Concrete is a construction material composed of cement 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. The word "cement" traces to the Romans, who used the term "opus caementicium" to describe masonry which resembled concrete and was made from crushed rock with burnt lime as binder (commonly Portland cement Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time) and up to 5% minor) and other cementitious materials such as fly ash Fly ash is one of the residues generated in the combustion of coal. Fly ash is generally captured from the chimneys of coal-fired power plants, and is one of two types of ash that jointly are known as coal ash; the other, bottom ash, is removed from the bottom of coal furnaces. Depending upon the source and makeup of the coal being burned, the and slag cement Ground granulated blast furnace slag 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, aggregate Construction aggregate, or simply "aggregate", is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates. Aggregates are a component of composite materials such as concrete and asphalt concrete; the aggregate serves as reinforcement (generally a coarse aggregate made of gravels or crushed rocks such as limestone Limestone is a sedimentary rock composed largely of the mineral calcite . Like most other sedimentary rocks, limestones are composed of grains; however, most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera. Other carbonate grains comprising limestones are ooids, peloids, intraclasts, and extraclasts, or granite Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granites usually have a medium to coarse grained texture. Occasionally some individual crystals (phenocrysts) are larger than the groundmass in which case the texture is known as porphyritic. A granitic rock with a porphyritic texture is sometimes known as a porphyry, plus a fine aggregate such as sand Sand is a naturally occurring granular material composed of finely divided rock and mineral particles), water Water is the most abundant compound on Earth's surface, constituting about 70% of the planet's surface. In nature it exists in liquid, solid, and gaseous states. It is in dynamic equilibrium between the liquid and gas states at standard temperature and pressure. At room temperature, it is a nearly colorless with a hint of blue, tasteless, and, and chemical Chemistry is the science of matter and the changes it undergoes. The science of matter is also addressed by physics, but while physics takes a more general and fundamental approach, chemistry is more specialized, being concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical admixtures.

The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the past participle of "concresco", from "com-" (together) and "cresco" (to grow).

Concrete solidifies and hardens after mixing with water and placement due to a chemical process A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, often coming about only after the input of some type of energy, viz. heat, light or electricity. Classically, chemical reactions encompass known as hydration Mineral hydration is an inorganic chemical reaction where water adds to the crystal structure of a mineral, usually creating a new mineral, usually called a hydrate. The water reacts with the cement, which bonds the other components together, eventually creating a stone-like material. Concrete is used to make pavements A sidewalk is a path along the side of a road. A sidewalk may accommodate moderate changes in grade (height) and is normally separated from the vehicular section by a curb (British spelling: kerb), there may also be a strip of vegetation, grass or bushes or trees or a combination of these between the pedestrian section and the vehicular section (, pipe, architectural structures The structure may be permanent. Typical examples include buildings and nonbuilding structures such as bridges, dams, electricity pylons, and radio masts, foundations A foundation is a structure that transfers loads to the earth. Foundations are generally broken into two categories: shallow foundations and deep foundations.[citation needed], motorways A motorway is a dual-carriageway limited access highway with grade separated junctions designed and built solely for motorised traffic. In English-speaking countries the term is used in the United Kingdom, some parts of Australia, New Zealand, Pakistan, some other Commonwealth nations, and Ireland (a motorway is also called a mótarbhealach in/roads A road is an identifiable thoroughfare, route, way or path between two places which may or may not be available for use by the public; public roads, especially major roads connecting significant destinations are termed highways. Modern roads are normally smoothed, paved, or otherwise prepared to allow easy travel although historically many roads, bridges A bridge is a structure built to span a valley, road, body of water, or other physical obstacle, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it/overpasses An overpass is a bridge, road, railway or similar structure that crosses over another road or railway. An overpass structure is one that carries a higher capacity road above a lower capacity road, whereas a structure that permits a lower capacity road to travel above a larger capacity road is an underpass.[citation needed] Capacity is determined, parking Parking is the act of stopping a vehicle and leaving it unoccupied for more than a brief time. Parking on one or both sides of a road is commonly permitted, though often with restrictions. Parking facilities are constructed in combination with most buildings, to facilitate the coming and going of the buildings' users structures, brick A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar/block In the United States, a concrete masonry unit — also called concrete block, cement block or foundation block — is a large rectangular brick used in construction. Concrete blocks are made from cast concrete, i.e. Portland cement and aggregate, usually sand and fine gravel for high-density blocks. Lower density blocks may use industrial wastes walls and footings A foundation is a structure that transfers loads to the earth. Foundations are generally broken into two categories: shallow foundations and deep foundations.[citation needed] for gates, fences A fence is a freestanding structure designed to restrict or prevent movement across a boundary. It is generally distinguished from a wall by the lightness of its construction: a wall is usually restricted to such barriers made from solid brick or concrete, blocking vision as well as passage and poles A utility pole is a pole used to support overhead power lines and various other public utilities, such as cable, fibre optic cable, and related equipment such as transformers and street lights. It can alternately be referred to as a telephone pole, power pole, telegraph pole or telegraph post, but these are all names commonly misused colloquially,.

Concrete is used more than any other man-made material in the world.^[2] As of 2006, about 7.5 cubic kilometres of concrete are made each year—more than one cubic metre for every person on Earth.^[3]

Concrete powers a US$ The United States dollar is the official currency of the United States. The U.S. dollar is normally abbreviated as the dollar sign, $, or as USD or US$ to distinguish it from other dollar-denominated currencies and from others that use the $ symbol. It is divided into 100 cents35 billion industry, employing more than two million workers in the United States ^ b. English is the de facto language of American government and the sole language spoken at home by 80% of Americans age five and older. Spanish is the second most commonly spoken language alone.^{[citation needed]} More than 55,000 miles (89,000 km) of highways A highway is a public road, especially a major road connecting two or more destinations. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a "highway transportation system". Each country has its own national highway system. Major highways are often named and in the United States are paved with this material. Reinforced concrete Reinforced concrete is concrete in which reinforcement bars , reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. The term Ferro Concrete refers only to concrete that is reinforced with iron or steel. Other materials used to reinforce concrete can be organic and inorganic fibres as well as composites, prestressed concrete Prestressed concrete is a method for overcoming concrete's natural weakness in tension. It can be used to produce beams, floors or bridges with a longer span than is practical with ordinary reinforced concrete. Prestressing tendons are used to provide a clamping load which produces a compressive stress that offsets the tensile stress that the and precast concrete Precast Concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and lifted into place. In contrast, standard concrete is poured into site-specific forms and cured on site. Precast stone is distinguished from precast are the most widely used types of concrete functional extensions in modern days.

Contents 1 History 1.1 Additives 2 Composition 2.1 Cement 2.2 Water 2.3 Aggregates 2.4 Reinforcement 2.5 Chemical admixtures 2.6 Mineral admixtures and blended cements 3 Concrete production 3.1 Mixing concrete 3.2 Workability 3.3 Concrete mixture placement 3.4 Concrete compaction 3.5 Curing 4 Properties 5 Environmental concerns 5.1 Worldwide CO2 emissions and global change 5.2 Surface runoff 5.3 Urban heat 5.4 Concrete dust 6 Health concerns 6.1 Concrete handling/safety precautions 7 Damage modes 8 Concrete repair 9 Concrete recycling 10 World records 10.1 Concrete pumping 10.2 Continuous pours 11 Use of concrete in infrastructure 11.1 Mass concrete structures 11.2 Reinforced concrete structures 11.3 Prestressed concrete structures 11.4 Concrete textures 12 Building with concrete 12.1 Environmentally sustainable 12.2 Energy efficiency 12.3 Fire safety and quality of life 12.4 Recycling and recyclable 13 See also 14 References 14.1 Notes 14.2 Bibliography 15 External links

History

Concrete has been used for construction in various ancient civilizations.^[4] An analysis of ancient Egyptian pyramids There are 138 pyramids discovered in Egypt as of 2008. Most were built as tombs for the country's Pharaohs and their consorts during the Old and Middle Kingdom periods has shown that concrete was employed in their construction.^[5]

During the Roman Empire The Roman Empire was the post-Republican phase of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean. The term is used to describe the Roman state during and after the time of the first emperor, Augustus, Roman concrete Roman concrete was a material used in construction during the Roman Empire. Roman concrete was based on a hydraulic-setting cement with many material qualities similar to modern Portland cement. By the middle of the first century AD, the material was used frequently as brick-faced concrete, although variations in aggregate allowed different (or opus caementicium) was made from quicklime Calcium oxide , commonly known as quicklime, is a widely used chemical compound. It is a white, caustic and alkaline crystalline solid at room temperature, pozzolana Pozzolana, also known as pozzolanic ash, is a fine, sandy volcanic ash, originally discovered and dug in Italy at Pozzuoli in the region around Vesuvius, but later at a number of other sites. Vitruvius speaks of four types of pozzolana: black, white, grey and red, all of which can be found in the volcanic areas of Italy, such as Naples, and an aggregate of pumice Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid cooling and rapid depressurization. The depressurization. Its widespread use in many Roman structures The Architecture of Ancient Rome adopted the external Greek architecture around 12th century B.C. for their own purposes, creating a new architectural style. The Romans absorbed Greek influence, apparent in many aspects closely related to architecture; for example, this can be seen in the introduction and use of the Triclinium in Roman villas as a, a key event in the history of architecture Neolithic architecture is the architecture of the Neolithic period. In Southwest Asia, Neolithic cultures appear soon after 10000 BC, initially in the Levant and from there spread eastwards and westwards. There are early Neolithic cultures in Southeast Anatolia, Syria and Iraq by 8000 BC, and food-producing societies first appear in southeast termed the Roman Architectural Revolution, freed Roman construction Romans are generally 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 from the restrictions of stone and brick material and allowed for revolutionary new designs both in terms of structural complexity and dimension.^[6]

Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of arches An arch is a structure that spans a space while supporting weight . Arches appeared as early as the 2nd millennium BC in Mesopotamian brick architecture and their systematic use started with the Ancient Romans who were the first to apply the technique to a wide range of structures, vaults A Vault is an architectural term for an arched form used to provide a space with a ceiling or roof. The parts of a vault exert a thrust that require a counter resistance. When vaults are built underground, the ground gives all the resistance required. However, when the vault is built above ground, various replacements are employed to supply the and domes This is a List of Roman domes. The Romans were the first builders in the history of architecture to realize the potential of domes for the creation of large and well-defined interior spaces. During the Roman Architectural Revolution, domes were introduced in a number of Roman building types such as temples, thermae, palaces, mausolea and later, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that trouble the builders of similar structures in stone or brick.^[7]

Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete (ca. 200 kg/cm²).^[8] However, due to the absence of steel reinforcement Reinforced concrete is concrete in which reinforcement bars , reinforcement grids, plates or fibers have been incorporated to strengthen the concrete in tension. The term Ferro Concrete refers only to concrete that is reinforced with iron or steel. Other materials used to reinforce concrete can be organic and inorganic fibres as well as composites, its tensile strength was far lower and its mode of application was also different:

Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble Rubble is broken stone, of irregular size, shape and texture. This word is closely connected in derivation with "rubbish", which was formerly also applied to what we now call "rubble". Rubble naturally found in the soil is known also as 'brash' . Where present, it becomes more noticeable when the land is ploughed. Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.^[9]

The widespread use of concrete in many Roman structures The Architecture of Ancient Rome adopted the external Greek architecture around 12th century B.C. for their own purposes, creating a new architectural style. The Romans absorbed Greek influence, apparent in many aspects closely related to architecture; for example, this can be seen in the introduction and use of the Triclinium in Roman villas as a has ensured that many survive to the present day. The Baths of Caracalla The Baths of Caracalla in Rome, Italy were Roman public baths, or thermae, built in Rome between AD 212 and 216, during the reign of the Emperor Caracalla. The baths remained in use until the 6th century when the complex was sacked by the Ostrogoths during the Gothic War, destroying the hydraulic installations . The extensive ruins of the baths in Rome Rome (English pronunciation: /ˈroʊm/; Italian: Roma listen , pronounced [ˈroːma]; Latin: Rōma) is the capital of Italy and the country's largest and most populated municipality (central area), with over 2.7 million residents in 1,285.3 km2 (496.3 sq mi). While the population of the urban area was estimated by Eurostat to have been 3.46 are just one example. Many Roman aqueducts The Romans constructed numerous aqueducts to serve any large city in their empire, as well as many small towns and industrial sites. The city of Rome had the largest concentration of aqueducts, with water being supplied by eleven aqueducts constructed over a period of about 500 years. Scholars can even predict the size of the city by its water and bridges A bridge is a structure built to span a valley, road, body of water, or other physical obstacle, for the purpose of providing passage over the obstacle. Designs of bridges vary depending on the function of the bridge, the nature of the terrain where the bridge is constructed, the material used to make it and the funds available to build it have masonry cladding on a concrete core, as does the dome of the Pantheon.

Some have stated that 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. However, the Canal du Midi was constructed using concrete in 1670 suggesting a continuous unpublished use since Roman times.^[10] Likewise there are concrete structures in Finland that date back to the 1500s.^{[citation needed]} Portland cement was first used in concrete in the early 1840s.

Additives

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.^[11]

Recently, the use of recycled materials as concrete ingredients has been gaining popularity because of increasingly stringent environmental legislation. The most conspicuous of these is fly ash, a by-product of coal-fired power plants. This significantly reduces the amount of quarrying and landfill space required, and, as it acts as a cement replacement, reduces the amount of cement required.

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. Marconite is one example.

Cement and sand ready to be mixed.

Composition

There are many types of concrete available, created by varying the proportions of the main ingredients below. By varying the proportions of materials, or by substitution for the cemetitious and aggregate phases, the finished product can be tailored to its application with varying strength, density, or chemical and thermal resistance properties.

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. It is a basic ingredient of concrete, mortar, and plaster. English masonry worker 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. It consists of a mixture of oxides of calcium, silicon and aluminium. 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).

Water

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

Less water in the cement paste will yield a stronger, more durable concrete; more water will give an freer-flowing concrete with a higher slump.^[12]

Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.

Hydration involves many different reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles, and other components of the concrete, to form a solid mass.

Reaction:

Cement chemist notation: C₃S + H → C-S-H + CH

Standard notation: Ca₃SiO₅ + H₂O → (CaO)·(SiO₂)·(H₂O)(gel) + Ca(OH)₂

Balanced: 2Ca₃SiO₅ + 7H₂O → 3(CaO)·2(SiO₂)·4(H₂O)(gel) + 3Ca(OH)₂

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. 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.

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.

Distribution of aggregates after compaction is inhomogeneous due to the influence of vibration. As a result, gradients of strength may be significant ("Article" http://www.concreteresearch.org).

Installing rebar in a floor slab during a concrete pour.

Reinforcement

Concrete is strong in compression, as the aggregate efficiently carries the compression load. 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 either steel reinforcing bars, steel fibers, glass fiber, or plastic fiber to carry tensile loads.

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. 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.^[13] The common types of admixtures^[14] are as follows.

• Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are CaCl₂ and NaCl. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries.
• Retarders slow the hydration of concrete, and are used in large or difficult pours where partial setting before the pour is complete is undesirable. Typical polyol retarders are sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.
• Air entrainments add and entrain tiny air bubbles in the concrete, which will reduce damage during freeze-thaw cycles thereby increasing the concrete's durability. However, entrained air is a trade-off with strength, as each 1% of air may result in 5% decrease in compressive strength.
• Plasticizers/superplasticizers (water-reducing admixtures) increase the workability of plastic or "fresh" concrete, allowing it be placed more easily, with less consolidating effort. Typical plasticizers are liginsulfate, polyol type. 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. Such treatment improves its strength and durability characteristics. Superplasticizers (high-range water-reducing admixtures) are a class of plasticizers that have fewer deleterious effects when used to significantly increase workability. Representative superplasticizers are sulfonated naphthalene formaldehyde condensate, sulfonated melamine, formaldehy condensate, and acetone formaldehyde condensate. More advanced superplasticizers are polycarboxylate types.
• Pigments can be used to change the color of concrete, for aesthetics.
• Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.
• Bonding agents are used to create a bond between old and new concrete.
• Pumping aids improve pumpability, thicken the paste, and reduce separation and bleeding.

Blocks of concrete in Belo Horizonte, Brazil.

Mineral admixtures and blended cements

There are inorganic materials that also have pozzolanic or latent hydraulic properties. These very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures),^[13] or as a replacement for Portland cement (blended cements).^[15]

• 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). 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.^[16]
• 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). It has latent hydraulic properties.^[17]
• Silica fume: A by-product of the production of silicon and ferrosilicon alloys. 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. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability.^[18]
• High reactivity Metakaolin (HRM): Metakaolin produces concrete with strength and durability similar to concrete made with silica fume. 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.

Concrete production

Concrete plant facility (background) with concrete delivery trucks.

The processes used vary dramatically, from hand tools to heavy industry, but result in the concrete being placed where it cures into a final form. Wide range of technological factors may occur during production of concrete elements and their influence to basic characteristics may vary (article of Maksym Bulavytskyi (Ukraine) at www.concreteresearch.org)

When initially mixed together, Portland cement and water rapidly form a gel, formed of tangled chains of interlocking crystals. These continue to react over time, with the initially fluid gel often aiding in placement by improving workability. As the concrete sets, the chains of crystals join up, and form a rigid structure, gluing the aggregate particles in place. During curing, more of the cement reacts with the residual water (hydration).

This curing process develops physical and chemical properties. Among other qualities, mechanical strength, low moisture permeability, and chemical and volumetric stability.

Cement being mixed with sand and water to form concrete.

Mixing concrete

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.^[19] The paste is generally mixed in a high-speed, shear-type mixer at a w/cm (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, plasticizers, pigments, or silica fume. The latter is added to fill the gaps between the cement particles. This reduces the particle distance and leads to a higher final compressive strength and a higher water impermeability.^[20] The premixed paste is then blended with aggregates and any remaining batch water, and final mixing is completed in conventional concrete mixing equipment.^[21]

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. It is then added to a plasticizer admixture and mixed after that with aggregates in conventional concrete mixer. This paste can be used itself or foamed (expanded) for lightweight concrete.^[22] 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. It is recommended for precast concrete in order to reduce quantity of cement, as well as for concrete roof and siding tiles, paving stones and lightweight concrete block production.

Pouring a concrete floor for a commercial building, slab-on-ground. Concrete pump. A concrete slab ponded while curing.

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. 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. 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. 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. 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 eight inches.

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. It is bad practice to add water on-site that exceeds the water-cement ratio of the mix design, 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. 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.

After mixing, concrete is a fluid and can be pumped to where it is needed.

Concrete mixture placement

Concrete mixture placement

Concrete compaction

Concrete compaction

Curing

Main article: Concrete curing

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. In around 3 weeks, over 90% of the final strength is typically reached, though it may continue to strengthen for decades.^[23]

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 that increases shrinkage and cracking. Strength of concrete changes (increases) up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation. Resulting strength distribution in vertical elements researched and presented at the article "Concrete Inhomogeneity of Vertical Cast-In-Place Elements In Skeleton-Type Buildings"

During this period concrete needs to be in conditions with a 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 (the Hoover Dam used pipes carrying coolant during setting to avoid damaging overheating). Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.

Properties

Main article: Properties of concrete

Concrete has relatively high compressive strength, but significantly lower tensile strength, and as such is usually reinforced with materials that are strong in tension (often steel). The elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete has a very low coefficient of thermal expansion, and as it matures concrete shrinks. All concrete structures will crack to some extent, due to shrinkage and tension. Concrete that is subjected to long-duration forces is prone to creep.

Tests can be made to ensure the properties of concrete correspond to specifications for the application.

Environmental concerns

For the environmental impact of cement production see Cement

Worldwide CO₂ emissions and global change

The cement industry is one of two primary producers of carbon dioxide (CO₂), creating up to 5% of worldwide emissions of this gas, of which 50% is from the chemical process, and 40% from burning fuel.^[24] The embodied carbon dioxide (ECO₂) of one tonne of concrete varies with mix design and is in the range of 75 – 175 kg CO₂/tonne concrete.^[25] The CO₂ emission from the concrete production is directly proportional to the cement content used in the concrete mix. Indeed, 900 kg of CO₂ are emitted for the fabrication of every ton of cement.^[26] Cement manufacture contributes greenhouse gases both directly through the production of carbon dioxide when calcium carbonate is thermally decomposed, producing lime and carbon dioxide,^[27] and also through the use of energy, particularly from the combustion of fossil fuels. However, some companies have recognized the problem and are envisaging solutions to counter their CO₂ emissions. The principle of carbon capture and storage consists of directly capturing the CO₂ at the outlet of the cement kiln in order to transport it and to store the captured CO₂ in an adequate and deep geological formation.

Surface runoff

Surface runoff, when water runs off impervious surfaces, such as non-porous concrete, can cause heavy soil erosion. Urban runoff tends to pick up gasoline, motor oil, heavy metals, trash and other pollutants from sidewalks, roadways and parking lots.^[28][29] The impervious cover in a typical city sewer system prevents groundwater percolation five times than that of a typical woodland of the same size.^[30] A 2008 report by the United States National Research Council identified urban runoff as a leading source of water quality problems.^[31]

Urban heat

Both concrete and asphalt are the primary contributors to what is known as the urban heat island effect.

Using light-colored concrete has proven effective in reflecting up to 50% more light than asphalt and reducing ambient temperature.^[32] A low albedo value, characteristic of black asphalt, absorbs a large percentage of solar heat and contributes to the warming of cities. By paving with light colored concrete, in addition to replacing asphalt with light-colored concrete, communities can lower their average temperature.^[33]

Many U.S. cities show that pavement comprise approximately 30-40% of their surface area.^[32] This directly impacts the temperature of the city, as demonstrated by the urban heat island effect. In addition to decreasing the overall temperature of parking lots and large paved areas by paving with light-colored concrete, there are supplemental benefits. One example is 10-30% improved nighttime visibility.^[32] The potential of energy saving within an area is also high. With lower temperatures, the demand for air conditioning decreases, saving vast amounts of energy.

Atlanta has tried to mitigate the heat-island effect. City officials noted that when using heat-reflecting concrete, their average city temperature decreased by 6 °F.^[34] New York City offers another example. The Design Trust for Public Space in New York City found that by slightly raising the albedo value in their city, beneficial effects such as energy savings could be achieved. It was concluded that this could be accomplished by the replacement of black asphalt with light-colored concrete.^[33]

Concrete dust

Building demolition, and natural disasters such as earthquakes often release a large amount of concrete dust into the local atmosphere. Concrete dust was concluded to be the major source of dangerous air pollution following the Great Hanshin earthquake.^[35]

Health concerns

The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns. Natural radioactive elements (K, U and Th) can be present in various concentration in concrete dwellings, depending on the source of the raw materials used.^[36] Toxic substances may also be added to the mixture for making concrete by unscrupulous makers. Dust from rubble or broken concrete upon demolition or crumbling may cause serious health concerns depending also on what had been incorporated in the concrete.

Concrete handling/safety precautions

Handling of wet concrete must always be done with proper protective equipment. Contact with wet concrete can cause skin burns due to the caustic nature of the mixture of cement and water.

Secondary efflorescence: Water seeping through the concrete, often in cracks, having dissolved components of cement stone. Osteoporosis of concrete often happens in parking garages, as road salt comes off cars to the concrete floor as a saline solution in the winter.

Damage modes

Main article: Concrete degradation Concrete spalling caused by the corrosion of reinforcement bars after that carbonation of cement decreased the pH below the passivation threshold for steel.

Concrete can be damaged by many processes such as, e.g., the expansion of corrosion products of the steel reinforcement bars, freezing of trapped water, fire or radiant heat, aggregate expansion, sea water effects, bacterial corrosion, leaching, erosion by fast-flowing water, physical damage and chemical damage (from carbonation, chlorides, sulfates and distillate water).

Manufacturers of cement and concrete admixtures must keep on top of microbiological contamination in raw materials, intermediates and final products to prevent product spoilage. One method of keeping controlling contamination is through 2nd Generation ATP test.^[37]

Concrete repair

Concrete pavement preservation (CPP) and concrete pavement restoration (CPR) are techniques used to manage the rate of pavement deterioration on concrete streets, highways and airports. Without changing concrete grade, this non-overlay method is used to repair isolated areas of distress. CPP and CPR techniques include slab stabilization, full- and partial-depth repair, dowel bar retrofit, cross stitching longitudinal cracks or joints, diamond grinding and joint and crack resealing. CPR methods, developed over the last 40 years, are utilized in lieu of short-lived asphalt overlays and bituminous patches to repair roads. These methods are often less expensive^{[citation needed]}than an asphalt overlay but last three times longer and provide a greener solution.^[38]

CPR techniques can be used to address specific problems or bring a pavement back to its original quality. When repairing a road, design data, construction data, traffic data, environmental data, previous CPR activities and pavement condition, must all be taken into account. Pavements repaired using CPR methods usually last 15 years. The methods are described below.

• Slab stabilization restores support to concrete slabs by filling small voids that develop underneath the concrete slab at joints, cracks or the pavement edge.
• Full-depth repairs fixes cracked slabs and joint deterioration by removing at least a portion of the existing slab and replacing it with new concrete.
• Partial-depth repairs corrects surface distress and joint-crack deterioration in the upper third of the concrete slab. Placing a partial-depth repair involves removing the deteriorated concrete, cleaning the patch area and placing new concrete.
• Dowel bar retrofit consists of cutting slots in the pavement across the joint or crack, cleaning the slots, placing the dowel bars and backfilling the slots with new concrete. Dowel bar retrofits link slabs together at transverse cracks and joints so that the load is evenly distributed across the crack or joint.
• Cross-stitching longitudinal cracks or joints repairs low-severity longitudinal cracks. This method adds reinforcing steel to hold the crack together tightly.
• Diamond grinding, by removing faulting, slab warping, studded tire wear and unevenness resulting from patches, diamond grinding, creates a smooth, uniform pavement profile. Diamond grinding reduces road noise by providing a longitudinal texture, which is quieter than transverse textures. The longitudinal texture also enhances surface texture and skid resistance in polished pavements.
• Joint and crack sealing minimizes the infiltration of surface water and incompressible material into the joint system. Minimizing water entering the joint reduces sub-grade softening, slows pumping and erosion of the sub-base fines, and may limit dowel-bar corrosion caused by de-icing chemicals.^[39]

Concrete recycling

Recycling:The multiple use of a product represents another way to conserve natural resources and avoid wastes. This process is usually termed as “recycling”.

Recycled Concrete : Hardened concrete that has been processed for reuse, usually as aggregates.

Main article: Concrete recycling

Concrete recycling is an increasingly common method of disposing of concrete structures. Concrete debris was once routinely shipped to landfills for disposal, but recycling is increasing due to improved environmental awareness, governmental laws, and economic benefits.

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.

Reinforced concrete contains rebar and other metallic reinforcements, which are removed with magnets and recycled elsewhere. 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. 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.codep) approximated that almost 17% of worldwide landfill was by-products of concrete based waste.

Recycling concrete provides environmental benefits, conserving landfill space and use as aggregate reduces the need for gravel mining.

World records

The world record for the largest concrete pour in a single project is the Three Gorges Dam in Hubei Province, China by the Three Gorges Corporation. The amount of concrete used in the construction of the dam is estimated at 16 million cubic meters over 17 years. The previous record was 3.2 million cubic meters held by Itaipu hydropower station in Brazil. ^{[40] [41]}

Concrete pumping

The world record for vertical concrete pumping was achieved in India by Schwing Stetter in August 2009.Concrete was pumped to a height of 715m for the construction of the Parbati hydro-electric power project in the Indian state of Himachal Pradesh.

Continuous pours

The world record for largest continuously poured concrete raft was achieved in August, 2007 in Abu Dhabi by contracting firm, Al Habtoor-CCC Joint Venture. The pour (a part of the foundation for the Abu Dhabi's Landmark Tower) was 16,000 cubic meters of concrete poured within a two day period.^[42] The previous record (close to 10,500 cubic meters) was held by Dubai Contracting Company and achieved March 23, 2007.^[43]

The world record for largest continuously poured concrete floor was completed November 8, 1997 in Louisville, Kentucky by design-build firm, EXXCEL Project Management. The monolithic placement consisted of 225,000 square feet of concrete placed within a 30 hour period, finished to a flatness tolerance of F_F 54.60 and a levelness tolerance of F_L 43.83. This surpassed the previous record by 50% in total volume and 7.5% in total area.^[44][45]

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

Use of concrete in infrastructure

Mass concrete structures

These include gravity dams such as the Itaipu, Hoover Dam and the Three Gorges Dam and large breakwaters. 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.

Prestressed concrete structures

Main article: Prestressed concrete

Prestressed concrete is a form of reinforced concrete that builds in compressive stresses during construction to oppose those found when in use. 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.

Concrete textures

When one thinks of concrete, oftentimes the image of a dull, gray concrete wall comes to mind. With the use of form liner, concrete can be cast and molded into different textures and used for decorative concrete applications. Sound/retaining walls, bridges, office buildings and more serve as the optimal canvases for concrete art. For example, the Pima Freeway/Loop 101 retaining and sound walls in Scottsdale, Arizona, feature desert flora and fauna, a 67-foot lizard and 40-foot cacti along the 8-mile stretch. The project, titled "The Path Most Traveled," is one example of how concrete can be shaped using elastomeric form liner.

Three textures of concrete featured in Scottsdale, AZ, created with form liner.

A 67-foot concrete lizard basks in the sun, featured on a sound/retaining wall in Scottsdale, AZ.

40-foot cacti decorate a sound/retaining wall in Scottsdale, AZ.

Building with concrete

Concrete is the safest, most durable and sustainable building material.^{[citation needed]} It provides superior fire resistance, gains strength over time and has an extremely long service life. Concrete is the most widely used construction material in the world with annual consumption estimated at between 21 and 31 billion tonnes^{[citation needed]}. Concrete construction minimizes the long-term costs of a building or infrastructure project.^{[citation needed]}

Environmentally sustainable

With its 100-year service life, concrete conserves resources by reducing the need for reconstruction. Its ingredients are cement and readily available natural materials: water, aggregate (sand and gravel or crushed stone). Concrete does not require any CO₂ absorbing trees to be cut down. The land required to extract the materials needed to make concrete is only a fraction of that used to harvest forests for lumber.

The Baths of Caracalla, Rome, Italy, in 2003.

Concrete absorbs CO₂ throughout its lifetime through carbonation, helping reduce its carbon footprint. A recent study ^[46] indicates that in countries with the most favorable recycling practices, it is realistic to assume that approximately 86% of the concrete is carbonated after 100 years. During this time, the concrete will absorb approximately 57% of the CO₂ emitted during the original calcination. About 50% of the CO₂ is absorbed within a short time after concrete is crushed during recycling operations.

Concrete consists of between 7% and 15% cement, its only energy-intensive ingredient. A study ^[47] comparing the CO₂ emissions of several different building materials for construction of residential and commercial buildings found that concrete accounted for 147 kg of CO₂ per 1000 kg used, metals accounted for 3000 kg of CO₂ and wood accounted for 127 kg of CO₂. The quantity of CO₂ generated during the cement manufacturing process can be reduced by changing the raw materials used in its manufacture.

A new environmentally friendly blend of cement known as Portland-limestone cement (PLC) is gaining ground all over the world. It contains up to 15% limestone, rather than the 5% in regular Portland cement and results in 10% less CO₂ emissions from production with no impact on product performance. Concrete made with PLC performs similarly to concrete made with regular cement and thus PLC-based concrete can be widely used as a replacement. In Europe, PLC-based concrete has replaced about 40% of general use concrete. In Canada, PLC will be included in the National Building Code in 2010. The approval of PLC is still under consideration in the United States.

Energy efficiency

Energy requirements for transportation of concrete are low because it is produced locally from local resources, typically manufactured within 100 kilometers of the job site. Once in place, concrete offers significant energy efficiency over the lifetime of a building .^[48] Concrete walls leak air far less than those made of wood-frames. Air leakage accounts for a large percentage of energy loss from a home. The thermal mass properties of concrete increase the efficiency of both residential and commercial buildings. By storing and releasing the energy needed for heating or cooling, concrete's thermal mass delivers year-round benefits by reducing temperature swings inside and minimizing heating and cooling costs. While insulation reduces energy loss through the building envelope, thermal mass uses walls to store and release energy. Modern concrete wall systems use both insulation and thermal mass to create an energy-efficient building. Insulating Concrete Forms (ICFs) are hollow blocks or panels made of either insulating foam or rastra that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.

Models of Porsche automobiles, made out of concrete, part of an exhibition, "Best of Austria," in the Lentos Museum in Linz, Austria in 2009.

Fire safety and quality of life

Concrete buildings are more resistant to fire than those constructed using wood or steel frames. Since concrete does not burn and stops fire from spreading, it offers total fire protection for occupants and their property. Concrete reduces the risk of structural collapse and is an effective fire shield, providing safe means of escape for occupants and protection for firefighters. Furthermore, it does not produce any smoke or toxic gases and does not drip molten particles, which can spread fire. Neither heat, flames nor the water used to extinguish a fire seriously affect the structure of concrete walls and floors making repairs after a fire a relatively simple task.

A study was conducted in Sweden by Olle Lundberg on the cost of fire damage associated with larger fires in multi-unit buildings, based on statistics from the insurance association in Sweden (Forsakrings Forbundet). The study was limited to buildings with an insured value greater than €150,000. It covered 125 fires that occurred between 1995 and 2004, about 10% of the fires in multi-family homes, but 56% of the major fires.) The results showed that:

• the average insurance payout per fire, per unit in wood frame buildings was around five times that of fires in concrete buildings (approximately €50,000 compared with €10,000)
• a major fire is more than 11 times more likely to develop in a wood-frame house than in one built using concrete
• among the burned houses, 50% of those made with wood had to be demolished, whereas only 9% of the concrete ones were beyond repair
• the fire spread to neighbouring apartments in only three of the 55 fires in concrete houses
• of those 55 fires, 45 were in attics and roofing

Options for non-combustible construction include floors, ceilings and roofs made of cast-in-place and hollow-core precast concrete. For walls, concrete masonry technology and Insulating Concrete Forms (ICFs) are additional options. ICFs are hollow blocks or panels made of fire-proof insulating foam that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.

“Fire-wall” tests, in which ICF walls were subjected to a continuous gas flame with a temperature of more than 1000°C for as long as 4 hours showed no significant breaks in the concrete layer or dangerous transmission of heat. In comparison, wood frame walls normally collapse in an hour or less under these conditions. Concrete provides stable compartmentation in large industrial and multi-storey buildings so a fire starting in one section does not spread to others.

Using concrete to construct buildings offers the best possible protection and safety in fires:

• it does not burn or add to fire load
• it has high resistance to fire, preventing it from spreading thus reduces resulting environmental pollution
• it does not produce any smoke, toxic gases or drip molten particles
• it reduces the risk of structural collapse
• it provides safe means of escape for occupants and access for firefighters as it is an effective fire shield
• it is not affected by the water used to put out a fire
• it is easy to repair after a fire and thus helps residents and businesses recover sooner
• it resists extreme fire conditions, making it ideal for storage facilities with a high fire load
• it provides complete fire protection so there is normally no need for additional measures

Concrete also provides the best resistance of any building material to high winds, hurricanes, tornadoes due to its lateral stiffness that results in minimal horizontal movement. When properly designed for ductility, it also provides superior resistance to seismic events. It does not rust, rot or sustain growth of mold and stands up well to the freeze – thaw cycle. As a result of all these benefits, insurance for concrete homes is often 15 to 25 percent lower than for comparable wood frame homes.

Concrete buildings also have excellent indoor air quality with no off-gassing, toxicity and release of volatile organic compounds so they are generally healthier to live in than those made of wood or steel. As it is practically inert and waterproof, concrete does not need volatile organic-based preservatives, special coatings or sealers. Concrete can be easily cleaned with organic, non-toxic substances. Its sound insulating properties make buildings and homes a quiet and comfortable living environment. After accounting for sound passing through windows, a concrete home is about two-thirds quieter than a comparable wood-frame home.^[49]

Due to the long life of concrete structures, their impacts on the environment are negligible. Once built, they have minimal maintenance requirements and as a result minimal social disruption. Using concrete reduces construction waste as it is used on an as-required basis, thereby minimizing the waste put into landfills.

Recycling and recyclable

Recycled crushed concrete being loaded into a semi-dump truck to be used as granular fill.

A nearly inert material, concrete is suitable as a medium for recycling waste and industrial byproducts. Fly ash, slag and silica fume are used in making concrete, which helps reduce embodied energy, carbon footprint and quantity of landfill materials. The process of making cement also uses waste materials. Tires have high energy content and can supplement coal as fuel in the kiln. Industrial byproducts such as ash from coal combustion, fly ash from power stations as well as mill scale and foundry sand from steel casting provide the silica, calcium, alumina and iron needed for making cement. Even kiln dust, a solid waste generated by cement manufacturing, is often recycled back into the kiln as a raw material. Old concrete that has reached the end of its service life can be recycled and reused as granular fill for road beds.

See also

Anthropic rock Biorock Construction Bunding Brutalist architecture, encouraging visible concrete surfaces Cement Geopolymers, a class of synthetic aluminosilicate materials Hempcrete, a mixture with hemp hurds Mudcrete, a soil-cement mixture Papercrete, a paper-cement mixture Portland cement, the classical concrete cement Cement accelerator Concrete moisture meter Concrete canoe Concrete curing Concrete leveling Concrete mixer Concrete masonry unit

Concrete recycling Concrete step barrier Efflorescence Fireproofing Foam Index Form liner Formwork Controlled permeability formwork LiTraCon High performance fiber reinforced cementitious composites High Reactivity Metakaolin International Grooving & Grinding Association Mortar Plasticizer Prefabrication Pykrete, a composite material of ice and cellulose Silica fume Shallow foundation

Types of concrete Asphalt concrete Aerated autoclaved concrete Decorative concrete Fiber reinforced concrete Lunarcrete Prestressed concrete Precast concrete Ready-mix concrete Reinforced concrete Salt-concrete Seacrete Terrazzo Whitetopping World of Concrete Diamond grinding of pavement

1930s vibrated concrete, manufactured in Croydon and installed by the LMS railway after an Art Deco refurbishment in Meols, United Kingdom.

References

Notes

1. ^ The Roman Pantheon: The Triumph of Concrete
2. ^ The Skeptical Environmentalist: Measuring the Real State of the World, by Bjorn Lomborg, p 138.
3. ^ "Minerals commodity summary - cement - 2007". US United States Geographic Service. 2007-06-01. http://minerals.usgs.gov/minerals/pubs/commodity/cement/index.html. Retrieved 2008-01-16.
4. ^ Stella L. Marusin (January 1, 1996). Ancient Concrete Structures. 18. Concrete International. pp. 56–58
5. ^ Donald H. Campbell and Robertt L. Folk. "Ancient Egyptian Pyramids--Concrete or Rock". Concrete International 13 (8): 28 & 30–39
6. ^ Lancaster, Lynne (2005). Concrete Vaulted Construction in Imperial Rome. Innovations in Context. Cambridge University Press. ISBN 978-0-511-16068-4
7. ^ D.S. Robertson: Greek and Roman Architecture, Cambridge, 1969, p. 233
8. ^ Henry Cowan: The Masterbuilders, New York 1977, p. 56, ISBN 978-0-471-02740-9
9. ^ Robert Mark, Paul Hutchinson: "On the Structure of the Roman Pantheon", Art Bulletin, Vol. 68, No. 1 (1986), p. 26, fn. 5
10. ^ http://www.allacademic.com/meta/p_mla_apa_research_citation/0/2/0/1/2/p20122_index.html
11. ^ http://www.djc.com/special/concrete/10003364.htm
12. ^ olemiss.edu - Missing File
13. ^ ^{a b} U.S. Federal Highway Administration. "Admixtures". http://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.html. Retrieved 2007-01-25.
14. ^ Cement Admixture Association. "CAA". www.admixtures.org.uk. http://www.admixtures.org.uk/publications.asp. Retrieved 2008-04-02.
15. ^ Kosmatka, S.H.; Panarese, W.C. (1988). Design and Control of Concrete Mixtures. Skokie, IL, USA: Portland Cement Association. pp. 17, 42, 70, 184. ISBN 0-89312-087-1.
16. ^ U.S. Federal Highway Administration. "Fly Ash". http://www.fhwa.dot.gov/infrastructure/materialsgrp/flyash.htm. Retrieved 2007-01-24.
17. ^ U.S. Federal Highway Administration. "Ground Granulated Blast-Furnace Slag". http://www.fhwa.dot.gov/infrastructure/materialsgrp/ggbfs.htm. Retrieved 2007-01-24.
18. ^ U.S. Federal Highway Administration. "Silica Fume". http://www.fhwa.dot.gov/infrastructure/materialsgrp/silica.htm. Retrieved 2007-01-24.
19. ^ Premixed Cement Paste
20. ^ The use of micro- and nanosilica in concrete
21. ^ Measuring, Mixing, Transporting, and Placing Concrete
22. ^ U.S. Patent 5,443,313 - Method for producing construction mixture for concrete
23. ^ "Concrete Testing". http://technology.calumet.purdue.edu/cnt/rbennet/concrete%20lab.htm. Retrieved 2008-11-10.
24. ^ The Cement Sustainability Initiative: Progress report, World Business Council for Sustainable Development, published 2002-06-01
25. ^ http://www.sustainableconcrete.org.uk/main.asp?page=0
26. ^ Mahasenan, Natesan; Steve Smith, Kenneth Humphreys, Y. Kaya (2003). "The Cement Industry and Global Climate Change: Current and Potential Future Cement Industry CO₂ Emissions". Greenhouse Gas Control Technologies - 6th International Conference. Oxford: Pergamon. pp. 995–1000. ISBN 9780080442761. http://www.sciencedirect.com/science/article/B873D-4P9MYFN-BK/2/c58323fdf4cbc244856fe80c96447f44. Retrieved 2008-04-09.
27. ^ EIA - Emissions of Greenhouse Gases in the U.S. 2006-Carbon Dioxide Emissions
28. ^ Water Environment Federation, Alexandria, VA; and American Society of Civil Engineers, Reston, VA. "Urban Runoff Quality Management." WEF Manual of Practice No. 23; ASCE Manual and Report on Engineering Practice No. 87. 1998. ISBN 1-57278-039-8. Chapter 1.
29. ^ G. Allen Burton, Jr., Robert Pitt (2001). Stormwater Effects Handbook: A Toolbox for Watershed Managers, Scientists, and Engineers. New York: CRC/Lewis Publishers. ISBN 0-87371-924-7. http://unix.eng.ua.edu/~rpitt/Publications/BooksandReports/Stormwater%20Effects%20Handbook%20by%20%20Burton%20and%20Pitt%20book/MainEDFS_Book.html. Chapter 2.
30. ^ U.S. Environmental Protection Agency (EPA). Washington, DC. "Protecting Water Quality from Urban Runoff." Document No. EPA 841-F-03-003. February 2003.
31. ^ United States. National Research Council. Washington, DC. "Urban Stormwater Management in the United States." October 15, 2008. pp. 18-20.
32. ^ ^{a b c} "Cool Pavement Report" (PDF). Environmental Protection Agency. June 2005. http://www.epa.gov/heatisland/resources/pdf/CoolPavementReport_Former%20Guide_complete.pdf. Retrieved 2009-02-06.
33. ^ ^{a b} Gore, A; Steffen, A (2008). World Changing: A User's Giode for the 21st Century. New York: Abrams. pp. 258.
34. ^ "Concrete facts". Pacific Southwest Concrete Alliance. http://www.concreteresources.net/categories/4F26A962-D021-233F-FCC5EF707CBD860A/fun_facts.html. Retrieved 2009-02-06.
35. ^ http://jeq.scijournals.org/cgi/reprint/31/3/718.pdf
36. ^ Radionuclide content of concrete building blocks and radiation dose rates in some dwellings in Ibadan, Nigeria
37. ^ http://www.luminultra.com/dmdocuments/Product%20Validation%20-%20Cement_Concrete%20Admixtures%20QGOM.pdf
38. ^ [1] Minnesota DOT
39. ^ [2] Airport Business
40. ^ "Concrete Pouring of Three Gorges Project Sets World Record". People’s Daily. 2001-01-04. http://english.peopledaily.com.cn/200101/02/eng20010102_59432.html. Retrieved 2009-08-24.
41. ^ China’s Three Gorges Dam By The Numbers
42. ^ [3]
43. ^ Record concrete pour takes place on Al Durrah
44. ^ "Continuous cast: Exxcel Contract Management oversees record concrete pour". US Concrete Products. 1998-03-01. http://concreteproducts.com/mag/concrete_continuous_cast_exxcel/?smte=wr. Retrieved 2009-08-25.
45. ^ Exxcel Project Management - Design Build, General Contractors -
46. ^ Nordic Innovation Centre Project 03018 http://www.nordicinnovation.net/img/03018_carbon_dioxide_uptake_in_demolished_and_crushed_concrete.pdf
47. ^ Pentalla, Vesa, Concrete and Sustainable Development, ACI Materials Journal, September- October 1997, American Concrete Institute, Farmington Hills, MI, 1997
48. ^ Gajda, John, Energy Use of Single Family Houses with Various Exterior Walls, Construction Technology Laboratories Inc, 2001
49. ^ Wikipedia Article “Sound Transmission Class” http://en.wikipedia.org/wiki/Sound_transmission_class citing Cyril M. Harris, "Noise Control in Buildings: A Practical Guide for Architects and Engineers", 1994

Bibliography

• Matthias Dupke: Textilbewehrter Beton als Korrosionsschutz. Diplomica Verlag, Hamburg 2010, ISBN 978-3-8366-9405-6.

External links

Wikimedia Commons has media related to: Concrete

• FLY ASH: ITs origin, applications and the environment
• Fly ash in concrete How Fly Ash Contributes to Concrete Durability and Strength.
• Concrete History Oct 1 2009
• Refractory Concrete Information related to heat resistant concrete; recipes, ingredients mixing ratio, work with and applications.
• The effect of curing on the tensile strength of medium to high strength concrete
• Inhomogeneity of concrete strength distribution by volume of vertical monolithic (cast in situ) elements Reserves of concrete strength. Information may be used when design buildings against progressive failure.
• The History of Concrete
• Concrete carbonation chemistry at the TU Dresden
• Howard Kanare - Problems With Moisture in Concrete
• Concrete Moisture Testing - Relative Humidity vs. Calcium Chloride
• Short film on the reinforced concrete buildings that Ove Arup helped design for Dudley Zoo in the 1930s
• British Precast Concrete Federation
• Free Concrete Books :
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  • High Performance Concrete Structural
  • Roller Compacted Concrete
  • Concrete Crack Repair

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