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84-616: Smith Mountain Dam is a concrete arch dam located on the Roanoke River in Virginia , creating Smith Mountain Lake . The dam was built by Appalachian Power (a division of American Electric Power ) between 1960 and 1963 for the purposes of pumped-storage hydroelectricity . The dam created Smith Mountain Lake as its reservoir, where recreation and real estate have become popular. In

168-425: A Warren truss , and also thought of this rebar as shear reinforcement. Kahn's reinforcing system was built in concrete beams, joists, and columns. The system was both praised and criticized by Kahn's engineering contemporaries: Turner voiced strong objections to this system as it could cause catastrophic failure to concrete structures. He rejected the idea that Kahn's reinforcing system in concrete beams would act as

252-412: 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

336-481: A mortar joint (every fourth or fifth course of block) or vertically (in the horizontal voids of cement blocks and cored bricks, which is then fixed in place with grout . Masonry structures held together with grout have similar properties to concrete – high compressive resistance but a limited ability to carry tensile loads. When rebar is added they are known as "reinforced masonry". A similar approach (of embedding rebar vertically in designed voids in engineered blocks)

420-433: 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

504-422: A Warren truss and also noted that this system would not provide the adequate amount of shear stress reinforcement at the ends of the simply supported beams, the place where the shear stress is greatest. Furthermore, Turner warned that Kahn's system could result in a brittle failure as it did not have longitudinal reinforcement in the beams at the columns. This type of failure manifested in the partial collapse of

588-452: 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 ,

672-400: 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

756-434: 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

840-452: 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

924-559: 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

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1008-415: 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

1092-461: 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

1176-399: A larger-scale collapse of the structure. To prevent such a failure, rebar is either deeply embedded into adjacent structural members (40–60 times the diameter), or bent and hooked at the ends to lock it around the concrete and other rebar. This first approach increases the friction locking the bar into place, while the second makes use of the high compressive strength of concrete. Common rebar

1260-495: 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. Rebar The most common type of rebar is carbon steel , typically consisting of hot-rolled round bars with deformation patterns embossed into its surface. Steel and concrete have similar coefficients of thermal expansion , so a concrete structural member reinforced with steel will experience minimal differential stress as

1344-469: 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

1428-405: 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

1512-424: 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

1596-493: 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

1680-467: 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

1764-435: A specific performance requirement that carbon steel does not provide. Reinforcing bars in masonry construction have been used since antiquity , with Rome using iron or wooden rods in arch construction. Iron tie rods and anchor plates were later employed across Medieval Europe, as a device to reinforce arches, vaults , and cupolas . 2,500 meters of rebar was used in the 14th-century Château de Vincennes . During

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1848-409: 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

1932-417: Is also used in dry-laid landscape walls, at least pinning the lowest course in place into the earth, also employed securing the lowest course and/or deadmen in walls made of engineered concrete or wooden landscape ties. In unusual cases, steel reinforcement may be embedded and partially exposed, as in the steel tie bars that constrain and reinforce the masonry of Nevyansk Tower or ancient structures in Rome and

2016-424: Is also used in high-corrosion environments. It is available in many forms, such as spirals for reinforcing columns, common rods, and meshes. Most commercially available rebar is made from unidirectional fibers set in a thermoset polymer resin and is often referred to as FRP. Some special construction such as research and manufacturing facilities with very sensitive electronics may require the use of reinforcement that

2100-424: Is approximated as (bar size/9)² square inches. For example, the area of #8 bar is (8/9)² = 0.79 square inches. Bar sizes larger than #8 follow the 1 ⁄ 8 -inch rule imperfectly and skip sizes #12–13, and #15–17 due to historical convention. In early concrete construction bars of one inch and larger were only available in square sections, and when large format deformed round bars became available around 1957,

2184-473: 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

2268-432: Is made of unfinished tempered steel, making it susceptible to rusting . Normally the concrete cover is able to provide a pH value higher than 12 avoiding the corrosion reaction. Too little concrete cover can compromise this guard through carbonation from the surface, and salt penetration . Too much concrete cover can cause bigger crack widths which also compromises the local guard. As rust takes up greater volume than

2352-426: 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

2436-522: Is non-conductive to electricity, and medical imaging equipment rooms may require non-magnetic properties to avoid interference. FRP rebar, notably glass fibre types have low electrical conductivity and are non-magnetic which is commonly used for such needs. Stainless steel rebar with low magnetic permeability is available and is sometimes used to avoid magnetic interference issues. Reinforcing steel can also be displaced by impacts such as earthquakes , resulting in structural failure. The prime example of this

2520-604: Is one of the most notable figures for the invention and popularization of reinforced concrete. As a French gardener, Monier patented reinforced concrete flowerpots in 1867, before proceeding to build reinforced concrete water tanks and bridges. Ernest L. Ransome , an English engineer and architect who worked in the United States, made a significant contribution to the development of reinforcing bars in concrete construction. He invented twisted iron rebar, which he initially thought of while designing self-supporting sidewalks for

2604-566: 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

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2688-765: Is subject to the requirements of Australian Standards AS3600 (Concrete Structures) and AS/NZS4671 (Steel Reinforcing for Concrete). There are other standards that apply to testing, welding and galvanizing. The designation of reinforcement is defined in AS/NZS4671 using the following formats: Shape/ Section D- deformed ribbed bar, R- round / plain bar, I- deformed indented bar Ductility Class L- low ductility, N- normal ductility, E- seismic (Earthquake) ductility Standard grades (MPa) 250N, 300E, 500L, 500N, 500E Bars are typically abbreviated to simply 'N' (hot-rolled deformed bar), 'R' (hot-rolled round bar), 'RW' (cold-drawn ribbed wire) or 'W' (cold-drawn round wire), as

2772-718: Is the collapse of the Cypress Street Viaduct in Oakland, California as a result of the 1989 Loma Prieta earthquake , causing 42 fatalities. The shaking of the earthquake caused rebars to burst from the concrete and buckle . Updated building designs, including more circumferential rebar, can address this type of failure. US/Imperial bar sizes give the diameter in units of 1 ⁄ 8 inch (3.2 mm) for bar sizes #2 through #8, so that #8 = 8 ⁄ 8 inch = 1-inch (25 mm) diameter. There are no fractional bar sizes in this system. The "#" symbol indicates

2856-559: 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

2940-566: 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

3024-399: 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

3108-791: The Masonic Hall in Stockton, California. His twisted rebar was, however, not initially appreciated and even ridiculed at the Technical Society of California, where members stated that the twisting would weaken the iron. In 1889, Ransome worked on the West Coast mainly designing bridges. One of these, the Alvord Lake Bridge in San Francisco's Golden Gate Park, was the first reinforced concrete bridge built in

3192-480: 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

3276-404: The number sign , and thus "#6" is read as "number six". The use of the "#" sign is customary for US sizes, but "No." is sometimes used instead. Within the trades rebar is known by a shorthand utilizing the bar diameter as descriptor, such as "four-bar" for bar that is four-eighths (or one-half) of an inch. The cross-sectional area of a bar, as given by πr ², works out to (bar size/9.027)², which

3360-533: The 18th century, rebar was used to form the carcass of the Leaning Tower of Nevyansk in Russia, built on the orders of the industrialist Akinfiy Demidov . The cast iron used for the rebar was of high quality, and there is no corrosion on the bars to this day. The carcass of the tower was connected to its cast iron tented roof , crowned with one of the first known lightning rods . However, not until

3444-932: The Bixby Hotel in Long Beach, California and total collapse of the Eastman Kodak Building in Rochester, New York, both during construction in 1906. It was, however, concluded that both failures were the consequences of poor-quality labor. With the increase in demand of construction standardization, innovative reinforcing systems such as Kahn's were pushed to the side in favor of the concrete reinforcing systems seen today. Requirements for deformations on steel bar reinforcement were not standardized in US construction until about 1950. Modern requirements for deformations were established in "Tentative Specifications for

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3528-501: The Deformations of Deformed Steel Bars for Concrete Reinforcement", ASTM A305-47T. Subsequently, changes were made that increased rib height and reduced rib spacing for certain bar sizes, and the qualification of “tentative” was removed when the updated standard ASTM A305-49 was issued in 1949. The requirements for deformations found in current specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, among others, are

3612-508: 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

3696-486: The Smith Mountain Lake for this purpose. Hydro-electricity is usually produced during high-demand times (day) and pumped back into the lake during low demand times (night). The Leesville Dam also produces hydro-electricity as well. In December 2009, The U.S. Federal Energy Regulatory Commission granted Appalachian Power a new license to operate the hydro-electricity plant. The new 30-year license replaces

3780-456: The United States. He used twisted rebar in this structure. At the same time Ransome was inventing twisted steel rebar, C.A.P. Turner was designing his "mushroom system" of reinforced concrete floor slabs with smooth round rods and Julius Kahn was experimenting with an innovative rolled diamond-shaped rebar with flat-plate flanges angled upwards at 45° (patented in 1902). Kahn predicted concrete beams with this reinforcing system would bend like

3864-494: The Vatican. Steel has a thermal expansion coefficient nearly equal to that of modern concrete . If this were not so, it would cause problems through additional longitudinal and perpendicular stresses at temperatures different from the temperature of the setting. Although rebar has ribs that bind it mechanically to the concrete, it can still be pulled out of the concrete under high stresses, an occurrence that often accompanies

3948-643: 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

4032-535: The bars and corrosion under the epoxy film have been reported. These epoxy-coated bars are used in over 70,000 bridge decks in the US, but this technology was slowly being phased out in favor of stainless steel rebar as of 2005 because of its poor performance. Requirements for deformations are found in US-standard product specifications for steel bar reinforcing, such as ASTM A615 and ASTM A706, and dictate lug spacing and height. Fibre-reinforced plastic rebar

4116-526: 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

4200-399: 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

4284-461: 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

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4368-483: 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

4452-562: 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 ,

4536-431: 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

4620-929: The industry manufactured them to provide the cross-sectional area equivalent of standard square bar sizes that were formerly used. The diameter of the equivalent large format round shape is rounded to the nearest 1 ⁄ 8 inch to provide the bar size. For example, #9 bar has a cross section of 1.00 square inch (6.5 cm ), and therefore a diameter of 1.128 inches (28.7 mm). #10, #11, #14, and #18 sizes correspond to 1 1 ⁄ 8 inch, 1 1 ⁄ 4 , 1 1 ⁄ 2 , and 2-inch square bars, respectively. Sizes smaller than #3 are no longer recognized as standard sizes. These are most commonly manufactured as plain round undeformed rod steel but can be made with deformations. Sizes smaller than #3 are typically referred to as "wire" products and not "bar" and specified by either their nominal diameter or wire gage number. #2 bars are often informally called "pencil rod" as they are about

4704-554: 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

4788-533: The late 1920s, Appalachian Power began purchasing land and planning for a hydroelectricity dam within the Smith Mountain Gorge that is split by the Roanoke River . After several delays and the completion of engineering studies, construction began in 1960. Construction on the smaller Leesville Dam also began downstream at this time as well. Concrete pouring began in 1961 and in 1962, the re-construction of roads and bridges that would be affected by

4872-406: 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

4956-531: 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

5040-568: The mid-19th century, with the embedding of steel bars into concrete (thus producing modern reinforced concrete ), did rebar display its greatest strengths. Several people in Europe and North America developed reinforced concrete in the 1850s. These include Joseph-Louis Lambot of France, who built reinforced concrete boats in Paris (1854) and Thaddeus Hyatt of the United States, who produced and tested reinforced concrete beams. Joseph Monier of France

5124-419: 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

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5208-478: 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

5292-441: 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

5376-446: The nominal bar diameter in millimeters, as an "alternate size" specification. Substituting a true metric size for a US/Imperial size is called a hard conversion , and sometimes results in the use of a physically different sized bar. bar size size (soft) Metric bar designations represent the nominal bar diameter in millimeters, rounded to the nearest 5 mm. bar size (kg/m) (mm) Area (mm ) Metric bar designations represent

5460-466: The nominal bar diameter in millimetres. Preferred bar sizes in Europe are specified to comply with Table 6 of the standard EN 10080 , although various national standards still remain in force (e.g. BS 4449 in the United Kingdom). In Switzerland some sizes are different from European standard. bar size density (kg/m) diameter (mm) area (mm ) Reinforcement for use in concrete construction

5544-479: The original 50-year license and also addresses recreational and environmental management. 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, is twice that of steel, wood, plastics, and aluminium combined. When aggregate

5628-506: 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

5712-468: 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

5796-416: The reservoir was complete. Filling of the reservoir, Smith Mountain Lake , began on September 24, 1963. In 1964, the first four hydro- electrical generators were installed. The first commercial saturation dives were performed by Westinghouse to replace faulty trash racks at 200 feet (61 m) on the dam in 1965. On March 7, 1966, the reservoir was full. In 1979, a fifth hydro-electrical generator

5880-650: 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

5964-506: The same as those specified in ASTM A305-49. Concrete is a material that is very strong in compression , but relatively weak in tension . To compensate for this imbalance in concrete's behavior, rebar is cast into it to carry the tensile loads . Most steel reinforcement is divided into primary and secondary reinforcement: Secondary applications include rebar embedded in masonry walls, which includes both bars placed horizontally in

6048-491: The same size as a pencil. When US/Imperial sized rebar are used in projects with metric units, the equivalent metric size is typically specified as the nominal diameter rounded to the nearest millimeter. These are not considered standard metric sizes, and thus is often referred to as a soft conversion or the "soft metric" size. The US/Imperial bar size system recognizes the use of true metric bar sizes (No. 10, 12, 16, 20, 25, 28, 32, 36, 40, 50 and 60 specifically) which indicates

6132-413: The service life of the project. Extra care is taken during the transport, fabrication, handling, installation, and concrete placement process when working with epoxy-coated rebar, because damage will reduce the long-term corrosion resistance of these bars. Even damaged epoxy-coated bars have shown better performance than uncoated reinforcing bars, though issues from debonding of the epoxy coating from

6216-628: The steel from which it was formed, it causes severe internal pressure on the surrounding concrete, leading to cracking, spalling , and, ultimately, structural failure . This phenomenon is known as oxide jacking . This is a particular problem where the concrete is exposed to salt water, as in bridges where salt is applied to roadways in winter, or in marine applications. Uncoated, corrosion-resistant low- carbon / chromium (microcomposite), silicon bronze , epoxy -coated, galvanized , or stainless steel rebars may be employed in these situations at greater initial expense, but significantly lower expense over

6300-411: 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

6384-497: 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

6468-535: 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

6552-646: The temperature changes. Other readily available types of rebar are manufactured of stainless steel , and composite bars made of glass fiber , carbon fiber , or basalt fiber . The carbon steel reinforcing bars may also be coated in zinc or an epoxy resin designed to resist the effects of corrosion, especially when used in saltwater environments. Bamboo has been shown to be a viable alternative to reinforcing steel in concrete construction. These alternative types tend to be more expensive or may have lesser mechanical properties and are thus more often used in specialty construction where their physical characteristics fulfill

6636-655: 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

6720-439: 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

6804-524: 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

6888-602: 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

6972-516: Was installed, increasing the generation capacity to 560 megawatts (750,000 hp). Smith Mountain Dam houses five hydroelectric generators with a combined installed capacity of 560 MW. Smith Mountain Lake Dam uses pumped-storage hydroelectricity by which water that is released downstream can be pumped back into Smith Mountain Lake for re-use. The Leesville Dam regulates the Smith Mountain Lake's outflows and stores water to be pumped back into

7056-622: 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 ,

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