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| [[File:Portland Cement Bags.jpg|thumb|right|225px|A pallet with Portland cement]]
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| [[File:BlueCircleSouthernCementBerrimaNSW.JPG|thumb|right|225px|[[Blue Circle]] Southern Cement works near [[Berrima, New South Wales|Berrima]], [[New South Wales]], [[Australia]].]]
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| '''Portland cement''' (often referred to as '''OPC''', from {{italics correction|''Ordinary Portland Cement''}}) is the most common type of [[cement]] in general use around the world, used as a basic ingredient of [[concrete]], [[mortar (masonry)|mortar]], [[stucco]], and most non-specialty [[grout]]. It usually originates from [[limestone]]. It is a fine [[powder (substance)|powder]] produced by [[wikt:grinding|grinding]] Portland cement [[Clinker (cement)|clinker]] (more than 90%), a limited amount of [[calcium sulfate]] (which controls the set time) and up to 5% minor constituents as allowed by various standards such as the [[European Committee for Standardization|European Standard]] EN 197-1:
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| {{bquote|Portland cement clinker is a [[hydraulic lime|hydraulic]] material which shall consist of at least two-thirds by mass of [[calcium silicate]]s [[alite|(3 CaO·SiO<sub>2</sub>]] and [[belite|2 CaO·SiO<sub>2</sub>)]], the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of [[calcium oxide|CaO]] to [[silicon dioxide|SiO<sub>2</sub>]] shall not be less than 2.0. The magnesium oxide content ([[magnesium oxide|MgO]]) shall not exceed 5.0% by mass. }}(The last two requirements were already set out in the [[German Standard]], issued in 1909).
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| [[ASTM International|ASTM]] [http://www.astm.org/Standards/C150.htm C150] defines Portland cement as "hydraulic cement (cement that not only hardens by reacting with water but also forms a water-resistant product) produced by pulverizing clinkers consisting essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition." Clinkers are nodules (diameters, 0.2–1.0 inch [5–25 mm]) of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperature. The low cost and widespread availability of the limestone, shales, and other naturally occurring materials make Portland cement one of the lowest-cost materials widely used over the last century throughout the world. Concrete is one of the most versatile construction materials available in the world.
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| Portland cement clinker is made by heating, in a [[Cement kiln|kiln]], a homogeneous mixture of raw materials to a [[calcining]] temperature, which is about 1450°C for modern cements. The aluminium oxide and iron oxide are present as a [[Flux (metallurgy)|flux]] and contribute little to the strength. For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of [[tricalcium aluminate]] (3 CaO·Al<sub>2</sub>O<sub>3</sub>) formed. The major raw material for the clinker-making is usually [[limestone]] (CaCO<sub>3</sub>) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO<sub>2</sub> is used. The CaCO<sub>3</sub> content of these limestones can be as low as 80%. Secondary raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the materials used are [[clay]], [[shale]], [[sand]], [[iron ore]], [[bauxite]], [[fly ash]], and [[slag]]. When a [[cement kiln]] is fired by coal, the ash of the coal acts as a secondary raw material.
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| ==History==
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| Portland cement was developed from natural cements made in [[United Kingdom|Britain]] in the early part of the nineteenth century, and its name is derived from its similarity to [[Portland stone]], a type of building stone that was quarried on the [[Isle of Portland]] in [[Dorset]], England.<ref name="miljö">{{cite book| coauthors= Gillberg, B. Fagerlund, G. Jönsson, Å. Tillman, A-M.|title= Betong och miljö|trans_title= Concrete and environment|year= 1999|publisher= AB Svensk Byggtjenst|location=Stockholm|language=Swedish|isbn=91-7332-906-1}}</ref>
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| [[Joseph Aspdin]], a British [[bricklayer]] from Leeds, is considered to be the originator of Portland cement. A process for the manufacture of Portland cement was patented in 1824.<ref name="miljö" /> This cement was an artificial cement similar in properties to the material known as "[[Roman cement]]", which had been patented in 1796 by James Parker. Aspdin's process was similar to a process patented in 1822 and used since 1811 by [[James Frost (cement maker)|James Frost]] who called his cement "British cement". The name "Portland cement" is also recorded in a directory published in 1823 being associated with a William Lockwood, Dave Stewart, and possibly others.<ref name=Francis>{{cite book |last1= Francis|first1=A.J. |title= The Cement Industry 1796–1914: A History |year=1977 |publisher= |location= |isbn= |oclc= |doi= |id= |page= |pages=}}</ref>
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| James Frost is reported to have erected a manufactory for making of an artificial cement in 1826.<ref name=Reid>{{cite book |last1= Reid |first1= Henry |title= A practical treatise on the manufacture of Portland Cement |year=1868 |publisher= E. & F.N. Spon |location= London |pages=}}</ref> In 1843, Aspdin's son [[William Aspdin|William]] improved their cement, which was initially called "Patent Portland cement", although he had no patent. In 1848, William Aspdin further improved his cement; in 1853, he moved to Germany where he was involved in cement making.<ref name=Francis/> William Aspdin made what could be called meso-Portland cement (a mix of Portland cement and hydraulic lime).<ref>{{cite journal |last=Rayment |first=D. L. |year=1986 |title=The electron microprobe analysis of the C-S-H phases in a 136 year old cement paste |journal=Cement and Concrete Research |volume=16 |issue=3 |pages=341–344 |doi=10.1016/0008-8846(86)90109-2 }}</ref> John Grant of the Metropolitan Board of Works in 1859 set out requirements for cement to be used in the London sewer project. This became a specification for Portland cement. The Hoffman "endless" kiln which gave "perfect control over combustion" was tested in 1860 and showed the process produced a better grade of cement. This cement was made at the Portland Cementfabrik Stern at Stettin, which was the first to utilize a Hoffman kiln.<ref>{{cite book |last1= Reid|first1=Henry |title= The Science and Art of the Manufacture of Portland Cement with observations on some of its constructive Applications |year=1877 |publisher= E&F.N. Spon |location=London }}</ref> It is thought that the first modern Portland cement was made there. The Association of German Cement Manufacturers issued a standard on Portland cement in 1878.<ref>{{cite web |url=http://www.vdz-online.de/2259.html?&L=1 |title=125 Years of Research for Quality and Progress |publisher=German Cement Works' Association |accessdate=2012-09-30}}</ref>
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| ==Cement grinding==
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| {{Main|Cement mill}}
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| [[Image:LDCementFM10MW.jpg|thumb|300px|right|A 10 MW cement mill, producing cement at 270 tonnes per hour]]
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| In order to achieve the desired setting qualities in the finished product, a quantity (2–8%, but typically 5%) of calcium sulfate (usually [[gypsum]] or [[anhydrite]]) is added to the clinker and the mixture is finely ground to form the finished cement powder. This is achieved in a [[cement mill]]. The grinding process is controlled to obtain a powder with a broad [[particle size distribution|particle size range]], in which typically 15% by mass consists of particles below 5 μm diameter, and 5% of particles above 45 μm. The measure of fineness usually used is the "[[air permeability specific surface|specific surface area]]", which is the total particle surface area of a unit mass of cement. The rate of initial reaction (up to 24 hours) of the cement on addition of water is [[Proportionality_(mathematics)#Direct_proportionality|directly proportional]] to the specific surface area. Typical values are 320–380 m<sup>2</sup>·kg<sup>−1</sup> for general purpose cements, and 450–650 m<sup>2</sup>·kg<sup>−1</sup> for "rapid hardening" cements. The cement is conveyed by belt or powder pump to a silo for storage. Cement plants normally have sufficient silo space for 1–20 weeks production, depending upon local demand cycles. The cement is delivered to end-users either in bags or as bulk powder blown from a pressure vehicle into the customer's silo. In industrial countries, 80% or more of cement is delivered in bulk.
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| {| class="wikitable" border="1"
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| |+Typical constituents of Portland clinker plus gypsum<br /><small>[[Cement chemists notation]] under CCN.</small>
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| !Clinker
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| !CCN
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| !Mass %
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| |-
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| |[[alite|Tricalcium silicate]] (CaO)<sub>3</sub> · SiO<sub>2</sub>||C<sub>3</sub>S ||45–75%
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| |[[belite|Dicalcium silicate]] (CaO)<sub>2</sub> · SiO<sub>2</sub>||C<sub>2</sub>S|| 7–32%
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| |-
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| |[[Tricalcium aluminate]] (CaO)<sub>3</sub> · Al<sub>2</sub>O<sub>3</sub>||C<sub>3</sub>A|| 0–13%
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| |[[Calcium Aluminoferrite|Tetracalcium aluminoferrite]] (CaO)<sub>4</sub> · Al<sub>2</sub>O<sub>3</sub> · Fe<sub>2</sub>O<sub>3</sub>||C<sub>4</sub>AF|| 0–18%
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| |[[Gypsum]] CaSO<sub>4</sub> · 2 H<sub>2</sub>O || || 2–10%
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| |}
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| {| class="wikitable" border="1"
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| |+Typical constituents of Portland cement<br /><small>[[Cement chemists notation]] under CCN.</small>
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| !Cement
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| !CCN
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| !Mass %
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| | Calcium oxide, CaO||C||61–67%
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| |Silicon dioxide, SiO<sub>2</sub>||S|| 19–23%
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| |Aluminum oxide, Al<sub>2</sub>O<sub>3</sub>||A|| 2.5–6%
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| |-
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| |Ferric oxide, Fe<sub>2</sub>O<sub>3</sub>||F|| 0–6%
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| |-
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| |Sulfate || <math>\bar{\mathsf{S}}</math> ||1.5–4.5%
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| |}
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| ==Setting and hardening==
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| Cement sets when mixed with water by way of a complex series of chemical reactions still only partly understood. The different constituents slowly crystallise and the interlocking of their crystals gives cement its strength. [[Carbon dioxide]] is slowly absorbed to convert the [[portlandite]] (Ca(OH)<sub>2</sub>) into insoluble [[calcium carbonate]]. After the initial setting, immersion in warm water will speed up setting. [[Gypsum]] is added as an inhibitor to prevent flash setting.
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| ==Use==
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| {{Unreferenced section|date=January 2010}}
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| [[Image:Grosvenor estate, Westminster, London.jpg|thumb|250px|right|Decorative use of Portland cement panels on London’s [[Grosvenor estate]]<ref>[http://housingprototypes.org/project?File_No=GB017 Housing Prototypes: Page Street<!-- Bot generated title -->]</ref>
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| ]]
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| The most common use for Portland cement is in the production of concrete. [[Concrete]] is a composite material consisting of [[Construction aggregate|aggregate]] ([[gravel]] and [[sand]]), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Users may be involved in the factory production of pre-cast units, such as panels, beams, [[road furniture]], or may make cast-''in situ'' concrete such as building superstructures, [[road]]s, [[dam]]s. These may be supplied with concrete mixed on site, or may be provided with "[[ready-mixed]]" concrete made at permanent mixing sites. Portland cement is also used in [[Mortar (masonry)|mortar]]s (with sand and water only) for [[plaster]]s and screeds, and in [[grout]]s (cement/water mixes squeezed into gaps to consolidate foundations, road-beds, etc.).
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| When water is mixed with Portland cement, the product sets in a few hours and hardens over a period of weeks. These processes can vary widely depending upon the mix used and the conditions of [[curing]] of the product, but a typical concrete sets in about 6 hours and develops a [[compressive strength]] of 8 MPa in 24 hours. The strength rises to 15 MPa at 3 days, 23 MPa at 1 week, 35 MPa at 4 weeks and 41 MPa at 3 months. In principle, the strength continues to rise slowly as long as water is available for continued hydration, but concrete is usually allowed to dry out after a few weeks and this causes strength growth to stop.
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| ==Types==
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| {{Unreferenced section|date=January 2010}}
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| ===General===
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| There are different standards for classification of Portland cement. The two major standards are the [[ASTM International|ASTM]] C150 used primarily in the USA and European EN 197. EN 197 cement types CEM I, II, III, IV, and V do not correspond to the similarly named cement types in ASTM C150.
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| ===ASTM C150===
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| There are five types of Portland cements with variations of the first three according to [[ASTM]] C150.
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| '''Type I''' Portland cement is known as common or general purpose cement. It is generally assumed unless another type is specified. It is commonly used for general construction especially when making precast and precast-prestressed concrete that is not to be in contact with soils or ground water. The typical compound compositions of this type are:
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| 55% (C<sub>3</sub>S), 19% (C<sub>2</sub>S), 10% (C<sub>3</sub>A), 7% (C<sub>4</sub>AF), 2.8% MgO, 2.9% (SO<sub>3</sub>), 1.0% [[Loss on ignition|Ignition loss]], and 1.0% free CaO.
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| A limitation on the composition is that the (C<sub>3</sub>A) shall not exceed fifteen percent.
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| '''Type II''' gives off less heat during hydration. This type of cement costs about the same as Type I. Its typical compound composition is:
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| 51% (C<sub>3</sub>S), 24% (C<sub>2</sub>S), 6% (C<sub>3</sub>A), 11% (C<sub>4</sub>AF), 2.9% MgO, 2.5% (SO<sub>3</sub>), 0.8% Ignition loss, and 1.0% free CaO.
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| A limitation on the composition is that the (C<sub>3</sub>A) shall not exceed eight percent which reduces its vulnerability to sulfates. This type is for general construction that is exposed to moderate sulfate attack and is meant for use when concrete is in contact with soils and ground water especially in the western United States due to the high sulfur content of the soil. Because of similar price to that of Type I, Type II is much used as a general purpose cement, and the majority of Portland cement sold in North America meets this specification.
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| Note: Cement meeting (among others) the specifications for types I and II has become commonly available on the world market.
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| '''Type III''' has relatively high early strength. Its typical compound composition is:
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| 57% (C<sub>3</sub>S), 19% (C<sub>2</sub>S), 10% (C<sub>3</sub>A), 7% (C<sub>4</sub>AF), 3.0% MgO, 3.1% (SO<sub>3</sub>), 0.9% Ignition loss, and 1.3% free CaO.
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| This cement is similar to Type I, but ground finer. Some manufacturers make a separate clinker with higher C<sub>3</sub>S and/or C<sub>3</sub>A content, but this is increasingly rare, and the general purpose clinker is usually used, ground to a [[specific surface area|specific surface]] typically 50–80% higher. The gypsum level may also be increased a small amount. This gives the concrete using this type of cement a three day compressive strength equal to the seven day compressive strength of types I and II. Its seven day compressive strength is almost equal to types I and II 28 day compressive strengths. The only downside is that the six month strength of type III is the same or slightly less than that of types I and II. Therefore the long-term strength is sacrificed a little. It is usually used for precast concrete manufacture, where high 1-day strength allows fast turnover of molds. It may also be used in emergency construction and repairs and construction of machine bases and gate installations.
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| '''Type IV''' Portland cement is generally known for its low heat of hydration. Its typical compound composition is:
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| 28% (C<sub>3</sub>S), 49% (C<sub>2</sub>S), 4% (C<sub>3</sub>A), 12% (C<sub>4</sub>AF), 1.8% MgO, 1.9% (SO<sub>3</sub>), 0.9% Ignition loss, and 0.8% free CaO.
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| The percentages of (C<sub>2</sub>S) and (C<sub>4</sub>AF) are relatively high and (C<sub>3</sub>S) and (C<sub>3</sub>A) are relatively low. A limitation on this type is that the maximum percentage of (C<sub>3</sub>A) is seven, and the maximum percentage of (C<sub>3</sub>S) is thirty-five. This causes the heat given off by the [[hydration reaction]] to develop at a slower rate. However, as a consequence the strength of the [[concrete]] develops slowly. After one or two years the strength is higher than the other types after full curing. This cement is used for very large concrete structures, such as dams, which have a low surface to volume ratio. This type of cement is generally not stocked by manufacturers but some might consider a large special order. This type of cement has not been made for many years, because Portland-pozzolan cements and [[ground granulated blast furnace slag]] addition offer a cheaper and more reliable alternative.
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| '''Type V''' is used where sulfate resistance is important. Its typical compound composition is:
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| 38% (C<sub>3</sub>S), 43% (C<sub>2</sub>S), 4% (C<sub>3</sub>A), 9% (C<sub>4</sub>AF), 1.9% MgO, 1.8% (SO<sub>3</sub>), 0.9% Ignition loss, and 0.8% free CaO.
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| This cement has a very low (C<sub>3</sub>A) composition which accounts for its high sulfate resistance. The maximum content of (C<sub>3</sub>A) allowed is five percent for Type V Portland cement. Another limitation is that the (C<sub>4</sub>AF) + 2(C<sub>3</sub>A) composition cannot exceed twenty percent. This type is used in concrete that is to be exposed to [[alkali]] soil and ground water [[sulfates]] which react with (C<sub>3</sub>A) causing disruptive expansion. It is unavailable in many places although its use is common in the western United States and Canada. As with Type IV, Type V Portland cement has mainly been supplanted by the use of ordinary cement with added ground granulated blast furnace slag or tertiary blended cements containing slag and fly ash.
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| '''Types Ia, IIa, and IIIa''' have the same composition as types I, II, and III. The only difference is that in Ia, IIa, and IIIa an air-entraining agent is ground into the mix. The air-entrainment must meet the minimum and maximum optional specification found in the ASTM manual. These types are only available in the eastern United States and Canada but can only be found on a limited basis. They are a poor approach to air-entrainment which improves resistance to freezing under low temperatures.
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| '''Types II(MH) and II(MH)a''' have a similar composition as types II and IIa but with a mild heat.
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| ===EN 197===
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| [[European Committee for Standardization|EN]] 197-1 defines 5 classes of common cement that comprise Portland cement as a main constituent. These classes differ from the ASTM classes.
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| {|cellspacing="5"
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| |I || Portland cement || Comprising Portland cement and up to 5% of minor additional constituents
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| |-
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| |II || Portland-composite cement || Portland cement and up to 35% of other single constituents
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| |-
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| |III || Blastfurnace cement || Portland cement and higher percentages of blastfurnace slag
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| |-
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| |IV || Pozzolanic cement || Portland cement and up to 55% of pozzolanic constituents(volcanic ash)
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| |-
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| |V || Composite cement || Portland cement, blastfurnace slag or fly ash and pozzolana
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| |}
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| Constituents that are permitted in Portland-composite cements are artificial pozzolans (blastfurnace slag, silica fume, and fly ashes) or natural pozzolans (siliceous or siliceous aluminous materials such as volcanic ash glasses, calcined clays and shale).
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| ===White Portland cement===
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| {{Main|White Portland cement}}
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| White Portland cement or white ordinary Portland cement (WOPC) is similar to ordinary, gray Portland cement in all respects except for its high degree of whiteness. Obtaining this color requires some modification to the method of manufacture; because of this, it is somewhat more expensive than the grey product. The main requirement is to have low iron content which should be less than 0.5% expressed as Fe<sub>2</sub>O<sub>3</sub> for white cement and less than 0.9% for off-white cement. It helps to have the iron oxide as ferrous oxide (FeO) which is obtained via slight reducing conditions i.e. operating with zero excess oxygen at the kiln exit. This gives the clinker and cement a green tinge. Other metals such as Cr, Mn, Ti etc. in trace content can also give color tinges so for a project it is best to use cement from a single source.§
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| ==Safety issues==
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| Bags of cement routinely have health and safety warnings printed on them because not only is cement highly [[alkali]]ne, but the setting process is [[exothermic]]. As a result, wet cement is strongly [[causticity|caustic]] and can easily cause severe [[skin burn]]s if not promptly washed off with water. Similarly, dry cement powder in contact with [[mucous membrane]]s can cause severe eye or respiratory irritation. Cement users should wear protective clothing.<ref>http://www.hse.gov.uk/pubns/cis26.pdf</ref><ref>{{cite news| url=http://www.dailymail.co.uk/news/article-1357208/Mother-left-horrific-burns-knees-kneeling-cement-doing-kitchen-DIY.html | location=London | work=Daily Mail | title=Mother left with horrific burns to her knees after kneeling in B&Q cement while doing kitchen DIY | date=2011-02-15}}</ref><ref>{{cite news| url=http://www.thesun.co.uk/sol/homepage/news/3412957/Mums-horror-cement-burns.html | location=London | work=The Sun | first=Jamie | last=Pyatt | title=Mums horror cement burns | date=2011-02-15}}</ref>
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| When traditional Portland cement is mixed with water the dissolution of [[hydroxide]]s of [[calcium]], [[sodium]], and [[potassium]] produces a highly [[alkaline]] solution ([[pH]] ~13). [[Glove]]s, [[goggle]]s, and a [[filter mask]] should be used for protection, and hands should be washed after contact as most cement can cause acute ulcerative damage 8–12 hours after contact if skin is not washed promptly.<ref>{{cite book |last = Bolognia|first= Jean L.|coauthors=Joseph L. Jorizzo, Ronald P. Rapini|title = Dermatology, volume 1|publisher=Mosby|year= 2003|isbn=0-323-02409-2}}</ref> The reaction of cement dust with moisture in the sinuses and lungs can also cause a chemical burn as well as headaches, fatigue,<ref>{{cite journal|last= Oleru| first=U. G.|title= Pulmonary function and symptoms of Nigerian workers exposed to cement dust|journal = Environ. Research |volume=33|pages=379–385|year=1984}}</ref> and lung cancer.<ref>{{Cite journal| last = Rafnsson| first = V |coauthors = H. Gunnarsdottir and M. Kiilunen |title= Risk of lung cancer among masons in Iceland |journal= Occup. Environ. Med |volume= 54 |pages = 184–188 |year= 1997}}</ref>
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| The development of formulations of cement that include fast-reacting [[pozzolan]]s such as [[silica fume]] as well as some slow-reacting products such as [[fly ash]] have allowed for the production of comparatively low-alkalinity cements (pH<11)<ref>{{Cite journal | last = Coumes | first = Céline Cau Dit| coauthors = Simone Courtois, Didier Nectoux, Stéphanie Leclercq, Xavier Bourbon | title = Formulating a low-alkalinity, high-resistance and low-heat concrete for radioactive waste repositories |journal= Cement and Concrete Research | volume = 36 | issue = 12 | pages = 2152–2163 | publisher = Elsevier Ltd.|date=December 2006|doi=10.1016/j.cemconres.2006.10.005 }}</ref>
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| that are much less toxic and which have become widely commercially available, largely replacing high-pH formulations in much of the USA. After any cement sets, the hardened mass loses chemical reactivity and can be safely touched without gloves.
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| In [[Scandinavia]], France, and [[UK]], the level of [[chromium#Precautions|chromium(VI)]], which is considered to be toxic and a major skin irritant, may not exceed 2 [[Parts per million|ppm]].
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| ==Environmental effects==
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| Portland cement manufacture can cause environmental impacts at all stages of the process. These include [[Cement kiln emissions|emissions]] of airborne pollution in the form of dust, gases, noise, and vibration when operating machinery and during blasting in quarries, consumption of large quantities of fuel during manufacture, release of CO<sub>2</sub> from the raw materials during manufacture, 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.
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| {{quote|Epidemiologic Notes and Reports Sulfur Dioxide Exposure in Portland Cement Plants, from the Centers for Disease Control, states "Workers at Portland cement facilities, particularly those burning fuel containing sulfur, should be aware of the acute and chronic effects of exposure to SO<sub>2</sub> [sulfur dioxide], and peak and full-shift concentrations of SO<sub>2</sub> should be periodically measured."|<ref>[http://www.cdc.gov/mmwr/preview/mmwrhtml/00000317.htm Epidemiologic Notes and Reports Sulfur Dioxide Exposure in Portland Cement Plants<!-- Bot generated title -->]</ref>}}
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| "The [[Arizona]] Department of Environmental Quality was informed this week that the Arizona Portland Cement Co. failed a second round of testing for emissions of hazardous air pollutants at the company's Rillito plant near [[Tucson]]. The latest round of testing, performed in January 2003 by the company, is designed to ensure that the facility complies with federal standards governing the emissions of dioxins and furans, which are byproducts of the manufacturing process."<ref>http://www.azdeq.gov/function/news/2003/jan.html</ref> Cement Reviews' "Environmental News" web page details case after case of environmental problems with cement manufacturing.<ref>[http://www.cemnet.com/public/news/enviro.asp CemNet.com | The latest cement news and information<!-- Bot generated title -->]</ref></blockquote>
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| An independent research effort of [[AEA Technology]] to identify critical issues for the cement industry today concluded the most important environment, health and safety performance issues facing the cement industry are atmospheric releases (including greenhouse gas emissions, dioxin, NO<sub>x</sub>, SO<sub>2</sub>, and particulates), accidents, and worker exposure to dust.<ref>[http://www.wbcsd.ch/web/projects/cement/tf3/final_report10.pdf Toward a Sustainable Cement Industry: Environment, Health & Safety Performance Improvement<!-- Bot generated title -->]</ref>
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| The CO<sub>2</sub> associated with Portland cement manufacture falls into 3 categories:
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| Source 1. CO<sub>2</sub> derived from decarbonation of [[limestone]],
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| Source 2. CO<sub>2</sub> from kiln fuel combustion,
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| Source 3. CO<sub>2</sub> produced by vehicles in cement plants and distribution.
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| Source 1 is fairly constant: minimum around {{nobreak|0.47 kg}} CO<sub>2</sub> per kg of cement, maximum 0.54, typical value around 0.50 worldwide.{{Citation needed|date=August 2010}} Source 2 varies with plant efficiency: efficient precalciner plant {{nobreak|0.24 kg}} CO<sub>2</sub> per kg cement, low-efficiency wet process as high as 0.65, typical modern practices (e.g. UK) averaging around 0.30.{{Citation needed|date=August 2010}} Source 3 is almost insignificant at 0.002–0.005. So typical total CO<sub>2</sub> is around {{nobreak|0.80 kg}} CO<sub>2</sub> per kg finished cement. This omits the CO<sub>2</sub> associated with electric power consumption because this varies according to the local generation type and efficiency. Typical electrical energy consumption is of the order of 90–150 kWh per tonne cement, equivalent to {{nobreak|0.09–0.15 kg}} CO<sub>2</sub> per kg finished cement if the electricity is coal-generated.
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| Overall, with nuclear- or hydroelectric power and efficient manufacturing, CO<sub>2</sub> generation can be reduced to {{nobreak|0.7 kg}} per kg cement, but can be twice as high. The thrust of innovation for the future is to reduce sources 1 and 2 by modification of the chemistry of cement, by the use of wastes, and by adopting more efficient processes. Although cement manufacturing is clearly a very large CO<sub>2</sub> emitter, [[concrete]] (of which cement makes up about 15%) compares quite favorably with other building systems in this regard.{{Citation needed|date=July 2008}}
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| ==Cement plants used for waste disposal or processing==
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| [[Image:LDWisconsinTireInject.jpg|thumb|400px|right|Used tires being fed to a pair of [[cement kiln]]s]]
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| Due to the high temperatures inside [[cement kiln]]s, combined with the oxidizing (oxygen-rich) atmosphere and long residence times, cement kilns are used as a processing option for various types of waste streams: indeed, they efficiently destroy many hazardous organic compounds. The waste streams also often contain combustible materials which allow the substitution of part of the fossil fuel normally used in the process.
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| Waste materials used in cement kilns as a fuel supplement:<ref>{{cite web
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| |url=http://www.wbcsdcement.org/pdf/lafarge1_en.pdf
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| |title=Recovery of Wastes in Cement Kilns
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| |author=Chris Boyd
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| |publisher=[[World Business Council for Sustainable Development]]
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| |date=December 2001
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| |accessdate=2008-09-25 |archiveurl = http://web.archive.org/web/20080624230936/http://www.wbcsdcement.org/pdf/lafarge1_en.pdf <!-- Bot retrieved archive --> |archivedate = 2008-06-24}}</ref>
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| * Car and truck [[tire]]s – steel belts are easily tolerated in the kilns
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| * Paint sludge from automobile industries
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| * Waste solvents and lubricants
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| * [[Meat and bone meal]] – [[slaughterhouse]] waste due to [[bovine spongiform encephalopathy]] contamination concerns
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| * Waste [[plastics]]
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| * Sewage [[sludge]]
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| * [[Rice hulls]]
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| * [[Sugarcane]] waste
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| * Used wooden [[railroad tie]]s (railway sleepers)
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| * Spent Cell Liner (SCL) from the aluminium smelting industry (also called Spent Pot Liner or SPL)
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| Portland cement manufacture also has the potential to benefit from using industrial by-products from the waste-stream.<ref>{{cite book | coauthors=S.H. Kosmatka, W.C. Panarese | title=Design and Control of Concrete Mixtures | publisher=Portland Cement Association | year=1988 | location=[[Skokie, Illinois]] | pages=15 |isbn=0-89312-087-1 |quote=As a generalization, probably 50% of all industrial byproducts have potential as raw materials for the manufacture of Portland cement.}}</ref> These include in particular:
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| * [[Slag]]
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| * [[Fly ash]] (from power plants)
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| * [[Silica fume]] (from steel mills)
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| * Synthetic [[gypsum]] (from desulfurisation)
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| == See also ==
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| {{colbegin|2}}
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| * [[Calcium silicate hydrate]]
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| * [[Cement]]
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| * [[Energetically modified cement]]
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| * [[Joseph Aspdin]]
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| * [[Lime mortar]]
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| * [[Mortar (masonry)]]
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| * [[Rosendale cement]]
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| * [[White Portland cement]]
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| {{colend}}
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| ==References==
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| {{reflist|2}}
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| == External links ==
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| * [http://www.indexmundi.com/en/commodities/minerals/cement/cement_t22.html World Production of Hydraulic Cement, by Country]
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| * [http://www.cement.org PCA – The Portland Cement Association]
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| * [http://www.sil.si.edu/exhibitions/doodles/cf/doodles_enlarge.cfm?id_image=68 Alpha The Guaranteed Portland Cement Company: 1917 Trade Literature from Smithsonian Institution Libraries]
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| * [http://www.wbcsdcement.org/ Cement Sustainability Initiative]
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| * [http://technology.guardian.co.uk/weekly/story/0,,1771589,00.html A cracking alternative to cement]
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| * [http://www.the-artistic-garden.com/concrete-vs-cement.html What is the Difference Between Cement, Portland Cement & Concrete?]
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| * Aerial views of the world's largest concentration of cement manufacturing capacity, [[Saraburi Province]], [[Thailand]], at {{Coord|14.6325|N|101.0771|E|region:TH_type:landmark}}
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| *{{cite news|author=Fountain, Henry|title=Concrete Is Remixed With Environment in Mind|url=http://www.nytimes.com/2009/03/31/science/earth/31conc.html|date=March 30, 2009|publisher=The New York Times|accessdate=2009-03-30}}
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| * [http://www.cdc.gov/niosh/npg/npgd0521.html CDC - NIOSH Pocket Guide to Chemical Hazards]
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| {{DEFAULTSORT:Portland Cement}}
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| [[Category:Cement]]
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| [[Category:Concrete]]
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| [[Category:English inventions]]
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| [[Category:Limestone]]
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| [[Category:Isle of Portland|Cement]]
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| [[de:Zement#Portlandzement]]
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