The interior of the Pantheon in the 18th century, painted by Giovanni Paolo Panini

The Baths of Caracalla, in 2003

Concrete being poured, raked and vibrated into place in residential construction in Toronto, Ontario, Canada. Giovanni Paolo Pannini or Panini ( June 17 1691 &ndash Rome, October 21 1765) was an Italian painter and In the fields of Architecture and Civil engineering, construction is a process that consists of the Building or assembling of Infrastructure Toronto (təˈrɒntoʊ colloquially pronounced or) is the largest city in Canada and is the provincial capital of Ontario Ontario (ɒnˈtɛrioʊ is a province located in the central part of Canada, the largest by population and second largest after Quebec Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page

1930s vibrated concrete, manufactured in Croydon and installed by the LMS railway after an art deco refurbishment in Meols. Croydon is a large town and major commercial centre in South London, and the principal settlement of the London Borough of Croydon. Art Deco was a popular international design movement from 1925 until 1939 affecting the decorative arts such as Architecture, Interior design, and Industrial This article is about the village on the Wirral Peninsula. See also Meols Cop for the Southport suburb

Concrete is a construction material composed of cement (commonly Portland cement) as well as other cementitious materials such as fly ash and slag cement, aggregate (generally a coarse aggregate such as gravel limestone or granite, plus a fine aggregate such as sand), water, and chemical admixtures. In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together Portland cement is the most common type of Cement in general usage in many parts of the world as it is a basic ingredient of Concrete, mortar, Stucco Fly ash is one of the residues generated in the Combustion of Coal. Ground granulated blast furnace slag ( GGBS or GGBFS) is obtained by quenching molten Iron Slag (a by-product of iron and Steel making Construction aggregate, or simply " aggregate " is a broad category of coarse particulate Material used in Construction, including Gravel is rock that is of a specific Particle size range In Geology, gravel is any loose rock that is larger than two millimeters (2mm Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Water ( H2[[oxygen O]] H OH) is the most abundant Molecule on Earth 's surface composing of about 70% of the Earth's surface as Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties The word concrete comes from the Latin word "concretus", which means "hardened" or "hard".

Concrete solidifies and hardens after mixing with water and placement due to a chemical process known as hydration. A chemical reaction is a process that always results in the interconversion of Chemical substances The substance or substances initially involved in a chemical reaction are called Mineral hydration is an inorganic chemical reaction where water is added to the Crystal structure of a Mineral, usually creating a new mineral usually called a The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material. The reactions are highly exothermic and care must be taken that the build-up in heat does not affect the integrity of the structure. In Thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases Energy usually in the form of Heat, but Concrete is used to make pavements, architectural structures, foundations, motorways/roads, bridges/overpasses, parking structures, brick/block walls and footings for gates, fences and poles. A sidewalk (chiefly North American English) pavement ( British English and Philadelphia dialect) footpath ( Australian English An architectural Structure is a free-standing immobile outdoor construction A foundation is a Structure that transfers loads to the earth Motorway is a term for both a type of Road and a classification or designation A road is an identifiable route, way or path between two or more places. A bridge is a Structure built to span a Gorge, Valley, Road, railroad track, River, Body of water An overpass (called a flyover in the UK and most Commonwealth countries is a Bridge, Road, Railway or Parking is the act of stopping a Vehicle and leaving it unoccupied for more than a brief time A brick is a block of Ceramic material used in Masonry construction laid using mortar. A fence is a freestanding structure designed to restrict or prevent movement across a boundary Polymerase (DNA directed epsilon, also known as POLE, is a human Gene.

More concrete is used than any other man-made material in the world. ^[1] As of 2006, about seven billion cubic meters of concrete are made each year—more than one cubic meter for every person on Earth. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. CM3 redirects here If you were looking for the 3rd game in the Cooking Mama series abbreviated as CM3 see here. ^[2] Concrete powers a $US 35-billion industry which employs more than two million workers in the United States alone. The United States dollar ( sign: $; code: USD) is the unit of Currency of the United States; it has also been The United States of America —commonly referred to as the More than 55,000 miles of highways in America are paved with this material. A mile is a unit of Length, usually used to measure Distance, in a number of different systems including Imperial units United States * * * * * * * * * * * * * * * * * * * * * * Before adding any more images to this * * page please do carefully consider * * whether they would be mere decoration * * or actually improve The People's Republic of China currently consumes 40% of the world's cement [concrete] production. Talk People's Republic of China) PEOPLE'S REPUBLIC OF CHINA ARTICLE GUIDELINES

History

In Serbia, remains of a hut dating from 5600 BC have been found, with a floor made of red lime, sand, and gravel. Serbia (Србија Srbija) officially the Republic of Serbia (Република Србија Republika Srbija) is a Landlocked Country Lime is a general term for various naturally occurring Minerals and materials derived from them in which Carbonates Oxides and Hydroxides of The pyramids of Shaanxi in China, built thousands of years ago, contain a mixture of lime and volcanic ash or clay ^[3]. A pyramid is a Building where the upper surfaces are triangular and converge on one point ( Postal map spelling: Shensi) is a north-central province of the People's Republic of China, and includes portions of the Loess China ( Wade-Giles ( Mandarin) Chung¹kuo² is a cultural region, an ancient Civilization, and depending on perspective a National Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter The Assyrians and Babylonians used clay as cement in their concrete. The Assyrians are an Ethnic group whose origins lie in what is today Iraq, Iran, Turkey and Syria. Babylonia was an Amorite state in lower Mesopotamia (modern southern Iraq) with Babylon as its capital Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and The Egyptians used lime and gypsum cement. Ancient Egypt was an Ancient Civilization in eastern North Africa, concentrated along the lower reaches of the Nile River in what is now Lime is a general term for various naturally occurring Minerals and materials derived from them in which Carbonates Oxides and Hydroxides of Gypsum is a very soft Mineral composed of Calcium sulfate dihydrate with the Chemical formula Ca[[sulfur S]] O 4·2

Roman invention

During the Roman Empire, Roman concrete was made from quicklime, pozzolanic ash/pozzolana, and an aggregate of pumice; it was very similar to modern Portland cement concrete. The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial Roman concrete was a Ceramic material used in construction during the Roman Empire. Calcium oxide ( CaO) commonly known as burnt lime, lime or quicklime, is a widely used Chemical compound. Pozzolana, also known as pozzolanic ash is a fine sandy Volcanic ash, originally discovered and dug in Italy at Pozzuoli in the region around Pozzolana, also known as pozzolanic ash is a fine sandy Volcanic ash, originally discovered and dug in Italy at Pozzuoli in the region around Pumice is a textural term for a volcanic rock that is a solidified frothy lava composed of highly microvesicular glass Pyroclastic with very thin translucent The widespread use of concrete in many Roman structures has ensured that many survive almost intact to the present day. The Baths of Caracalla in Rome are just one example of the longevity of concrete, which allowed the Romans to build this and similar structures across the Roman Empire. The Baths of Caracalla were Roman public baths or Thermae, built in Rome between AD 212 and 216 during the reign of the Emperor Caracalla Rome ( Roma ˈroma Roma is the capital city of Italy and Lazio, and is Italy's largest and most populous city with more than 2 The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial Many Roman aqueducts have masonry cladding to a concrete core, a technique they used in structures such as the Pantheon, Rome, the interior dome of which is unclad concrete. The ancient Romans constructed numerous aqueducts ( Latin aquaeductūs, sing The Pantheon ( Latin Pantheon, from Greek Πάνθειον Pantheon, meaning "Temple of all the gods" is a building in Rome

The secret of concrete was lost for 13 centuries until 1756, when the British engineer John Smeaton pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate. Year 1756 ( MDCCLVI) was a Leap year starting on Thursday (link will display the full calendar of the Gregorian calendar (or a The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located This article is about the 18th century civil engineer For the baggage handler involved in the 2007 Glasgow International Airport attack, see John Smeaton (baggage Hydraulic lime is a variety of Slaked lime used to make Lime mortar. Portland cement was first used in concrete in the early 1840s. Portland cement is the most common type of Cement in general usage in many parts of the world as it is a basic ingredient of Concrete, mortar, Stucco

Recently, the use of recycled materials as concrete ingredients is gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a byproduct of coal-fired power plants. Fly ash is one of the residues generated in the Combustion of Coal. This has a significant impact by reducing the amount of quarrying and landfill space required, and, as it acts as a cement replacement, reduces the amount of cement required to produce a solid concrete. As cement production creates massive quantities of carbon dioxide, cement-replacement technology such as this will play an important role in future attempts to cut carbon dioxide. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single

Concrete additives have been used since Roman and Egyptian times, when it was discovered that adding volcanic ash to the mix allowed it to set under water. Similarly, the Romans knew that adding horse hair made concrete less liable to crack while it hardened, and adding blood made it more frost-resistant. Horsehair refers to hair taken from the Mane or tail of Horses It has various uses including Brushes and the bows of musical instruments

In modern times, researchers have experimented with the addition of other materials to create concrete with improved properties, such as higher strength or electrical conductivity.

Composition

There are many types of concrete available, created by varying the proportions of the main ingredients below. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag

The mix design depends on the type of structure being built, how the concrete will be mixed and delivered, and how it will be placed to form this structure.

Cement

Portland cement is the most common type of cement in general usage. Portland cement is the most common type of Cement in general usage in many parts of the world as it is a basic ingredient of Concrete, mortar, Stucco It is a basic ingredient of concrete, mortar and plaster. Mortar is a workable paste formed by mixture of Cement, Water and fine aggregate Masonry to bind construction blocks together and fill the gaps between The term plaster can refer to plaster of Paris Lime plaster, or Cement plaster. English engineer Joseph Aspdin patented Portland cement in 1824; it was named because of its similarity in colour to Portland limestone, quarried from the English Isle of Portland and used extensively in London architecture. Joseph Aspdin (December? 1778 – 20 March 1855) was a British cement manufacturer who obtained the Patent for Portland cement on Portland stone is a Limestone from the Jurassic period quarried on the Isle of Portland, Dorset. The Isle of Portland ( is a limestone tied island long by wide in the English Channel. London ( ˈlʌndən is the capital and largest urban area in the United Kingdom. It consists of a mixture of oxides of calcium, silicon and aluminium. Calcium oxide ( CaO) commonly known as burnt lime, lime or quicklime, is a widely used Chemical compound. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Portland cement and similar materials are made by heating limestone (a source of calcium) with clay, and grinding this product (called clinker) with a source of sulfate (most commonly gypsum). Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 In the manufacture of Portland cement, clinker is the solid material produced by the Cement kiln stage that has sintered into lumps or nodules typically Gypsum is a very soft Mineral composed of Calcium sulfate dihydrate with the Chemical formula Ca[[sulfur S]] O 4·2

High-temperature applications, such as masonry ovens and the like, generally require the use of a refractory cement; concretes based on Portland cement can be damaged or destroyed by elevated temperatures, but refractory concretes are better able to withstand such conditions. A masonry oven, sometimes colloquially known as a brick oven, is an Oven consisting of a baking chamber made of fireproof Brick, Concrete, In Metallurgy, refraction is a property of Metals that indicates their ability to withstand Heat.

Water

Combining water with a cementitious material forms a cement paste. The cement paste glues the aggregate together, fills voids within it, and allows it to flow more easily.

Less water in the cement paste will yield a stronger, more durable concrete; more water will give an easier-flowing concrete with a higher slump. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag ^[4]

Impure water used to make concrete can cause problems, either when setting, or later on.

Aggregates

Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel and crushed stone are mainly used for this purpose. Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Crushed stone or angular rock is a form of Construction aggregate, typically produced by mining a suitable rock deposit and breaking the removed rock down to the desired Recycled aggregates (from construction, demolition and excavation waste) are increasingly used as partial replacements of natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted. A blast furnace is a type of metallurgical Furnace used for Smelting to produce metals generally Iron. Bottom ash refers to the non- Combustible constituents of Coal with traces of combustibles embedded in forming clinkers and sticking to hot side walls of furnace during

Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers. Quartzite (from German Quarzit) not to be confused with the Mineral Quartz, is a hard Metamorphic rock which was originally

Reinforcement

Installing rebar in a floor slab during a concrete pour

Concrete is strong in compression, as the aggregate efficiently carries the compression load. A rebar, or reinforcing bar, is a common Steel bar and is commonly used in Reinforced concrete and reinforced Masonry structures However, it is weak in tension as the cement holding the aggregate in place can crack, allowing the structure to fail. Reinforced concrete solves these problems by adding metal reinforcing bars, glass fiber, or plastic fiber to carry tensile loads. Reinforced concrete is Concrete in which reinforcement bars (" Rebars quot or fibers have been incorporated to strengthen a material that would otherwise be A rebar, or reinforcing bar, is a common Steel bar and is commonly used in Reinforced concrete and reinforced Masonry structures

Chemical admixtures

Chemical 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. Chemistry (from Egyptian kēme (chem meaning "earth") is the Science concerned with the composition structure and properties In normal use, admixture dosages are less than 5% by mass of cement, and are added to the concrete at the time of batching/mixing. ^[5] The most common types of admixtures ^[6] are:

• Accelerators speed up the hydration (hardening) of the concrete. Accelerants play a major role in chemistry Most chemical reactions can be hastened with an accelerant
• Retarders slow the hydration of concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable.
• Air-entrainers add and distribute tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles thereby increasing the concrete's durability. Weathering is the decomposition of earth rocks, Soils and their Minerals through direct contact with the planet's Atmosphere. However, entrained air is a trade-off with strength, as each 1% of air may result in 5% decrease in compressive strength.
• Plasticizers (water-reducing admixtures) increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and Superplasticizers (high-range water-reducing admixtures) are a class of plasticizers which have fewer deleterious effects when used to significantly increase workability. Alternatively, plasticizers can be used to reduce the water content of a concrete (and have been called water reducers due to this application) while maintaining workability. This improves its strength and durability characteristics.
• Pigments can be used to change the color of concrete, for aesthetics. For the drug referred to as "pigment" see Black tar heroin.
• Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete. A corrosion inhibitor is a chemical compound that when added to a fluid or gas decreases the corrosion rate of a Metal or an Alloy.
• Bonding agents are used to create a bond between old and new concrete.
• Pumping aids improve pumpability, thicken the paste, and reduce dewatering – the tendency for the water to separate out of the paste.

Mineral admixtures and blended cements

There are inorganic materials that also have pozzolanic or latent hydraulic properties. A pozzolan is a material which when combined with Calcium hydroxide, exhibits Cementitious properties These very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures),^[5] or as a replacement for Portland cement (blended cements). See also Grain and Film grain Granularity is a measure of the size of the components or descriptions of components that make up ^[7]

• Fly ash: A by product of coal fired electric generating plants, it is used to partially replace Portland cement (by up to 60% by mass). Fly ash is one of the residues generated in the Combustion of Coal. A power station (also referred to as generating station, power plant or powerhouse) is an industrial facility for the generation of The properties of fly ash depend on the type of coal burnt. In general, silicious fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties. A pozzolan is a material which when combined with Calcium hydroxide, exhibits Cementitious properties Calcareous refers to a Sediment, Sedimentary rock, or Soil type which is formed from or contains a high proportion of Calcium carbonate in the ^[8]
• Ground granulated blast furnace slag (GGBFS or GGBS): A by product of steel production, is used to partially replace Portland cement (by up to 80% by mass). Ground granulated blast furnace slag ( GGBS or GGBFS) is obtained by quenching molten Iron Slag (a by-product of iron and Steel making Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 It has latent hydraulic properties. ^[9]
• Silica fume: A byproduct of the production of silicon and ferrosilicon alloys. Silica fume, also known as microsilica, is a by-product of the reduction of high-purity Quartz with coke in Electric arc furnaces in the production Ferrosilicon, or ferrosilicium, is a Ferroalloy an alloy of Iron and Silicon with between 15 and 90% silicon Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface to volume ratio and a much faster pozzolanic reaction. A pozzolan is a material which when combined with Calcium hydroxide, exhibits Cementitious properties Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability. ^[10]
• High Reactivity Metakaolin (HRM): Metakaolin produces concrete with strength and durability similar to concrete made with silica fume. Metakaolin is a dehydroxylated form of the clay mineral Kaolinite. While silica fume is usually dark gray or black in color, high reactivity metakaolin is usually bright white in color, making it the preferred choice for architectural concrete where appearance is important.

Mixing concrete

Pouring a concrete floor for a commercial building, (slab-on-grade)

Thorough mixing is essential for the production of uniform, high quality concrete. Therefore, equipment and methods should be capable of effectively mixing concrete materials containing the largest specified aggregate to produce uniform mixtures of the lowest slump practical for the work. Separate paste mixing has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete. In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together Construction aggregate, or simply " aggregate " is a broad category of coarse particulate Material used in Construction, including Compressive strength is the capacity of a Material to withstand axially directed pushing forces ^[11] The paste is generally mixed in a high-speed, shear-type mixer at a w/cm (water to cement ratio) of 0. Water-cement ratio is the ratio of weight of Water to the weight of Cement used in a Concrete mix 30 to 0. 45 by mass. The premixed paste is then blended with aggregates and any remaining batch water, and final mixing is completed in conventional concrete mixing equipment. Construction aggregate, or simply " aggregate " is a broad category of coarse particulate Material used in Construction, including ^[12]

High-Energy Mixed Concrete (HEM concrete) is produced by means of high-speed mixing of cement, water and sand with net specific energy consumption at least 5 kilojoules per kilogram of the mix. Energy density is the amount of Energy stored in a given system or region of space per unit Volume, or per unit Mass, depending on the context although It is then added to a plasticizer admixture and mixed after that with aggregates in conventional concrete mixer. Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and A concrete mixer (also commonly called a cement mixer) is a device that homogeneously combines Cement, aggregate such as sand or gravel and Water This paste can be used itself or foamed (expanded) for lightweight concrete. ^[13] Sand effectively dissipates energy in this mixing process. HEM concrete fast hardens in ordinary and low temperature conditions, and possesses increased volume of gel, drastically reducing capillarity in solid and porous materials. Capillary action, capillarity, capillary motion, or wicking is the ability of a substance to draw another substance into it It is recommended for precast concrete in order to reduce quantity of cement, as well as concrete roof and siding tiles, paving stones and lightweight concrete block production.

Characteristics

During hydration and hardening, concrete needs to develop certain physical and chemical properties. A chemical property is any of a material's properties that becomes evident during a Chemical reaction; that is any quality that can be established only by changing a substance's Among other qualities, mechanical strength, low moisture permeability, and chemical and volumetric stability are necessary. In Materials science, the strength of a material refers to the material's ability to resist an applied force

Workability

Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (vibration) and without reducing the concrete's quality. In the vernacular quality can mean a high degree of excellence (“a quality product” a degree of excellence or the lack of it (“work of average quality” or a property of 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. Construction aggregate, or simply " aggregate " is a broad category of coarse particulate Material used in Construction, including Raising the water content or adding chemical admixtures will increase concrete workability. Excessive water will lead to increased bleeding (surface water) and/or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. For Water masses on the surface of the world ocean see Surface water (ocean. The use of an aggregate with an undesirable gradation can result in a very harsh mix design with a very low slump, which cannot be readily made more workable by addition of reasonable amounts of water.

Workability can be measured by the Concrete Slump Test, a simplistic measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN 12350-2 test standards. In Construction and Civil engineering, the Concrete Slump Test (or simply the Slump Test is an In situ test or a laboratory test used to determine ASTM International ( ASTM) originally known as the American Society for Testing and Materials is an international Standards organization that develops and publishes Slump is normally measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod in order to consolidate the layer. When the cone is carefully lifted off, the enclosed material will slump a certain amount due to gravity. A relatively dry sample will slump very little, having a slump value of one or two inches (25 or 50 mm). A relatively wet concrete sample may slump as much as six or seven inches (150 to 175 mm).

Slump can be increased by adding chemical admixtures such as mid-range or high-range water reducing agents (super-plasticizers) without changing the water/cement ratio. In Statistics, the mid-range or mid-extreme of a set of statistical data values is the Arithmetic mean of the maximum and minimum values in a Data A reducing agent (also called a reductant or reducer) is the element or a compound in a Redox (reduction-oxidation reaction (see Electrochemistry Water-cement ratio is the ratio of weight of Water to the weight of Cement used in a Concrete mix It is bad practice to add excessive water upon delivery to the jobsite, however in a properly designed mixture it is important to reasonably achieve the specified slump prior to placement as design factors such as air content, internal water for hydration/strength gain, etc. are dependent on placement at design slump values.

High-flow concrete, like self-consolidating concrete, is tested by other flow-measuring methods. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag One of these methods includes placing the cone on the narrow end and observing how the mix flows through the cone while it is gradually lifted.

Curing

A concrete slab ponded while curing

Concrete columns curing while wrapped in plastic

In all but the least critical applications, care needs to be taken to properly cure concrete, and achieve best strength and hardness. This happens after the concrete has been placed. Cement requires a moist, controlled environment to gain strength and harden fully. The cement paste hardens over time, initially setting and becoming rigid though very weak, and gaining in strength in the days and weeks following.

Even thought the cement reaction with water is completed over period of time (normally about around 240 minutes which is referred to as final setting time), the hardening of concrete and gain of strength is over a period of time 95% to 98% strength is achieved in 3 weeks or about 28 days. During this period concrete needs to be in a ideal conditions, controlled temperature and humid atmosphere, in practice this is achieved by spraying or ponding the concrete surface with water, thereby protecting concrete mass from ill effects of ambient conditions. The pictures to the right show two of many ways to achieve this, ponding – submerging setting concrete in water, and wrapping in plastic to contain the water in the mix.

Properly curing concrete leads to increased strength and lower permeability, and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing, or overheating due to the exothermic setting of cement. In Thermodynamics, the word exothermic "outside heating" describes a process or reaction that releases Energy usually in the form of Heat, but Improper curing can cause scaling, reduced strength and abrasion resistance and cracking.

Strength

Concrete has relatively high compressive strength, but significantly lower tensile strength (about 10% of the compressive strength). Compressive strength is the capacity of a Material to withstand axially directed pushing forces Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms As a result, without compensating, concrete would almost always fail from tensile stresses – even when loaded in compression. Stress is a measure of the average amount of Force exerted per unit Area. The practical implication of this is that concrete elements subjected to tensile stresses must be reinforced with materials that are strong in tension. Concrete is most often constructed with the addition of steel reinforcement. The reinforcement can be by bars (rebar), mesh, or structural fibers, which provide the required tensile strength to concrete producing reinforced concrete. A rebar, or reinforcing bar, is a common Steel bar and is commonly used in Reinforced concrete and reinforced Masonry structures Reinforced concrete is Concrete in which reinforcement bars (" Rebars quot or fibers have been incorporated to strengthen a material that would otherwise be Concrete can also be prestressed (reducing tensile stress) using internal steel cables (tendons), allowing for beams or slabs with a longer span than is practical with reinforced concrete alone. Prestressed concrete is a method for overcoming the Concrete 's natural weakness in tension. Stress is a measure of the average amount of Force exerted per unit Area. Span is a section between two intermediate supports eg of a beam or a Bridge. Inspection of concrete structures can be non-destructive if carried out with equipment such as a Schmidt hammer, which is used to estimate concrete strength. A Schmidt hammer, also known as a Swiss hammer, is a device to measure the elastic properties or strength of Concrete or rock.

The ultimate strength of concrete is influenced by the water-cementitious ratio (w/cm), the design constituents, and the mixing, placement and curing methods employed. All things being equal, concrete with a lower water-cement (cementitious) ratio makes a stronger concrete than that with a higher ratio. The total quantity of cementitious materials (Portland cement, slag cement, pozzolans) can affect strength, water demand, shrinkage, abrasion resistance and density. All concrete will crack independent of whether or not it has sufficient compressive strength. In fact, high Portland cement content mixtures can actually crack more readily due to increased hydration rate. As concrete transforms from its plastic state, hydrating to a solid, the material undergoes shrinkage. Plastic shrinkage cracks can occur soon after placement but if the evaporation rate is high they often can actually occur during finishing operations, for example in hot weather or a breezy day. In very high strength concrete mixtures (greater than 10,000 psi) the crushing strength of the aggregate can be a limiting factor to the ultimate compressive strength. A limiting factor or limiting resource is one that controls a process such as organism growth or species Population size or distribution In lean concretes (with a high water-cement ratio) the crushing strength of the aggregates is not so significant.

Experimentation with various mix designs begins by specifying desired "workability" as defined by a given slump, "durability" requirements taking into consideration the weather exposure conditions (freeze-thaw) to which the concrete will be exposed in service, and the required "28 day compressive strength" as determined by properly molded standard-cured cylinder samples. The characteristics of the cementitious content, coarse and fine aggregates, and chemical admixtures determine the water demand of the mix in order to achieve the desired workability. The 28 day compressive strength is obtained by determination of the correct amount of cementitious (and often chemical admixtures) to achieve the target water-cementitious ratio.

The internal forces in common shapes of structure, such as arches, vaults, columns and walls are predominantly compressive forces, with floors and pavements subjected to tensile forces. An arch is a structure that spans a space while supporting weight (e A Vault (French voute Italian volta German Gewölbe Polish sklepienie, Spanish Compressive strength is widely used for specification requirement and quality control of concrete. The engineer knows his target tensile (flexural) requirements and will express these in terms of compressive strength.

Wired. com reported on April 13, 2007 that a team from the University of Tehran, competing in a contest sponsored by the American Concrete Institute, demonstrated several blocks of concretes with abnormally high compressive strengths between 50,000 and 60,000 PSI at 28 days. Events 1111 - Henry V is crowned Holy Roman Emperor. 1204 - The Fourth Crusade sacks Constantinople Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. The University of Tehran ( also known as Tehran University and UT, is the oldest and largest university of Iran. The American Concrete Institute (ACI is a non-profit technical society and standard developing organization ( SDO) ^[14] The blocks appeared to use an aggregate of steel fibres and quartz – a mineral with a compressive strength of 160,000 PSI, much higher than typical high-strength aggregates such as granite (15,000-20,000 PSI). Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock.

Elasticity

The modulus of elasticity of concrete is a function of the modulus of elasticity of the aggregates and the cement matrix and their relative proportions. The modulus of elasticity of concrete is relatively linear at low stress levels but becomes increasingly non-linear as matrix cracking develops. This article describes the use of the term nonlinearity in mathematics The elastic modulus of the hardened paste may be in the order of 10-30 GPa and aggregates about 45 to 85 GPa. The concrete composite is then in the range of 30 to 50 GPa.

Expansion and shrinkage

Concrete has a very low coefficient of thermal expansion. When the Temperature of a substance changes the energy that is stored in the Intermolecular bonds between atoms changes However, if no provision is made for expansion, very large forces can be created, causing cracks in parts of the structure not capable of withstanding the force or the repeated cycles of expansion and contraction.

As concrete matures it continues to shrink, due to the ongoing reaction taking place in the material, although the rate of shrinkage falls relatively quickly and keeps reducing over time (for all practical purposes concrete is usually considered to not shrink due to hydration any further after 30 years). The relative shrinkage and expansion of concrete and brickwork require careful accommodation when the two forms of construction interface.

Because concrete is continuously shrinking for years after it is initially placed, it is generally accepted that under thermal loading it will never expand to its originally placed volume.

Cracking

Salginatobel Bridge

All concrete structures will crack to some extent. Salginatobel Bridge is a Reinforced concrete arch Bridge designed by renowned Swiss Civil engineer Robert Maillart. One of the early designers of reinforced concrete, Robert Maillart, employed reinforced concrete in a number of arched bridges. Robert Maillart ( February 6, 1872 - April 5, 1940) was a Swiss Civil engineer who revolutionized Reinforced concrete His first bridge was simple, using a large volume of concrete. He then realized that much of the concrete was very cracked, and could not be a part of the structure under compressive loads, yet the structure clearly worked. His later designs simply removed the cracked areas, leaving slender, beautiful concrete arches. The Salginatobel Bridge is an example of this. Salginatobel Bridge is a Reinforced concrete arch Bridge designed by renowned Swiss Civil engineer Robert Maillart.

Concrete cracks due to tensile stress induced by shrinkage or stresses occurring during setting or use. Various means are used to overcome this. Fiber reinforced concrete uses fine fibers distributed throughout the mix or larger metal or other reinforcement elements to limit the size and extent of cracks. Fiber reinforced concrete (FRC is Concrete containing fibrous material which increases its structural integrity A rebar, or reinforcing bar, is a common Steel bar and is commonly used in Reinforced concrete and reinforced Masonry structures In many large structures joints or concealed saw-cuts are placed in the concrete as it sets to make the inevitable cracks occur where they can be managed and out of sight. Water tanks and highways are examples of structures requiring crack control.

Shrinkage cracking

Shrinkage cracks occur when concrete members undergo restrained volumetric changes (shrinkage) as a result of either drying, autogenous shrinkage or thermal effects. Restraint is provided either externally (i. e. supports, walls, and other boundary conditions) or internally (differential drying shrinkage, reinforcement). Once the tensile strength of the concrete is exceeded, a crack will develop. The number and width of shrinkage cracks that develop are influenced by the amount of shrinkage that occurs, the amount of restraint present and the amount and spacing of reinforcement provided.

Concrete is placed while in a wet (or plastic) state, and therefore can be manipulated and moulded as needed. 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 significant strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased by keeping it damp for a longer period 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 which increases shrinkage and cracking.

Plastic-shrinkage cracks are immediately apparent, visible within 0 to 2 days of placement, while drying-shrinkage cracks develop over time.

Tension cracking

Concrete members may be put into tension by applied loads. This is most common in concrete beams where a transversely applied load will put one surface into compression and the opposite surface into tension due to induced bending. This article is about structural behavior For other meanings see Bending (disambiguation. The portion of the beam that is in tension may crack. The size and length of cracks is dependent on the magnitude of the bending moment and the design of the reinforcing in the beam at the point under consideration. Reinforced concrete beams are designed to crack in tension rather than in compression. This is achieved by providing reinforcing steel which yields before failure of the concrete in compression occurs and allowing remediation, repair, or if necessary, evacuation of an unsafe area.

Creep

Because it is a fluid, concrete can be pumped to where it is needed. Here a concrete transport truck is feeding concrete to a concrete pumper, which is pumping it to where a slab is being poured.

Creep is the term used to describe the permanent movement or deformation of a material in order to relieve stresses within the material. Concrete which is subjected to forces is prone to creep. Creep is the tendency of a solid material to slowly move or deform permanently under the influence of stresses It occurs as a result of long term exposure to levels of Creep can sometimes reduce the amount of cracking that occurs in a concrete structure or element, but it also must be controlled. The amount of primary and secondary reinforcing in concrete structures contributes to a reduction in the amount of shrinkage, creep and cracking.

Physical properties

The coefficient of thermal expansion of Portland cement concrete is 0. 000008 to 0. 000012 (per degree Celsius) (8-12 1/MK) ^[15]. The density varies, but is around 150 pounds per cubic foot (2400 kg/m³). ^[16]

Damage modes

Fire

Due to its low thermal conductivity, a layer of concrete is frequently used for fireproofing of steel structures. In Physics, thermal conductivity, k is the property of a material that indicates its ability to conduct Heat. "Fireproof" redirects here For the album see Fireproof (album. However, concrete itself may be damaged by fire.

Up to about 300 °C, the concrete undergoes normal thermal expansion. Thermal Expansion is the tendency of matter to change in Volume in response to a change in temperature Above that temperature, shrinkage occurs due to water loss; however, the aggregate continues expanding, which causes internal stresses. Up to about 500 °C, the major structural changes are carbonation and coarsening of pores. At 573 °C, quartz undergoes rapid expansion due to Phase transition, and at 900 °C calcite starts shrinking due to decomposition. Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in In Thermodynamics, phase transition or phase change is the transformation of a thermodynamic system from one phase to another Calcite is a carbonate mineral and the most stable polymorph of Calcium carbonate ( Ca[[carbon C]] O 3 At 450-550 °C the cement hydrate decomposes, yielding calcium oxide. Calcium carbonate decomposes at about 600 °C. Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3 Rehydration of the calcium oxide on cooling of the structure causes expansion, which can cause damage to material which withstood fire without falling apart. Concrete in buildings that experienced a fire and were left standing for several years shows extensive degree of carbonation.

Concrete exposed to up to 100 °C is normally considered as healthy. The parts of a concrete structure that is exposed to temperatures above approximately 300 °C (dependent of water/cement ratio) will most likely get a pink color. Over approximately 600 °C the concrete will turn light grey, and over approximately 1000 °C it turns yellow-brown. ^[17] One rule of thumb is to consider all pink colored concrete as damaged, and to be removed.

Fire will expose the concrete to gases and liquids that can be harmful to the concrete, among other salts and acids that occur when gasses produced by fire come into contact with water.

Aggregate expansion

Various types of aggregate undergo chemical reactions in concrete, leading to damaging expansive phenomena. The most common are those containing reactive silica, that can react (in the presence of water) with the alkalis in concrete (K₂O and Na₂O, coming principally from cement). Among the more reactive mineral components of some aggregates are opal, chalcedony, flint and strained quartz. OPAL ( Open Pool Australian Lightwater reactor) is a 20 megawatt pool-type nuclear research reactor that was officially opened in April 2007 Chalcedony is a Cryptocrystalline form of Silica, composed of very fine intergrowths of the minerals Quartz and Moganite. Flint (or flintstone) is a hard sedimentary Cryptocrystalline form of the Mineral Quartz, categorized as a variety of Chert Quartz (from German) is the most abundant Mineral in the Earth 's Continental crust (although Feldspar is more common in Following the reaction (Alkali Silica Reaction or ASR), an expansive gel forms, that creates extensive cracks and damage on structural members. Alkali-Silica Reaction (ASR is a reaction between reactive Silica (in the Concrete aggregates and an Alkali (usually present in the Cement) On the surface of concrete pavements the ASR can cause pop-outs, i. e. the expulsion of small cones (up to 3 cm about in diameter) in correspondence of aggregate particles. When some aggregates containing dolomite are used, a dedolomitization reaction occurs where the magnesium carbonate compound reacts with hydroxyl ions and yields magnesium hydroxide and a carbonate ion. Dolomite (ˈdɒləmaɪt is the name of a Sedimentary Carbonate rock and a Mineral, both composed Magnesium carbonate, MgCO3 is a white Solid that occurs in nature as a Mineral. Magnesium hydroxide is an inorganic compound with the chemical formula Mg(OH2 In Chemistry, a carbonate is a salt or Ester of Carbonic acid. The resulting expansion may cause destruction of the material. Far less common are pop-outs caused by the presence of pyrite, an iron sulfide that generates expansion by forming iron oxide and ettringite. Ettringite is a hexacalcium aluminate trisulfate Hydrate, (CaO6(Al2O3(SO33 · 32 H2O Other reactions and recrystallizations, e. g. hydration of clay minerals in some aggregates, may lead to destructive expansion as well. Clay minerals are hydrous Aluminium phyllosilicates, sometimes with variable amounts of Iron, Magnesium, Alkali metals Alkaline

Sea water effects

Concrete exposed to sea water is susceptible to its corrosive effects. Seawater is Water from a Sea or Ocean. On average seawater in the world's oceans has a Salinity of about 3 The effects are more pronounced above the tidal zone than where the concrete is permanently submerged. In the submerged zone, magnesium and hydrogen carbonate ions precipitate about 30 micrometers thick layer of brucite on which a slower deposition of calcium carbonate as aragonite occurs. In Inorganic chemistry, bicarbonate ( IUPAC -recommended nomenclature hydrogencarbonate) is an intermediate form in the Deprotonation Brucite is the Mineral form of Magnesium hydroxide, with the chemical formula Mg ( OH)2 Aragonite is a Carbonate mineral, one of the two common naturally occurring polymorphs of Calcium carbonate, Ca[[carbon C]] O 3 These layers somewhat protect the concrete from other processes, which include attack by magnesium, chloride and sulfate ions and carbonation. Above the water surface, mechanical damage may occur by erosion by waves themselves or sand and gravel they carry, and by crystallization of salts from water soaking into the concrete pores and then drying up. Erosion is the carrying away or displacement of solids ( Sediment, Soil, rock and other particles usually by the agents of currents such as wind Pozzolanic cements and cements using more than 60% of slag as aggregate are more resistant to sea water than pure Portland cement. A pozzolan is a material which when combined with Calcium hydroxide, exhibits Cementitious properties

Bacterial corrosion

Bacteria themselves do not have noticeable effect on concrete. However, anaerobic bacteria (Thiobacillus) in untreated sewage tend to produce hydrogen sulfide, which is then oxidized by aerobic bacteria present in biofilm on the concrete surface above the water level to sulfuric acid which dissolves the carbonates in the cured cement and causes strength loss. An anaerobic organism is any Organism that does not require Oxygen for growth and may even die in its presence The Hydrogenophilaceae are a family of Betaproteobacteria, with two genera Hydrogen sulfide (or hydrogen sulphide) is the Chemical compound with the formula H 2 S. An aerobic organism or aerobe is an Organism that has an Oxygen based Metabolism. A biofilm is a structured community of Microorganisms encapsulated within a self-developed polymeric matrix and adherent to a living or inert surface Sulfuric (or sulphuric acid, H 2 S[[oxygen O]]4 is a strong Mineral acid. Concrete floors lying on ground that contains pyrite are also at risk. Using limestone as the aggregate makes the concrete more resistant to acids, and the sewage may be pretreated by ways increasing pH or oxidizing or precipitating the sulfides in order to inhibit the activity of sulfide utilizing bacteria. Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3

Chemical damage

Carbonation

Carbonation-iniated deterioration of concrete (at Hippodrome Wellington)

Carbon dioxide from air can react with the calcium hydroxide in concrete to form calcium carbonate. The Hippodrome Wellington is a Horse racing track in Ostend in the Flemish Region of Belgium built Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Calcium hydroxide, traditionally called slaked lime, hydrated lime, or pickling lime, is a Chemical compound with the chemical formula Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3 This process is called carbonation, which is essentially the reversal of the chemical process of calcination of lime taking place in a cement kiln. Calcination (also referred to as calcining) is a thermal treatment process applied to ores and other solid materials in order to bring about a Thermal decomposition Calcium carbonate is a Chemical compound with the Chemical formula Ca[[Carbon C]] O 3 Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate Carbonation of concrete is a slow and continuous process progressing from the outer surface inward, but slows down with increasing diffusion depth. Carbonation has two effects: it increases mechanical strength of concrete, but it also decreases alkalinity, which is essential for corrosion prevention of the reinforcement steel. Alkalinity or AT is a measure of the ability of a solution to neutralize acids to the Equivalence point of carbonate or bicarbonate Corrosion means the breaking down of essential properties in a material due to Chemical reactions with its surroundings Below a pH of 10, the steel's thin layer of surface passivation dissolves and corrosion is promoted. pH is the measure of the acidity or alkalinity of a Solution. For the latter reason, carbonation is an unwanted process in concrete chemistry. Carbonation can be tested by applying Phenolphthalein solution, a pH indicator, over a fresh fracture surface, which indicates non-carbonated and thus alkaline areas with a violet color. Phenolphthalein is a Chemical compound with the formula C 20 H 14 O 4 (often written as " HIn A pH indicator is a halochromic chemical compound that is added in small amounts to a Solution so that the PH ( Acidity or

Chlorides

Chlorides, particularly calcium chloride, have been used to shorten the setting time of concrete. Calcium chloride (CaCl2 is an ionic compound of Calcium and Chlorine. ^[18] However, calcium chloride and (to a lesser extent) sodium chloride have been shown to leach calcium hydroxide and cause chemical changes in Portland cement, leading to loss of strength,^[19] as well as attacking the steel reinforcement present in most concrete. For sodium chloride in the diet see Salt. Sodium chloride, also known as common salt, table salt, or Halite, is a Calcium hydroxide, traditionally called slaked lime, hydrated lime, or pickling lime, is a Chemical compound with the chemical formula

Sulphates

Sulphates in solution in contact with concrete can cause chemical changes to the cement, which can cause significant microstructural effects leading to the weakening of the cement binder.

Leaching

Physical damage

Damage can occur during the casting and de-shuttering processes. The corners of beams for instance, can be damaged during the removal of shuttering because they are less effectively compacted by means of vibration (improved by using form-vibrators). Other physical damage can be caused by the use of steel shuttering without base plates. The steel shuttering pinches the top surface of a concrete slab due to weight of the next slab being constructed.

Types of concrete

A highway paved with concrete. * * * * * * * * * * * * * * * * * * * * * * Before adding any more images to this * * page please do carefully consider * * whether they would be mere decoration * * or actually improve

Regular concrete paving blocks

Various types of concrete have been developed for specialist application and have become known by these names.

Regular concrete

Regular concrete is the lay term describing concrete that is produced by following the mixing instructions that are commonly published on packets of cement, typically using sand or other common material as the aggregate, and often mixed in improvised containers. This concrete can be produced to yield a varying strength from about 10 MPa to about 40 MPa, depending on the purpose, ranging from blinding to structural concrete respectively. Many types of pre-mixed concrete are available which include powdered cement mixed with an aggregate, needing only water.

Typically, a batch of concrete can be made by using 1 part Portland cement, 2 parts dry sand, 3 parts dry stone, 1/2 part water. The parts are in terms of weight – not volume. For example, 1 cubic foot of concrete would be made using 22 lbs cement, 10 lbs water, 41 lbs dry sand, 70 lbs dry stone (1/2" to 3/4" stone). This would make 1 cubic foot of concrete and would weigh about 143 lbs. The sand should be mortar or brick sand (washed and filtered if possible) and the stone should be washed if possible. Organic materials (leaves, twigs, etc) should be removed from the sand and stone to ensure the highest strength.

High-strength concrete

High-strength concrete has a compressive strength generally greater than 6,000 pounds per square inch (40 MPa). High-strength concrete is made by lowering the water-cement (W/C) ratio to 0. 35 or lower. Often silica fume is added to prevent the formation of free calcium hydroxide crystals in the cement matrix, which might reduce the strength at the cement-aggregate bond.

Low W/C ratios and the use of silica fume make concrete mixes significantly less workable, which is particularly likely to be a problem in high-strength concrete applications where dense rebar cages are likely to be used. To compensate for the reduced workability, superplasticizers are commonly added to high-strength mixtures. Aggregate must be selected carefully for high-strength mixes, as weaker aggregates may not be strong enough to resist the loads imposed on the concrete and cause failure to start in the aggregate rather than in the matrix or at a void, as normally occurs in regular concrete.

In some applications of high-strength concrete the design criterion is the elastic modulus rather than the ultimate compressive strength. An elastic modulus, or modulus of elasticity, is the mathematical description of an object or substance's tendency to be deformed elastically (i

High-performance concrete

High-performance concrete (HPC) is a relatively new term used to describe concrete that conforms to a set of standards above those of the most common applications, but not limited to strength. While all high-strength concrete is also high-performance, not all high-performance concrete is high-strength. Some examples of such standards currently used in relation to HPC are:

Self-consolidating concretes

During the 1980s a number of countries including Japan, Sweden and France developed concretes that are self-compacting, known as self-consolidating concrete in the United States. This self-consolidating concrete (SCCs) is characterized by:

• extreme fluidity as measured by flow, typically between 650-750 mm on a flow table, rather than slump(height)
• no need for vibrators to compact the concrete
• placement being easier. A vibrator is a mechanical device that is designed to generate vibrations The vibration is often generated by an Electric motor with an unbalanced
• no bleed water, or aggregate segregation
• Increased Liquid Head Pressure, Can be detrimental to Safety and workmanship

SCC can save up to 50% in labor costs due to 80% faster pouring and reduced wear and tear on formwork. Wear and tear is a term for damage that naturally and inevitably occurs as a result of normal use or aging Formwork is the term given to either temporary or permanent moulds into which Concrete or similar materials are poured

As of 2005, self-consolidating concretes account for 10-15% of concrete sales in some European countries. Year 2005 ( MMV) was a Common year starting on Saturday (link displays full calendar of the Gregorian calendar. In the US precast concrete industry, SCC represents over 75% of concrete production. 38 departments of transportation in the US accept the use of SCC for road and bridge projects. Overview Road transportation In comparison to most of the Western world, the United States relies much more

This emerging technology is made possible by the use of polycarboxylates plasticizer instead of older naphthalene based polymers, and viscosity modifiers to address aggregate segregation. Plasticizers are additives that increase the Plasticity or Fluidity of the material to which they are added these include plastics cement concrete wallboard and

Shotcrete

Main article: Shotcrete

Shotcrete (also known by the trade name Gunite) uses compressed air to shoot concrete onto (or into) a frame or structure. Shotcrete and gunite are two commonly used terms for substances applied via Pressure hoses Shotcrete is mortar or (usually Concrete conveyed Shotcrete is frequently used against vertical soil or rock surfaces, as it eliminates the need for formwork. Formwork is the term given to either temporary or permanent moulds into which Concrete or similar materials are poured It is sometimes used for rock support, especially in tunneling.

There are two application methods for shotcrete.

• dry-mix – the dry mixture of cement and aggregates is filled into the machine and conveyed with compressed air through the hoses. Compressed air The water needed for the hydration is added at the nozzle.
• wet-mix – the mixes are prepared with all necessary water for hydration. The mixes are pumped through the hoses. At the nozzle compressed air is added for spraying.

For both methods additives such as accelerators and fiber reinforcement may be used. Accelerants play a major role in chemistry Most chemical reactions can be hastened with an accelerant ^[20]

Pervious concrete

Pervious concrete contains a network of holes or voids, to allow air or water to move through the concrete. Permeable paving, is different than pervious paving or porous pavement, by virtue of the fact that rainwater passes around the paver as opposed to passing through

It is formed by leaving out some or all of the fine aggregate (fines), the remaining large aggregate then is bound by a relatively small amount of cement paste. When set, typically between 15 and 25% of the concrete volume are voids, allowing water to drain at around 5 gal/ft²/ min or 200 L/m²/min) through the concrete.

Pervious concrete allows water to drain naturally through roadway or other structures, reducing the amount of artificial drainage needed, and allowing the water to naturally replenish groundwater

It can significantly reduce noise, by allowing air squeezed between vehicle tires and the roadway to escape. Drainage is the natural or artificial removal of surface and sub-surface water from a given area Groundwater is Water located beneath the Ground surface in Soil pore spaces and in the Fractures of lithologic formations

Cellular concrete

Aerated concrete produced by the addition of an air entraining agent to the concrete (or a lightweight aggregate like expanded clay pellets or cork granules and vermiculite) is sometimes called Cellular concrete. Expanded clay pellets, most commonly known under the brand name LECA (acronym of light expanded clay aggregate) also known as Hydroton and under the non-proprietary Expanded clay pellets, most commonly known under the brand name LECA (acronym of light expanded clay aggregate) also known as Hydroton and under the non-proprietary Cork material is a Prime-subset of generic cork tissue, harvested for commercial use primarily from the Cork Oak tree Quercus Vermiculite is a natural Mineral that expands with the application of Heat.

See also: Aerated autoclaved concrete

Cork-cement composites

Cork granules are obtained during production of bottle stoppers from the treated bark of Cork oak or Quercus suber trees. Autoclaved Aerated Concrete (AAC or otherwise known as Autoclave Cellular Concrete (ACC is a lightweight precast building material Cork material is a Prime-subset of generic cork tissue, harvested for commercial use primarily from the Cork Oak tree Quercus The Cork Oak ( Quercus suber) is a medium-sized Evergreen Oak tree in the section ''Quercus'' sect ^[21] These trees are mainly found in Portugal, Spain and North Africa. ^[22] Portugal is the largest cork producing country, followed by Spain. The waste cork granules have a density of about 300 kg/m³, which is lower than that of most of the lightweight aggregates used for making lightweight concrete. It has been found that cork granules do not significantly influence cement hydration. However, cork dust can influence hydration. ^[23] Cork cement composites have several advantages over standard concrete, such as lower thermal conductivities, lower densities and good energy absorption characteristics. These composites can be made of density from 400 to 1500 kg/m³, compressive strength from 1 to 26 MPa, and flexural strength from 0. 5 to 4. 0 MPa.

Roller-compacted concrete

Roller-compacted concrete, sometimes called rollcrete, is a low-cement-content stiff concrete placed using techniques borrowed from earthmoving and paving work. The concrete is placed on the surface to be covered, and is compacted in place using large heavy rollers typically used in earthwork. The concrete mix achieves a high density and cures over time into a strong monolithic block. ^[24] Roller-compacted concrete is typically used for concrete pavement, but has also been used to build concrete dams, as the low cement content causes less heat to be generated while curing than typical for conventionally placed massive concrete pours.

Glass concrete

The use of recycled glass as aggregate in concrete has become popular in modern times, with large scale research being carried out at Columbia University in New York. This greatly enhances the aesthetic appeal of the concrete. Recent research findings have shown that concrete made with recycled glass aggregates have shown better long term strength and better thermal insulation due to its better thermal properties of the glass aggregates. [1]

Asphalt concrete

Strictly speaking, asphalt is a form of concrete as well, with bituminous materials replacing cement as the binder. Asphalt concrete, normally known simply as Asphalt, is a Composite material commonly used for construction of pavement, Highways and Bitumen is a mixture of organic Liquids that are highly Viscous, black sticky entirely soluble in Carbon disulfide, and composed primarily

Rapid strength concrete

This type of concrete is able to develop high resistance within few hours after being manufactured. This feature has advantages such as removing the formwork early and to move forward in the building process at record time, repair road surfaces that become fully operational in just a few hours.

Rubberized concrete

While "rubberized asphalt concrete" is common, rubberized Portland cement concrete ("rubberized PCC") is still undergoing experimental tests, as of 2007 [2] [3] [4] [5]. Rubberized asphalt is pavement material that consists of regular Asphalt concrete mixed with Crumb rubber -- ground used tires that would otherwise be

Polymer concrete

Polymer concrete is concrete which uses polymers to bind the aggregate. Polymer concrete is part of group of concretes that use polymers to supplement or replace cement as a binder Polymer concrete can gain a lot of strength in a short amount of time. For example, a polymer mix may reach 5000 psi in only four hours. Polymer concrete is generally more expensive than conventional concretes.

Geopolymer or green concrete

Geopolymer concrete is a greener alternative to ordinary Portland cement made from inorganic aluminosilicate (Al-Si) polymer compounds that can utilise 100% recycled industrial waste (e. Geopolymer is a term covering a class of synthetic Aluminosilicate materials with potential use in a number of areas but predominantly as a replacement for Portland cement g. fly ash and slag) as the manufacturing inputs resulting in up to 80% lower carbon dioxide emissions. Greater chemical and thermal resistance, and better mechanical properties, are said to be achieved by the manufacturer at both atmospheric and extreme conditions. ^[25]

Similar concretes have not only been used in Ancient Rome (see Roman concrete) as mentioned but also in the former Soviet Union in the 1950s and 1960s. Ancient Rome was a Civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC Roman concrete was a Ceramic material used in construction during the Roman Empire. The Union of Soviet Socialist Republics (USSR was a constitutionally Socialist state that existed in Eurasia from 1922 to 1991 Buildings in the Ukraine are still standing after 45 years so that this kind of formulation has a sound track record. Ukraine (Україна Ukrayina, /ukrɑˈjinɑ/ is a country in Eastern Europe. ^[26]

Limecrete

Limecrete or lime concrete is concrete where cement is replaced by lime. Lime is a general term for various naturally occurring Minerals and materials derived from them in which Carbonates Oxides and Hydroxides of ^[27]

Concrete testing

Compression testing of a concrete cylinder

Same cylinder after failure

Engineers usually specify the required compressive strength of concrete, which is normally given as the 28 day compressive strength in megapascals (MPa) or pounds per square inch (psi). A square inch (plural square inches) is a unit of Area, equal to the area of a square with sides of one Inch. Twenty eight days is a long wait to determine if desired strengths are going to be obtained, so three-day and seven-day strengths can be useful to predict the ultimate 28-day compressive strength of the concrete. A 25% strength gain between 7 and 28 days is often observed with 100% OPC (ordinary Portland cement) mixtures, and up to 40% strength gain can be realized with the inclusion of pozzolans and supplementary cementitious materials (SCMs) such as fly ash and/or slag cement. As strength gain depends on the type of mixture, its constituents, the use of standard curing, proper testing and care of cylinders in transport, etc. it becomes imperative to proactively rely on testing the fundamental properties of concrete in its fresh, plastic state.

Concrete is typically sampled while being placed, with testing protocols requiring that test samples be cured under laboratory conditions (standard cured). Additional samples may be field cured (non-standard) for the purpose of early 'stripping' strengths, that is, form removal, evaluation of curing, etc. but the standard cured cylinders comprise acceptance criteria. Concrete tests can measure the "plastic" (unhydrated) properties of concrete prior to, and during placement. As these properties affect the hardened compressive strength and durability of concrete (resistance to freeze-thaw), the properties of slump (workability), temperature, density and age are monitored to ensure the production and placement of 'quality' concrete. Tests are performed per ASTM International or CSA (Canadian Standards Association) and European methods and practices. ASTM International ( ASTM) originally known as the American Society for Testing and Materials is an international Standards organization that develops and publishes Established in 1919 the Canadian Standards Association (CSA is a not-for-profit association composed of representatives from government industry and Technicians performing concrete tests MUST be certified. Structural design, material design and properties are often specified in accordance with ACI American Concrete Institute) code (www. In Structural engineering, structural design is an Iterative process of applying Engineering mechanics and past experience to create a functional economic The American Concrete Institute (ACI is a non-profit technical society and standard developing organization ( SDO) concrete. org); with test methods, production and delivery under the "prescription" or "performance" purchasing options per ASTM C94 (www. astm. org).

Compressive-strength tests are conducted using an instrumented hydraulic ram to compress a cylindrical or cubic sample to failure. A hydraulic ram is a cyclic water pump powered by Hydropower. Tensile strength tests are conducted either by three-point bending of a prismatic beam specimen or by compression along the sides of a cylindrical specimen.

Concrete recycling

Main article: Concrete recycling

Concrete recycling is an increasingly common method of disposing of concrete structures. When structures made of Concrete are to be demolished concrete recycling is an increasingly common method of disposing of the rubble Concrete debris was once routinely shipped to landfills for disposal, but recycling is increasing due to improved environmental awareness, governmental laws, and economic benefits. For other uses see Water treatment and Land reclamation. A landfill, also known as a dump (and historically as

Concrete, which must be free of trash, wood, paper and other such materials is collected from demolition sites and put through a crushing machine, often along with asphalt, bricks, and rocks. A crusher is a Machine designed to reduce large Solid Material Objects into a smaller volume or smaller pieces

Reinforced concrete contains rebar and other metallic reinforcements, which are removed with magnets and recycled elsewhere. A rebar, or reinforcing bar, is a common Steel bar and is commonly used in Reinforced concrete and reinforced Masonry structures A magnet (from Greek grc μαγνήτης λίθος " Magnesian stone" is a material or object that produces a Magnetic field. The remaining aggregate chunks are sorted by size. Larger chunks may go through the crusher again. Smaller pieces of concrete are used as gravel for new construction projects. Aggregate base gravel is laid down as the lowest layer in a road, with fresh concrete or asphalt placed over it. Aggregate base is typically composed of crushed rock comprised of material capable of passing through a 3/4 inch rock screen Crushed recycled concrete can sometimes be used as the dry aggregate for brand new concrete if it is free of contaminants, though the use of recycled concrete limits strength and is not allowed in many jurisdictions. On March 3, 1983, a government funded research team (the VIRL research. Events 1284 - Statute of Rhuddlan incorporated the Principality of Wales into England 1575 - Indian Year 1983 ( MCMLXXXIII) was a Common year starting on Saturday (link displays the 1983 Gregorian calendar) codep) approximated that almost 17% of worldwide landfill was byproducts of concrete based waste.

Recycling concrete provides environmental benefits, conserving landfill space and use as aggregate reduces the need for gravel mining. Construction aggregate, or simply " aggregate " is a broad category of coarse particulate Material used in Construction, including Open-pit mining, also known as opencast mining and open-cut mining and strip mining, refers to a method of extracting rock or Minerals

Use of concrete in structures

Mass concrete structures

These include gravity dams such as the Itaipu, Hoover Dam and the Three Gorges Dam and large breakwaters. A dam is a barrier that divides waters. Dams generally serve the primary purpose of retaining water while other structures such as Floodgates, Levees Itaipu ( Guarani: Itaipu, Portuguese: Itaipu, Spanish: Itaipú; itaiˈpu is a hydroelectric dam on Hoover Dam, also sometimes known as Boulder Dam, is a Concrete Arch-gravity dam in the Black Canyon of the Colorado River, on the Zh-yue三峽大壩 The Three Gorges Dam ( is a hydroelectric River Dam that spans the Yangtze River in Sandouping, Breakwaters are structures constructed on coasts as part of coastal defence or to protect an anchorage from the effects of Weather and Longshore drift. Concrete that is poured all at once in one block (so that there are no weak points where the concrete is "welded" together) is used for tornado shelters.

Reinforced concrete structures

Main article: Reinforced concrete

Reinforced concrete contains steel reinforcing that is designed and placed in structural members at specific positions to cater for all the stress conditions that the member is required to accommodate. Reinforced concrete is Concrete in which reinforcement bars (" Rebars quot or fibers have been incorporated to strengthen a material that would otherwise be

Prestressed concrete structures

Main article: Prestressed concrete

Prestressed concrete is a form of reinforced concrete which builds in compressive stresses during construction to oppose those found when in use. Prestressed concrete is a method for overcoming the Concrete 's natural weakness in tension. Compressive stress is the stress applied to materials resulting in their compaction (decrease of volume This can greatly reduce the weight of beams or slabs, by better distributing the stresses in the structure to make optimal use of the reinforcement.

For example a horizontal beam will tend to sag down. If the reinforcement along the bottom of the beam is prestressed, it can counteract this.

In pre-tensioned concrete, the prestressing is achieved by using steel or polymer tendons or bars that are subjected to a tensile force prior to casting, or for post-tensioned concrete, after casting.

See also

References

External links

Related article and publications

• Refractory Concrete Information related to heat resistant concrete; recipes, ingredients mixing ratio, work with and applications.
• Concrete BasicsPDF (1. 12 MiB)
• The effect of curing on the tensile strength of medium to high strength concrete
• The History of Concrete
• Concrete carbonation chemistry at the TU Dresden
• Doctionary of Civil Engineering

Industry associations

• American Concrete Institute (ACI)
• American Concrete Pavement Association (ACPA)
• Cement Concrete and Aggregates Australia (CCAA)
• Concrete Foundations Association (CFA)
• Concrete Institute of Australia
• The Concrete Centre
• The Concrete Society
• FixConcrete.org
• Concrete Resources
• National Ready Mixed Concrete Association (NRMCA)
• Tilt-Up Concrete Association (TCA)