Portal:Concrete
Portal maintenance status: (October 2018)
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Introduction
Concrete, usually Portland cement concrete, is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens over time—most frequently a lime-based cement binder, such as Portland cement, but sometimes with other hydraulic cements, such as a calcium aluminate cement. It is distinguished from other, non-cementitious types of concrete all binding some form of aggregate together, including asphalt concrete with a bitumen binder, which is frequently used for road surfaces, and polymer concretes that use polymers as a binder.
When aggregate is mixed together with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts chemically with the water and other ingredients to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of the wet mix or the finished material. Most concrete is poured with reinforcing materials (such as rebar) embedded to provide tensile strength, yielding reinforced concrete.
Selected general articles
- Polymer concretes are a type of concrete that use polymers to replace lime-type cements as a binder. In some cases the polymer is used in addition to portland cement to form Polymer Cement Concrete (PCC) or Polymer Modified Concrete (PMC). Polymers in concrete have been overseen by Committee 548 of the American Concrete Institute since 1971. Read more...
- A power trowel (also known as a "power float") is a piece of light construction equipment used by construction companies and contractors to apply a smooth finish to concrete slabs. Read more...
- Mass concrete is defined by American Concrete Institute Committee 207 as "any volume of concrete with dimensions large enough to require that measures be taken to cope with the generation of heat from hydration of cement and attendant volume change to minimize cracking."
As interior temperature of mass concrete rises due to the process of cement hydration, the outer concrete may be cooling and contracting. If the temperature differs too much within the structure, the material can crack.
The main factors influencing temperature variation in the mass concrete structure are: the size of the structure, the ambient temperature, the initial temperature of the concrete at time of placement and curing program, the cement type, and the cement contents in the mix. Read more...
A volumetric concrete mixer (also known as volumetric mobile mixer) is a mixer mounted on a truck or trailer that contains separate compartments for sand, stone, cement and water. Materials are mixed on a job site to produce the exact amount of concrete needed. Read more...
Reinforced concrete (RC) (also called reinforced cement concrete or RCC) is a composite material in which concrete's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded passively in the concrete before the concrete sets. Reinforcing schemes are generally designed to resist tensile stresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure. Modern reinforced concrete can contain varied reinforcing materials made of steel, polymers or alternate composite material in conjunction with rebar or not. Reinforced concrete may also be permanently stressed (concrete in compression, reinforcement in tension), so as to improve the behaviour of the final structure under working loads. In the United States, the most common methods of doing this are known as pre-tensioning and post-tensioning.
For a strong, ductile and durable construction the reinforcement needs to have the following properties at least:- High relative strength
- High toleration of tensile strain
- Good bond to the concrete, irrespective of pH, moisture, and similar factors
- Thermal compatibility, not causing unacceptable stresses (such as expansion or contraction) in response to changing temperatures.
- Durability in the concrete environment, irrespective of corrosion or sustained stress for example.
- Concrete cover, in reinforced concrete, is the least distance between the surface of embedded reinforcement and the outer surface of the concrete (ACI 130). The concrete cover depth can be measured with a cover meter. Read more...
A concrete plant, also known as a batch plant or batching plant or a concrete batching plant, is equipment that combines various ingredients to form concrete. Some of these inputs include water, air, admixtures, sand, aggregate (rocks, gravel, etc.), fly ash, silica fume, slag, and cement. There are two main types of concrete plants: Dry mix plants and Wet mix plants, and also plants that contain both a transit mix side and a central mix side while utilizing common material storage points. A concrete plant can have a variety of parts and accessories, including: mixers (either tilt drum or horizontal or in some cases both), cement batchers, aggregate batchers, conveyors, radial stackers, aggregate bins, cement bins, heaters, chillers, cement silos, batch plant controls, and dust collectors.
The heart of the concrete batching plant is the mixer, and there are many types of mixers such as Tilt Drum, Pan, Planetary, Single Shaft and Twin shaft mixer. The twin shaft mixer can ensure an even mixture of concrete through the use of high horsepower motors, while the tilt mixer offers a comparatively large batch of concrete mix. In North America, the predominant central mixer type is a tilt drum style, while in Europe and other parts of the world, a Twin Shaft Mixer is more prevalent. A Pan or Planetary mixer is more common at a precast plant. Aggregate bins have 2 to 6 compartments for storage of various sand and aggregate (rocks, gravel, etc.) sizes, while cement silos are typically one or two compartments, but at times up to 4 compartments in a single silo. Conveyors are typically between 24-48 inches wide and carry aggregate from the ground hopper to the aggregate bin, as well as from the aggregate batcher to the charge chute. Read more...- The Institution of Structural Engineers is a professional body for structural engineering based in the United Kingdom. It has 27,000 members operating in 105 countries. The Institution provides professional accreditation for structural engineers. It publishes a monthly magazine, The Structural Engineer. The institution also has a research journal titled Structures,published by Elsevier, Inc.
The Institution is an internationally recognised source of expertise and information concerning all issues that involve structural engineering and public safety within the built environment. Read more...
The American Concrete Institute (ACI, formerly National Association of Cement Users or NACU) is a non-profit technical society and standards developing organization. ACI was founded in January 1905 during a convention in Indianapolis. The Institute's headquarters are currently located in Farmington Hills, Michigan, USA. ACI's mission is "ACI develops and disseminates consensus-based knowledge on concrete and its uses." Read more...- A concrete mixer (often colloquially called a cement mixer) is a device that homogeneously combines cement, aggregate such as sand or gravel, and water to form concrete. A typical concrete mixer uses a revolving drum to mix the components. For smaller volume works, portable concrete mixers are often used so that the concrete can be made at the construction site, giving the workers ample time to use the concrete before it hardens. An alternative to a machine is mixing concrete by hand. This is usually done in a wheelbarrow; however, several companies have recently begun to sell modified tarps for this purpose.
The concrete mixer was invented by Columbus, Ohio industrialist Gebhardt Jaeger. Read more...
Limestone quarry.
Construction aggregate, or simply "aggregate", is a broad category of coarse to medium grained particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are the most mined materials in the world. Aggregates are a component of composite materials such as concrete and asphalt concrete; the aggregate serves as reinforcement to add strength to the overall composite material. Due to the relatively high hydraulic conductivity value as compared to most soils, aggregates are widely used in drainage applications such as foundation and French drains, septic drain fields, retaining wall drains, and road side edge drains. Aggregates are also used as base material under foundations, roads, and railroads. In other words, aggregates are used as a stable foundation or road/rail base with predictable, uniform properties (e.g. to help prevent differential settling under the road or building), or as a low-cost extender that binds with more expensive cement or asphalt to form concrete.
Preferred bitumenous aggregate sizes for road construction are given in EN 13043 as d/D (where the range shows the smallest and largest square mesh grating that the particles can pass). The same classification sizing is used for larger armour stone sizes in EN 13383, EN 12620 for concrete aggregate, EN 13242 for base layers of road construction and EN 13450 for railway ballast. Read more...- Foam concrete, also known as aircrete, foamed concrete, foamcrete, cellular lightweight concrete or reduced density concrete, is defined as a cement based slurry, with a minimum of 20% (per volume) foam entrained into the plastic mortar. As mostly no coarse aggregate is used for production of foam concrete the correct term would be called mortar instead of concrete; it may be called "foamed cement" as well. The density of foam concrete usually varies from 400 kg/m³ to 1600 kg/ m³. The density is normally controlled by substituting fully or part of the fine aggregate with foam. Read more...
- Voided biaxial slabs are reinforced concrete slabs in which voids reduce the amount of concrete.
While concrete has been used for thousands of years, the use of reinforced concrete is usually attributed to Joseph-Louis Lambot in 1848. Joseph Monier, a French gardener, patented a design for reinforced garden tubs in 1868, and later patented reinforced concrete beams and posts for railway and road guardrails. Read more... - Concrete sealers are applied to concrete to protect it from surface damage, corrosion, and staining. They either block the pores in the concrete to reduce absorption of water and salts or form an impermeable layer which prevents such materials from passing.
Research from major concrete authorities, including American Concrete Institute, Portland Cement Association, and National Ready Mix Concrete Association; confirm that most concrete damage is attributable to surface moisture intrusion. The most pervasive form of concrete damage is surface scaling from freeze/thaw. Other forms of damage include alkali-silica reaction (ASR), chemical intrusion, and corrosion of steel reinforcements. Read more...
A tied rebar beam cage. This will be embedded inside cast concrete to increase its tensile strength.
Rebar (short for reinforcing bar), collectively known as reinforcing steel and reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the concrete under tension. Concrete is strong under compression, but has weak tensile strength. Rebar significantly increases the tensile strength of the structure. Rebar's surface is often deformed to promote a better bond with the concrete.
The most common type of rebar is carbon steel, typically consisting of hot-rolled round bars with deformation patterns. Other readily available types include stainless steel, and composite bars made of glass fiber, carbon fiber, or basalt fiber. The steel reinforcing bars may also be coated in an epoxy resin designed to resist the effects of corrosion mostly in saltwater environments, but also land based constructions. Bamboo has been shown to be a viable alternative to reinforcing steel in concrete construction. These alternate 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 a specific performance requirement that carbon steel does not provide. Steel and concrete have similar coefficients of thermal expansion, so a concrete structural member reinforced with steel will experience minimal stress as the temperature changes. Read more...- The environmental impact of concrete, its manufacture and applications, are complex. Some effects are harmful; others welcome. Many depend on circumstances. A major component of concrete is cement, which has its own environmental and social impacts and contributes largely to those of concrete.
The cement industry is one of the primary producers of carbon dioxide, a potent greenhouse gas. Concrete causes damage to the most fertile layer of the earth, the topsoil.
Concrete is used to create hard surfaces which contribute to surface runoff that may cause soil erosion, water pollution and flooding. Conversely, concrete is one of the most powerful tools for proper flood control, by means of damming, diversion, and deflection of flood waters, mud flows, and the like.
Light-colored concrete can reduce the urban heat island effect, due to its higher albedo.
Concrete dust released by building demolition and natural disasters can be a major source of dangerous air pollution.
The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns due to toxicity and radioactivity.
Wet concrete is highly alkaline and should always be handled with proper protective equipment. Concrete recycling is increasing in response to improved environmental awareness, legislation, and economic considerations. Read more...
Climbing formwork on a future residential skyscraper in Takapuna, New Zealand—the whole white upperstructure is actually formwork and associated working facilities.
Climbing formwork is a special type formwork for vertical concrete structures that rises with the building process. While relatively complicated and costly, it can be an effective solution for buildings that are either very repetitive in form (such as towers or skyscrapers) or that require a seamless wall structure (using gliding formwork, a special type of climbing formwork).
Various types of climbing formwork exist, which are either relocated from time to time, or can even move on their own (usually on hydraulic jacks, required for self-climbing and gliding formworks). Read more...
Concrete must be kept moist during curing in order to achieve optimal strength and durability. During curing hydration occurs, allowing calcium-silicate hydrate (C-S-H) to form. Over 90% of a mix's final strength is typically reached within four weeks, with the remaining 10% achieved over years or even decades. The conversion of calcium hydroxide in the concrete into calcium carbonate from absorption of CO2 over several decades further strengthens the concrete and makes it more resistant to damage. This carbonation reaction, however, lowers the pH of the cement pore solution and can corrode the reinforcement bars.
Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking. High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. The strength of concrete changes (increases) for up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation. Addition of short-cut polymer fibers can improve (reduce) shrinkage-induced stresses during curing and increase early and ultimate compression strength. Read more...- Nanocem is a consortium of academic and private industry groups that researches the properties of cement and concrete on the nano- and micro-scales, with a particular focus on reducing carbon dioxide emissions at all stages of production. Nanocem was founded as an independent consortium in 2004 after a rejection of a 2002 bid to the Network of Excellence (European Framework Programme). The consortium is headquartered in Lausanne, Switzerland. As of 2018, it includes 34 organizations and supports more than 120 researchers.
Nanocem's eleven completed core projects have included studies of interactions between admixtures and cement, concrete durability, the kinetics of cement hydration, and the use of magnetic resonance imaging techniques in concrete analysis. Recent Nanocem-sponsored projects have included the use of nanotechnology in cementitious materials, the effects of sulfate on concrete, the development of a bipolar mineral organic composite that can bond with Portland cement on one pole and polymerize with the other, and studies of cement hydration at the molecular level. Its research has led to more than one hundred published papers and conference papers. Read more... - Self-consolidating concrete or self-compacting concrete (commonly abbreviated to SCC) is a concrete mix which has a low yield stress, high deformability, good segregation resistance (prevents separation of particles in the mix), and moderate viscosity (necessary to ensure uniform suspension of solid particles during transportation, placement (without external compaction), and thereafter until the concrete sets).
In everyday terms, when poured, SCC is an extremely fluid mix with the following distinctive practical features – it flows very easily within and around the formwork, can flow through obstructions and around corners ("passing ability"), is close to self-levelling (although not actually self-levelling), does not require vibration or tamping after pouring, and follows the shape and surface texture of a mold (or form) very closely once set. As a result, pouring SCC is also much less labor-intensive compared to standard concrete mixes. Once poured, SCC is usually similar to standard concrete in terms of its setting and curing time (gaining strength), and strength. SCC does not use a high proportion of water to become fluid – in fact SCC may contain less water than standard concretes. Instead, SCC gains its fluid properties from an unusually high proportion of fine aggregate, such as sand (typically 50%), combined with superplasticizers (additives that ensure particles disperse and do not settle in the fluid mix) and viscosity-enhancing admixtures (VEA). Read more...
In the eurocode series of European standards (EN) related to construction, Eurocode 2: Design of concrete structures (abbreviated EN 1992 or, informally, EC 2) specifies technical rules for the design of concrete, reinforced concrete and prestressed concrete structures, using the limit state design philosophy. It was approved by the European Committee for Standardization (CEN) on 16 April 2004 to enable designers across Europe to practice in any country that adopts the code.
Concrete is a very strong and economical material that performs exceedingly well under compression. Its weakness lies in its capability to carry tension forces and thus has its limitations. Steel on the other hand is slightly different; it is similarly strong in both compression and tension. Combining these two materials means engineers would be able to work with a composite material that is capable of carrying both tension and compression forces. Read more...
A cement is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete.
Cements used in construction are usually inorganic, often lime or calcium silicate based, and can be characterized as either hydraulic or non-hydraulic, depending on the ability of the cement to set in the presence of water (see hydraulic and non-hydraulic lime plaster). Read more...
The rebuilt upper reservoir of the Taum Sauk plant, nearing completion in this photo, is the largest RCC dam in North America.
Roller-compacted concrete (RCC) or rolled concrete (rollcrete) is a special blend of concrete that has essentially the same ingredients as conventional concrete but in different ratios, and increasingly with partial substitution of fly ash for Portland cement. RCC is a mix of cement/fly ash, water, sand, aggregate and common additives, but contains much less water. The produced mix is drier and essentially has no slump. RCC is placed in a manner similar to paving; the material is delivered by dump trucks or conveyors, spread by small bulldozers or specially modified asphalt pavers, and then compacted by vibratory rollers.
In dam construction, roller-compacted concrete began its initial development with the construction of the Alpe Gera Dam near Sondrio in North Italy between 1961 and 1964. Concrete was laid in a similar form and method but not rolled. RCC had been touted in engineering journals during the 1970s as a revolutionary material suitable for, among other things, dam construction. Initially and generally, RCC was used for backfill, sub-base and concrete pavement construction, but increasingly it has been used to build concrete gravity dams because the low cement content and use of fly ash cause less heat to be generated while curing than do conventional mass concrete placements. Roller-compacted concrete has many time and cost benefits over conventional mass concrete dams; these include higher rates of concrete placement, lower material costs and lower costs associated with post-cooling and formwork. Read more...- The Filigree Wideslab method is a process for construction of concrete floor decks from two interconnected concrete placements, one precast in a factory, and the other done in the field. The method was developed during the late 1960s by Harry H. Wise as a more efficient and economic construction process than conventional cast-in-place technologies. Read more...
Romans are famous for their advanced engineering accomplishments, although some of their own inventions were improvements on older ideas, concepts and inventions. Technology for bringing running water into cities was developed in the east, but transformed by the Romans into a technology inconceivable in Greece. The architecture used in Rome was strongly influenced by Greek and Etruscan sources.
Roads were common at that time, but the Romans improved their design and perfected the construction to the extent that many of their roads are still in use today. Their accomplishments surpassed most other civilizations of their time, and after their time, and many of their structures have withstood the test of time to inspire others, especially during the Renaissance. Moreover, their contributions were described in some detail by authors such as Vitruvius, Frontinus and Pliny the Elder, so there is a printed record of their many inventions and achievements. Read more...- Energetically modified cements (EMC) are a class of cementitious materials made from pozzolans (e.g. fly ash, volcanic ash, pozzolana), silica sand, blast furnace slag, or Portland cement (or blends of these ingredients). Read more...
- The water–cement ratio is the ratio of the weight of water to the weight of cement used in a concrete mix. A lower ratio leads to higher strength and durability, but may make the mix difficult to work with and form. Workability can be resolved with the use of plasticizers or super-plasticizers.
Often, the ratio refers to the ratio of water to cement plus pozzolan ratio, w/(c+p). The pozzolan is typically a fly ash, or blast furnace slag. It can include a number of other materials, such as silica fume, rice husk ash or natural pozzolans. Pozzolans can be added to strengthen concrete. Read more...
Characteristic crack pattern associated with the alkali–silica reaction affecting a concrete step barrier on a US motorwayFor less common types of alkali-driven concrete degradation, see Alkali-aggregate reaction.The alkali–silica reaction (ASR), more commonly known as "concrete cancer", is a swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive non-crystalline (amorphous) silica found in many common aggregates, given sufficient moisture.
This reaction causes the expansion of the altered aggregate by the formation of a soluble and viscous gel of sodium silicate (Na2SiO3 · n H2O, also noted Na2H2SiO4 · n H2O, or N-S-H (sodium silicate hydrate), depending the adopted convention). This hygroscopic gel swells and increases in volume when absorbing water: it exerts an expansive pressure inside the siliceous aggregate, causing spalling and loss of strength of the concrete, finally leading to its failure. Read more...
During the time of natural cement, a majority of it came from cement rock mined in Ulster County, New York, near a town called Rosendale. Nearly half of all natural cement used was Rosendale Rosendale cement refers to hydraulic, natural cement that was produced in and around Rosendale, New York, from argillaceous limestone beginning in 1825. Rosendale cement set faster than other natural cement mortars and proved to be more efficient than the mortars based on lime and sand. Because of its reputation, Rosendale cement has also been used as both a trade name and as a generic term referring to any natural hydraulic cement. It was used in the construction of many of the United States' most important landmarks, including the Brooklyn Bridge, the pedestal of the Statue of Liberty, Federal Hall National Memorial, and the west wing of the United States Capitol building. Read more...- Ground-granulated blast-furnace slag (GGBS or GGBFS) is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder. Read more...
Self-leveling concrete is polymer-modified cement that has high flow characteristics and, in contrast to traditional concrete, does not require the addition of excessive amounts of water for placement. Self-leveling concrete is typically used to create a flat and smooth surface with a compressive strength similar to or higher than that of traditional concrete prior to installing interior floor coverings. Self-leveling concrete has increased in popularity as the degree of flatness and smoothness required for floor covering products has increased, with vinyl goods becoming thinner and floor tiles becoming larger, for example.
Self-consolidating (or self-compacting) concrete (SCC) is a separate type of highly mobile (fluid) concrete formulation, which is based on superplasticizers, and is therefore also somewhat self-leveling. Read more...
Water is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's streams, lakes, and oceans, and the fluids of most living organisms. It is vital for all known forms of life, even though it provides no calories or organic nutrients. Its chemical formula is H2O, meaning that each of its molecules contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is the name of the liquid state of H2O at standard ambient temperature and pressure. It forms precipitation in the form of rain and aerosols in the form of fog. Clouds are formed from suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor. Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.
Water covers 71% of the Earth's surface, mostly in seas and oceans. Small portions of water occur as groundwater (1.7%), in the glaciers and the ice caps of Antarctica and Greenland (1.7%), and in the air as vapor, clouds (formed of ice and liquid water suspended in air), and precipitation (0.001%). Read more...
The flow table test or flow test is a method to determine consistency of fresh concrete. Flow table test is also used to identify transportable moisture limit of solid bulk cargoes. It is used primarily for assessing concrete that is too fluid (workable) to be measured using the slump test, because the concrete will not retain its shape when the cone is removed. Read more...- The concrete slump test measures the consistency of fresh concrete before it sets. It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows. It can also be used as an indicator of an improperly mixed batch. The test is popular due to the simplicity of apparatus used and simple procedure. The slump test is used to ensure uniformity for different loads of concrete under field conditions.
A separate test, known as the flow table, or slump-flow, test, is used for concrete that is too fluid (workable) to be measured using the standard slump test, because the concrete will not retain its shape when the cone is removed. Read more...
A concrete pump is a machine used for transferring liquid concrete by pumping. There are two types of concrete pumps.
The first type of concrete pump is attached to a truck or longer units are on semi-trailers. It is known as a boom concrete pump because it uses a remote-controlled articulating robotic arm (called a boom) to place concrete accurately. Boom pumps are used on most of the larger construction projects as they are capable of pumping at very high volumes and because of the labour saving nature of the placing boom. They are a revolutionary alternative to line-concrete pumps. Read more...
Reinforced concrete (RC) (also called reinforced cement concrete or RCC) is a composite material in which concrete's relatively low tensile strength and ductility are counteracted by the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded passively in the concrete before the concrete sets. Reinforcing schemes are generally designed to resist tensile stresses in particular regions of the concrete that might cause unacceptable cracking and/or structural failure. Modern reinforced concrete can contain varied reinforcing materials made of steel, polymers or alternate composite material in conjunction with rebar or not. Reinforced concrete may also be permanently stressed (concrete in compression, reinforcement in tension), so as to improve the behaviour of the final structure under working loads. In the United States, the most common methods of doing this are known as pre-tensioning and post-tensioning.
For a strong, ductile and durable construction the reinforcement needs to have the following properties at least:- High relative strength
- High toleration of tensile strain
- Good bond to the concrete, irrespective of pH, moisture, and similar factors
- Thermal compatibility, not causing unacceptable stresses (such as expansion or contraction) in response to changing temperatures.
- Durability in the concrete environment, irrespective of corrosion or sustained stress for example.
Slipforming Grain silo in Zürich for Swissmill in 2015 with "Bitschnau Slipform" Height: 118m
Slip forming, continuous poured, continuously formed, or slipform construction is a construction method in which concrete is poured into a continuously moving form. Slip forming is used for tall structures (such as bridges, towers, buildings, and dams), as well as horizontal structures, such as roadways. Slipforming enables continuous, non-interrupted, cast-in-place "flawless" (i.e. no joints) concrete structures which have superior performance characteristics to piecewise construction using discrete form elements. Slip forming relies on the quick-setting properties of concrete, and requires a balance between quick-setting capacity and workability. Concrete needs to be workable enough to be placed into the form and consolidated (via vibration), yet quick-setting enough to emerge from the form with strength. This strength is needed because the freshly set concrete must not only permit the form to "slip" by the concrete without disturbing it, but also support the pressure of the new concrete as well as resist collapse caused by the vibration of the compaction machinery.
In vertical slip forming the concrete form may be surrounded by a platform on which workers stand, placing steel reinforcing rods into the concrete and ensuring a smooth pour. Together, the concrete form and working platform are raised by means of hydraulic jacks. Generally, the slipform rises at a rate which permits the concrete to harden by the time it emerges from the bottom of the form. Read more...- Metakaolin is the anhydrous calcined form of the clay mineral kaolinite. Minerals that are rich in kaolinite are known as china clay or kaolin, traditionally used in the manufacture of porcelain. The particle size of metakaolin is smaller than cement particles, but not as fine as silica fume. Read more...
Silica fume particles viewed in a transmission electron microscope
Silica fume, also known as microsilica, (CAS number 69012-64-2, EINECS number 273-761-1) is an amorphous (non-crystalline) polymorph of silicon dioxide, silica. It is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production and consists of spherical particles with an average particle diameter of 150 nm. The main field of application is as pozzolanic material for high performance concrete.
It is sometimes confused with fumed silica (also known as pyrogenic silica, CAS number 112945-52-5). However, the production process, particle characteristics and fields of application of fumed silica are all different from those of silica fume. Read more...
A concrete float is a tool used to finish a concrete surface by making it smooth. A float is used after the surface has been made level using a screed. In addition to removing surface imperfections, floating will compact the concrete as preparation for further steps.
A float can be a small hand tool, a larger bull float with a long handle, or a power trowel (also called a power float) with an engine. Read more...- Lunarcrete, also known as "mooncrete", an idea first proposed by Larry A. Beyer of the University of Pittsburgh in 1985, is a hypothetical aggregate building material, similar to concrete, formed from lunar regolith, that would reduce the construction costs of building on the Moon. Read more...
- A cover meter is an instrument to locate rebars and measure the exact concrete cover. Rebar detectors are less sophisticated devices that can only locate metallic objects below the surface. Due to the cost-effective design, the pulse-induction method is one of the most commonly used solutions. Read more...
- A reinforced concrete column is a structural member designed to carry compressive loads, composed of concrete with an embedded steel frame to provide reinforcement. For design purposes, the columns are separated into two categories: short columns and slender columns. Read more...
Did you know...
- ... that One Kemble Street was built using precast cruciform concrete blocks to avoid the use of scaffolding?
- ... that Canal Lake Concrete Arch Bridge, a National Historic Site of Canada, is an example of a "transitional structure" between stone arch bridges and reinforced bridges?
- ... that when Whitefoord Russell Cole threatened striking workers with dismissal and pension loss in 1921, his house was "bombarded with bottles until its concrete porch was littered with glass"?
- ... that Viaduto do Chá, São Paulo's first viaduct, was originally constructed from German iron before being replaced by a concrete span?
- ... that the floor tiles of the Kerr Cultural Center were made with a now-rare mix of cement and white marble dust?
- ... that the Milam Building was both the tallest brick and reinforced concrete structure and first office building with built in air conditioning in the United States when it opened in 1928?
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Selected images
Concrete plant showing a concrete mixer being filled from ingredient silos
Opus caementicium exposed in a characteristic Roman arch. In contrast to modern concrete structures, the concrete used in Roman buildings was usually covered with brick or stone.
Interior of the Pantheon dome, seen from beneath. The concrete for the coffered dome was laid on moulds, mounted on temporary scaffolding.
The Tunkhannock Viaduct in northeastern Pennsylvania opened in 1912 and is still in regular use today
Several tons of bagged cement, about two minutes of output from a 10,000 ton per day cement kiln
Aerial photo of reconstruction at Taum Sauk (Missouri) pumped storage facility in late November, 2009. After the original reservoir failed, the new reservoir was made of roller-compacted concrete.
Constructing a rebar cage that will be permanently embedded in a finished reinforced concrete structure
Concrete floor of a parking garage being placed
Boston City Hall (1968) is a Brutalist design constructed largely of precast and poured in place concrete. It was voted "The World's Ugliest Building" in 2008
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