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A cement is a binder, a substance used for construction that sets, hardens, and adheres to other
material Material is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, anything that has mass and t ...

material
s 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 Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
for masonry, or with
sand Sand is a granular material composed of finely divided rock (geology), rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer ...

sand
and
gravel Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
, produces
concrete Concrete is a composite material A composite material (also called a composition material or shortened to composite, which is the common name) is a material Material is a substance Substance may refer to: * Substance (Jainism), a ter ...

concrete
. Concrete is the most widely used material in existence and is behind only water as the planet's most-consumed resource. Cements used in construction are usually
inorganic In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they under ...
, often
lime Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...
or
calcium silicate Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and is sometimes formulated as 2CaO·SiO2. It is also referred to by the shortened trade name Cal-Sil or Calsil. It occurs naturally as the mineral larnite. ...
based, which can be characterized as non-hydraulic or hydraulic respectively, 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 Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
in the air. It is resistant to attack by chemicals after setting. Hydraulic cements (e.g.,
Portland cement Portland cement is the most common type of cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used ...

Portland cement
) set and become
adhesive Adhesive, also known as glue, cement, mucilage, or paste, is any non-metallic substance applied to one or both surfaces of two separate items that them together and resists their separation. The use of adhesives offers certain advantages over ...
due to a
chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...

chemical reaction
between the dry ingredients and water. The chemical reaction results in mineral
hydrate In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, m ...
s 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 was found by ancient Romans who used
volcanic ash Volcanic ash consists of fragments of rock, mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure ...
(
pozzolana Pozzolana or pozzuolana ( , ), also known as pozzolanic ash ( la, pulvis puteolanus), is a natural silica, siliceous or siliceous-Aluminium oxide, aluminous material which reacts with calcium hydroxide in the presence of water at room temperature ( ...
) with added lime (calcium oxide). The word "cement" can be traced back to the Ancient Roman term , 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 Hydraulics (from Greek language, Greek: Υδραυλική) is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the ...
, were later referred to as , , ''cäment'', and ''cement''. In modern times, organic polymers are sometimes used as cements in concrete. World production is about four billion tonnes per year, of which about half is made in China. If the cement industry were a country, it would be the third largest carbon dioxide emitter in the world with up to 2.8 billion tonnes, surpassed only by China and the United States. The initial
calcination Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment Thermal treatment is any ...
reaction in the production of cement is responsible for about 4% of global emissions. The overall process is responsible for about 8% of global emissions, as the
cement kiln Cement kilns are used for the pyroprocessing stage of manufacture of Portland cement, portland and other types of hydraulic cement, in which calcium carbonate reacts with silicon dioxide, silica-bearing minerals to form a mixture of calcium silicat ...
in which the reaction occurs is typically fired by coal or
petroleum coke Petroleum coke, abbreviated coke or petcoke, is a final carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up onl ...
due to the luminous flame required to heat the kiln by radiant heat transfer. As a result, the production of cement is a major contributor to
climate change Contemporary climate change includes both the global warming caused by humans, and its impacts on Earth's weather patterns. There have been previous periods of climate change, but the current changes are more rapid than any known even ...
.


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 cement setting and hardening involves hydration reactions and therefore requires water, while non-hydraulic cements only react with a gas and can directly set under air.


Hydraulic cement

By far the most common type of cement is hydraulic cement, which 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 notationCement chemist notation (CCN) was developed to simplify the formula In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowle ...
, being: :C3S:
Alite Alite is an impure form of tricalcium silicate, , sometimes formulated as ( in cement chemist notation), typically with 3-4% of substituent oxides. It is the major, and characteristic, phase in Portland cement. The name was given by Törnebohm in ...
(3CaO·SiO2); :C2S:
Belite Belite is an industrial mineral Industrial resources (minerals) are geological materials which are mined for their commercial value, which are not fuel (fuel minerals or mineral fuels) and are not sources of metals (metal A metal (from Ancien ...
(2CaO·SiO2); :C3A:
Tricalcium aluminate Tricalcium aluminate Ca3Al2O6, often formulated as 3CaO·Al2O3 to highlight the proportions of the oxides from which it is made, is the most basic of the calcium aluminates. It does not occur in nature, but is an important mineral phase in Portl ...
(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 Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction In materials science The interdisciplinary ...
(
firing Dismissal (also referred to as firing) is the termination of employment Termination of employment is an employee's departure from a job and the end of an employee's duration with an employer. Termination may be voluntary on the employee's part, o ...

firing
) process of clinker at high temperature in the
kiln , Wrecclesham Wrecclesham is a village on the southern outskirts of the large town of Farnham Farnham is a market town in Surrey, England, within the Borough of Waverley Borough Council, Waverley.OS Explorer map 145:Guildford and Farnham ...
. The chemistry of these reactions is not completely clear and is still the object of research. First, the
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
(calcium carbonate) is burned to remove its carbon, producing
lime Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...

lime
(calcium oxide) in what is known as a
calcination Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment Thermal treatment is any ...
reaction. This single chemical reaction is a major emitter of global
carbon dioxide emissions Greenhouse gas emissions from human activities strengthen the greenhouse effect, causing climate change. Most is carbon dioxide from burning fossil fuels: coal, petroleum, oil, and natural gas. The top contributors to greenhouse gas emissions, lar ...

carbon dioxide emissions
. :CaCO3 -> CaO + CO2 The lime reacts with silicon dioxide to produce dicalcium silicate and tricalcium silicate. :2CaO + SiO2 -> 2CaO.SiO2 :3CaO + SiO2 -> 3CaO.SiO2 The lime also reacts with aluminum oxide to form tricalcium aluminate. :3CaO + Al2O3 -> 3CaO.Al2O3 In the last step, calcium oxide, aluminum oxide, and ferric oxide react together to form cement. :4CaO + Al2O3 + Fe2O3 -> 4CaO.Al2O3.Fe2O3


Non-hydraulic cement

A less common form of cement is non-hydraulic cement, such as
slaked lime Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula calcium, Ca(Hydroxide, OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaking (ge ...
(
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms f ...

calcium oxide
mixed with water), hardens by
carbonation Carbonation is the chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matt ...
in contact with
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, which is present in the air (~ 412 vol. ppm ≃ 0.04 vol. %). First
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms f ...

calcium oxide
(lime) is produced from
calcium carbonate Calcium carbonate is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togethe ...

calcium carbonate
(
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
or
chalk Chalk is a soft, white, porous Porosity or void fraction is a measure of the (i.e. "empty") spaces in a , and is a of voids over the total volume, between 0 and 1, or as a between 0% and 100%. Strictly speaking, some tests measure the "acce ...

chalk
) by
calcination Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment Thermal treatment is any ...
at temperatures above 825 °C (1,517 °F) for about 10 hours at
atmospheric pressure Atmospheric pressure, also known as barometric pressure (after the barometer A barometer is a scientific instrument that is used to measure air pressure Atmospheric pressure, also known as barometric pressure (after the barometer), is the ...
: :CaCO3 -> CaO + CO2 The calcium oxide is then ''spent'' (slaked) mixing it with water to make slaked lime (
calcium hydroxide Calcium hydroxide (traditionally called slaked lime) is an inorganic compound with the chemical formula calcium, Ca(Hydroxide, OH)2. It is a colorless crystal or white powder and is produced when quicklime (calcium oxide) is mixed or slaking (ge ...

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 is slow, because the
partial pressure In a mixture of gases, each constituent gas has a partial pressure which is the notional pressure of that constituent gas if it alone occupied the entire volume of the original mixture at the same temperature. The total pressure of an ideal gas mix ...
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''.


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.


Alternatives to cement used in antiquity

Cement, chemically speaking, is a product that includes
lime Lime refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany * Austra ...

lime
as the primary binding ingredient, but is far from the first material used for cementation. The
Babylonia Babylonia () was an and based in central-southern which was part of Ancient Persia (present-day and ). A small -ruled state emerged in 1894 BCE, which contained the minor administrative town of . It was merely a small provincial town dur ...
ns and
Assyria Assyria (), also called the Assyrian Empire, was a Mesopotamia Mesopotamia ( grc, Μεσοποταμία ''Mesopotamíā''; ar, بِلَاد ٱلرَّافِدَيْن ; syc, ܐܪܡ ܢܗܪ̈ܝܢ, or , ) is a historical region of We ...

Assyria
ns used
bitumen Asphalt, also known as bitumen (, ), is a sticky, black, highly viscous The viscosity of a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or externa ...

bitumen
to bind together burnt brick or
alabaster Alabaster is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure fo ...

alabaster
slabs. In
Ancient Egypt Ancient Egypt was a civilization  A civilization (or civilisation) is a that is characterized by , , a form of government, and systems of communication (such as ). Civilizations are intimately associated with additional char ...

Ancient Egypt
, stone blocks were cemented together with a
mortar Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
made of
sand Sand is a granular material composed of finely divided rock (geology), rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer ...

sand
and roughly burnt
gypsum Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

gypsum
(CaSO4 · 2H2O), which often contained calcium carbonate (CaCO3).


Greeks and Romans

Lime (calcium oxide) was used on
Crete Crete ( el, Κρήτη, translit=, Modern Modern may refer to: History *Modern history Human history, also known as world history, is the description of humanity's past. It is informed by archaeology Archaeology or archeology ...

Crete
and by the
Ancient Greeks Ancient Greece ( el, Ἑλλάς, Hellás) was a civilization belonging to a period of History of Greece, Greek history from the Greek Dark Ages of the 12th–9th centuries BC to the end of Classical Antiquity, antiquity ( AD 600). This era was ...
. There is evidence that the Minoans of Crete used crushed potsherds as an artificial
pozzolan Pozzolans are a broad class of siliceous Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical phy ...
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 The pozzolanic activity is a measure for the degree of reaction over time or the reaction rate has a ''low'' reaction rate. This process is slow. The reaction rate or rate of reaction is the speed at which a chemical reaction A chemical reactio ...
), but such concrete was used by the
Ancient Macedonians The Macedonians ( el, Μακεδόνες, ''Makedónes'') were an ancient tribe that lived on the alluvial plain around the rivers Haliacmon and lower Vardar, Axios in the northeastern part of Geography of Greece#Mainland, mainland Greece. Es ...
, and three centuries later on a large scale by Roman engineers. The Greeks used from the island of
Thera Santorini ( el, Σαντορίνη, ), officially Thira (Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in S ...

Thera
as their pozzolan and the Romans used crushed
volcanic ash Volcanic ash consists of fragments of rock, mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure ...
(activated
aluminium silicate Aluminium silicate (or aluminum silicate) is a name commonly applied to chemical compounds which are derived from aluminium oxide Aluminium oxide is a chemical compound of aluminium Aluminium (aluminum in American English, American and ...
s) with lime. This mixture could set under water, increasing its resistance to corrosion like rust. The material was called ''pozzolana'' from the town of
Pozzuoli Pozzuoli (; ; ) is a city and ''comune'' of the Metropolitan City of Naples, in the Italy, Italian region of Campania. It is the main city of the Campi Flegrei, Phlegrean Peninsula. History Pozzuoli began as the Greek colony of ''Dicaearchia'' ...
, west of
Naples Naples (; it, Napoli ; nap, Napule ), from grc, Νεάπολις, Neápolis, lit=new city. is the regional capital of and the third-largest city of , after and , with a population of 967,069 within the city's administrative limits as of ...

Naples
where volcanic ash was extracted. 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 A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

dome
of the
Pantheon Pantheon may refer to: * Pantheon (religion), the set of gods belonging to a particular religion, mythology or tradition * Pantheon (mythical creature), a mythical or imaginary creature used in heraldry, particularly in Britain Computing *Pant ...

Pantheon
in Rome and the massive
Baths of Caracalla , native_name_lang = , alternate_name = it, Terme di Caracalla , image = File:Baths of Caracalla, facing Caldarium.jpg , image_size = 250px , alt = , caption = The baths as viewed from the south-west. The cald ...

Baths of Caracalla
are examples of ancient structures made from these concretes, many of which still stand. The vast system of
Roman aqueduct The Ancient Rome, Romans constructed Aqueduct (bridge), aqueducts throughout their Roman Republic, Republic and later Roman Empire, Empire, to bring water from outside sources into cities and towns. Aqueduct water supplied Thermae, public baths, ...

Roman aqueduct
s also made extensive use of hydraulic cement. Roman concrete was rarely used on the outside of buildings. The normal technique was to use brick facing material as the
formwork Placing a formwork component Formwork is temporary or permanent molds into which concrete File:Pantheon cupola.jpg, Interior of the Pantheon dome, seen from beneath. The concrete for the coffered dome was laid on moulds, mounted on temp ...
for an infill of
mortar Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
mixed with an aggregate of broken pieces of stone, brick,
potsherds This page is a glossary of archaeology Archaeology or archeology is the study of human activity through the recovery and analysis of material culture. Archaeology is often considered a branch of socio-cultural anthropology, but archaeologist ...
, recycled chunks of concrete, or other building rubble.


Middle Ages

Any preservation of this knowledge in literature from the
Middle Ages In the history of Europe The history of Europe concerns itself with the discovery and collection, the study, organization and presentation and the interpretation of past events and affairs of the people of Europe since the beginning of ...
is unknown, but medieval and some military engineers actively used hydraulic cement in structures such as
canal Canals are waterways channels Channel, channels, channeling, etc., may refer to: Geography * Channel (geography), in physical geography, a landform consisting of the outline (banks) of the path of a narrow body of water. Australia * ...

canal
s, fortresses,
harbor A harbor (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. Currently, American Engl ...

harbor
s, and .Sismondo, Sergio (2009)
''An Introduction to Science and Technology Studies''
. John Wiley and Sons, 2nd edition, p. 142. .
Mukerji, Chandra (2009)
''Impossible engineering: technology and territoriality on the Canal du Midi''
. Princeton University Press, p. 121, .
A mixture of lime mortar and aggregate with brick or stone facing material was used in the
Eastern Roman Empire The Byzantine Empire, also referred to as the Eastern Roman Empire, or Byzantium, was the continuation of the Roman Empire The Roman Empire ( la, Imperium Rōmānum ; grc-gre, Βασιλεία τῶν Ῥωμαίων, Basileía tôn ...

Eastern Roman Empire
as well as in the West into the
Gothic period (''ca.'' 1145). These architectural statues are the earliest Gothic sculptures and were a revolution in style and the model for a generation of sculptors. Gothic art was a style of medieval art that developed in Northern France out of Romanesque a ...
. The German
Rhineland The Rhineland (german: Rheinland; french: Rhénanie; nl, Rijnland; ksh, Rhingland; Latinised name: ''Rhenania'') is the name used for a loosely defined area of Western Germany along the Rhine, chiefly Middle Rhine, its middle section. Term ...

Rhineland
continued to use hydraulic mortar throughout the Middle Ages, having local pozzolana deposits called
trassTrass is the local name of a volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's sur ...
.


16th century

Tabby A tabby is any domestic cat The cat (''Felis catus'') is a domestic Domestic may refer to: In the home * Anything relating to the human home A home, or domicile, is a space used as a permanent or semi-permanent residence fo ...
is a
building material Building material is material used for construction. Many naturally occurring substances, such as clay, rocks, sand, and wood, even twigs and leaves, have been used to construct buildings. Apart from naturally occurring materials, many man-mad ...

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"
, ''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 John Smeaton (8 June 1724 – 28 October 1792) was a British civil engineer A civil engineer is a person who practices civil engineering Civil engineering is a Regulation and licensure in engineering, professional engineering discip ...

John Smeaton
made an important contribution to the development of cements while planning the construction of the third
Eddystone Lighthouse The Eddystone Lighthouse is a lighthouse that is located on the dangerous Eddystone Rocks, south of Rame Head in Cornwall, England. The rocks are submerged below the surface of the sea and are composed of Precambrian gneiss. View at 1:50000 s ...

Eddystone Lighthouse
(1755–59) in the
English Channel The English Channel,, "The Sleeve"; nrf, la Maunche, "The Sleeve" (Cotentinais Cotentinais is the dialect The term dialect (from Latin , , from the Ancient Greek word , , "discourse", from , , "through" and , , "I speak") is used in two ...

English Channel
now known as
Smeaton's Tower Smeaton's Tower is a memorial to civil engineer John Smeaton, designer of the third and most notable Eddystone Lighthouse#Smeaton.27s lighthouse, Eddystone Lighthouse. A major step forward in lighthouse design, Smeaton's structure was in use from ...

Smeaton's Tower
. He needed a hydraulic mortar that would set and develop some strength in the twelve-hour period between successive high
Tide Tides are the rise and fall of sea level Mean sea level (MSL) (often shortened to sea level) is an average In colloquial, ordinary language, an average is a single number taken as representative of a list of numbers, usually the sum of ...

Tide
s. He performed experiments with combinations of different
Limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

Limestone
s and additives including trass and
pozzolana Pozzolana or pozzuolana ( , ), also known as pozzolanic ash ( la, pulvis puteolanus), is a natural silica, siliceous or siliceous-Aluminium oxide, aluminous material which reacts with calcium hydroxide in the presence of water at room temperature ( ...
sBlezard, 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.
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 Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
content of the
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
used to make it. Smeaton was a civil engineer by profession, and took the idea no further. In the of the United States,
tabby A tabby is any domestic cat The cat (''Felis catus'') is a domestic Domestic may refer to: In the home * Anything relating to the human home A home, or domicile, is a space used as a permanent or semi-permanent residence fo ...
relying on the oyster-shell
midden A midden (also kitchen midden or shell heap) is an old dump for domestic waste which may consist of animal bone A bone is a Stiffness, rigid tissue (anatomy), tissue that constitutes part of the skeleton in most vertebrate animals. Bones ...
s 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 Stucco or render is a construction Construction is a general term meaning the and to form , , or ,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and c ...
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 Roman cement is a substance developed by James Parker in the 1780s, being patented in 1796. The name is misleading as it is nothing like any material used by the Romans, but was a "natural cement Cement block construction examples from the M ...
". 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 Concretions with lens shape from island in Vltava river, Prague, Czech Republic. File:Marlstone aggregate concretion (Sault Ste. Marie, Michigan, USA.JPG, Marlstone aggregate concretion, Sault Ste. Marie, Michigan. A concretion is a hard, comp ...
nodules that are found in certain clay deposits, and that contain both
clay minerals Clay minerals are hydrous aluminium Aluminium (aluminum in American English, American and Canadian English) is a chemical element with the Symbol (chemistry), symbol Al and atomic number 13. Aluminium has a density lower than thos ...
and
calcium carbonate Calcium carbonate is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togethe ...

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 Hydraulic lime (HL) is a general term for calcium oxide Calcium Calcium is a chemical element with the Symbol (chemistry), symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride ...
cements of
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
and
chalk Chalk is a soft, white, porous Porosity or void fraction is a measure of the (i.e. "empty") spaces in a , and is a of voids over the total volume, between 0 and 1, or as a between 0% and 100%. Strictly speaking, some tests measure the "acce ...

chalk
. Roman cement quickly became popular but was largely replaced by
Portland cement Portland cement is the most common type of cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used ...

Portland cement
in the 1850s.


19th century

Apparently unaware of work, the same principle was identified by Frenchman
Louis Vicat 250px, Portrait of Louis Vicat young. Louis Vicat (31 March 1786, Nevers Nevers ( , ; la, Noviodunum, later ''Nevirnum'' and ''Nebirnum'') is the prefecture of the Nièvre Departments of France, department in the Bourgogne-Franche-Comté Regi ...
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 considered the "principal forerunner" of Portland cement and "...Edgar Dobbs of
Southwark Southwark ( ) is a district of Central London situated on the south bank of the River Thames, forming the north-western part of the wider modern London Borough of Southwark. The district, which is the oldest part of South London, developed ...

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 Saint Petersburg, 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.
Portland cement Portland cement is the most common type of cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used ...

Portland cement
, the most common type of cement in general use around the world as a basic ingredient of concrete,
mortar Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
,
stucco Stucco or render is a construction Construction is a general term meaning the and to form , , or ,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and c ...
, and non-speciality grout, was developed in England in the mid 19th century, and usually originates from
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
. James Frost (cement maker), James Frost 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 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 silicate Calcium silicate is the chemical compound Ca2SiO4, also known as calcium orthosilicate and is sometimes formulated as 2CaO·SiO2. It is also referred to by the shortened trade name Cal-Sil or Calsil. It occurs naturally as the mineral larnite. ...
s 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 wheel, 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. Setting time and "early strength" are important characteristics of cements. Hydraulic limes, "natural" cements, and "artificial" cements all rely on their belite (2 CaO · SiO2, abbreviated as C2S) content for Strength of materials, strength development. Belite develops strength slowly. Because they were burned at temperatures below , they contained no alite (3 CaO · SiO2, abbreviated as C3S), 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 analysis 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 Clinker nodules produced by sintering Sintering or frittage is the process of compacting and forming a solid mass of material by heat or pressure without melting it to the point of liquefaction In materials science The interdisciplinary ...
the mix in the
kiln , Wrecclesham Wrecclesham is a village on the southern outskirts of the large town of Farnham Farnham is a market town in Surrey, England, within the Borough of Waverley Borough Council, Waverley.OS Explorer map 145:Guildford and Farnham ...
. In the US the first large-scale use of cement was Rosendale cement, a natural cement mined from a massive deposit of Dolomite (rock), dolomite 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, United States Capitol, Capitol Building, Brooklyn Bridge) and lining water pipes."Natural Cement Comes Back"
, October 1941, ''Popular Science''
Sorel cement, or magnesia-based cement, was patented in 1867 by the Frenchman Stanislas Sorel.Stanislas Sorel (1867).
Sur un nouveau ciment magnésien
. ''Comptes rendus hebdomadaires des séances de l'Académie des sciences'', volume 65, pages 102–104.
It was stronger than Portland cement but its poor water resistance (leaching) and corrosive properties (pitting corrosion due to the presence of leachable chloride anions and the low pH (8.5–9.5) of its pore water) limited its use as reinforced concrete for building construction. The next development in the manufacture of Portland cement was the introduction of the rotary kiln. It produced a clinker (cement), clinker mixture that was both stronger, due to increased alite (C3S) formation at the higher temperature it achieved (1450 °C), and more homogeneous. Because raw material is constantly fed into a rotary kiln, it allowed a continuous production, continuous manufacturing process to replace lower capacity batch production processes.


20th century

Calcium aluminate cements were patented in 1908 in France by Jules Bied for better resistance to sulfates. Also in 1908, Thomas Edison experimented with pre-cast concrete in houses in Union, N.J. 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. 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.


Modern cements

Modern hydraulic development began with the start of the Industrial Revolution (around 1800), driven by three main needs: * Hydraulic cement render (
stucco Stucco or render is a construction Construction is a general term meaning the and to form , , or ,"Construction" def. 1.a. 1.b. and 1.c. ''Oxford English Dictionary'' Second Edition on CD-ROM (v. 4.0) Oxford University Press 2009 and c ...
) 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 Modern cements are often
Portland cement Portland cement is the most common type of cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used ...

Portland cement
or Portland cement blends, but industry also uses other cements.


Portland cement

Portland cement, a form of hydraulic cement, is by far the most common type of cement in general use around the world. This cement is made by heating
limestone Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
(calcium carbonate) with other materials (such as
clay Clay is a type of fine-grained natural soil Surface-water- gley developed in glacial till, Northern Ireland.">Northern_Ireland.html" ;"title="glacial till, Northern Ireland">glacial till, Northern Ireland. Soil is a mixture of organic m ...

clay
) to in a kiln, in a process known as
calcination Calcination refers to heating a solid to high temperatures in absence of air or oxygen, generally for the purpose of removing impurities or volatile substances. However, calcination is also used to mean a thermal treatment Thermal treatment is any ...
that liberates a molecule of
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
from the calcium carbonate to form
calcium oxide Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms f ...

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 Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

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 Mortar may refer to: * Mortar (weapon), an indirect-fire infantry weapon * Mortar (masonry), a material used to fill the gaps between blocks and bind them together * Mortar and pestle, a tool pair used to crush or grind * Mortar, Bihar, a village in ...
, 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 Gravel is a loose aggregation of rock fragments. Gravel occurs naturally throughout the world as a result of sedimentary and erosive geologic processes; it is also produced in large quantities commercially as crushed stone. Gravel is classifie ...

gravel
and
sand Sand is a granular material composed of finely divided rock (geology), rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer ...

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, white.


Portland cement blend

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. 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. 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. Portland pozzolan cement includes fly ash cement, since fly ash is a
pozzolan Pozzolans are a broad class of siliceous Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical phy ...
, but also includes cements made from other natural or artificial pozzolans. In countries where
volcanic ash Volcanic ash consists of fragments of rock, mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure ...
es 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. Masonry cements are used for preparing bricklaying mortar (masonry), 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 North America 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.


Other cements

''Pozzolan-lime cements'' are mixtures of ground pozzolanic ash, pozzolan and Agricultural lime, lime. These are the cements the Romans used, and are present in surviving Roman structures like the
Pantheon Pantheon may refer to: * Pantheon (religion), the set of gods belonging to a particular religion, mythology or tradition * Pantheon (mythical creature), a mythical or imaginary creature used in heraldry, particularly in Britain Computing *Pant ...

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 Gypsum is a soft sulfate mineral The sulfate minerals are a class of mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with ...

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 Limestone is a common type of carbonate In chemistry, a carbonate is a salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of Salt (chemistry), salts; salt in its na ...

limestone
and bauxite. The active ingredients are monocalcium aluminate CaAl2O4 (CaO · Al2O3 or CA in
cement chemist notationCement chemist notation (CCN) was developed to simplify the formula In science Science (from the Latin word ''scientia'', meaning "knowledge") is a systematic enterprise that Scientific method, builds and Taxonomy (general), organizes knowle ...
, 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 in Cement chemist notation, 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. 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 minerals, 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. Sorel cement, ''Sorel Cement'' is a hard, durable cement made by combining magnesium oxide and a magnesium chloride solution ''Fiber mesh cement'' or Fiber-reinforced concrete, fiber reinforced concrete is cement that is made up of fibrous materials like synthetic fibers, glass fibers, natural fibers, and steel fibers. This type of mesh is distributed evenly throughout the wet concrete. The purpose of fiber mesh is to reduce water loss from the concrete as well as enhance its structural integrity. When used in plasters, fiber mesh increases cohesiveness, tensile strength, impact resistance, and to reduce shrinkage; ultimately, the main purpose of these combined properties is to reduce cracking.


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 °C is recommended, and no more than 30 °C. The concrete at young age must be protected against water evaporation due to direct insolation, elevated temperature, low relative humidity and wind. The ''interfacial transition zone'' (ITZ) is a region of the cement paste around the Aggregate (composite), aggregate particles in
concrete Concrete is a composite material A composite material (also called a composition material or shortened to composite, which is the common name) is a material Material is a substance Substance may refer to: * Substance (Jainism), a ter ...

concrete
. In the zone,a gradual transition in the Microstructure, microstructural features occurs. This zone can be up to 35 micrometer wide. Other studies have shown that the width can be up to 50 micrometer. The average content of unreacted clinker phase decreases and porosity decreases towards the aggregate surface. Similarly, the content of ettringite increases in ITZ.


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 causticity, 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 contact dermatitis, allergic dermatitis. Reducing agents such as ferrous sulfate (FeSO4) are often added to cement to convert the carcinogenic hexavalent Chromate ion, chromate (CrO42−) into trivalent chromium (Cr3+), a less toxic chemical species. Cement users need also to wear appropriate gloves and protective clothing.


Cement industry in the world

In 2010, the world production of hydraulic cement was Orders of magnitude (mass)#1012 to 1017 kg, . The top three producers were Cement industry in China, China with 1,800, India with 220, and Cement industry in the United States, USA with 63.5 million tonnes for a total of over half the world total by the world's three most populated states. 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. Over 2011 and 2012, global consumption continued to climb, rising to 3585 Mt in 2011 and 3736 Mt in 2012, while annual Economic growth, 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. 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. 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.


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." In 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
, ''Netherlands Environmental Assessment Agency, 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." 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


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 quarry, 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

Carbon concentration in cement spans from ≈5% in cement structures to ≈8% in the case of roads in cement. Cement manufacturing releases in the atmosphere both directly when
calcium carbonate Calcium carbonate is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held togethe ...

calcium carbonate
is heated, producing lime (mineral), lime and
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, and also indirectly through the use of energy if its production involves the emission of CO2. The cement industry produces about 10% of global Anthropogenic greenhouse gas, human-made CO2 emissions, of which 60% is from the chemical process, and 40% from burning fuel. A Chatham House study from 2018 estimates that the 4 billion tonnes of cement produced annually account for 8% of worldwide CO2 emissions. 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. 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. 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. Newly developed cement types from Novacem and Eco-cement can absorb
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
from ambient air during hardening. carbon capture and storage is about to be trialed, but its financial viability is uncertain.


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 metal (chemistry), heavy metals, e.g. Thallium#Thallium pollution, thallium, cadmium and mercury (element), 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), Sphalerite, 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."


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 < 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 ion, 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 Gigajoule, 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. 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. Clinker is manufactured by heating raw materials inside the main burner of a kiln to a temperature of 1,450 °C. The flame reaches temperatures of 1,800 °C. The material remains at 1,200 °C for 12–15 seconds at 1,800 °C (and/ or?) 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. The 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 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.


Ecological cement

Ecological 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 ecological cement are being researched with the goal to reduce, or even eliminate, the production and release of damaging pollutants and greenhouse gasses, particularly CO2. 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
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 Sand is a granular material composed of finely divided rock (geology), rock and mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer ...

sand
and urine, can produce mortar blocks with a compressive strength 70% of that of conventional construction materials. An overview of climate-friendly methods for cement production can be found here.


See also

* BET theory * Cement chemist notation * Cement render * Cenocell * Energetically modified cement (EMC) * Fly ash * Geopolymer cement *
Portland cement Portland cement is the most common type of cement A cement is a binder (material), binder, a substance used for construction that solidification, sets, hardens, and adheres to other materials to bind them together. Cement is seldom used ...

Portland cement
* Rosendale cement * Tiocem * Void (composites)


References


Further reading

* * * * * Friedrich W. Locher: ''Cement : Principles of production and use'', Düsseldorf, Germany: Verlag Bau + Technik GmbH, 2006, * Javed I. Bhatty, F. MacGregor Miller, Steven H. Kosmatka; editors: ''Innovations in Portland Cement Manufacturing'', SP400, Portland Cement Association, Skokie, Illinois, U.S., 2004,
"Why cement emissions matter for climate change"
''Carbon Brief'' 2018 * * *


External links

* * {{Authority control Cement, Concrete Building materials