Portland cement

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Bags of portland cement wrapped and stacked on a pallet. Portland Cement Bags.jpg
Bags of portland cement wrapped and stacked on a pallet.
Blue Circle Southern Cement works near Berrima, New South Wales, Australia. BlueCircleSouthernCementBerrimaNSW.JPG
Blue Circle Southern Cement works near Berrima, New South Wales, Australia.

Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th century by Joseph Aspdin, and is usually made from limestone. It is a fine powder, produced by heating limestone and clay minerals in a kiln to form clinker, grinding the clinker, and adding 2 to 3 percent of gypsum. Several types of portland cement are available. The most common, called ordinary portland cement (OPC), is grey, but white portland cement is also available. Its name is derived from its resemblance to Portland stone which is quarried on the Isle of Portland in Dorset, England. It was named by Joseph Aspdin who obtained a patent for it in 1824. His son William Aspdin is regarded as the inventor of "modern" portland cement due to his developments in the 1840s. [1]

Contents

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. Its most common use is in the production of concrete, a composite material consisting of aggregate (gravel and sand), cement, and water.

History

Plaque in Leeds commemorating Joseph Aspdin Joseph Aspdin plaque 7 Sep 2017.jpg
Plaque in Leeds commemorating Joseph Aspdin
William Aspdin is considered the inventor of "modern" portland cement. William Aspdin Radford cyclopedia Volume 1.jpg
William Aspdin is considered the inventor of "modern" portland cement.
Freshly laid concrete 2014-06-12 10 38 10 Fresh sidewalk along U.S. Route 95 (West Winnemucca Boulevard) near Melarkey Street and Nevada State Route 289 (Winnemucca Boulevard) in Winnemucca, Nevada.JPG
Freshly laid concrete

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. [2]

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, [3] now known as Smeaton's Tower. In the late 18th century, Roman cement was developed and patented in 1796 by James Parker. [4] Roman cement quickly became popular, but was largely replaced by portland cement in the 1850s. [3] In 1811, James Frost produced a cement he called British cement. [4] James Frost is reported to have erected a manufactory for making of an artificial cement in 1826. [5] 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" [3] of Portland cement.

The name portland cement is recorded in a directory published in 1823 being associated with a William Lockwood and possibly others. [6] In his 1824 cement patent, Joseph Aspdin called his invention "portland cement" because of its resemblance to Portland stone. [2] 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". [3]

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. [6] William Aspdin made what could be called "meso-portland cement" (a mix of portland cement and hydraulic lime). [7] 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. [8]

In 1859, John Grant of the Metropolitan Board of Works, set out requirements for cement to be used in the London sewer project. This became a specification for portland cement. The next development in the manufacture of portland cement was the introduction of the rotary kiln, patented by Frederick Ransome in 1885 (U.K.) and 1886 (U.S.); which allowed a stronger, more homogeneous mixture and a continuous manufacturing process. [3] The Hoffmann "endless" kiln which was said to give "perfect control over combustion" was tested in 1860 and shown to produce a superior grade of cement. This cement was made at the Portland Cementfabrik Stern at Stettin, which was the first to use a Hoffmann kiln. [9] The Association of German Cement Manufacturers issued a standard on Portland cement in 1878. [10]

Portland cement had been imported into the United States from Germany and England, 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. [11] By the early 20th century, American-made portland cement had displaced most of the imported portland cement.

Composition

ASTM C150 [12] 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 which consist essentially of hydraulic calcium silicates, usually containing one or more of the forms of calcium sulfate as an inter ground addition. [13]

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 German Standard, issued in 1909).

Clinkers make up more than 90% of the cement, along with a limited amount of calcium sulfate (CaSO4, which controls the set time), and up to 5% minor constituents (fillers) as allowed by various standards. Clinkers are nodules (diameters, 0.2–1.0 inch [5.1–25.4 millimetres]) of a sintered material that is produced when a raw mixture of predetermined composition is heated to high temperature. The key chemical reaction distinguishing portland cement from other hydraulic limes occurs at these high temperatures (>1,300 °C (2,370 °F)) as belite (Ca2SiO4) combines with calcium oxide (CaO) to form alite (Ca3SiO5). [14]

Manufacturing

A father and a son in Goma, Congo, in 2017. Cement can cause significant harm to skin. Father and son loading and unloading cement in Goma, Congo.jpg
A father and a son in Goma, Congo, in 2017. Cement can cause significant harm to skin.

Portland cement clinker is made by heating, in a cement kiln, a mixture of raw materials to a calcining temperature of above 600 °C (1,112 °F) and then a fusion temperature, which is about 1,450 °C (2,640 °F) for modern cements, to sinter 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 sulfate 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 limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Secondary raw materials (materials in the raw mix 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.

Cement grinding

A 10 MW cement mill, producing cement at 270 tonnes per hour. LDCementFM10MW.jpg
A 10 MW cement mill, producing cement at 270 tonnes per hour.

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 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 '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 directly proportional 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)
ClinkerCCNMass
Tricalcium silicate (CaO)3 · SiO2C3S25–50%
Dicalcium silicate (CaO)2 · SiO2C2S20–45%
Tricalcium aluminate (CaO)3 · Al2O3C3A5–12%
Tetracalcium aluminoferrite (CaO)4 · Al2O3 · Fe2O3C4AF6–12%
Gypsum CaSO4 · 2 H2OCS̅H22–10%
Typical constituents of portland cement
showing cement chemist notation
CementCCNMass
Calcium oxide, CaOC61–67%
Silicon dioxide, SiO2S19–23%
Aluminium oxide, Al2O3A2.5–6%
Ferric oxide, Fe2O3F0–6%
Sulfur (VI) oxide, SO3S̅1.5–4.5%

Setting and hardening

Cement sets when mixed with water by way of a complex series of chemical reactions still only partly understood.[ citation needed ] 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)2) 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 (or quick) setting.

Use

Decorative use of portland cement panels on London's Grosvenor estate Grosvenor estate, Westminster, London.jpg
Decorative use of portland cement panels on London's Grosvenor estate

The most common use for portland cement is in the production of concrete. [17] Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. As a construction material, concrete can be cast in almost any shape desired, and once hardened, can become a structural (load bearing) element. Concrete can be used in the construction of structural elements like panels, beams, and street furniture, or may be cast-in situ for superstructures like roads and dams. 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 mortars (with sand and water only), for plasters and screeds, and in grouts (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, 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.

Types

General

ASTM C150

Five types of portland cements exist, with variations of the first three according to ASTM C150. [12] [18]

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 sulfate 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 sulfates. This type is for general construction 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 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 hydration reaction to develop at a slower rate. Consequently, 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.

Type V is used where sulfate 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 sulfate 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 alkali soil and ground water sulfates 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.

EN 197 norm

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.

ClassDescriptionConstituents
CEM IPortland cementComprising portland cement and up to 5% of minor additional constituents
CEM IIPortland-composite cementPortland cement and up to 35% of other* single constituents
CEM IIIBlast furnace cementPortland cement and higher percentages of blast furnace slag
CEM IVPozzolanic cementPortland cement and up to 55% of pozzolanic constituents
CEM VComposite cementPortland 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).

CSA A3000-08

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).

ClassDescription
GU, GUL (a.k.a. Type 10 (GU) cement)General use cement
MSModerate sulphate resistant cement
MH, MHLModerate heat cement
HE, HELHigh early strength cement
LH, LHLLow heat cement
HSHigh sulphate resistant; generally develops strength less rapidly than the other types.

White portland cement

White portland cement or white ordinary portland cement (WOPC) is similar to ordinary, grey, 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.

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 also exothermic. As a result, wet cement is strongly caustic 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. [19] [20] The reaction of cement dust with moisture in the sinuses and lungs can also cause a chemical burn, as well as headaches, fatigue, [21] and lung cancer. [22]

The production of comparatively low-alkalinity cements (pH<11) is an area of ongoing investigation. [23]

In Scandinavia, France, and the United Kingdom, the level of chromium(VI), which is considered to be toxic and a major skin irritant, may not exceed 2 parts per million (ppm).

In the US, the Occupational Safety and Health Administration (OSHA) has set the legal limit (permissible exposure limit) for portland cement exposure in the workplace as 50 mppcf (million particles per cubic foot) over an 8-hour workday. The National Institute for Occupational Safety and Health (NIOSH) has set a recommended exposure limit (REL) of 10 mg/m3 total exposure and 5 mg/m3 respiratory exposure over an 8-hour workday. At levels of 5000 mg/m3, portland cement is immediately dangerous to life and health. [24]

Environmental effects

Portland cement manufacture can cause environmental impacts at all stages of the process. These include emissions of airborne pollution in the form of dust; gases; noise and vibration when operating machinery and during blasting in quarries; 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 caustic, so it can cause chemical burns. [12] The powder can cause irritation or, with severe exposure, lung cancer, and can contain a number of hazardous components, including crystalline silica and hexavalent chromium. Environmental concerns are the high energy consumption required to mine, manufacture, and transport the cement, and the related air pollution, including the release of the greenhouse gas carbon dioxide, dioxin,[ citation needed ]NOx, SO2, and particulates. Production of portland cement contributes about 10% of world carbon dioxide emissions. [25] The International Energy Agency has estimated that cement production will increase by between 12 and 23% by 2050 to meet the needs of the world's growing population. [26] There are several ongoing researches targeting a suitable replacement of portland cement by supplementary cementitious materials. [27]

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. [28]

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, NOx, SO
2, and particulates), accidents, and worker exposure to dust. [29] [ better source needed ]

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 combustionVaries 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 distributionAlmost 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 generationVaries 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. [30]

Cement plants used for waste disposal or processing

Used tyres being fed to a pair of cement kilns LDWisconsinTireInject.jpg
Used tyres being fed to a pair of cement kilns

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: [31]

Portland cement manufacture also has the potential to benefit from using industrial byproducts from the waste stream. [32] These include in particular:

See also

Related Research Articles

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Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.

<span class="mw-page-title-main">Cement</span> Hydraulic binder used in the composition of mortar and concrete

A cement is a binder, a chemical substance used for construction that sets, hardens, and adheres to other materials to bind them together. Cement is seldom used on its own, but rather to bind sand and gravel (aggregate) together. Cement mixed with fine aggregate produces mortar for masonry, or with sand and gravel, produces concrete. Concrete is the most widely used material in existence and is behind only water as the planet's most-consumed resource.

Cement chemist notation (CCN) was developed to simplify the formulas cement chemists use on a daily basis. It is a shorthand way of writing the chemical formula of oxides of calcium, silicon, and various metals.

<span class="mw-page-title-main">Lime (material)</span> Calcium oxides and/or hydroxides

Lime is an inorganic material composed primarily of calcium oxides and hydroxides, usually calcium oxide and/or calcium hydroxide. It is also the name for calcium oxide which occurs as a product of coal-seam fires and in altered limestone xenoliths in volcanic ejecta. The International Mineralogical Association recognizes lime as a mineral with the chemical formula of CaO. The word lime originates with its earliest use as building mortar and has the sense of sticking or adhering.

<span class="mw-page-title-main">Hydraulic lime</span>

Hydraulic lime (HL) is a general term for calcium oxide, a variety of lime also called quicklime, that sets by hydration. This contrasts with calcium hydroxide, also called slaked lime or air lime that is used to make lime mortar, the other common type of lime mortar, which sets by carbonation (re-absorbing carbon dioxide (CO2) from the air). Hydraulic lime provides a faster initial set and higher compressive strength than air lime, and hydraulic lime will set in more extreme conditions, including under water.

<span class="mw-page-title-main">Ground granulated blast-furnace slag</span> Granular slag by-product of iron and steel-making used as supplementary cementitious material

Ground granulated blast-furnace slag is obtained by quenching molten iron slag from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder. Ground granulated blast furnace slag is a latent hydraulic binder forming calcium silicate hydrates (C-S-H) after contact with water. It is a strength-enhancing compound improving the durability of concrete. It is a component of metallurgic cement. Its main advantage is its slow release of hydration heat, allowing limitation of the temperature increase in massive concrete components and structures during cement setting and concrete curing, or to cast concrete during hot summer.

<span class="mw-page-title-main">Ettringite</span> Hydrous calcium sulfo-aluminate

Ettringite is a hydrous calcium aluminium sulfate mineral with formula: Ca6Al2(SO4)3(OH)12·26H2O. It is a colorless to yellow mineral crystallizing in the trigonal system. The prismatic crystals are typically colorless, turning white on partial dehydration. It is part of the ettringite-group which includes other sulfates such as thaumasite and bentorite.

<span class="mw-page-title-main">Ye'elimite</span> Natural form of anhydrous calcium sulfoaluminate

Ye'elimite is the naturally occurring form of anhydrous calcium sulfoaluminate, Ca
4(AlO
2)
6SO
4. It gets its name from Har Ye'elim in Israel in the Hatrurim Basin west of the Dead Sea where it was first found in nature by Shulamit Gross, an Israeli mineralogist and geologist who studied the Hatrurim Formation.

<span class="mw-page-title-main">Cement kiln</span> High temperature rotating oven used for producing clinker

Cement kilns are used for the pyroprocessing stage of manufacture of portland and other types of hydraulic cement, in which calcium carbonate reacts with silica-bearing minerals to form a mixture of calcium silicates. Over a billion tonnes of cement are made per year, and cement kilns are the heart of this production process: their capacity usually defines the capacity of the cement plant. As the main energy-consuming and greenhouse-gas–emitting stage of cement manufacture, improvement of kiln efficiency has been the central concern of cement manufacturing technology. Emissions from cement kilns are a major source of greenhouse gas emissions, accounting for around 2.5% of non-natural carbon emissions worldwide.

Alite is an impure form of tricalcium silicate, Ca3SiO5, sometimes formulated as 3CaO·SiO2, typically with 3-4% of substituent oxides. It is the major, and characteristic, phase in Portland cement. The name was given by Törnebohm in 1897 to a crystal identified in microscopic investigation of Portland cement. Hatrurite is the name of a mineral that is substituted C3S.

Belite is an industrial mineral important in Portland cement manufacture. Its main constituent is dicalcium silicate, Ca2SiO4, sometimes formulated as 2 CaO · SiO2 (C2S in cement chemist notation).

<span class="mw-page-title-main">Cement clinker</span> Main component of Portland cement

Cement clinker is a solid material produced in the manufacture of portland cement as an intermediary product. Clinker occurs as lumps or nodules, usually 3 millimetres (0.12 in) to 25 millimetres (0.98 in) in diameter. It is produced by sintering limestone and aluminosilicate materials such as clay during the cement kiln stage.

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 Portland cement.

<span class="mw-page-title-main">Calcium aluminate cements</span> Rapidly setting hydraulic cements

Calcium aluminate cements are cements consisting predominantly of hydraulic calcium aluminates. Alternative names are "aluminous cement", "high-alumina cement", and "Ciment fondu" in French. They are used in a number of small-scale, specialized applications.

<span class="mw-page-title-main">Cement mill</span>

A cement mill is the equipment used to grind the hard, nodular clinker from the cement kiln into the fine grey powder that is cement. Most cement is currently ground in ball mills and also vertical roller mills which are more effective than ball mills.

<span class="mw-page-title-main">Rawmill</span>

A raw mill is the equipment used to grind raw materials into "rawmix" during the manufacture of cement. Rawmix is then fed to a cement kiln, which transforms it into clinker, which is then ground to make cement in the cement mill. The raw milling stage of the process effectively defines the chemistry of the finished cement, and has a large effect upon the efficiency of the whole manufacturing process.

White Portland cement or white ordinary Portland cement (WOPC) is similar to ordinary, gray Portland cement in all aspects except for its high degree of whiteness. Obtaining this color requires substantial modifications to the method of manufacturing. It requires a much lower content in colored impurities in the raw materials used to produce clinker: low levels of Cr2O3, Mn2O3, and Fe2O3), but above all, a higher temperature is needed for the final sintering step in the cement kiln because of the higher melting point of the mix depleted in iron oxides. Because of this, the process is more energy demanding and the white cement is somewhat more expensive than the gray product.

Cement hydration and strength development mainly depend on two silicate phases: tricalcium silicate (C3S) (alite), and dicalcium silicate (C2S) (belite). Upon hydration, the main reaction products are calcium silicate hydrates (C-S-H) and calcium hydroxide Ca(OH)2, written as CH in the cement chemist notation. C-S-H is the phase playing the role of the glue in the cement hardened paste and responsible of its cohesion. Cement also contains two aluminate phases: C3A and C4AF, respectively the tricalcium aluminate and the tetracalcium aluminoferrite. C3A hydration products are AFm, calcium aluminoferrite monosulfate, and ettringite, a calcium aluminoferrite trisulfate (AFt). C4AF hydrates as hydrogarnet and ferrous ettringite.

The cement industry in the United States produced 82.8 million tonnes of cement in 2015, worth US$9.8 billion, and was used to manufacture concrete worth about US$50 billion. The US was the world's third-largest producer of cement, after China and India. The US cement industry includes 99 cement mills in 34 states, plus two plants in Puerto Rico. The industry directly employed 10,000 workers in 2015. Ten percent of the cement used in the United States in 2015 was imported.

AFt Phases refer to the calcium Aluminate Ferrite trisubstituted, or calcium aluminate trisubstituted, phases present in hydrated cement paste (HCP) in concrete.

References

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