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{{Other uses}}{{distinguish|Concrete|mortar (masonry)}}{{Use dmy dates|date=January 2019}}(File:USMC-110806-M-IX060-148.jpg|thumb|Cement powder, here conditioned in bag, is mixed with fine and coarse aggregates and water.)A cement is a binder, a substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Cement is the most widely used material in existence and is only behind water as the planet's most-consumed resource.NEWS,weblink The massive CO2 emitter you may not know about, Rodgers, Lucy, 17 December 2018, BBC News, 17 December 2018, Cements used in construction are usually inorganic, often lime or calcium silicate based, and can be characterized as either hydraulic or non-hydraulic, depending on the ability of the cement to set in the presence of water (see hydraulic and non-hydraulic lime plaster).Non-hydraulic cement does not set in wet conditions or under water. Rather, it sets as it dries and reacts with carbon dioxide in the air. It is resistant to attack by chemicals after setting.Hydraulic cements (e.g., Portland cement) set and become adhesive due to a chemical reaction between the dry ingredients and water. The chemical reaction results in mineral hydrates that are not very water-soluble and so are quite durable in water and safe from chemical attack. This allows setting in wet conditions or under water and further protects the hardened material from chemical attack. The chemical process for hydraulic cement found by ancient Romans used volcanic ash (pozzolana) with added lime (calcium oxide).The word "cement" can be traced back to the Roman term opus caementicium, used to describe masonry resembling modern concrete that was made from crushed rock with burnt lime as binder. The volcanic ash and pulverized brick supplements that were added to the burnt lime, to obtain a hydraulic binder, were later referred to as cementum, cimentum, cäment, and cement. In modern times, organic polymers are sometimes used as cements in concrete.

Chemistry

Cement materials can be classified into two distinct categories: non-hydraulic cements and hydraulic cements according to their respective setting and hardening mechanisms. Hydraulic cements setting and hardening involve hydration reactions and therefore require water, while non-hydraulic cements only react with a gas and can directly set under air.

Non-hydraulic cement

missing image!
- Calcium oxide powder.JPG -
Calcium oxide obtained by thermal decomposition of calcium carbonate at high temperature (above 825 Â°C).
Non-hydraulic cement, such as slaked lime (calcium oxide mixed with water), hardens by carbonation in contact with carbon dioxide, which is present in the air (~ 412 vol. ppm ≃ 0.04 vol. %). First calcium oxide (lime) is produced from calcium carbonate (limestone or chalk) by calcination at temperatures above 825 Â°C (1,517 Â°F) for about 10 hours at atmospheric pressure:
CaCO3 → CaO + CO2
The calcium oxide is then spent (slaked) mixing it with water to make slaked lime (calcium hydroxide):
CaO + H2O → Ca(OH)2
Once the excess water is completely evaporated (this process is technically called setting), the carbonation starts:
Ca(OH)2 + CO2 → CaCO3 + H2O
This reaction takes time, because the partial pressure of carbon dioxide in the air is low (~ 0.4 millibar). The carbonation reaction requires that the dry cement be exposed to air, so the slaked lime is a non-hydraulic cement and cannot be used under water. This process is called the lime cycle.

Hydraulic cement

missing image!
- LDClinkerScaled.jpg -
Clinker nodules produced by sintering at 1450 Â°C.
Conversely, hydraulic cement hardens by hydration of the clinker minerals when water is added. Hydraulic cements (such as Portland cement) are made of a mixture of silicates and oxides, the four main mineral phases of the clinker, abbreviated in the cement chemist notation, being:
C3S: Alite (3CaO·SiO2); C2S: Belite (2CaO·SiO2); C3A: Tricalcium aluminate (3CaO·Al2O3) (historically, and still occasionally, called 'celite'); C4AF: Brownmillerite (4CaO·Al2O3·Fe2O3).
The silicates are responsible for the cement's mechanical properties — the tricalcium aluminate and brownmillerite are essential for the formation of the liquid phase during the sintering (firing) process of clinker at high temperature in the kiln. The chemistry of these reactions is not completely clear and is still the object of research.Cement's basic molecular structure finally decoded (MIT, 2009) {{webarchive|url=https://web.archive.org/web/20130221105202weblink |date=21 February 2013 }}

History

Perhaps the earliest known occurrence of cement is from twelve million years ago. A deposit of cement was formed after an occurrence of oil shale located adjacent to a bed of limestone burned due to natural causes. These ancient deposits were investigated in the 1960s and 1970s.WEB, The History of Concrete,weblink Dept. of Materials Science and Engineering, University of Illinois, Urbana-Champaign, 8 January 2013, live,weblink" title="web.archive.org/web/20121127052951weblink">weblink 27 November 2012,

Alternatives to cement used in antiquity

Cement, chemically speaking, is a product that includes lime as the primary curing ingredient, but is far from the first material used for cementation. The Babylonians and Assyrians used bitumen to bind together burnt brick or alabaster slabs. In Egypt stone blocks were cemented together with a mortar made of sand and roughly burnt gypsum (CaSO4 · 2H2O), which often contained calcium carbonate (CaCO3).

Macedonians and Romans

Lime (calcium oxide) was used on Crete and by the ancient Greeks. There is evidence that the Minoans of Crete used crushed potshards as an artificial pozzolan for hydraulic cement. Nobody knows who first discovered that a combination of hydrated non-hydraulic lime and a pozzolan produces a hydraulic mixture (see also: Pozzolanic reaction)—but such concrete was used by the Ancient Macedonians,Brabant, Malcolm (12 April 2011). Macedonians created cement three centuries before the Romans {{webarchive|url=https://web.archive.org/web/20190409224527weblink |date=9 April 2019 }}, BBC News.Heracles to Alexander The Great: Treasures From The Royal Capital of Macedon, A Hellenic Kingdom in the Age of Democracy {{webarchive|url=https://web.archive.org/web/20120117164459weblink |date=17 January 2012 }}, Ashmolean Museum of Art and Archaeology, University of Oxford and three centuries later on a large scale by Roman engineers.Hill, Donald (1984). A History of Engineering in Classical and Medieval Times, Routledge, p. 106, {{ISBN|0415152917}}.WEB,weblink History of cement, www.understanding-cement.com, 17 December 2018, WEB,weblink How the Ancient Romans Made Better Concrete Than We Do Now, Trendacosta, Katharine, 18 December 2014, Gizmodo, The Greeks used volcanic tuff from the island of Thera as their pozzolan and the Romans used crushed volcanic ash (activated aluminium silicates) with lime. This mixture could set under water, increasing its resistance.{{clarify|reason=resistance to what?|date=October 2015}} The material was called pozzolana from the town of Pozzuoli, west of Naples where volcanic ash was extracted.JOURNAL, Francesca, Ridi, Hydration of Cement: still a lot to be understood, La Chimica & l'Industria,weblink 3, April 2010, 110–117, live,weblink" title="web.archive.org/web/20151117023718weblink">weblink 17 November 2015, In the absence of pozzolanic ash, the Romans used powdered brick or pottery as a substitute and they may have used crushed tiles for this purpose before discovering natural sources near Rome. The huge dome of the Pantheon in Rome and the massive Baths of Caracalla are examples of ancient structures made from these concretes, many of which still stand.WEB,weblink Pure natural pozzolan cement, 12 January 2009, bot: unknown,weblink" title="web.archive.org/web/20061018162743weblink">weblink 18 October 2006, . chamorro.com The vast system of Roman aqueducts also made extensive use of hydraulic cement.Russo, Ralph (2006) "Aqueduct Architecture: Moving Water to the Masses in Ancient Rome" {{webarchive|url=https://web.archive.org/web/20081012075152weblink |date=12 October 2008 }}, in Math in the Beauty and Realization of Architecture, Vol. IV, Curriculum Units by Fellows of the Yale-New Haven Teachers Institute 1978–2012, Yale-New Haven Teachers Institute. Roman concrete was rarely used on the outside of buildings. The normal technique was to use brick facing material as the formwork for an infill of mortar mixed with an aggregate of broken pieces of stone, brick, potsherds, recycled chunks of concrete, or other building rubble.JOURNAL, 10.1080/00038628.1975.9696342, An Historical Note on Concrete, Architectural Science Review, 18, 10–13, 1975, Cowan, Henry J.,

Middle Ages

Any preservation of this knowledge in literature from the Middle Ages is unknown, but medieval masons and some military engineers actively used hydraulic cement in structures such as canals, fortresses, harbors, and shipbuilding facilities.Sismondo, Sergio (2009). An Introduction to Science and Technology Studies {{webarchive|url=https://web.archive.org/web/20160510161613weblink |date=10 May 2016 }}. John Wiley and Sons, 2nd edition, p. 142. {{ISBN|978-1-4051-8765-7}}.Mukerji, Chandra (2009). Impossible engineering: technology and territoriality on the Canal du Midi {{webarchive|url=https://web.archive.org/web/20160426064235weblink |date=26 April 2016 }}. Princeton University Press, p. 121, {{ISBN|978-0-691-14032-2}}. A mixture of lime mortar and aggregate with brick or stone facing material was used in the Eastern Roman Empire as well as in the West into the Gothic period. The German Rhineland continued to use hydraulic mortar throughout the Middle Ages, having local pozzolana deposits called trass.

16th century

Tabby is a building material made from oyster-shell lime, sand, and whole oyster shells to form a concrete. The Spanish introduced it to the Americas in the sixteenth century.Taves, Loren Sickels (Mar–Apr 1995). "Tabby Houses of the South Atlantic Seaboard" {{webarchive|url=https://web.archive.org/web/20151027055427weblink |date=27 October 2015 }}, Old-House Journal. Back cover.

18th century

The technical knowledge for making hydraulic cement was formalized by French and British engineers in the 18th century.John Smeaton made an important contribution to the development of cements while planning the construction of the third Eddystone Lighthouse (1755–59) in the English Channel now known as Smeaton's Tower. He needed a hydraulic mortar that would set and develop some strength in the twelve-hour period between successive high tides. He performed experiments with combinations of different limestones and additives including trass and pozzolanasBlezard, Robert G. (2004) "The History of Calcareous Cements" in Hewlett, Peter C., ed.. Leaʼs chemistry of cement and concrete. 4th ed. Amsterdam: Elsevier Butterworth-Heinemann. pp. 1–24. {{ISBN|9780080535418}} and did 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 used to make it. Smeaton was a civil engineer by profession, and took the idea no further.In the South Atlantic seaboard of the United States, tabby relying on the oyster-shell middens of earlier Native American populations was used in house construction from the 1730s to the 1860s.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 was Parker's "Roman cement".Francis, A.J. (1977) The Cement Industry 1796–1914: A History, David & Charles. {{ISBN|0-7153-7386-2}}, Ch. 2. This was developed by James Parker in the 1780s, and finally patented in 1796. It was, in fact, nothing like 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 hydraulic lime cements of clay and chalk.Roman cement quickly became popular but was largely replaced by Portland cement in the 1850s.

19th century

Apparently unaware of Smeaton's work, the same principle was identified by Frenchman 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 1817WEB,weblink Who Discovered Cement, live,weblink" title="web.archive.org/web/20130204131106weblink">weblink 4 February 2013, dmy-all, 12 September 2012, considered the "principal forerunner" of Portland cement and "...Edgar Dobbs of Southwark patented a cement of this kind in 1811."In Russia, Egor Cheliev created a new binder by mixing lime and clay. His results were published in 1822 in his book A Treatise on the Art to Prepare a Good Mortar published in St. Petersburg. A few years later in 1825, he published another book, which described various methods of making cement and concrete, and the benefits of cement in the construction of buildings and embankments.BOOK, Znachko-Iavorskii, I. L., Egor Gerasimovich Chelidze, izobretatelʹ tsementa,weblink live,weblink" title="web.archive.org/web/20140201232847weblink">weblink 1 February 2014, Sabchota Sakartvelo, 1969, WEB, Lafarge History of Cement,weblink live,weblink" title="web.archive.org/web/20140202101113weblink">weblink 2 February 2014, File:William Aspdin Radford cyclopedia Volume 1.jpg|thumb|right|upright|William Aspdin is considered the inventor of "modern" (Portland cement]].BOOK, Courland, Robert, Concrete planet : the strange and fascinating story of the world's most common man-made material, 2011, Prometheus Books, Amherst, N.Y., 978-1616144814,weblink 190, )Portland cement, the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-speciality grout, was developed in England in the mid 19th century, and usually originates from limestone. James Frost produced what he called "British cement" in a similar manner around the same time, but did not obtain a patent until 1822.Francis, A.J. (1977) The Cement Industry 1796–1914: A History, David & Charles. {{ISBN|0-7153-7386-2}}, Ch. 5. 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 quarried on the Isle of Portland, Dorset, England. However, Aspdins' cement was nothing like modern Portland cement but was a first step in its development, called a proto-Portland cement. Joseph Aspdins' son William Aspdin had left his father's company and in his cement manufacturing apparently accidentally produced calcium silicates in the 1840s, a middle step in the development of Portland cement. William Aspdin's innovation was counterintuitive for manufacturers of "artificial cements", because they required more lime in the mix (a problem for his father), a much higher kiln temperature (and therefore more fuel), and 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 onward, and was soon the dominant use for cements. Thus Portland cement began its predominant role. Isaac Charles Johnson further refined the production of meso-Portland cement (middle stage of development) and claimed he was the real father of Portland cement.Hahn, Thomas F. and Kemp, Emory Leland (1994). Cement mills along the Potomac River. Morgantown, WV: West Virginia University Press. p. 16. {{ISBN|9781885907004}}Setting time and "early strength" are important characteristics of cements. Hydraulic limes, "natural" cements, and "artificial" cements all rely on their belite content for strength development. Belite develops strength slowly. Because they were burned at temperatures below {{convert|1250|C|F}}, they contained no alite, which is responsible for early strength in modern cements. The first cement to consistently contain alite was made by William Aspdin 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 Johnson) have claimed precedence in this invention, but recent analysisBOOK, Hewlett, Peter, Lea's Chemistry of Cement and Concrete,weblink 2003, Butterworth-Heinemann, 978-0-08-053541-8, Ch. 1, live,weblink 1 November 2015, 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.In the US the first large-scale use of cement was Rosendale cement, a natural cement mined from a massive deposit of a large dolomite deposit discovered in the early 19th century near Rosendale, New York. Rosendale cement was extremely popular for the foundation of buildings (e.g., Statue of Liberty, Capitol Building, Brooklyn Bridge) and lining water pipes."Natural Cement Comes Back" {{webarchive|url=https://web.archive.org/web/20160425093525weblink |date=25 April 2016 }}, October 1941, Popular ScienceSorel cement was patented in 1867 by Frenchman Stanislas Sorel. It was stronger than Portland cement but its poor water resistance and corrosive qualities limited its use in building construction. The next development in the manufacture of Portland cement was the introduction of the rotary kiln, which produced a stronger, more homogeneous mixture and facilitated a continuous manufacturing process.

20th century

File:Factory of National Cement Share Company.jpg|thumb|right|The National Cement Share Company of Ethiopia's new plant in Dire DawaDire DawaCalcium aluminate cements were patented in 1908 in France by Jules Bied for better resistance to sulfates.BOOK,weblink Engineering Materials Science: Properties, Uses, Degradation, Remediation, McArthur, H., Spalding, D., 1 January 2004, Elsevier, 9781782420491, In the US, after World War One, the long curing time of at least a month for Rosendale cement made it unpopular for constructing highways and bridges, and many states and construction firms turned to Portland cement. Because of the switch to Portland cement, by the end of the 1920s only one of the 15 Rosendale cement companies had survived. But in the early 1930s, builders discovered that, while Portland cement set faster, it was not as durable, especially for highways—to the point that some states stopped building highways and roads with cement. Bertrain H. Wait, an engineer whose company had helped construct the New York City's Catskill Aqueduct, was impressed with the durability of Rosendale cement, and came up with a blend of both Rosendale and Portland cements that had the good attributes of both. It was highly durable and had a much faster setting time. Wait convinced the New York Commissioner of Highways to construct an experimental section of highway near New Paltz, New York, using one sack of Rosendale to six sacks of Portland cement. It was a success, and for decades the Rosendale-Portland cement blend was used in highway and bridge construction.Cementitious materials have been used as a nuclear waste immobilizing matrix for more than a half-century.Glasser F. (2011). Application of inorganic cements to the conditioning and immobilisation of radioactive wastes. In: Ojovan M.I. (2011). Handbook of advanced radioactive waste conditioning technologies. Woodhead, Cambridge, 512 pp. Technologies of waste cementation have been developed and deployed at industrial scale in many countries. Cementitious wasteforms require a careful selection and design process adapted to each specific type of waste to satisfy the strict waste acceptance criteria for long-term storage and disposal.Abdel Rahman R.O., Rahimov R.Z., Rahimova N.R., Ojovan M.I. (2015). Cementitious materials for nuclear waste immobilization. Wiley, Chichester 232 pp.

Modern cements

Modern hydraulic development began with the start of the Industrial Revolution (around 1800), driven by three main needs:
  • Hydraulic cement render (stucco) 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
{{Components of Cement, Comparison of Chemical and Physical Characteristics}}Modern cements are often Portland cement or Portland cement blends, but industry also uses other cements.

Portland cement

Portland cement is by far the most common type of cement in general use around the world. This cement is made by heating limestone (calcium carbonate) with other materials (such as clay) to {{convert|1450|C}} in a kiln, in a process known as calcination that liberates a molecule of carbon dioxide from the calcium carbonate to form calcium oxide, or quicklime—which then chemically combines with the other materials in the mix to form calcium silicates and other cementitious compounds. 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).Portland cement is a basic ingredient of concrete, mortar, and most non-specialty grout. The most common use for Portland cement is to make concrete. Concrete is a composite material made of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape, and once it hardens, can be a structural (load bearing) element. Portland cement may be grey or white.

Portland cement blends

Portland cement blends are often available as inter-ground mixtures from cement producers, but similar formulations are often also mixed from the ground components at the concrete mixing plant.BOOK, Kosmatka, S.H., Panarese, W.C., Design and Control of Concrete Mixtures, Portland Cement Association, 1988, Skokie, IL, USA, 17, 42, 70, 184, 978-0-89312-087-0, Portland blast-furnace slag cement, or Blast furnace cement (ASTM C595 and EN 197-1 nomenclature respectively), contains up to 95% 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.WEB, U.S. Federal Highway Administration, Federal Highway Administration, Ground Granulated Blast-Furnace Slag,weblink 24 January 2007, dead,weblink" title="web.archive.org/web/20070122083859weblink">weblink 22 January 2007, dmy-all, Portland-fly ash cement contains up to 40% fly ash under ASTM standards (ASTM C595), or 35% under EN standards (EN 197-1). The fly ash is pozzolanic, so that ultimate strength is maintained. Because fly ash addition allows a lower concrete water content, early strength can also be maintained. Where good quality cheap fly ash is available, this can be an economic alternative to ordinary Portland cement.WEB, U.S. Federal Highway Administration, Federal Highway Administration, Fly Ash,weblink 24 January 2007, dead,weblink" title="web.archive.org/web/20070621161733weblink">weblink 21 June 2007, dmy-all, 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. The maximum replacement ratios are generally defined as for Portland-fly ash cement.Portland silica fume cement. Addition of silica fume can yield exceptionally high strengths, and cements containing 5–20% silica fume are occasionally produced, with 10% being the maximum allowed addition under EN 197-1. However, silica fume is more usually added to Portland cement at the concrete mixer.WEB, U.S. Federal Highway Administration, Federal Highway Administration, Silica Fume,weblink 24 January 2007, dead,weblink" title="web.archive.org/web/20070122022403weblink">weblink 22 January 2007, dmy-all, 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 a controlled bond with masonry blocks.Expansive cements contain, in addition to Portland clinker, expansive clinkers (usually sulfoaluminate clinkers), and are designed to offset the effects of drying shrinkage normally encountered in hydraulic cements. This cement can make concrete for floor slabs (up to 60 m square) without contraction joints.White blended cements may be made using white clinker (containing little or no iron) and white supplementary materials such as high-purity metakaolin. Colored cements serve decorative purposes. Some standards allow the addition of pigments to produce colored Portland cement. Other standards (e.g., ASTM) do not allow pigments in Portland cement, and colored cements are sold as blended hydraulic cements.Very finely ground cements are cement mixed with sand or with slag or other pozzolan type minerals that are extremely finely ground together. Such cements can have the same physical characteristics as normal cement but with 50% less cement, particularly due to their increased surface area for the chemical reaction. Even with intensive grinding they can use up to 50% less energy (and thus less carbon emissions) to fabricate than ordinary Portland cements.JOURNAL, Mechanism for performance of energetically modified cement versus corresponding blended cement,weblinkweblink" title="web.archive.org/web/20110710185446weblink">weblink 10 July 2011, Cement and Concrete Research, 35, 2005, 315–323, 10.1016/j.cemconres.2004.05.022, Justnes, Harald, Elfgren, Lennart, Ronin, Vladimir, 2,

Other cements

Pozzolan-lime cements are mixtures of ground pozzolan and lime. These are the cements the Romans used, and are present in surviving Roman structures like 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 in Portland cement.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.Supersulfated cements 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.Calcium aluminate cements are hydraulic cements made primarily from limestone and bauxite. The active ingredients are monocalcium aluminate CaAl2O4 (CaO · Al2O3 or CA in Cement chemist notation, CCN) and mayenite Ca12Al14O33 (12 CaO · 7 Al2O3, or 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 sulfoaluminate cements are made from clinkers that include ye'elimite (Ca4(AlO2)6SO4 or C4A3{{overline|S}} 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.Bye G.C. (1999), Portland Cement 2nd Ed., Thomas Telford. pp. 206–208. {{ISBN|0-7277-2766-4}}JOURNAL, 10.1680/adcr.1999.11.1.15, Development of the use of sulfo- and ferroaluminate cements in China, Advances in Cement Research, 11, 15–21, 1999, Zhang, Liang, Su, Muzhen, Wang, Yanmou, 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."Natural" cements corresponding to certain cements of the pre-Portland era, are 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 of free lime. As with any natural material, such cements have highly variable properties.Geopolymer cements are made from mixtures of water-soluble alkali metal silicates, and aluminosilicate mineral powders such as fly ash and metakaolin.Polymer cements are made from organic chemicals that polymerise. Producers often use thermoset materials. While they are often significantly more expensive, they can give a water proof material that has useful tensile strength.

Setting, hardening and curing

Cement starts to set when mixed with water, which causes a series of hydration chemical reactions. The constituents slowly hydrate and the mineral hydrates solidify and harden. The interlocking of the hydrates gives cement its strength. Contrary to popular belief, hydraulic cement does not set by drying out — proper curing requires maintaining the appropriate moisture content necessary for the hydration reactions during the setting and the hardening processes. If hydraulic cements dry out during the curing phase, the resulting product can be insufficiently hydrated and significantly weakened. A minimum temperature of 5 Â°C is recommended, and no more than 30 Â°C.WEB,weblink Using cement based products during winter months, 29 May 2018, sovchem.co.uk, The concrete at young age must be protected against water evaporation due to direct insolation, elevated temperature, low relative humidity and wind.

Safety issues

Bags of cement routinely have health and safety warnings printed on them because not only is cement highly alkaline, but the setting process is exothermic. As a result, wet cement is strongly caustic (pH = 13.5) and can easily cause severe skin burns if not promptly washed off with water. Similarly, dry cement powder in contact with mucous membranes can cause severe eye or respiratory irritation. Some trace elements, such as chromium, from impurities naturally present in the raw materials used to produce cement may cause allergic dermatitis.WEB,weblink Construction Information Sheet No 26 (revision2), 15 February 2011, live,weblink" title="web.archive.org/web/20110604222509weblink">weblink hse.gov.uk, 4 June 2011, Reducing agents such as ferrous sulfate (FeSO4) are often added to cement to convert the carcinogenic hexavalent chromate (CrO42−) into trivalent chromium (Cr3+), a less toxic chemical species. Cement users need also to wear appropriate gloves and protective clothing.CIS26 – cement {{webarchive|url=https://web.archive.org/web/20110604222509weblink |date=4 June 2011 }}. (PDF) . Retrieved on 5 May 2011.NEWS,weblink London, Daily Mail, Mother left with horrific burns to her knees after kneeling in B&Q cement while doing kitchen DIY, 15 February 2011, NEWS,weblink London, The Sun, Jamie, Pyatt, Mums horror cement burns, 15 February 2011, live,weblink" title="web.archive.org/web/20111107232258weblink">weblink 7 November 2011, dmy-all,

Cement industry in the world

(File:Cement Production 2010.png|thumb|250px|right|Global Cement Production in 2010)(File:Cement Capacity 2010.png|thumb|250px|right|Global Cement Capacity in 2010){{See also|List of countries by cement production }}In 2010, the world production of hydraulic cement was {{convert|3300 |e6t}}. The top three producers were China with 1,800, India with 220, and USA with 63.5 million tonnes for a total of over half the world total by the world's three most populated states.WEB, United States Geological Survey, USGS Mineral Program Cement Report. (Jan 2011),weblink live,weblink" title="web.archive.org/web/20111008062123weblink">weblink 8 October 2011, dmy-all, For the world capacity to produce cement in 2010, the situation was similar with the top three states (China, India, and USA) accounting for just under half the world total capacity.Edwards, P; McCaffrey, R. Global Cement Directory 2010. PRo Publications {{webarchive|url=https://web.archive.org/web/20140103095700weblink |date=3 January 2014 }}. Epsom, UK, 2010.Over 2011 and 2012, global consumption continued to climb, rising to 3585 Mt in 2011 and 3736 Mt in 2012, while annual growth rates eased to 8.3% and 4.2%, respectively.China, representing an increasing share of world cement consumption, remains the main engine of global growth. By 2012, Chinese demand was recorded at 2160 Mt, representing 58% of world consumption. Annual growth rates, which reached 16% in 2010, appear to have softened, slowing to 5–6% over 2011 and 2012, as China's economy targets a more sustainable growth rate.Outside of China, worldwide consumption climbed by 4.4% to 1462 Mt in 2010, 5% to 1535 Mt in 2011, and finally 2.7% to 1576 Mt in 2012.Iran is now the 3rd largest cement producer in the world and has increased its output by over 10% from 2008 to 2011.List of countries by cement production 2011 {{webarchive|url=https://web.archive.org/web/20130922070531weblink |date=22 September 2013 }} Retrieved 19 November 2013. Due to climbing energy costs in Pakistan and other major cement-producing countries, Iran is in a unique position as a trading partner, utilizing its own surplus petroleum to power clinker plants. Now a top producer in the Middle-East, Iran is further increasing its dominant position in local markets and abroad.ICR Newsroom. Pakistan loses Afghan cement market share to Iran {{webarchive|url=https://web.archive.org/web/20130922070531weblink |date=22 September 2013 }}. Retrieved 19 November 2013.The performance in North America and Europe over the 2010–12 period contrasted strikingly with that of China, as the global financial crisis evolved into a sovereign debt crisis for many economies in this region and recession. Cement consumption levels for this region fell by 1.9% in 2010 to 445 Mt, recovered by 4.9% in 2011, then dipped again by 1.1% in 2012.The performance in the rest of the world, which includes many emerging economies in Asia, Africa and Latin America and representing some 1020 Mt cement demand in 2010, was positive and more than offset the declines in North America and Europe. Annual consumption growth was recorded at 7.4% in 2010, moderating to 5.1% and 4.3% in 2011 and 2012, respectively.As at year-end 2012, the global cement industry consisted of 5673 cement production facilities, including both integrated and grinding, of which 3900 were located in China and 1773 in the rest of the world.Total cement capacity worldwide was recorded at 5245 Mt in 2012, with 2950 Mt located in China and 2295 Mt in the rest of the world.JOURNAL, Hargreaves, David, International Cement Review, The Global Cement Report 10th Edition, March 2013,weblink live,weblink" title="web.archive.org/web/20131126060704weblink">weblink 26 November 2013, dmy-all,

China

"For the past 18 years, China consistently has produced more cement than any other country in the world. [...] (However,) China's cement export peaked in 1994 with 11 million tonnes shipped out and has been in steady decline ever since. Only 5.18 million tonnes 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."Yan, Li Yong (7 January 2004) China's way forward paved in cement, Asia TimesIn 2006, it was estimated that China manufactured 1.235 billion tonnes of cement, which was 44% of the world total cement production.China now no. 1 in CO2 emissions; USA in second position: more info {{webarchive|url=https://web.archive.org/web/20070703030047weblink |date=3 July 2007 }}, NEAA (19 June 2007). "Demand for cement in China is expected to advance 5.4% annually and exceed 1 billion tonnes 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."weblink" title="web.archive.org/web/20090427075804weblink">China's cement demand to top 1 billion tonnes in 2008, CementAmericas (1 November 2004).In 2010, 3.3 billion tonnes of cement was consumed globally. Of this, China accounted for 1.8 billion tonnes.Coal and Cement. World Coal Association {{webarchive|url=https://web.archive.org/web/20110808003702weblink |date=8 August 2011 }}

{{anchor|Environmental and social impacts}}Environmental 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.

CO2 emissions

(File:Global Carbon Emissions.svg|thumb|Global carbon emission by type to 2004. Attribution: Mak Thorpe)Carbon concentration in cement spans from ≈5% in cement structures to ≈8% in the case of roads in cement.JOURNAL, Influence of 150 years of land use on anthropogenic and natural carbon stocks in Emilia-Romagna Region (Italy), Scalenghe, R., Malucelli, F., Ungaro, F., Perazzone, L., Filippi, N., Edwards, A.C., 2011, 45, 12, 5112–5117, 10.1021/es1039437, 21609007, Environmental Science & Technology, 2011EnST...45.5112S, Cement manufacturing releases {{CO2|link=yes}} in the atmosphere both directly when calcium carbonate is heated, producing lime and carbon dioxide,EIA – Emissions of Greenhouse Gases in the U.S. 2006-Carbon Dioxide Emissions {{webarchive|url=https://web.archive.org/web/20110523061426weblink |date=23 May 2011 }} US Department of Energy.JOURNAL, Striking a balance between profit and carbon dioxide emissions in the Saudi cement industry, Matar, W., Elshurafa, A. M., 2017, 61, 111–123, 10.1016/j.ijggc.2017.03.031, International Journal of Greenhouse Gas Control, and also indirectly through the use of energy if its production involves the emission of CO2. The cement industry produces about 10% of global man-made CO2 emissions, of which 60% is from the chemical process, and 40% from burning fuel.Trends in global CO2 emissions: 2014 Report {{webarchive|url=https://web.archive.org/web/20161014143722weblink |date=14 October 2016 }}. PBL Netherlands Environmental Assessment Agency & European Commission Joint Research Centre (2014). A Chatham House study from 2018 estimates that the 4 billion tonnes of cement produced annually account for 8% of worldwide CO2 emissions.WEB,weblink Making Concrete Change: Innovation in Low-carbon Cement and Concrete, Chatham House, 17 December 2018, Nearly 900 kg of CO2 are emitted for every 1000 kg of Portland cement produced. In the European Union, the specific energy consumption for the production of cement clinker has been reduced by approximately 30% since the 1970s. This reduction in primary energy requirements is equivalent to approximately 11 million tonnes of coal per year with corresponding benefits in reduction of CO2 emissions. This accounts for approximately 5% of anthropogenic CO2.BOOK, Mahasenan, Natesan< pH < 13.5) limits the mobility of many heavy metals by decreasing their solubility and increasing their sorption onto the cement mineral phases. Nickel, zinc and lead are commonly found in cement in non-negligible concentrations. Chromium may also directly arise as natural impurity from the raw materials or as secondary contamination from the abrasion of hard chromium steel alloys used in the ball mills when the clinker is ground. As chromate (CrO42−) is toxic and may cause severe skin allergies at trace concentration, it is sometimes reduced into trivalent Cr(III) by addition of ferrous sulfate (FeSO4).

Use of alternative fuels and by-products materials

A cement plant consumes 3 to 6 GJ 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 (referred to as co-processing), 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.Guidelines for the selection and use of fuels and raw materials in the cement manufacturing process {{webarchive |url=https://web.archive.org/web/20080910015447weblink |date=10 September 2008 }}, World Business Council for Sustainable Development (1 June 2005). Scrap automobile and truck tires are useful in cement manufacturing as they have high calorific value and the iron embedded in tires is useful as a feed stock.WEB,weblink Increasing the use of alternative fuels at cement plants: International best practice, International Finance Corporation, World Bank Group, 2017, {{rp|p. 27}}Clinker is manufactured by heating raw materials inside the main burner of a kiln to a temperature of 1450 Â°C. The flame reaches temperatures of 1800 Â°C. The material remains at 1200 Â°C for 12–15 seconds at 1800 Â°C for 5–8 seconds (also referred to as residence time). These characteristics of a clinker kiln offer numerous benefits and they ensure a complete destruction of organic compounds, a total neutralization of acid gases, sulphur oxides and hydrogen chloride. Furthermore, heavy metal traces are embedded in the clinker structure and no by-products, such as ash of residues, are produced.Cement, concrete & the circular economy. cembureau.euThe EU cement industry already uses more than 40% fuels derived from waste and biomass in supplying the thermal energy to the grey clinker making process. Although the choice for this so-called alternative fuels (AF) is typically cost driven, other factors are becoming more important. Use of alternative fuels provides benefits for both society and the company: CO2-emissions are lower than with fossil fuels, waste can be co-processed in an efficient and sustainable manner and the demand for certain virgin materials can be reduced. Yet there are large differences in the share of alternative fuels used between the European Union (EU) member states. The societal benefits could be improved if more member states increase their alternative fuels share. The Ecofys studyde Beer, Jeroen et al. (2017) Status and prospects of co-processing of waste in EU cement plants. ECOFYS study. assessed the barriers and opportunities for further uptake of alternative fuels in 14 EU member states. The Ecofys study found that local factors constrain the market potential to a much larger extent than the technical and economic feasibility of the cement industry itself.

Green cement

Green cement is a cementitious material that meets or exceeds the functional performance capabilities of ordinary Portland cement by incorporating and optimizing recycled materials, thereby reducing consumption of natural raw materials, water, and energy, resulting in a more sustainable construction material. One is Geopolymer cement.New manufacturing processes for producing green cement are being researched with the goal to reduce, or even eliminate, the production and release of damaging pollutants and greenhouse gasses, particularly CO2.WEB, Engineers develop cement with 97 percent smaller carbon dioxide and energy footprint – DrexelNow,weblink DrexelNow, 16 January 2016, live,weblink" title="web.archive.org/web/20151218144742weblink">weblink 18 December 2015, Growing environmental concerns and the increasing cost of fuels of fossil origin have resulted in many countries in a sharp reduction of the resources needed to produce cement and effluents (dust and exhaust gases).Alternative fuels in cement manufacture – CEMBUREAU brochure, 1997 {{webarchive |url=https://web.archive.org/web/20131002040331weblink |date=2 October 2013 }}A team at the University of Edinburgh has developed the 'DUPE' process based on the microbial activity of Sporosarcina pasteurii, a bacterium precipitating calcium carbonate, which, when mixed with sand and urine, can produce mortar blocks with a compressive strength 70% of that of conventional construction materials.WEB,weblink Would you live in a house made of sand and bacteria? It's a surprisingly good idea, Monks, Kieron, 22 May 2014, 20 July 2014, CNN, live,weblink" title="web.archive.org/web/20140720051919weblink">weblink 20 July 2014,

See also

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References

{{Reflist}}

Further reading

  • JOURNAL, Aitcin, Pierre-Claude, Cements of yesterday and today: Concrete of tomorrow, Cement and Concrete Research, 30, 9, 1349–1359
author3=Humphreysm Kenneth, Kaya, Y., Greenhouse Gas Control Technologies – 6th International Conference, The Cement Industry and Global Climate Change: Current and Potential Future Cement Industry CO2 Emissions, Pergamon, 978-0-08-044276-1, 995–1000, Oxford, 2003,weblink The majority of carbon dioxide emissions in the manufacture of Portland cement (approximately 60%) are produced from the chemical decomposition of limestone to lime, an ingredient in Portland cement clinker. These emissions may be reduced by lowering the clinker content of cement. They can also be reduced by alternative fabrication methods such as the intergrinding cement with sand or with slag or other pozzolan type minerals to a very fine powder.To reduce the transport of heavier raw materials and to minimize the associated costs, it is more economical to build cement plants closer to the limestone quarries rather than to the consumer centers.WEB, Chandak, Shobhit, Report on cement industry in India,weblink scribd, 21 July 2011, live,weblink" title="web.archive.org/web/20120222124243weblink">weblink 22 February 2012, In certain applications, lime mortar reabsorbs some of the CO2 as was released in its manufacture, and has a lower energy requirement in production than mainstream cement.{{citation needed|date=July 2018}} Newly developed cement types from NovacemNovacem {{webarchive|url=https://web.archive.org/web/20090803053655weblink |date=3 August 2009 }}. imperialinnovations.co.uk and Eco-cement can absorb carbon dioxide from ambient air during hardening.NEWS,weblink The Guardian, London, Revealed: The cement that eats carbon dioxide, Alok, Jha, 31 December 2008, 28 April 2010, live,weblink" title="web.archive.org/web/20130806151853weblink">weblink 6 August 2013, dmy-all, {{As of|2019}} carbon capture and storage is about to be trialled, but its financial viability is uncertain.NEWS, World's first zero-emission cement plant takes shape in Norway,weblink EURACTIV.COM Ltd., 13 Dec 2018,

Heavy metal emissions in the air

In some circumstances, mainly depending on the origin and the composition of the raw materials used, the high-temperature calcination process of limestone and clay minerals can release in the atmosphere gases and dust rich in volatile heavy metals, a.o, thallium,WEB,weblink 15 September 2009, Factsheet on: Thallium, live,weblink" title="web.archive.org/web/20120111232626weblink">weblink 11 January 2012, dmy-all, cadmium and mercury are the most toxic. Heavy metals (Tl, Cd, Hg, ...) and also selenium are often found as trace elements in common metal sulfides (pyrite (FeS2), zinc blende (ZnS), galena (PbS), ...) present as secondary minerals in most of the raw materials. Environmental regulations exist in many countries to limit these emissions. As of 2011 in the United States, cement kilns are "legally allowed to pump more toxins into the air than are hazardous-waste incinerators."WEB
, Berkes, Howard
, EPA Regulations Give Kilns Permission To Pollute : NPR
, NPR.org
, 17 November 2011
, 10 November 2011
,weblink
, live
,weblink" title="web.archive.org/web/20111117112612weblink">weblink
, 17 November 2011
, dmy-all
,

Heavy metals present in the clinker

The presence of heavy metals in the clinker arises both from the natural raw materials and from the use of recycled by-products or alternative fuels. The high pH prevailing in the cement porewater (12.5
year = 2000 ,
  • JOURNAL, van Oss, Hendrik G., Padovani, Amy C., Cement manufacture and the environment, Part I: Chemistry and Technology, Journal of Industrial Ecology, 6, 1, 89–105
year = 2002,
  • JOURNAL, van Oss, Hendrik G., Padovani, Amy C., Cement manufacture and the environment, Part II: Environmental challenges and opportunities, Journal of Industrial Ecology, 7, 1, 93–126
year = 2003,weblink 10.1.1.469.2404,
  • Friedrich W. Locher: Cement : Principles of production and use, Düsseldorf, 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, U.S., 2004, {{ISBN|0-89312-234-3}}
  • "Why cement emissions matter for climate change" Carbon Brief 2018
  • BOOK, Neville, A.M., 1996, Properties of concrete. Fourth and final edition standards, Pearson, Prentice Hall, 978-0-582-23070-5, 33837400
,
  • BOOK, Taylor, H.F.W., Cement chemistry, 1990, Academic Press, 978-0-12-683900-5, 475
,
  • JOURNAL, Ulm, Franz-Josef


, Roland J.-M. Pellenq, Akihiro Kushima, Rouzbeh Shahsavari, Krystyn J. Van Vliet, Markus J. Buehler, Sidney Yip, A realistic molecular model of cement hydrates, Proceedings of the National Academy of Sciences, 106, 38, 16102–16107
pmid = 19805265
, 2009
pmc=2739865,

External links

  • {{Commons category-inline|Cement}}
  • EB1911, Cement, 5, x,
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