In the most general sense of the word, cement is a binder, a substance which sets and hardens independently, and can bind other materials together. The name "cement" goes back to the Romans who used the term "opus caementitium" to describe masonry which resembled concrete and was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick additives which were added to the burnt lime to obtain a hydraulic binder were later referred to as cementum, cimentum, cäment and cement. Cements used in construction are characterized as hydraulic or non-hydraulic. Cement may refer to: Cement, a material for bonding stone or brick Cement (album), debut album from music group Cement. ...

The most important use of cement is the production of mortar and concrete - the bonding of natural or artificial aggregates to form a strong building material which is durable in the face of normal environmental effects. Mortar holding weathered bricks. ... This article is about the construction material. ...

Hydraulic cements

Hydraulic cements are materials which set and harden after combining with water, as a result of chemical reactions with the mixing water and, after hardening, retain strength and stability even under water. The key requirement for this is that the hydrates formed on immediate reaction with water are essentially insoluble in water. Most construction cements today are hydraulic, and most of these are based upon Portland cement, which is made primarily from limestone, certain clay minerals, and gypsum, in a high temperature process that drives off carbon dioxide and chemically combines the primary ingredients into new compounds. Non-hydraulic cements include such materials as (non-hydraulic) lime and gypsum plasters, which must be kept dry in order to gain strength, and oxychloride cements which have liquid components. Lime mortars, for example, "set" only by drying out, and gain strength only very slowly by absorption of carbon dioxide from the atmosphere to re-form calcium carbonate. Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Mineral hydration is an inorganic chemical reaction where water is added to the crystal structure of a mineral, usually creating a new mineral. ... Sampling fast set Portland cement Portland cement is the most common type of cement in general usage, as it is a basic ingredient of concrete, mortar and plaster. ... For other uses, see Limestone (disambiguation). ... For other uses, see Clay (disambiguation). ... It has been suggested that Selenite be merged into this article or section. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...

Setting and hardening of hydraulic cements is caused by the formation of water-containing compounds, forming as a result of reactions between cement components and water. The reaction and the reaction products are referred to as hydration and hydrates or hydrate phases, respectively. As a result of the immediately starting reactions, a stiffening can be observed which is very small in the beginning, but which increases with time. After reaching a certain level, this point in time is referred to as the start of setting. The consecutive further consolidation is called setting, after which the phase of hardening begins. The compressive strength of the material then grows steadily, over a period which ranges from a few days in the case of "ultra-rapid-hardening" cements, to several years in the case of ordinary cements.

History

Early uses

The earliest construction cements are as old as construction^[1], and were non-hydraulic. Wherever primitive mud bricks were used, they were bedded together with a thin layer of clay slurry. Mud-based materials were also used for rendering on the walls of timber or wattle and daub structures. Lime was probably used for the first time as an additive in these renders, and for stabilizing mud floors. A "daub" consisting of mud, cow dung and lime produces a tough and water-proof coating, due to coagulation, by the lime, of proteins in the cow dung. This simple system was common in Europe until quite recent times. With the advent of fired bricks, and their use in larger structures, various cultures started to experiment with higher-strength mortars based on bitumen (in Mesopotamia), gypsum (in Egypt) and lime (in many parts of the world). Categories: Stub | Construction ... This article or section does not adequately cite its references or sources. ...

It is uncertain where it was first discovered that a combination of hydrated non-hydraulic lime and a pozzolan produces a hydraulic mixture, but concrete made from such mixtures was first used on a large scale by the Romans. They used both natural pozzolans (trass or pumice) and artificial pozzolans (ground brick or pottery) in these concretes. Many excellent examples of structures made from these concretes are still standing, notably the huge monolithic dome of the Pantheon in Rome. The use of structural concrete disappeared in medieval Europe, although weak pozzolanic concretes continued to be used as a core fill in stone walls and columns. A pozzolan is a material which, when combined with calcium hydroxide, exhibits cementitious properties. ... Trass is the local name of a volcanic tuff occurring in the Eifel, where it is worked for hydraulic mortar. ... Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... Facade of the Pantheon The Pantheon (Latin Pantheon[1], from Greek Πάνθεον Pantheon, meaning Temple of all the gods) is a building in Rome which was originally built as a temple to the seven deities of the seven planets in the state religion of Ancient Rome. ...

Modern cement

Modern hydraulic cements began to be developed from the start of the Industrial Revolution (around 1700), driven by three main needs:

• Hydraulic renders for finishing brick buildings in wet climates
• Hydraulic mortars for masonry construction of harbor works etc, in contact with sea water.
• Development of strong concretes.

In Britain particularly, good quality building stone became ever more expensive during a period of rapid growth, and it became a common practice to construct prestige buildings from the new industrial bricks, and to finish them with a stucco to imitate stone. Hydraulic limes were favored for this, but the need for a fast set time encouraged the development of new cements. Most famous among these was Parker's "Roman cement"^[2]. This was developed by James Parker in the 1780s, and finally patented in 1796. It was, in fact, nothing like any material used by the Romans, but was a "Natural cement" made by burning septaria - nodules that are found in certain clay deposits, and that contain both clay minerals and calcium carbonate. The burnt nodules were ground to a fine powder. This product, made into a mortar with sand, set in 5-15 minutes. The success of "Roman Cement" led other manufacturers to develop rival products by burning artificial mixtures of clay and chalk. Stucco is a material made of an aggregate, a binder, and water which is applied wet, and hardens when it dries. ... Stucco is a material made of an aggregate, a binder, and water which is applied wet, and hardens when it dries. ... The Pantheon is one example of Roman concrete technology. ... James Parker was a British clergyman and cement manufacturer who invented one of the pioneering new cements of the late eighteenth century. ...

John Smeaton made an important contribution to the development of cements when he was planning the construction of the third Eddystone Lighthouse (1755-9) in the English Channel. He needed a hydraulic mortar that would set and develop some strength in the twelve hour period between successive high tides. He performed an exhaustive market research on the available hydraulic limes, visiting their production sites, and noted that the "hydraulicity" of the lime was directly related to the clay content of the limestone from which it was made. Smeaton was a civil engineer by profession, and took the idea no further. Apparently unaware of Smeaton's work, the same principle was identified by Louis Vicat in the first decade of the nineteenth century. Vicat went on to devise a method of combining chalk and clay into an intimate mixture, and, burning this, produced an "artificial cement" in 1817. James Frost^[3], working in Britain, produced what he called "British cement" in a similar manner around the same time, but did not obtain a patent until 1822. In 1824, Joseph Aspdin patented a similar material, which he called Portland cement, because the render made from it was in color similar to the prestigious Portland stone. Portrait of John Smeaton, with the Eddystone Lighthouse in the background John Smeaton, FRS, (June 8, 1724 – October 28, 1792) was a civil engineer – often regarded as the father of civil engineering – responsible for the design of bridges, canals, harbours and lighthouses. ... The Eddystone Lighthouse is situated some 9 miles (15km) South West of Rame Head Cornwall, England on the treacherous Eddystone Rocks 50°10. ... A civil engineer is a person who practices civil engineering. ... Portrait Louis Vicat (March 31, 1786 - April 10, 1861) French engineer, inventor of artificial cement. ... James Frost is the Guitarist for Welsh Indie/Rock band The Automatic. ... Joseph Aspdin (1788 – 20 March 1855) was an English mason, bricklayer and inventor who patented Portland cement on 21 October 1824. ... The Cenotaph, in Whitehall, London, England, is made from Portland stone Portland stone is limestone from the Jurassic period quarried on the Isle of Portland, Dorset. ...

All the above products could not compete with lime/pozzolan concretes because of fast-setting (giving insufficient time for placement) and low early strengths (requiring a delay of many weeks before formwork could be removed). Hydraulic limes, "natural" cements and "artificial" cements all rely upon their belite content for strength development. Belite develops strength slowly. Because they were burned at temperatures below 1250 °C, they contained no alite, which is responsible for early strength in modern cements. The first cement to consistently contain alite was that made by Joseph Aspdin's son William in the early 1840s. This was what we call today "modern" Portland cement. Because of the air of mystery with which William Aspdin surrounded his product, others (e.g. Vicat and I C Johnson) have claimed precedence in this invention, but recent analysis^[4] of both his concrete and raw cement have shown that William Aspdin's product made at Northfleet, Kent was a true alite-based cement. However, Aspdin's methods were "rule-of-thumb": Vicat is responsible for establishing the chemical basis of these cements, and Johnson established the importance of sintering the mix in the kiln. Belite is the mineralogical name for Dicalcium Silicate, Ca2SiO4. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... William Aspdin (23 September 1815 — 1864[1]) was a British cement manufacturer, and a pioneer of the Portland cement industry. ... Please wikify (format) this article or section as suggested in the Guide to layout and the Manual of Style. ... Location within the British Isles Northfleet as a name is derived from North creek (or inlet), and the settlement on the shore of the River Thames adjacent to Gravesend was known as Norfluet in the Domesday Book, and Northflet in 1201. ... The Kent coat of arms For other uses, see Kent (disambiguation). ...

William Aspdin's innovation was counter-intuitive for manufacturers of "artificial cements", because they required more lime in the mix (a problem for his father), because they required a much higher kiln temperature (and therefore more fuel) and because the resulting clinker was very hard and rapidly wore down the millstones which were the only available grinding technology of the time. Manufacturing costs were therefore considerably higher, but the product set reasonably slowly and developed strength quickly, thus opening up a market for use in concrete. The use of concrete in construction grew rapidly from 1850 onwards, and was soon the dominant use for cements. Thus Portland cement began its predominant role.

Types of modern cement

Blue Circle Southern Cement works near Berrima, New South Wales, Australia.

ImageMetadata File history File links Download high resolution version (2048x1536, 620 KB) Summary Blue Circle Southern Cement factory near Berrima, New South Wales, Australia. ... ImageMetadata File history File links Download high resolution version (2048x1536, 620 KB) Summary Blue Circle Southern Cement factory near Berrima, New South Wales, Australia. ... Berrima is a village in the Southern Highlands district on the old Hume Highway between Canberra and Sydney, Australia, and is now popular with visitors from both cities, especially on weekends. ... “NSW” redirects here. ...

Portland cement

Main article: Portland cement

Cement is made by heating limestone with small quantities of other materials (such as clay) to 1450°C in a kiln. The resulting hard substance, called ‘clinker’, is then ground with a small amount of gypsum into a powder to make ‘Ordinary Portland Cement’, the most commonly used type of cement (often referred to as OPC). Sampling fast set Portland cement Portland cement is the most common type of cement in general usage, as it is a basic ingredient of concrete, mortar and plaster. ...

Portland cement is a basic ingredient of concrete, mortar and most non-speciality grout. The most common use for Portland cement is in the production of concrete. Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Portland cement may be gray or white. This article is about the construction material. ... Mortar holding weathered bricks. ... Grout is a construction material used to embed rebars in masonry walls, connect sections of pre-cast concrete, fill voids, and seal joints (like those between tiles). ... Limestone Quarry Construction aggregate, or simply, aggregate, is a broad category of coarse particulate material used in construction, including sand, gravel, crushed stone, slag, and recycled concrete. ... White Portland cement is similar to ordinary, gray Portland cement in all respects except for its high degree of whiteness. ...

For details of the manufacture of Portland cement, see the main article.

Portland cement blends

These are often available as inter-ground mixtures from cement manufacturers, but similar formulations are often also mixed from the ground components at the concrete mixing plant.^[5]

Portland Blastfurnace Cement contains up to 70% ground granulated blast furnace slag, with the rest Portland clinker and a little gypsum. All compositions produce high ultimate strength, but as slag content is increased, early strength is reduced, while sulfate resistance increases and heat evolution diminishes. Used as an economic alternative to Portland sulfate-resisting and low-heat cements.^[6] Ground granulated blastfurnace slag (GGBS or GGBFS) is obtained by quenching molten iron blast furnace slag (a by-product of iron and steel making) in water or stream, to produce a glassy granular product that is then dried and ground into a fine powder. ...

Portland Flyash Cement contains up to 30% fly ash. The flyash is pozzolanic, so that ultimate strength is maintained. Because flyash addition allows a lower concrete water content, early strength can also be maintained. Where good quality cheap flyash is available, this can be an economic alternative to ordinary Portland cement.^[7] Fly ash (one of several coal combustion products, or CCPs) is the finely divided mineral residue resulting from the combustion of coal in electric generating plants. ...

Portland Pozzolan Cement includes fly ash cement, since fly ash is a pozzolan, but also includes cements made from other natural or artificial pozzolans. In countries where volcanic ashes are available (e.g. Italy, Chile, Mexico, the Philippines) these cements are often the most common form in use.

Portland Silica Fume cement. Addition of silica fume can yield exceptionally high strengths, and cements containing 5-20% silica fume are occasionally produced. However, silica fume is more usually added to Portland cement at the concrete mixer.^[8] Silica fume, also known as microsilica, is a byproduct of the reduction of high-purity quartz with coal in electric furnaces in the production of silicon and ferrosilicon alloys. ...

Masonry Cements are used for preparing bricklaying mortars and stuccos, and must not be used in concrete. They are usually complex proprietary formulations containing Portland clinker and a number of other ingredients that may include limestone, hydrated lime, air entrainers, retarders, waterproofers and coloring agents. They are formulated to yield workable mortars that allow rapid and consistent masonry work. Subtle variations of Masonry cement in the US are Plastic Cements and Stucco Cements. These are designed to produce controlled bond with masonry blocks. Mortar holding weathered bricks. ... Stucco is a material made of an aggregate, a binder, and water which is applied wet, and hardens when it dries. ...

Expansive Cements contain, in addition to Portland clinker, expansive clinkers (usually sulfoaluminate clinkers), and are designed to offset the effects of drying shrinkage that is normally encountered with hydraulic cements. This allows large floor slabs (up to 60 m square) to be prepared without contraction joints.

White blended cements may be made using white clinker and white supplementary materials such as high-purity metakaolin. Metakaolin is a dehyroxylated form of kaolinite. ...

Colored cements are used for decorative purposes. In some standards, the addition of pigments to produce "colored Portland cement" is allowed. In other standards (e.g. ASTM), pigments are not allowed constituents of Portland cement, and colored cements are sold as "blended hydraulic cements".

Non-Portland hydraulic cements

Pozzolan-lime cements. Mixtures of ground pozzolan and lime are the cements used by the Romans, and are to be found in Roman structures still standing (e.g. the Pantheon in Rome). They develop strength slowly, but their ultimate strength can be very high. The hydration products that produce strength are essentially the same as those produced by Portland cement. Pozzolanic ash is an alumino-siliceous material which reacts with calcium hydroxide in the presence of water to form compounds possessing cementitious properties at room temperature, producing C-S-H. This allowed it to be used in the Roman Empire to make cement by combining with lime and water. ...

Slag-lime cements. Ground granulated blast furnace slag is not hydraulic on its own, but is “activated” by addition of alkalis, most economically using lime. They are similar to pozzolan lime cements in their properties. Only granulated slag (i.e. water-quenched, glassy slag) is effective as a cement component. Ground granulated blastfurnace slag (GGBS or GGBFS) is obtained by quenching molten iron blast furnace slag (a by-product of iron and steel making) in water or stream, to produce a glassy granular product that is then dried and ground into a fine powder. ...

Supersulfated cements. These contain about 80% ground granulated blast furnace slag, 15% gypsum or anhydrite and a little Portland clinker or lime as an activator. They produce strength by formation of ettringite, with strength growth similar to a slow Portland cement. They exhibit good resistance to aggressive agents, including sulfate. Ettringite is Hexacalcium Aluminate Trisulfate, (CaO)6(Al2O3)(SO3)3. ...

Calcium aluminate cements are hydraulic cements made primarily from limestone and bauxite. The active ingredients are monocalcium aluminate CaAl₂O₄ (CA in Cement chemist notation) and Mayenite Ca₁₂Al₁₄O₃₃ (C₁₂A₇ in CCN). Strength forms by hydration to calcium aluminate hydrates. They are well-adapted for use in refractory (high-temperature resistant) concretes, e.g. for furnace linings. Calcium aluminate cements[1] are cements consisting predominantly of hydraulic calcium aluminates. ... Cement chemist notation (CCN) was developed to simplify the formulas cement chemists use on a daily basis. ...

Calcium sulfoaluminate cements are made from clinkers that include ye’elimite (Ca₄(AlO₂)₆SO₄ or C₄A₃ in Cement chemist’s notation) as a primary phase. They are used in expansive cements, in ultra-high early strength cements, and in "low-energy" cements. Hydration produces ettringite, and specialized physical properties (such as expansion or rapid reaction) are obtained by adjustment of the availability of calcium and sulfate ions. Their use as a low-energy alternative to Portland cement has been pioneered in China, where several million tonnes per year are produced^[9][10]. Energy requirements are lower because of the lower kiln temperatures required for reaction, and the lower amount of limestone (which must be endothermically decarbonated) in the mix. In addition, the lower limestone content and lower fuel consumption leads to a CO₂ emission around half that associated with Portland clinker. However, SO₂ emissions are usually significantly higher. Yeelimite is the mineralogical name of calcium sulfoaluminate, Ca4(AlO2)6SO4. ... Cement chemist notation (CCN) was developed to simplify the formulas cement chemists use on a daily basis. ...

“Natural” Cements correspond to certain cements of the pre-Portland era, produced by burning argillaceous limestones at moderate temperatures. The level of clay components in the limestone (around 30-35%) is such that large amounts of belite (the low-early strength, high-late strength mineral in Portland cement) are formed without the formation of excessive amounts free lime. As with any natural material, such cements have very variable properties.

Geopolymer cements are made from mixtures of water-soluble alkali metal silicates and aluminosilicate mineral powders such as fly ash and metakaolin. 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-based cements. ...

Environmental & social impacts

Cement manufacture causes environmental impacts at all stages of the process. These include emissions of airborne pollution in the form of dust, gases, noise and vibration when operating machinery and during blasting in quarries, and damage to countryside from quarrying. Equipment to reduce dust emissions during quarrying and manufacture of cement is widely used, and equipment to trap and separate exhaust gases are coming into increased use. Environmental protection also includes the re-integration of quarries into the countryside after they have been closed down by returning them to nature or re-cultivating them. For other uses, see Quarry (disambiguation). ...

Climate

Cement manufacture is an energy intensive process. Consuming energy from fossil fuels such as oil and coal creates carbon dioxide (CO2), the most important Greenhouse Gas (GHG) causing climate change. The cement industry produces 5% of global man-made CO2 emissions, of which 50% is from the chemical process, and 40% from burning fuel.^[11]

Fuels & raw materials

A cement plant consumes 3,000 to 6,500 MJ of fuel per tonne of clinker produced, depending on the raw materials and the process used. Most cement kilns today use coal and petroleum coke as primary fuels, and to a lesser extent natural gas and fuel oil. Selected waste and by-products with recoverable calorific value can be used as fuels in a cement kiln, replacing a portion of conventional fossil fuels, like coal, if they meet strict specifications. Selected waste and by-products containing useful minerals such as calcium, silica, alumina, and iron can be used as raw materials in the kiln, replacing raw materials such as clay, shale, and limestone. Because some materials have both useful mineral content and recoverable calorific value, the distinction between alternative fuels and raw materials is not always clear. For example, sewage sludge has a low but significant calorific value, and burns to give ash containing minerals useful in the clinker matrix. ^[12]

Local impacts

Producing cement has significant positive and negative impacts at a local level. On the positive side, the cement industry may create employment and business opportunities for local people, particularly in remote locations in developing countries where there are few other opportunities for economic development. Negative impacts include disturbance to the landscape, dust and noise, and disruption to local biodiversity from quarrying limestone (the raw material for cement).

Cement business

Cement output in 2004

In 2002 the world production of hydraulic cement was 1,800 million metric tons. The top three producers were China with 704, India with 100, and the United States with 91 million metric tons for a combined total of about half the world total by the world's three most populous states. ^[13] Image File history File links Size of this preview: 800 × 351 pixelsFull resolution (1425 × 625 pixel, file size: 59 KB, MIME type: image/png)This bubble map shows the global distribution of hydraulic cement output in 2004 as a percentage of the top producer (China - 933,690,000 tonnes). ... Image File history File links Size of this preview: 800 × 351 pixelsFull resolution (1425 × 625 pixel, file size: 59 KB, MIME type: image/png)This bubble map shows the global distribution of hydraulic cement output in 2004 as a percentage of the top producer (China - 933,690,000 tonnes). ...

"For the past 18 years, China consistently has produced more cement than any other country in the world. [...] China's cement export peaked in 1994 with 11 million tons shipped out and has been in steady decline ever since. Only 5.18 million tons were exported out of China in 2002. Offered at $34 a ton, Chinese cement is pricing itself out of the market as Thailand is asking as little as $20 for the same quality." ^[14]

"Demand for cement in China is expected to advance 5.4% annually and exceed 1 billion metric tons in 2008, driven by slowing but healthy growth in construction expenditures. Cement consumed in China will amount to 44% of global demand, and China will remain the world's largest national consumer of cement by a large margin." ^[15]

In 2006 is was estimated that China manufactured 1.235 billion metric tons of cement, which is 44% of the world total cement production.^[16]

See also

• Cement chemist notation
• Portland cement
• Fly ash
• BET theory

Cement chemist notation (CCN) was developed to simplify the formulas cement chemists use on a daily basis. ... Sampling fast set Portland cement Portland cement is the most common type of cement in general usage, as it is a basic ingredient of concrete, mortar and plaster. ... Fly ash (one of several coal combustion products, or CCPs) is the finely divided mineral residue resulting from the combustion of coal in electric generating plants. ... BET theory is a well-known rule for the physical adsorption of gas molecules on a solid surface. ...

External links

• British Cement Association (UK)
• Cembureau (EU)
• Portland Cement Association (US)
• Verein Deutscher Zementwerke e. V. (VDZ), (Germany)
• Carbon dioxide emission from the global cement industry (in 1994)
• International cement industry Sustainability Initiative

Literature

• Friedrich W. Locher: Cement : Principles of production and use, Duesseldorf, Germany: Verlag Bau + Technik GmbH, 2006, ISBN 3-7640-0420-7
• Javed I. Bhatty, F. MacGregor Miller, Steven H. Kosmatka; editors: Innovations in Portland Cement Manufacturing, SP400, Portland Cement Association, Skokie, Illinois, USA, 2004, ISBN 0-89312-234-3
• A. M. Neville Properties of Concrete: 4th Ed, Wiley, 1996, ISBN 0-582-23070-5

References