart from finished edges and shaping, cutaways, holes, and contours can also be shaped using routers. The spindle router

4841-399: Is usually reinforced with materials that are strong in tension, typically steel rebar . The mix design depends on the type of structure being built, how the concrete is mixed and delivered, and how it is placed to form the structure. Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar , and many plasters . It consists of

4944-480: The construction industry , whose demand is ever growing with greater impacts on raw material extraction, waste generation and landfill practices. Concrete production is the process of mixing together the various ingredients—water, aggregate, cement, and any additives—to produce concrete. Concrete production is time-sensitive. Once the ingredients are mixed, workers must put the concrete in place before it hardens. In modern usage, most concrete production takes place in

5047-769: The AAC was used. This problem was addressed in 1972 by the Swedish Radiation Safety Authority, and by 1975, Ytong abandoned alum shale in favor of a formulation made from quartz sand, calcined gypsum, lime (mineral), cement, water and aluminium powder currently in use by most major brands. In 1978, Siporex Sweden opened the Siporex Factory in Saudi Arabia , establishing the Lightweight Construction Company - Siporex - LCC SIPOREX, targeting markets in

5150-720: The Middle East, Africa, and Japan. This factory was still in use in 2018. Today, the production of AAC is widespread, concentrated in Europe and Asia with some facilities located in the Americas. Egypt has the sole manufacturing plant in Africa. Although the European AAC market has seen a reduction in growth, Asia is experiencing a rapid expansion in the industry, driven by an escalating need for residential and commercial spaces. Currently, China has

5253-504: The Romans knew it, was a new and revolutionary material. Laid in the shape of arches , vaults and domes , it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick. Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete (c. 200 kg/cm  [20 MPa; 2,800 psi]). However, due to

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5356-668: The Second World War. In Europe, it gained popularity in the mid-1950s as a cheaper and more lightweight alternative to conventional reinforced concrete, with documented widespread use in a number of European countries as well as Japan and former territories of the British Empire. RAAC was used in roof, floor and wall construction due to its lighter weight and lower cost compared to traditional concrete, and has good fire resistance properties; it does not require plastering to achieve good fire resistance and fire does not cause spalls . RAAC

5459-584: The United States. AAC is increasingly used worldwide by developers. Reinforced autoclaved aerated concrete (RAAC) is a reinforced version of autoclaved aerated concrete, commonly used in roofing and wall construction. The first structural reinforced roof and floor panels were manufactured in Sweden, soon after the first autoclaved aerated concrete block plant started up there in 1929, but Belgian and German technologies became market leaders for RAAC elements after

5562-639: The absence of reinforcement, its tensile strength was far lower than modern reinforced concrete , and its mode of application also differed: Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble . Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon

5665-407: The bit used must be shaped so it bores into the wood when lowered. The baseplate (sole plate) is generally circular (though this, too, varies by individual models) and may be used in conjunction with a fence attached to the base, which then braces the router against the edge of the work, or via a straight-edge clamped across the work to obtain a straight cut. Other means of guiding the machine include

5768-554: The chance of catastrophic failure. Professional engineering concern about the structural performance of RAAC was first publicly raised in the United Kingdom in 1995 following inspections of cracked units in British school roofs, and was subsequently reinforced in 2022 when the Government Property Agency declared the material to be life-expired, and in 2023 when, following the partial or total closure of 174 schools at risk of

5871-645: The compressive strength of regular concrete. In 1978, the first AAC material factory - the LCC Siporex- Lightweight Construction Company - was opened in the Persian Gulf state of Saudi Arabia , supplying Gulf Cooperation Council countries with aerated blocks and panels. Since 1980, there has been a worldwide increase in the use of AAC materials. New production plants are being built in Australia, Bahrain , China, Eastern Europe , India and

5974-526: The concrete at the time of batching/mixing. (See § Production below.) The common types of admixtures are as follows: Inorganic materials that have pozzolanic or latent hydraulic properties, these very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cements). Products which incorporate limestone , fly ash , blast furnace slag , and other useful materials with pozzolanic properties into

6077-399: The concrete can cause the initially placed material to begin to set before the next batch is added on top. This creates a horizontal plane of weakness called a cold joint between the two batches. Once the mix is where it should be, the curing process must be controlled to ensure that the concrete attains the desired attributes. During concrete preparation, various technical details may affect

6180-461: The concrete quality. Central mix plants must be close to the work site where the concrete will be used, since hydration begins at the plant. A concrete plant consists of large hoppers for storage of various ingredients like cement, storage for bulk ingredients like aggregate and water, mechanisms for the addition of various additives and amendments, machinery to accurately weigh, move, and mix some or all of those ingredients, and facilities to dispense

6283-477: The crack from spreading. The widespread use of concrete in many Roman structures ensured that many survive to the present day. The Baths of Caracalla in Rome are just one example. Many Roman aqueducts and bridges, such as the magnificent Pont du Gard in southern France, have masonry cladding on a concrete core, as does the dome of the Pantheon . After the Roman Empire, the use of burned lime and pozzolana

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6386-690: The dangerous situation of the bit coming out of the collet during operation. Many routers come with removable collets for the popular shank sizes (in the US 1 ⁄ 2  in and 1 ⁄ 4  in, in Great Britain 1 ⁄ 2  in, 8 mm and 1 ⁄ 4  in, and metric sizes in Europe—although in the United States the 3 ⁄ 8  in and 8 mm sizes are often only available for an extra cost). Many modern routers allow

6489-554: The desert. Some of these structures survive to this day. In the Ancient Egyptian and later Roman eras, builders discovered that adding volcanic ash to lime allowed the mix to set underwater. They discovered the pozzolanic reaction . The Romans used concrete extensively from 300 BC to AD 476. During the Roman Empire, Roman concrete (or opus caementicium ) was made from quicklime , pozzolana and an aggregate of pumice . Its widespread use in many Roman structures ,

6592-528: The diameter of their shank, with 1 ⁄ 2 -inch, 12 mm, 10 mm, 3 ⁄ 8 -inch, 8 mm and 1 ⁄ 4 -inch and 6 mm shanks (ordered from thickest to thinnest) being the most common. Half-inch bits cost more but, being stiffer, are less prone to vibration (giving smoother cuts) and are less likely to break than the smaller sizes. Care must be taken to ensure the bit shank and router collet sizes match exactly. Failure to do so can cause permanent damage to either or both and can lead to

6695-431: The finished product. Construction aggregates consist of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone , or granite , along with finer materials such as sand . Cement paste, most commonly made of Portland cement , is the most prevalent kind of concrete binder. For cementitious binders, water is mixed with the dry cement powder and aggregate, which produces

6798-559: The horizontal router table, in which the table remains horizontal but the router is mounted vertically above the table, so that the router bit cuts from the side. This alternative is for edge operations, such as panel raising and slot cutting. Router bits come in a large variety of designs to create either decorative effects or joinery aids. Generally, they are classified as either high-speed steel (HSS) or carbide-tipped , however some recent innovations such as solid carbide bits provide even more variety for specialized tasks. Aside from

6901-554: The interlinking of the silicates and aluminate components as well as their bonding to sand and gravel particles to form a solid mass. One illustrative conversion is the hydration of tricalcium silicate: The hydration (curing) of cement is irreversible. Fine and coarse aggregates make up the bulk of a concrete mixture. Sand , natural gravel, and crushed stone are used mainly for this purpose. Recycled aggregates (from construction, demolition, and excavation waste) are increasingly used as partial replacements for natural aggregates, while

7004-423: The joinery used in frame and panel construction. One bit is designed to cut the grove in the rail and stile pieces while the other shapes the edge of the panel to fit in the grove. A CNC wood router is a computer controlled machine to which the router or spindle mounts. The CNC Machine can be either a moving gantry style, where the table is fixed and the router spindle moves over it, or fixed bridge design, where

7107-655: The largest Aircrete market globally, with several hundred manufacturing plants. The most significant AAC production and consumption occur in China, Central Asia, India, and the Middle East, reflecting the dynamic growth and demand in these regions. Like other masonry materials, the product Aircrete is sold under many different brand names. Ytong and Hebel are brands of the international operating company Xella, headquartered in Duisburg. Other more internationally renowned brand names in Europe are H+H Celcon (Denmark) and Solbet (Poland). AAC

7210-406: The making of mortar. In an English translation from 1397, it reads "lyme ... is a stone brent; by medlynge thereof with sonde and water sement is made". From the 14th century, the quality of mortar was again excellent, but only from the 17th century was pozzolana commonly added. The Canal du Midi was built using concrete in 1670. Perhaps the greatest step forward in the modern use of concrete

7313-529: The material and are under review, but no other closures were anticipated at the time of the Science Centre closure. The high resource efficiency of autoclaved aerated concrete contributes to a lower environmental impact than conventional concrete, from raw material processing to the disposal of aerated concrete waste. Due to continuous improvements in efficiency, the production of aerated concrete blocks requires relatively little raw materials per m of product and

7416-404: The material is relatively ductile, although remaining strong even at a small scale. A Type II chip forms, and waste may be produced as continuous swarf . Cutter forces are high, so milling machines must be robust and rigid, usually substantial constructions of cast iron. Intermediate materials, such as plastics and sometimes soft aluminium, may be cut by either method, though routing aluminium

7519-531: The material. Mineral admixtures use recycled materials as concrete ingredients. Conspicuous materials include fly ash , a by-product of coal-fired power plants ; ground granulated blast furnace slag , a by-product of steelmaking ; and silica fume , a by-product of industrial electric arc furnaces . Structures employing Portland cement concrete usually include steel reinforcement because this type of concrete can be formulated with high compressive strength , but always has lower tensile strength . Therefore, it

7622-469: The materials they are made of, bits can be classified as edge bits or non-edge bits, and whether the bit is designed to be anti-kickback . Edge bits have a small wheel bearing to act as a fence against the work in making edge moldings. These bearings can be changed by using commercially available bearing kits. Changing the bearing, in effect, changes the diameter of the cutting edge. This is especially important with rabbeting/rebating bits. Non-edge bits require

7725-419: The mix, are being tested and used. These developments are ever growing in relevance to minimize the impacts caused by cement use, notorious for being one of the largest producers (at about 5 to 10%) of global greenhouse gas emissions . The use of alternative materials also is capable of lowering costs, improving concrete properties, and recycling wastes, the latest being relevant for circular economy aspects of

7828-478: The mixed concrete, often to a concrete mixer truck. Modern concrete is usually prepared as a viscous fluid, so that it may be poured into forms. The forms are containers that define the desired shape. Concrete formwork can be prepared in several ways, such as slip forming and steel plate construction . Alternatively, concrete can be mixed into dryer, non-fluid forms and used in factory settings to manufacture precast concrete products. Interruption in pouring

7931-441: The mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete. The paste is generally mixed in a high-speed , shear-type mixer at a w/c (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, superplasticizers , pigments , or silica fume . The premixed paste

8034-427: The more recently developed "D-handle". There are two standard types of router—plunge and fixed. When using a plunge-base router , the sole of the base is placed on the face of the work with the cutting bit raised above the work, then the motor is turned on and the cutter is lowered into the work. With a fixed-base router , the cut depth is set before the tool is turned on. The sole plate is then either rested flat on

8137-438: The operation safer and more accurate. A simple router table consists of a rigid top with the router bolted or screwed directly to the underside. More complex solutions can be developed to allow the router to be easily removed from the table as well as facilitate adjusting the router's bit height using a lift mechanism; there is a wide range of commercially available systems. In this mode, the router can perform tasks similar to

8240-506: The properties or increase the performance envelope of the mix. Design-mix concrete can have very broad specifications that cannot be met with more basic nominal mixes, but the involvement of the engineer often increases the cost of the concrete mix. Concrete mixes are primarily divided into nominal mix, standard mix and design mix. Nominal mix ratios are given in volume of Cement : Sand : Aggregate {\displaystyle {\text{Cement : Sand : Aggregate}}} . Nominal mixes are

8343-468: The quality and nature of the product. Design mix ratios are decided by an engineer after analyzing the properties of the specific ingredients being used. Instead of using a 'nominal mix' of 1 part cement, 2 parts sand, and 4 parts aggregate (the second example from above), a civil engineer will custom-design a concrete mix to exactly meet the requirements of the site and conditions, setting material ratios and often designing an admixture package to fine-tune

8446-463: The relatively low temperature used, AAC blocks are not considered to be a fired brick but a lightweight concrete masonry unit . After the autoclaving process, the material is stored and shipped to construction sites for use. Depending on its density , up to 80% of the volume of an AAC block is air. AAC's low density also accounts for its low structural compression strength. It can carry loads of up to 8,000 kPa (1,200 psi), approximately 50% of

8549-402: The router can be used as a fixed-base router. Some have a soft-start feature, meaning they build up speed gradually. This feature is particularly desirable for routers with a large cutter. Holding a 3-horsepower router and turning it on without a soft-start is potentially dangerous, due to the torque of the motor. Holding it with two hands is a must. For routers with a toggle type on/off switch it

8652-632: The royal palace of Tiryns , Greece, which dates roughly to 1400 to 1200 BC. Lime mortars were used in Greece, such as in Crete and Cyprus, in 800 BC. The Assyrian Jerwan Aqueduct (688 BC) made use of waterproof concrete . Concrete was used for construction in many ancient structures. Mayan concrete at the ruins of Uxmal (AD 850–925) is referenced in Incidents of Travel in the Yucatán by John L. Stephens . "The roof

8755-471: The speed of the bit's rotation to be varied. A slower rotation allows bits of larger cutting diameter to be used safely. Typical speeds range from 8,000 to 30,000 rpm. Router bits can be made to match almost any imaginable profile. Custom router bits can be ordered. They are especially beneficial for home restoration projects, where production of the original trim and molding has been discontinued. Sometimes complementary bits come in sets designed to facilitate

8858-414: The steam curing takes place at relatively low temperatures and the hot steam generated in the autoclaves is reused for subsequent batches. AAC has been produced for more than 70 years and has several advantages over other cement construction materials, one of the most important being its lower environmental impact. AAC has been produced for more than 70 years. However, some disadvantages were found when it

8961-411: The strength of the concrete bonding to resist tension. The long-term durability of Roman concrete structures has been found to be due to its use of pyroclastic (volcanic) rock and ash, whereby the crystallization of strätlingite (a specific and complex calcium aluminosilicate hydrate) and the coalescence of this and similar calcium–aluminium-silicate–hydrate cementing binders helped give the concrete

9064-497: The surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers. Admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. Admixtures are defined as additions "made as the concrete mix is being prepared". The most common admixtures are retarders and accelerators. In normal use, admixture dosages are less than 5% by mass of cement and are added to

9167-535: The surfaces of the aggregate together, and is typically the most expensive component. Thus, variation in sizes of the aggregate reduces the cost of concrete. The aggregate is nearly always stronger than the binder, so its use does not negatively affect the strength of the concrete. Redistribution of aggregates after compaction often creates non-homogeneity due to the influence of vibration. This can lead to strength gradients. Decorative stones such as quartzite , small river stones or crushed glass are sometimes added to

9270-406: The table moves underneath the router spindle, or hand-held style, where the operator moves the machine to the area to be cut and the machine controls the fine adjustments. CAD / CAM software programming is used to model the part that is to be created in the computer and then create a tool path for the machine to follow to cut out the part. The CNC moves along three axes (X-Y-Z). Most CNC routers have

9373-423: The template guide bushing secured in the base around the router cutter, or router cutters with built-in guide bearings. Both of these run against a straight edge or shaped template. Without this, the varying reaction of the wood against the torque of the tool makes it impossible to control with the precision normally required. A router may be mounted upside down in a router table or bench. The router's base plate

9476-412: The use of a fence, either on a router table or attached to the work or router. Anti-kickback bits employ added non-cutting bit material around the circumference of the bit's shoulders which serves to limit feed-rate. This reduces the chance that the workpiece is pushed too deeply into the bit (which would result in significant kickback from the cutting edge being unable to compensate). Bits also differ by

9579-655: The various ingredients used to produce a given quantity of concrete, the cement is the most energetically expensive. Even complex and efficient kilns require 3.3 to 3.6 gigajoules of energy to produce a ton of clinker and then grind it into cement . Many kilns can be fueled with difficult-to-dispose-of wastes, the most common being used tires. The extremely high temperatures and long periods of time at those temperatures allows cement kilns to efficiently and completely burn even difficult-to-use fuels. The five major compounds of calcium silicates and aluminates comprising Portland cement range from 5 to 50% in weight. Combining water with

9682-439: The water content or adding chemical admixtures increases concrete workability. Excessive water leads to increased bleeding or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. Changes in gradation can also affect workability of the concrete, although a wide range of gradation can be used for various applications. An undesirable gradation can mean using

9785-399: The workpiece overhanging the edge so that the cutting bit is not contacting the work (and then entering the work from the side once the motor is turned on), or the sole plate is placed at an angle with the bit above the work and the bit is "rocked" over into the work once the motor is turned on. In each case, the bit cuts its way in, but the plunge router does it in a more refined way, although

9888-515: Was Smeaton's Tower , built by British engineer John Smeaton in Devon , England, between 1756 and 1759. This third Eddystone Lighthouse pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. A method for producing Portland cement was developed in England and patented by Joseph Aspdin in 1824. Aspdin chose the name for its similarity to Portland stone , which

9991-519: Was established in Sweden in 1939, and presently licenses and owns plants in 35 locations around the world. Josef Hebel of Memmingen established another cellular concrete brand, Hebel, which opened their first plant in Germany in 1943. Ytong AAC was originally produced in Sweden using alum shale , which contained combustible carbon beneficial to the production process. However, these deposits were found to contain natural uranium , which decays over time to radon , which then accumulates in structures where

10094-529: Was first created in the mid-1920s by the Swedish architect and inventor Dr. Johan Axel Eriksson (1888–1961), along with Professor Henrik Kreüger at the Royal Institute of Technology . The process was patented in 1924. In 1929, production started in Sweden in the city of Yxhult . "Yxhults Ånghärdade Gasbetong" later became the first registered building materials brand in the world: Ytong. Another brand, "Siporex",

10197-602: Was greatly reduced. Low kiln temperatures in the burning of lime, lack of pozzolana, and poor mixing all contributed to a decline in the quality of concrete and mortar. From the 11th century, the increased use of stone in church and castle construction led to an increased demand for mortar. Quality began to improve in the 12th century through better grinding and sieving. Medieval lime mortars and concretes were non-hydraulic and were used for binding masonry, "hearting" (binding rubble masonry cores) and foundations. Bartholomaeus Anglicus in his De proprietatibus rerum (1240) describes

10300-449: Was introduced in the UK (where double-leaf masonry, also known as cavity walls , are the norm). Concrete Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures to a solid over time. Concrete is the second-most-used substance in the world after water , and is the most widely used building material. Its usage worldwide, ton for ton,

10403-614: Was quarried on the Isle of Portland in Dorset , England. His son William continued developments into the 1840s, earning him recognition for the development of "modern" Portland cement. Reinforced concrete was invented in 1849 by Joseph Monier . and the first reinforced concrete house was built by François Coignet in 1853. The first concrete reinforced bridge was designed and built by Joseph Monier in 1875. Prestressed concrete and post-tensioned concrete were pioneered by Eugène Freyssinet ,

10506-580: Was the foot-pedal operated router, such as the Barnes Former/Shaper, available in 1877. Barnes patented a reversible rotary cutting head in 1889. The first portable power router was patented in 1906 by George Kelley and marketed by the Kelley Electric Machine Company. The early electric routers were quite heavy, and only nominally "portable". In 1915 Oscar and Rudy Onsrud produced an air-powered router, which they referred to as

10609-487: Was used in construction in Europe, in buildings constructed after the mid-1950s. RAAC elements have also been used in Japan as walling units owing to their good behaviour in seismic conditions. RAAC has been shown to have limited structural reinforcement bar ( rebar ) integrity in 40 to 50 year-old RAAC roof panels, which began to be observed in the 1990s. The material is liable to fail without visible deterioration or warning. This

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