Portland cement

Blue Circle Southern Cement works near Berrima

, New South Wales, Australia.

Portland cement is the most common type of

. Several types of portland cement are available. The most common, historically called ordinary portland cement (OPC), is grey, but white portland cement is also available.

The cement was so named by Joseph Aspdin, who obtained a patent for it in 1824, because, once hardened, it resembled the fine, pale limestone known as

.

His son William Aspdin is regarded as the inventor of "modern" portland cement due to his developments in the 1840s.^[1]

The low cost and widespread availability of the limestone, shales, and other naturally occurring materials used in portland cement make it a relatively cheap building material. At 4.4 billion tons manufactured (in 2023), Portland cement ranks third in the list (by mass) of manufactured materials, outranked only by sand and gravel. These two are combined, with water, to make the most manufactured material, concrete. This is Portland cement's most common use. ^[2]

Portland cement was developed from natural cements made in Britain beginning in the middle of the 18th century. Its name is derived from its similarity to Portland stone, a type of building stone quarried on the Isle of Portland in Dorset, England.^[3] The development of modern portland cement (sometimes called ordinary or normal portland cement) began in 1756, when John Smeaton experimented with combinations of different limestones and additives, including trass and pozzolanas, intended for the construction of a lighthouse,^[4] now known as Smeaton's Tower. In the late 18th century, Roman cement was developed and patented in 1796 by James Parker.^[5] Roman cement quickly became popular, but was largely replaced by portland cement in the 1850s.^[4] In 1811, James Frost produced a cement he called British cement.^[5] James Frost is reported to have erected a manufactory for making of an artificial cement in 1826.^[6] In 1811 Edgar Dobbs of Southwark patented a cement of the kind invented 7 years later by the French engineer Louis Vicat. Vicat's cement is an artificial hydraulic lime, and is considered the "principal forerunner"^[4] of portland cement.

The name portland cement is recorded in a directory published in 1823 being associated with a William Lockwood and possibly others.^[7] In his 1824 cement patent, Joseph Aspdin called his invention "portland cement" because of its resemblance to Portland stone.^[3] Aspdin's cement was nothing like modern portland cement, but a first step in the development of modern portland cement, and has been called a "proto-portland cement".^[4]

William Aspdin had left his father's company, to form his own cement manufactury. In the 1840s William Aspdin, apparently accidentally, produced calcium silicates which are a middle step in the development of portland cement. In 1848, William Aspdin further improved his cement. Then, in 1853, he moved to Germany, where he was involved in cement making.^[7] William Aspdin made what could be called "meso-portland cement" (a mix of portland cement and hydraulic lime).^[8] Isaac Charles Johnson further refined the production of "meso-portland cement" (middle stage of development), and claimed to be the real father of portland cement.^[9]

In 1859, John Grant of the Metropolitan Board of Works, set out requirements for cement to be used in the

Portland cement had been imported into the United States from England and Germany, and in the 1870s and 1880s, it was being produced by Eagle Portland cement near Kalamazoo, Michigan. In 1875, the first portland cement was produced in the Coplay Cement Company Kilns under the direction of David O. Saylor in Coplay, Pennsylvania.^[12] By the early 20th century, American-made portland cement had displaced most of the imported portland cement.

ASTM C219^[13] defines portland cement as:

a hydraulic cement produced by pulverizing clinker, consisting essentially of crystalline hydraulic calcium silicates, and usually containing one or more of the following: water, calcium sulfate, up to 5 % limestone, and processing additions

The European Standard EN 197-1 uses the following definition:

Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates, (3 CaO·SiO₂, and 2 CaO·SiO₂), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. The ratio of CaO to SiO₂ shall not be less than 2.0. The magnesium oxide content (MgO) shall not exceed 5.0% by mass.

(The last two requirements were already set out in the

, issued in 1909).

Clinkers make up more than 90% of the cement, along with a limited amount of

Manufacturing

Portland cement clinker is made by heating, in a

the materials into clinker.

The materials in cement clinker are alite, belite, tricalcium aluminate, and tetracalcium alumino ferrite. The aluminium, iron, and magnesium oxides are present as a flux allowing the calcium silicates to form at a lower temperature,^[15] and contribute little to the strength. For special cements, such as low heat (LH) and sulphate resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate (3 CaO·Al₂O₃) formed.

The major raw material for the clinker-making is usually

. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.

Cement grinding

To achieve the desired setting qualities in the finished product, a quantity (2–8%, but typically 5%) of calcium sulphate (usually

to the specific surface area. Typical values are 320–380 m²·kg⁻¹ for general purpose cements, and 450–650 m²·kg⁻¹ 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 one to 20 weeks of 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.

Typical constituents of portland clinker plus gypsum
showing cement chemist notation (CCN)

Clinker	CCN	Mass
Tricalcium silicate (CaO)3 · SiO2	C3S	25–50%
Dicalcium silicate (CaO)2 · SiO2	C2S	20–45%
Tricalcium aluminate (CaO)3 · Al2O3	C3A	5–12%
Tetracalcium aluminoferrite (CaO)4 · Al2O3 · Fe2O3	C4AF	6–12%
Gypsum CaSO4 · 2 H2O	CS̅H2	2–10%

Typical constituents of portland cement
showing cement chemist notation

Cement	CCN	Mass
Calcium oxide, CaO	C	61–67%
Silicon dioxide, SiO2	S	19–23%
Aluminium oxide, Al2O3	A	2.5–6%
Ferric oxide, Fe2O3	F	0–6%
Sulphur (VI) oxide, SO3	S̅	1.5–4.5%

Setting and hardening

Cement sets when mixed with water by way of a complex series of chemical reactions that are still only partly understood.[16] A brief summary is as follows:

The clinker phases—calcium silicates and aluminates—dissolve into the water that is mixed with the cement, which results in a fluid containing relatively high concentrations of dissolved

Gypsum is included in the cement as an inhibitor to prevent flash (or quick) setting; if gypsum is not present, the initial formation of (needle-shaped) ettringite is not possible, and so (plate-shaped) hydrocalumite-group ("AFm") calcium aluminate phases form instead. This premature formation of AFm phases causes a rapid loss of flowability, which is generally not desirable because it means that placement of the cement or concrete is very difficult.^[18]

Hardening of the cement then proceeds through further C-S-H formation, as this fills in the spaces between the (still-dissolving) cement grains with newly formed solid phases. Portlandite also precipitates from the pore solution to form part of the solid microstructure, and some of the initially-formed ettringite may be converted to AFm phases, releasing part of the sulfate from its structure to continue reacting with any remaining tricalcium aluminate^[19]

Grosvenor estate^[20]

The most common use for portland cement is in the production of concrete.

(cement/water mixes squeezed into gaps to consolidate foundations, road-beds, etc.).

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,^[22] 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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Five types of portland cements exist, with variations of the first three according to ASTM C150.^[23][24]

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:

55% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 2.8% MgO, 2.9% (SO₃), 1.0% ignition loss, and 1.0% free CaO (utilizing cement chemist notation).

A limitation on the composition is that the (C₃A) shall not exceed 15%.

Type II provides moderate sulphate resistance, and gives off less heat during hydration. This type of cement costs about the same as type I. Its typical compound composition is:

51% (C₃S), 24% (C₂S), 6% (C₃A), 11% (C₄AF), 2.9% MgO, 2.5% (SO₃), 0.8% ignition loss, and 1.0% free CaO.

A limitation on the composition is that the (C₃A) shall not exceed 8%, which reduces its vulnerability to sulphates. This type is for general construction exposed to moderate sulphate 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 sulphur content of the soils. 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.

Note: Cement meeting (among others) the specifications for types I and II has become commonly available on the world market.

Type III has relatively high early strength. Its typical compound composition is:

57% (C₃S), 19% (C₂S), 10% (C₃A), 7% (C₄AF), 3.0% MgO, 3.1% (SO₃), 0.9% ignition loss, and 1.3% free CaO.

This cement is similar to type I, but ground finer. Some manufacturers make a separate clinker with higher C₃S and/or C₃A content, but this is increasingly rare, and the general purpose clinker is usually used, ground to a specific surface area 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 28-day compressive strengths of types I and II. 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. It is usually used for precast concrete manufacture, where high one-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.

Type IV portland cement is generally known for its low heat of hydration. Its typical compound composition is:

28% (C₃S), 49% (C₂S), 4% (C₃A), 12% (C₄AF), 1.8% MgO, 1.9% (SO₃), 0.9% ignition loss, and 0.8% free CaO.

The percentages of (C₂S) and (C₄AF) are relatively high and (C₃S) and (C₃A) are relatively low. A limitation on this type is that the maximum percentage of (C₃A) is seven, and the maximum percentage of (C₃S) is thirty-five. This causes the heat given off by the

addition offer a cheaper and more reliable alternative.

Type V is used where sulphate resistance is important. Its typical compound composition is:

38% (C₃S), 43% (C₂S), 4% (C₃A), 9% (C₄AF), 1.9% MgO, 1.8% (SO₃), 0.9% ignition loss, and 0.8% free CaO.

This cement has a very low (C₃A) composition which accounts for its high sulphate resistance. The maximum content of (C₃A) allowed is 5% for type V portland cement. Another limitation is that the (C₄AF) + 2(C₃A) composition cannot exceed 20%. This type is used in concrete to be exposed to

which react with (C₃A) 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.

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, only on a limited basis. They are a poor approach^{[clarification needed]} to air-entrainment which improves resistance to freezing under low temperatures.

Types II(MH) and II(MH)a have a similar composition as types II and IIa, but with a mild heat.

The European norm EN 197-1 defines five classes of common cement that comprise portland cement as a main constituent. These classes differ from the ASTM classes.

Class	Description	Constituents
CEM I	Portland cement	Comprising portland cement and up to 5% of minor additional constituents
CEM II	Portland-composite cement	Portland cement and up to 35% of other* single constituents
CEM III	Blast furnace cement	Portland cement and higher percentages of blast furnace slag
CEM IV	Pozzolanic cement	Portland cement and up to 55% of pozzolanic constituents
CEM V	Composite cement	Portland cement, blast furnace slag or fly ash and pozzolana

*Constituents that are permitted in portland-composite cements are artificial pozzolans (blast furnace slag (in fact a latent hydraulic binder), silica fume, and fly ashes), or natural pozzolans (siliceous or siliceous aluminous materials such as volcanic ash glasses, calcined clays and shale).

The Canadian standards describe six main classes of cement, four of which can also be supplied as a blend containing ground limestone (where a suffix L is present in the class names).

Class	Description
GU, GUL (a.k.a. Type 10 (GU) cement)	General use cement
MS	Moderate sulphate resistant cement
MH, MHL	Moderate heat cement
HE, HEL	High early strength cement
LH, LHL	Low heat cement
HS	High sulphate resistant; generally develops strength less rapidly than the other types.

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 colour requires high purity raw materials (low Fe₂O₃ content), and some modification to the method of manufacture, among others a higher kiln temperature required to sinter the clinker in the absence of ferric oxides acting as a flux in normal clinker. As Fe₂O₃ contributes to decrease the melting point of the clinker (normally 1450 °C), the white cement requires a higher sintering temperature (around 1600 °C). Because of this, it is somewhat more expensive than the grey product. The main requirement is to have a low iron content which should be less than 0.5 wt.% expressed as Fe₂O₃ for white cement, and less than 0.9 wt.% for off-white cement. It also helps to have the iron oxide as ferrous oxide (FeO) which is obtained via slightly reducing conditions in the kiln, i.e., operating with zero excess oxygen at the kiln exit. This gives the clinker and cement a green tinge. Other metallic oxides such as Cr₂O₃ (green), MnO (pink), TiO₂ (white), etc., in trace content, can also give colour tinges, so for a given project it is best to use cement from a single batch.

Bags of cement routinely have health and safety warnings printed on them, because not only is cement highly

The production of comparatively low-alkalinity cements (pH<11) is an area of ongoing investigation.[29]

In

(ppm).

In the US, the

Environmental effects

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Portland cement manufacture can cause

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
₂ 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.

Portland cement is

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
₂ [sulfur dioxide], and peak and full-shift concentrations of SO
₂ should be periodically measured.[34]

An independent research effort of

]

The CO
₂ associated with portland cement manufacture comes mainly from four sources:

CO 2 source	Amount
Decarbonation of limestone	Fairly constant: minimum around 0.47 kg (1.0 lb) CO 2 per kg of cement, maximum 0.54, typical value around 0.50 worldwide.[citation needed]
Kiln fuel combustion	Varies with plant efficiency: efficient precalciner plant 0.24 kg (0.53 lb) CO 2 per kg cement, low-efficiency wet process as high as 0.65, typical modern practices (e.g. UK) averaging around 0.30.[citation needed]
Produced by vehicles in cement plants and distribution	Almost insignificant at 0.002–0.005. So typical total CO 2 is around 0.80 kg (1.8 lb) CO 2 per kg finished cement.
Electrical power generation	Varies with local power source. Typical electrical energy consumption is on the order of 90–150 kWh per tonne cement, equivalent to 0.09–0.15 kg (0.20–0.33 lb) CO 2 per kg finished cement if the electricity is coal-generated.

Overall, with nuclear or hydroelectric power, and efficient manufacturing, CO
₂ generation can be reduced to 0.7 kg (1.5 lb) per kg cement, but can be twice as high.^{[clarification needed]} 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.^{[citation needed]} Although cement manufacturing is clearly a very large CO
₂ emitter, concrete (of which cement makes up about 15%) compares quite favourably with other modern building systems in this regard.^{[citation needed]}. Traditional materials such as lime based mortars as well as timber and earth based construction methods emit significantly less CO₂.^[36]

Due to the high temperatures inside cement kilns, combined with the oxidising (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.

Waste materials used in cement kilns as a fuel supplement:^[37]

• Car and truck tires – steel belts are easily tolerated in the kilns
• Paint sludge from automobile industries
• Waste solvents and lubricants
• Meat and bone meal – slaughterhouse waste due to bovine spongiform encephalopathy contamination concerns
• Waste plastics
• Sewage sludge
• Rice hulls
• Sugarcane waste
• Used wooden railroad ties (railway sleepers)
• Spent cell liner from the aluminium smelting industry (also called spent pot liner)

Portland cement manufacture also has the potential to benefit from using industrial byproducts from the waste stream.^[38] These include in particular:

• Slag
• Fly ash
  (from power plants)
• Silica fume (from steel mills)
• Synthetic gypsum (from desulphurisation)

External links

Wikimedia Commons has media related to Cement.

• World Production of Hydraulic Cement, by Country
• Alpha The Guaranteed Portland Cement Company: 1917 Trade Literature from Smithsonian Institution Libraries
• Cement Sustainability Initiative^[usurped]
• A cracking alternative to cement
• Aerial views of the world's largest concentration of cement manufacturing capacity,
  Saraburi Province, Thailand, at 14°37′57″N 101°04′38″E / 14.6325°N 101.0771°E / 14.6325; 101.0771
• Fountain, Henry (30 March 2009). "Concrete Is Remixed With Environment in Mind". The New York Times. Retrieved 30 March 2009.
• CDC – NIOSH Pocket Guide to Chemical Hazards

Further reading

• Gharpure, A.; Heim Jw, I. I.; Vander Wal, R. L. (2021). "Characterization and Hazard Identification of Respirable Cement and Concrete Dust from Construction Activities". International Journal of Environmental Research and Public Health. 18 (19): 10126.
  PMID 34639428
  .
• Liu, Jia; Zhang, Yongming; Zhang, Qixing; Wang, Jinjun (2018). "Scattering Matrix for Typical Urban Anthropogenic Origin Cement Dust and Discrimination of Representative Atmospheric Particulates". Journal of Geophysical Research: Atmospheres. 123 (6): 3159–3174.
  S2CID 135035398
  .
• ISBN 978-0-7277-2592-9
  .
• Peter Hewlett; Martin Liska (2019). Lea's Chemistry of Cement and Concrete. Butterworth-Heinemann.
  ISBN 978-0-08-100795-2
  .