Portland cement is the most common type of cement in general usage in many parts of the world, as it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout. In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag Mortar is a workable paste formed by mixture of Cement, Water and fine aggregate Masonry to bind construction blocks together and fill the gaps between Stucco or render is a material made of an aggregate, a binder, and water Grout is a Construction material used to embed Rebars in Masonry walls connect sections of pre-cast Concrete, fill voids and seal joints (like It is a fine powder produced by grinding Portland 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). In the manufacture of Portland cement, clinker is the solid material produced by the Cement kiln stage that has sintered into lumps or nodules typically Calcium sulfate is a common laboratory and industrial chemical

As defined by the European Standard EN197. European Committee for Standardization or Comité Européen de Normalisation ( CEN) is a private non-profit organisation whose mission is to foster the European economy 1, "Portland cement clinker is a hydraulic material which shall consist of at least two-thirds by mass of calcium silicates (3CaO.SiO₂ and 2CaO.SiO₂), the remainder consisting of aluminium- and iron-containing clinker phases and other compounds. For the mechanical technology see Hydraulic machinery and Hydraulic cylinder Hydraulics is a topic of science and Engineering Calcium silicates are a set of four compounds obtained by reacting Calcium oxide and silica in various ratios Alite is the mineralogical name for Tricalcium Silicate Ca3SiO5 Belite is the mineralogical name for Dicalcium Silicate Ca2SiO4 The ratio of CaO to SiO₂ shall not be less than 2. Calcium oxide ( CaO) commonly known as burnt lime, lime or quicklime, is a widely used Chemical compound. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide 0. The magnesium content (MgO) shall not exceed 5. Magnesium oxide, or magnesia, is a white solid Mineral that occurs naturally as Periclase and is a source 0% by mass. " (The last two requirements were already set out in the German Standard, issued in 1909).

Portland cement clinker is made by heating, in a kiln, a homogeneous mixture of raw materials to a sintering temperature, which is about 1450 °C for modern cements. Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate Sintering is a method for making objects from powder, by heating the material (below its Melting point - solid state sintering until its particles adhere The aluminium oxide and iron oxide are present as a flux and contribute little to the strength. In Metallurgy, a flux is a chemical cleaning agent which facilitates Soldering, Brazing, and Welding by removing Oxidation from For special cements, such as Low Heat (LH) and Sulfate Resistant (SR) types, it is necessary to limit the amount of tricalcium aluminate (3CaO. Tricalcium aluminate (3CaOAl2O3 is the most basic of the Calcium aluminates. Al₂O₃) formed. The major raw material for the clinker-making is usually limestone (CaCO₃) mixed with a second materials containing clay as source of alumino-silicate. Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Normally, an impure limestone which contains clay or SiO₂ is used. The CaCO₃ content of these limestones can be as low as 80%. Second raw materials (materials in the rawmix other than limestone) depend on the purity of the limestone. Some of the second raw materials used are: clay, shale, sand, iron ore, bauxite, fly ash and slag. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and Shale (also called mudstone) is a fine-grained Sedimentary rock whose original constituents were Clay minerals or Muds It is characterized by Sand is a naturally occurring Granular material composed of finely divided rock and Mineral particles Iron ores are rocks and Minerals from which Metallic Iron can be economically extracted Bauxite is the most important Aluminium Ore. It consists largely of the minerals Gibbsite Al(OH3 Boehmite γ-AlO(OH and Fly ash is one of the residues generated in the Combustion of Coal. Slag is the By-product of Smelting Ore to purify Metals They can be considered to be a mixture of metal Oxides however When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material. Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate

Contents 1 History 2 Production 2.1 Rawmix preparation 2.2 Rawmix blending 2.3 Formation of clinker 2.4 Cement grinding 3 Use 3.1 Setting and hardening 4 Types of Portland cement 4.1 General 4.2 ASTM C150 4.3 EN 197 4.4 White Portland cement 5 Safety and environmental effects 5.1 Safety 5.2 Environmental effects 6 Cement plants as alternatives to conventional waste disposal or processing 7 See also 8 References 9 External links

History

Portland was developed from cements (or correctly hydraulic limes) made in 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. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Portland stone is a Limestone from the Jurassic period quarried on the Isle of Portland, Dorset. The Isle of Portland ( is a limestone tied island long by wide in the English Channel. Dorset ( (or archaically, Dorsetshire) is a county in South West England on the English Channel coast England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Joseph Aspdin, a British bricklayer, in 1824 was granted a patent for a process of making a cement which he called Portland cement. Joseph Aspdin (December? 1778 – 20 March 1855) was a British cement manufacturer who obtained the Patent for Portland cement on His cement was an artificial hydraulic lime similar in properties to the material known as "Roman Cement" (patented in 1796 by James Parker) and his process was similar to that patented in 1822 and used since 1811 by James Frost who called his cement "British Cement". In the most general sense of the word a cement is a binder a substance which sets and hardens independently and can bind other materials together James Frost (1780?-1840? was a British Cement manufacturer and invented processes that led to the eventual development of Portland cement. The name "Portland cement" is also recorded in a directory published in 1823 being associated with a William Lockwood and possibly others. Aspdin's son William in 1843 made an improved version of this cement and he initially called it "Patent Portland cement" although he had no patent. William Aspdin ( 23 September 1815 — 1864 was an English Cement manufacturer and a pioneer of the Portland cement industry In 1848 William Aspdin further improved his cement and in 1853 moved to Germany where he was involved in cement making. ^[1] Many people have claimed to have made the first Portland cement in the modern sense, but it is generally accepted that it was first manufactured by William Aspdin at Northfleet, England in about 1842^[2]. For the ship wrecked on January 22nd 1873 see Northfleet (ship Northfleet is a town in Kent, England. England is a Country which is part of the United Kingdom. Its inhabitants account for more than 83% of the total UK population whilst its mainland Year 1842 ( MDCCCXLII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian Calendar (or a Common The German Government issued a standard on Portland cement in 1878.

Production

There are three fundamental stages in the production of Portland cement:

1. Preparation of the raw mixture
2. Production of the clinker
3. Preparation of the cement

The chemistry of cement is very complex, so cement chemist notation was invented to simplify the formula of common oxides found in cement. Texas Industries NYSE: TXI is headquartered in Dallas, Texas, USA. Midlothian is a city in northwest Ellis County, Texas, United States. In the manufacture of Portland cement, clinker is the solid material produced by the Cement kiln stage that has sintered into lumps or nodules typically Cement chemist notation (CCN was developed to simplify the Formulas which Cement chemists use on a daily basis This reflects the fact that most of the elements are present in their highest oxidation state, and chemical analyses of cement are expressed as mass percent of these notional oxides.

Rawmix preparation

Main article: Rawmill

The raw materials for Portland cement production are a mixture (as fine powder in the 'Dry process' or in the form of a slurry in the 'Wet process') of minerals containing calcium oxide, silicon oxide, aluminium oxide, ferric oxide, and magnesium oxide. A rawmill is the equipment used to grind raw materials into "rawmix" during the manufacture of Cement. A stacker is a large Machine used in Bulk material handling applications Calcium oxide ( CaO) commonly known as burnt lime, lime or quicklime, is a widely used Chemical compound. The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Iron(III oxide —also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply Rust —is Magnesium oxide, or magnesia, is a white solid Mineral that occurs naturally as Periclase and is a source The raw materials are usually quarried from local rock, which in some places is already practically the desired composition and in other places requires the addition of clay and limestone, as well as iron ore, bauxite or recycled materials. Clay is a naturally occurring material composed primarily of fine-grained Minerals which show plasticity through a variable range of Water content, and Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3 Iron ores are rocks and Minerals from which Metallic Iron can be economically extracted Bauxite is the most important Aluminium Ore. It consists largely of the minerals Gibbsite Al(OH3 Boehmite γ-AlO(OH and The individual raw materials are first crushed, typically to below 50 mm. In many plants, some or all of the raw materials are then roughly blended in a "prehomogenization pile". The raw materials are next ground together in a rawmill. A rawmill is the equipment used to grind raw materials into "rawmix" during the manufacture of Cement. Silos of individual raw materials are arranged over the feed conveyor belt. Accurately controlled proportions of each material are delivered onto the belt by weigh-feeders. Passing into the rawmill, the mixture is ground to rawmix. The fineness of rawmix is specified in terms of the size of the largest particles, and is usually controlled so that there are less than 5-15% by mass of particles exceeding 90 μm in diameter. It is important that the rawmix contains no large particles in order to complete the chemical reactions in the kiln, and to ensure the mix is chemically homogenous. In the case of a dry process, the rawmill also dries the raw materials, usually by passing hot exhaust gases from the kiln through the mill, so that the rawmix emerges as a fine powder. This is conveyed to the blending system by conveyor belt or by a powder pump. In the case of wet process, water is added to the rawmill feed, and the mill product is a slurry with moisture content usually in the range 25-45% by mass. This slurry is conveyed to the blending system by conventional liquid pumps.

Rawmix blending

The rawmix is formulated to a very tight chemical specification. Typically, the content of individual components in the rawmix must be controlled within 0. 1% or better. Calcium and silicon are present in order to form the strength-producing calcium silicates. Aluminium and iron are used in order to produce liquid ("flux") in the kiln burning zone. The liquid acts as a solvent for the silicate-forming reactions, and allows these to occur at an economically low temperature. Insufficient aluminium and iron lead to difficult burning of the clinker, while excessive amounts lead to low strength due to dilution of the silicates by aluminates and ferrites. Very small changes in calcium content lead to large changes in the ratio of alite to belite in the clinker, and to corresponding changes in the cement's strength-growth characteristics. The relative amounts of each oxide are therefore kept constant in order to maintain steady conditions in the kiln, and to maintain constant product properties. In practice, the rawmix is controlled by frequent chemical analysis (hourly by X-Ray fluorescence analysis, or every 3 minutes by prompt gamma neutron activation analysis). X-ray fluorescence (XRF is the emission of characteristic "secondary" (or fluorescent X-rays from a material that has been excited by bombarding with high-energy Neutron Activation Analysis (NAA is a nuclear process used for determining certain concentrations of elements in a vast amount of materials The analysis data is used to make automatic adjustments to raw material feed rates. Remaining chemical variation is minimized by passing the raw mix through a blending system that homogenizes up to a day's supply of rawmix (15,000 tonnes in the case of a large kiln).

Formation of clinker

Main article: Cement kiln

The raw mixture is heated in a cement kiln, a slowly rotating and sloped cylinder, with temperatures increasing over the length of the cylinder up to a peak temperature of 1400-1450 °C. Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate The Celsius Temperature scale was previously known as the centigrade scale. A complex succession of chemical reactions take place (see cement kiln) as the temperature rises. Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate The peak temperature is regulated so that the product contains sintered but not fused lumps. Sintering is a method for making objects from powder, by heating the material (below its Melting point - solid state sintering until its particles adhere Sintering consists of the melting of 25-30% of the mass of the material. The resulting liquid draws the remaining solid particles together by surface tension, and acts as a solvent for the final chemical reaction in which alite is formed. Alite is the mineralogical name for Tricalcium Silicate Ca3SiO5 Too low a temperature causes insufficient sintering and incomplete reaction, but too high a temperature results in a molten mass or glass, destruction of the kiln lining, and waste of fuel. When all goes to plan, the resulting material is clinker. In the manufacture of Portland cement, clinker is the solid material produced by the Cement kiln stage that has sintered into lumps or nodules typically On cooling, it is conveyed to storage. Some effort is usually made to blend the clinker, because although the chemistry of the rawmix may have been tightly controlled, the kiln process potentially introduces new sources of chemical variability. The clinker can be stored for a number of years before use. Prolonged exposure to water decreases the reactivity of cement produced from weathered clinker.

The enthalpy of formation of clinker from calcium carbonate and clay minerals is ~1700 kJ/kg. However, because of heat loss during production, actual values can be much higher. The high energy requirements and the release of significant amounts of carbon dioxide makes cement production a concern for global warming. Global warming is the increase in the average measured temperature of the See "Environmental effects" below.

Cement grinding

Main article: Cement mill

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. A cement mill (or finish mill in North American usage is the equipment used to grind the hard nodular clinker from the Cement kiln into the fine grey powder that Gypsum is a very soft Mineral composed of Calcium sulfate dihydrate with the Chemical formula Ca[[sulfur S]] O 4·2 Anhydrite is a mineral - anhydrous Calcium Sulfate, CaSO4 It is in the Orthorhombic crystal system with three directions of perfect cleavage This is achieved in a cement mill. A cement mill (or finish mill in North American usage is the equipment used to grind the hard nodular clinker from the Cement kiln into the fine grey powder that 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 particle size distribution (PSD of a powder or granular material or particles dispersed in fluid is a list of values or a mathematical function that defines the relative amounts The measure of fineness usually used is the "specific surface", which is the total particle surface area of a unit mass of cement. The air permeability specific surface of a powder material is a single-parameter measurement of the fineness of the powder The rate of initial reaction (up to 24 hours) of the cement on addition of water is directly proportional to the specific surface. 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 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 developed countries, 80% or more of cement is delivered in bulk, and many cement plants have no bag-packing facility. In developing countries, bags are the normal mode of delivery.

Typical constituents of Portland clinker and Portland cement. Cement industry style notation in italics:

Clinker	Mass%	Cement	Mass%
Tricalcium silicate (CaO)3. Alite is the mineralogical name for Tricalcium Silicate Ca3SiO5 SiO2, C3S	45-75%	Calcium oxide, CaO, C	61-67%
Dicalcium silicate (CaO)2. Belite is the mineralogical name for Dicalcium Silicate Ca2SiO4 SiO2, C2S	7-32%	Silicon oxide, SiO2, S	19-23%
Tricalcium aluminate (CaO)3. Tricalcium aluminate (3CaOAl2O3 is the most basic of the Calcium aluminates. Al2O3, C3A	0-13%	Aluminium oxide, Al2O3, A	2. 5-6%
Tetracalcium aluminoferrite (CaO)4. Calcium Aluminoferrite (Ca2(AlFe2O5 is a dark brown crystalline phase commonly found in Cements It also exists rarely in nature as Brownmillerite Al2O3. Fe2O3, C4AF	0-18%	Ferric oxide, Fe2O3, F	0-6%
Gypsum CaSO4 · 2 H2O	2-10%	Sulfate

Use

The most common use for Portland cement is in the production of concrete. Gypsum is a very soft Mineral composed of Calcium sulfate dihydrate with the Chemical formula Ca[[sulfur S]] O 4·2 Concrete is a composite material consisting of aggregate (gravel and sand), cement, and water. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag 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, roads, 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).

Setting and hardening

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 (i. e. becomes rigid) 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 one week, 35~ MPa at 4 weeks, and 41~ MPa at three 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.

Setting and hardening of Portland cement is caused by the formation of water-containing compounds, forming as a result of reactions between cement components and water. Usually, cement reacts in a plastic mixture only at water/cement ratios between 0. 25 and 0. 75. The reaction and the reaction products are referred to as hydration and hydrates or hydrate phases, respectively. As a result of the reactions (which start immediately), a stiffening can be observed which is very small in the beginning, but which increases with time. The point in time at which it reaches a certain level is called the start of setting. The consecutive further consolidation is called setting, after which the phase of hardening begins.

Stiffening, setting and hardening are caused by the formation of a microstructure of hydration products of varying rigidity which fills the water-filled interstitial spaces between the solid particles of the cement paste, mortar or concrete. The behaviour with time of the stiffening, setting and hardening therefore depends to a very great extent on the size of the interstitial spaces, i. e. on the water/cement ratio. The hydration products primarily affecting the strength are calcium silicate hydrates ("C-S-H phases"). Calcium Silicate Hydrate is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials Further hydration products are calcium hydroxide, sulfatic hydrates (AFm and AFt phases), and related compounds, hydrogarnet, and gehlenite hydrate. An AFm phase is an "alumina ferric oxide monosulfate" phase Calcium silicates or silicate constituents make up over 70 % by mass of silicate-based cements. The hydration of these compounds and the properties of the calcium silicate hydrates produced are therefore particularly important. Calcium silicate hydrates contain less CaO than the calcium silicates in cement clinker, so calcium hydroxide is formed during the hydration of Portland cement. This is available for reaction with supplementary cementitious materials such as ground granulated blast furnace slag and pozzolans. Ground granulated blast furnace slag ( GGBS or GGBFS) is obtained by quenching molten Iron Slag (a by-product of iron and Steel making The simplified reaction of alite with water may be expressed as:

2Ca₃OSiO₄ + 6H₂O → 3CaO. Alite is the mineralogical name for Tricalcium Silicate Ca3SiO5 2SiO₂. 3H₂O + 3Ca(OH)₂

This is a relatively fast reaction, causing setting and strength development in the first few weeks. The reaction of belite is:

2Ca₂SiO₄ + 4H₂O → 3CaO. Belite is the mineralogical name for Dicalcium Silicate Ca2SiO4 2SiO₂. 3H₂O + Ca(OH)₂

This reaction is relatively slow, and is mainly responsible for strength growth after one week. Tricalcium aluminate hydration is controlled by the added calcium sulfate, which immediately goes into solution when water is added. Firstly, ettringite is rapidly formed, causing a slowing of the hydration (see tricalcium aluminate):

Ca₃(AlO₃)₂ + 3CaSO₄ + 32H₂O → Ca₆(AlO₃)₂(SO₄)₃. Ettringite is a hexacalcium aluminate trisulfate Hydrate, (CaO6(Al2O3(SO33 · 32 H2O Tricalcium aluminate (3CaOAl2O3 is the most basic of the Calcium aluminates. 32H₂O

The ettringite subsequently reacts slowly with further tricalcium aluminate to form "monosulfate" - an "AFm phase":

Ca₆(AlO₃)₂(SO₄)₃. 32H₂O + Ca₃(AlO₃)₂ + 4H₂O → 3Ca₄(AlO₃)₂(SO₄). 12H₂O

This reaction is complete after 1-2 days. The calcium aluminoferrite reacts slowly due to precipitation of hydrated iron oxide:

2Ca₂AlFeO₅ + CaSO₄ + 16H₂O → Ca₄(AlO₃)₂(SO₄). A number of species are dubbed iron(III oxide-hydroxide. These chemicals are Oxide - Hydroxides of Iron, and may occur in Anhydrous (( or 12H₂O + Ca(OH)₂ + 2Fe(OH)₃

The pH-value of the pore solution reaches comparably high values and is of importance for most of the hydration reactions.

Soon after Portland cement is mixed with water, a brief and intense hydration starts (pre-induction period). Calcium sulfates dissolve completely and alkali sulfates almost completely. Short, hexagonal needle-like ettringite crystals form at the surface of the clinker particles as a result of the reactions between calcium- and sulfate ions with tricalcium aluminate. Further, originating from tricalcium silicate, first calcium silicate hydrates (C-S-H) in colloidal shape can be observed. Alite is the mineralogical name for Tricalcium Silicate Ca3SiO5 Calcium Silicate Hydrate is the main product of the hydration of Portland cement and is primarily responsible for the strength in cement based materials Caused by the formation of a thin layer of hydration products on the clinker surface, this first hydration period ceases and the induction period starts during which almost no reaction takes place. The first hydration products are too small to bridge the gap between the clinker particles and do not form a consolidated microstructure. Consequently the mobility of the cement particles in relation to one another is only slightly affected, i. e. the consistency of the cement paste turns only slightly thicker. Setting starts after approximately one to three hours, when first calcium silicate hydrates form on the surface of the clinker particles, which are very fine-grained in the beginning. After completion of the induction period, a further intense hydration of clinker phases takes place. This third period (accelerated period) starts after approximately four hours and ends after 12 to 24 hours. During this period a basic microstructure forms, consisting of C-S-H needles and C-S-H leafs, platy calcium hydroxide and ettringite crystals growing in longitudinal shape. Due to growing crystals, the gap between the cement particles is increasingly bridged. During further hydration, the hardening steadily increases, but with decreasing speed. The density of the microstructure rises and the pores fill: the filling of pores causes strength gain.

Types of Portland cement

General

There are different standards for classification of Portland cement. The two major standards are the ASTM C150 used primarily in the U. ASTM International ( ASTM) originally known as the American Society for Testing and Materials is an international Standards organization that develops and publishes S. 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 C 150.

ASTM C150

There are five types of Portland cements with variations of the first three according to ASTM C150. ASTM International ( ASTM) originally known as the American Society for Testing and Materials is an international Standards organization that develops and publishes

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. Loss on Ignition is a test used in inorganic Analytical chemistry, particularly in the analysis of Minerals It consists of strongly heating ( "igniting" 0% free CaO.

A limitation on the composition is that the (C₃A) shall not exceed fifteen percent.

Type II is intended to have moderate sulfate resistance with or without moderate heat of 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 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.

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

Type III is 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 typically 50-80% higher. Specific surface area is a material property of Solids which measures the total Surface area per unit of Mass, solid or bulk Volume, or cross-sectional 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.

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. In Organic chemistry, a hydration reaction is a Chemical reaction in which a Hydroxyl group (OH- and a Hydrogen Cation However, as a consequence the strength of the concrete develops slowly. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag 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. Ground granulated blast furnace slag ( GGBS or GGBFS) is obtained by quenching molten Iron Slag (a by-product of iron and Steel making

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 five percent for Type V Portland cement. Another limitation is that the (C₄AF) + 2(C₃A) 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 (C₃A) causing disruptive expansion. In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal 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 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.

EN 197

EN 197-1 defines 5 classes of common cement that comprise Portland cement as a main constituent. European Committee for Standardization or Comité Européen de Normalisation ( CEN) is a private non-profit organisation whose mission is to foster the European economy These classes differ from the ASTM classes.

I	Portland cement	Comprising Portland cement and up to 5% of minor additional constituents
II	Portland-composite cement	Portland cement and up to 35% of other single constituents
III	Blastfurnace cement	Portland cement and higher percentages of blastfurnace slag
IV	Pozzolanic cement	Portland cement and up to 55% of pozzolanic constituents
V	Composite cement	Portland cement, blastfurnace slag and pozzolana or fly ash

Constituents that are permitted in Portland-composite cements are blastfurnace slag, silica fume, natural and industrial pozzolans, silicious and calcareous fly ash, burnt shale and limestone. Silica fume, also known as microsilica, is a by-product of the reduction of high-purity Quartz with coke in Electric arc furnaces in the production A pozzolan is a material which when combined with Calcium hydroxide, exhibits Cementitious properties Fly ash is one of the residues generated in the Combustion of Coal.

White Portland cement

Main article: White Portland cement

White Portland cement differs physically from the gray form only in its color, and as such can fall into many of the above categories (e. 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 g. ASTM Type I, II and/or III). However, its manufacture is significantly different from that of the gray product, and is treated separately.

Safety and environmental effects

Safety

When cement is mixed with water a highly alkaline solution (pH ~13) is produced by the dissolution of calcium, sodium and potassium hydroxides. In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal pH is the measure of the acidity or alkalinity of a Solution. Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 In Chemistry, hydroxide is the most common name for the diatomic Anion OH− consisting of Oxygen and Hydrogen Gloves, goggles and a filter mask should be used for protection. A glove ( Middle English from Old English glof) is a type of Garment (and more specifically a Fashion Goggles or safety glasses are forms of protective eyewear that usually enclose or protect the eye area in order to prevent particulates water or chemicals from Hands should be washed after contact. Cement can cause serious burns if contact is prolonged or if skin is not washed promptly. Once the cement hydrates, the hardened mass can be safely touched without gloves.

In Scandinavia, France and the UK, the level of chromium(VI), which is thought to be toxic and a major skin irritant, may not exceed 2 ppm (parts per million). Terminology and usage As a cultural term "Scandinavia" has no official definition and is subject to usage by those who identify with the culture in question as well This article is about the country For a topic outline on this subject see List of basic France topics. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Chromium (ˈkroʊmiəm is a Chemical element which has the symbol Cr and Atomic number 24 "Parts-per" notation is used especially in Science and Engineering, to denote Ratios (relative proportions in measured quantities particularly

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 CO₂ from the raw materials during manufacture, and damage to countryside from quarrying. Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate 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.

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 SO₂ [sulfur dioxide], and peak and full-shift concentrations of SO₂ should be periodically measured. " ^[4] "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. " ^[5] Cement Reviews' "Environmental News" web page details case after case of environmental problems with cement manufacturing. ^[6]

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_x, SO₂, and particulates), accidents and worker exposure to dust. AEA Technology plc was formed in 1996 as the privatised offshoot of the United Kingdom Atomic Energy Authority. ^[7]

The CO₂ associated with Portland cement manufacture falls into 3 categories:

(1) CO₂ derived from decarbonation of limestone,

(2) CO₂ from kiln fuel combustion,

(3) CO₂ produced by vehicles in cement plants and distribution. Limestone is a Sedimentary rock composed largely of the Mineral Calcite ( Calcium carbonate: CaCO3

Source 1 is fairly constant: minimum around 0. 47 kg CO₂ per kg of cement, maximum 0. 54, typical value around 0. 50 world-wide. Source 2 varies with plant efficiency: efficient precalciner plant 0. 24 kg CO₂ per kg cement, low-efficiency wet process as high as 0. 65, typical modern practices (e. g UK) averaging around 0. 30. Source 3 is almost insignificant at 0. 002-0. 005. So typical total CO₂ is around 0. 80 kg CO₂ per kg finished cement. This leaves aside the CO₂ associated with electric power consumption, since 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 0. 09-0. 15 kg CO₂ per kg finished cement if the electricity is coal-generated.

Overall, with nuclear- or hydroelectric power and efficient manufacturing, CO₂ generation can be as little as 0. 7 kg per kg cement, but can be as high as twice this amount. 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 CO₂ emitter, concrete (of which cement makes up about 15%) compares quite favorably with other building systems in this regard. Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag See also cement kiln emissions. Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate

Cement plants as alternatives to conventional waste disposal or processing

Due to the high temperatures inside cement kilns, combined with the oxidizing (oxygen-rich) atmosphere and long residence times, cement kilns have been used as a processing option for various types of waste streams. Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate Cement kilns are used for the Pyroprocessing stage of manufacture of Portland and other types of hydraulic Cement, in which Calcium carbonate The waste streams often contain combustible material which allows the substitution of part of the fossil fuel normally used in the process.

Waste materials used in cement kilns as a fuel supplement: [1]

1. Car and truck tires; steel belts are easily tolerated in the kilns
2. Waste solvents and lubricants.
3. Hazardous waste; cement kilns completely destroy hazardous organic compounds
4. Bone meal; slaughter house waste due to bovine spongiform encephalopathy contamination concerns
5. Waste plastics
6. Sewage sludge
7. Rice shells
8. Sugar cane waste

Portland cement manufacture also has the potential to remove industrial byproducts from the waste-stream, effectively sequestering some environmentally damaging wastes. Bovine Spongiform Encephalopathy ( BSE) commonly known as Mad-Cow Disease ( MCD) is a fatal Neurodegenerative disease in Cattle ^[8] These include:

1. Slag
2. Fly ash (from power plants)
3. Silica fume (from steel mills)
4. Synthetic gypsum (from desulfurisation)

See also

• Lime mortar
• Mortar (masonry)
• Rosendale cement
• White Portland cement

References

1. ^ "The Cement Industry 1796-1914: A History," by A. Slag is the By-product of Smelting Ore to purify Metals They can be considered to be a mixture of metal Oxides however Fly ash is one of the residues generated in the Combustion of Coal. Silica fume, also known as microsilica, is a by-product of the reduction of high-purity Quartz with coke in Electric arc furnaces in the production Gypsum is a very soft Mineral composed of Calcium sulfate dihydrate with the Chemical formula Ca[[sulfur S]] O 4·2 Lime mortar is a type of mortar. It was used in the construction of the vast majority of brick and stone buildings worldwide from ancient times until the widespread adoption Mortar is a workable paste formed by mixture of Cement, Water and fine aggregate Masonry to bind construction blocks together and fill the gaps between Rosendale cement refers to a type of natural Cement produced in and around Rosendale New York. 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 J. Francis, 1977
2. ^ P. C. Hewlett (Ed)Lea's Chemistry of Cement and Concrete: 4th Ed, Arnold, 1998, ISBN 0-340-56589-6, Chapter 1
3. ^ Housing Prototypes: Page Street
4. ^ Epidemiologic Notes and Reports Sulfur Dioxide Exposure in Portland Cement Plants
5. ^ http://www.azdeq.gov/function/news/2003/jan.html
6. ^ CemNet.com | The latest cement news and information
7. ^ Toward a Sustainable Cement Industry: Environment, Health & Safety Performance Improvement
8. ^ "As a generalization, probably 50% of all industrial byproducts have potential as raw materials for the manufacture of Portland cement. " Kosmatka, S. H. ; Panarese, W. C. (1988). Design and Control of Concrete Mixtures. Skokie, IL, USA: Portland Cement Association, p. 15. ISBN 0-89312-087-1.  

External links

• World Production of Hydraulic Cement, by Country
• PCA - The Portland Cement Association
• Alpha The Guaranteed Portland Cement Company: 1917 Trade Literature from Smithsonian Institution Libraries
• Cement Sustainability Initiative
• A cracking alternative to cement
• What is the Difference Between Cement, Portland Cement & Concrete?
• Aerial views of the world's largest concentration of cement manufacturing capacity, Saraburi Province, Thailand, at 14.6325° N 101.0771° E

Saraburi (สระบุรี is one of the central provinces ( changwat) of Thailand. The Kingdom of Thailand (ˈtaɪlænd ราชอาณาจักรไทย, râːtɕʰa-ʔaːnaːtɕɑ̀k-tʰɑj

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