Glossary Version 2.5 © WHD Microanalysis Consultants Ltd 2009

Glossary of some terms used in , and in the analysis of cementitious materials

NOTES:

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90µm residue See raw meal.

AFm AFm (Al2O3-Fe2O3-mono) represents another group of calcium aluminate hydrates with the general formula:

[Ca2(Al, Fe)(OH6)].X.nH2O

where X represents a singly charged anion or 'half' a doubly charged anion. X may be one of many anions; the most important in hydration are hydroxyl, sulfate and carbonate.

‘Monosulfate’ –present in most mature Portland cement –has the formula:

C3A.CaSO4.12H2O

AFt AFt (Al2O3-Fe2O3-tri) represents a group of calcium sulfoaluminate hydrates. AFt has the general formula:

[Ca3(Al,Fe)(OH)6.12H2O]2.X3.xH2O

where X represents a doubly charged anion or, sometimes, two singly charged anions. is the most common and important member of the AFt group (X in this case denoting sulfate.) The formula for ettringite (ignoring any iron substitution for aluminium) can also be written as:

[Ca3Al(OH)6.12H2O]2.(SO4)3.2H2O or C3A.3CaSO4.32H2O

Aggregate Sand and gravel mixed with cement and to make concrete.

Air setting Loss of flowability or formation of lumps of cement during storage. Can be due to cement hydration from water in gypsum added during grinding, or to syngenite formation.

Åkermanite, Akermanite Calcium magnesium silicate (C2MS2 or 2CaO.MgO.2SiO2). Not generally present in Portland cement; may be present as a minor component in slag.

Alite Impure tricalcium silicate. The main hydraulic mineral in Portland cement, typically comprising 50%-70% of the unhydrated cement.

For more information, see: www.understanding-cement.com/clinker.html

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Alkali sulfate Alkali sulfate in the context of Portland cement clinkers means primarily sodium sulfate (mineral name thenardite), potassium sulfate (mineral name arcanite), a sodium-potassium sulfate (mineral name aphthitalite) or calcium langbeinite. Exactly which minerals form depends on the amounts and proportions of potassium and sodium in the clinker, and the ratio of available alkali to sulfate.

For more information, see: www.understanding-cement.com/variability.html

Alkali-carbonate reaction Some aggregates containing dolomite react with the alkaline (dedolomitization) cement pore fluid. The process is not fully understood but involves the replacement of dolomite by calcite and magnesium hydroxide crystals:

- 2- CaMg(CO3)2+2OH  CaCO3+Mg(OH)2+CO3

The presence of clay in the aggregate appears to be of importance.

Alkali-silica reaction A reaction between the cement pore fluid in concrete with certain types of silica, which may occur in concrete aggregate. Susceptible types of silica include strained or microcrystalline quartz, glass, cristobalite, tridymite, opal, flint, and chert. A gel is formed which exerts an expansive force within the concrete and which may lead to widespread cracking and failure of the concrete.

For more information, see: www.understanding-cement.com/alkali-silica.html

Alkali-sulfur ratio in Ratio of K2O and Na2O to SO3 in clinker. Can be expressed as clinker ratio of Na2O-equivalent to sulfate. Important because an excess of alkali over sulfate may lead to the formation of alkali and aluminate. Alkali-stabilised belite is difficult to convert to and alkali aluminate (=prismatic or orthorhombic C3A) may cause setting problems.

Alumina Ratio (AR or An important parameter in composition. A/F) Given by:

Al2O3 / Fe2O3

Where Al2O3 and Fe2O3 are the relevant contents of the clinker.

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Aluminate Impure . Very reactive on contact with water but only weakly hydraulic. Typically comprises 5%-10% of Ordinary Portland Cement. Plays an important role in the setting of cement.

For more information, see: www.understanding-cement.com/clinker.html

AR (or A/F) See Alumina Ratio

ASTM C150 American Society for Testing and Materials standard specification for Portland cement. Cement is classified into eight types: Type I cement –general purpose cement where the special properties of cement of other types is not required. Type IA –air entraining cement for use in the same applications as Type I where air-entrainment is required. Type II cement –general use; also where moderate heat of hydration or moderate sulfate resistance is required. Type IIA –air-entraining cement for use in the same applications as Type II where air-entrainment is required. Type III –high early strength cement. Type IIIA –air-entraining cement for use in the same applications as Type III where air-entrainment is required. Type IV –low heat of hydration cement. Type V –cement with a high sulfate resistance.

Autoclaved aerated Lightweight concrete, usually in the form of blocks. AAC has a concrete (AAC) low density due to the inclusion of large numbers of air cells, typically 1mm –5mm across.

Produced in an autoclave at high pressure and temperature. Materials used in AAC production are typically cement and as the binder, with sand or pulverized fuel ash (PFA) as the source of silica. The air cells are formed by the addition of aluminium powder, which generates hydrogen bubbles in the alkaline environment of the mix.

AAC does not contain the normal cement hydration products present in concrete cured at normal temperatures. The main constituent of AAC is 1.1nm tobermorite.

Belite Impure dicalcium silicate. A hydraulic mineral in Portland cement, typically comprising 5%-30% of the clinker. Also an important hydraulic mineral in natural hydraulic lime.

For more information, see: www.understanding-cement.com/clinker.html

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Bleeding After concrete has been placed and before it has set, the effect of gravity tends to cause segregation, where coarser aggregate particles settle downwards and water rises upwards. The rising water carries cement fines. This effect is called ‘bleeding.’ Bleeding occurs only to a minor extent where the mix is cohesive. Excessive bleeding may indicate a high water-cement ratio and results in a light-coloured and porous, friable concrete surface. It may also affect the strength and durability of the concrete due to the sub-optimal distribution of cement fines.

Bogue calculation Calculation to give the approximate proportions of the four main clinker minerals in Portland cement clinker, requiring the clinker bulk analysis and the free lime content, the free lime being subtracted from the total CaO before calculating the mineral proportions.

Approximately given by:

C3S=4.0710CaO - 7.602SiO2 - 6.7187Al2O3 - 1.429Fe2O3

C2S=-3.0710CaO + 8.6024SiO2 + 5.0683Al2O3 + 1.0785Fe2O3

C3A=2.6504Al2O3 - 1.6920Fe2O3

C4AF=3.0432Fe2O3

Can be applied to by subtracting 0.7SO3 from the CaO, as well as the correction for free lime. This assumes all the sulfate is present as calcium sulfate; this is unlikely to be strictly the case as some sulfate will be present as clinker alkali sulfate. A further error will be introduced if the cement contains other material such as fine limestone; this may be added as a “minor additional constituent” (mac) in the cement mill.

For more information, see: www.understanding-cement.com/bogue.html

C2S C2S represents dicalcium silicate in cement chemistry notation. Belite in cement clinker is C2S with impurities.

For more information, see: www.understanding-cement.com/clinker.html

C3A C3A represents tricalcium aluminate in cement chemistry notation. Aluminate phase in cement clinker is C3A with impurities.

For more information, see: www.understanding-cement.com/clinker.html

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C3S C3S represents tricalcium silicate in cement chemistry notation. Alite in cement clinker is C3S with impurities.

For more information, see: www.understanding-cement.com/clinker.html

C4AF C4AF represents tetracalcium aluminoferrite in cement chemistry notation. Ferrite phase in cement clinker may approximate to this composition but the proportions of C, A and F may also vary considerably. Ferrite also contains impurities.

For more information, see: www.understanding-cement.com/clinker.html

Calciner Additional burner placed in the preheater tower. See: http://www.understanding-cement.com/kiln.html

Calcium Aluminate Typically made from limestone and bauxite, or other material Cement (=CAC, High with a high alumina content, heated to about 1500 C, at which Alumina Cement, HAC) temperature it is completely molten. When cooled, the cooled liquid contains principally calcium aluminate (CA) with C12A7. Other calcium aluminates may be present. CACs typically show rapid strength growth and good resistance to sulfates and chemical attack generally. Often used in grouts, floor screeds and other cementitious applications blended with Portland cement and gypsum.

See also conversion.

Calcium hydroxide See cement hydration products (Portlandite)

Calcium silicate bricks Dense bricks, blocks or pavers, usually produced by autoclaving sand and lime mixes. 1.1nm tobermorite is the principal constituent.

Carbon dioxide (CO2) An odourless, colourless gas essential to plant life for photosynthesis. By volume CO2 comprises about 380 ppm (parts per million) of the earth’s atmosphere. Cement production releases CO2 when limestone is calcined. CO2 is also released from the burning of fossil fuels in the kiln and from electricity generation to power the mills and other parts of the production process. Total CO2 emissions from Portland cement production are approximately 900kg-1000kg per tonne cement (eg: 970kg/tonne in USA in 2001 - source: CO2 Emissions Profile of the U.S. Cement Industry Hanle et al 2004) but the actual values will vary appreciably between different cement plants depending on their efficiency and the extent to which they use supplementary fuels.

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Cement Hydraulic powder which reacts with water to form a solid mass. The most common type of cement in use is Portland Cement, of which there are a number of different types. See cement types.

Cement Chemistry An arcane but convenient notation where single letters Notation represent :

C=CaO, S=SiO2, F=Fe2O3, A=Al2O3, N=Na2O, K=K2O T=TiO2, H=H2O, M=MgO, P=P2O5, also: _ S = SO3 – spoken as ‘Ess-bar’ _ C = CO2 - spoken as ‘See-bar’

The last two are becoming used rather less-commonly; it is easy to write a line above a letter when writing with a pen but more difficult with a word processor.

For example, C3S represents tricalcium silicate and C3A represents tricalcium aluminate.

For more information, see: www.understanding-cement.com/notation.html

Cement clinker Portland cement clinker is the unground (unmilled) nodular product from the kiln. Clinker is typically composed of nodules ranging in size from 30mm to dust.

For more information, see: www.understanding-cement.com/clinker.html

Cement hydration Process of reaction of cement with water. The most important cement hydration product is hydrate, often abbreviated to ‘C-S-H’.

For more information, see: www.understanding-cement.com/hydration.html

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Cement hydration In-situ hydration product: hydration product which has products formed within the volume formerly occupied by a cement grain - usually this is only visible for the larger grains by SEM. In- situ hydration product is usually relatively pure C-S-H. Also known as 'inner product.' See also ‘Undesignated product.’

Undesignated product: hydration product forming the matrix containing all other hydration products in the concrete apart from in-situ hydration product. Strictly, the space originally occupied by water on mixing but in practice also includes the volumes formerly occupied by small cement grains, the outlines of which later are obscured. Also known as 'outer-product' and 'undifferentiated product.' See also ‘In-situ hydration product’.

Calcium hydroxide (Portlandite): Ca(OH)2 or CH, Probably forms mainly in regions in concrete initially occupied by water on mixing.

Ettringite: forms mainly in the early stages of cement hydration. After a few days, monosulfate, rather than ettringite, is normally the main sulfate-containing phase in hydrated cement. Formula is C3A.3CaSO4.32H2O. Ettringite is commonly found in concrete subjected to sulfate attack. See also AFt phase.

Monosulfate: the main sulfate-containing phase in mature concrete. Formula is C3A.CaSO4.12H2O. See also AFm phase.

For more information, see: www.understanding-cement.com/hydration.html

Cement mill In principle, a large rotating cylinder containing steel balls which smash the clinker particles to produce a fine powder. In practice the product of much engineering evolution to achieve maximum efficiency. Cement mills typically contain several chambers with different sized grinding media (steel balls) to grind the cement particles increasingly finely. Screens (meshes) within the mill control particle size. Oversized particles may be returned for further grinding.

For more information, see: www.understanding-cement.com/milling.html

Cement sulfate content Sulfates in Portland cement are generally of two types: sulfate originally present in the clinker and sulfate added in the form of gypsum when the clinker was ground into cement. Too little sulfate may lead to flash setting; too much sulfate may lead to false setting (or plaster set), and possibly also to damaging expansion due to sulfate attack. In Portland cement, sulfate is typically approximately 3% SO3 by weight of cement. Sulfate contents are limited by standard specifications for cement.

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Cement types There are many different types of cement. The most common is Portland Cement. Other types include:

calcium aluminate cement, or CAC; also known as high alumina cement, or HAC calcium sulfoaluminate cement (CSA) hydraulic lime extended cements –mixtures of Portland Cement with other reactive material which take part in the hydration process, such as fly ash or ground slag; also known as blended cements or composite cements or combination cements.

Cementitious Adjective –a material that is cementitious has the ability to bond other materials together.

CH CH represents calcium hydroxide in cement chemistry notation.

Chloride Present in trace amounts in Portland cement. Can act as an accelerator with eg: calcium chloride addition but is highly detrimental to steel reinforcement in concrete as it accelerates corrosion. Chloride contents in cements are limited by cement standards eg: a maximum of 0.1% specified in EN-197.

Clinker See cement clinker.

Clinker milling or clinker Process of reducing the clinker particle size. Clinker is ground grinding finely, usually interground with gypsum, to produce cement. Particle size of the ground clinker in cement is typically 100µm down to sub-micron. There are various ways of controlling the cement particle size, most commonly by cement surface area (eg: 350m2 kg-1) but particle size distribution or sieve residue are also sometimes used.

For more information, see: www.understanding-cement.com/milling.html

Clinker mineral Proportions of the four main minerals in Portland cement clinker proportions (alite - C3S; belite –C2S; aluminate - C3A and ferrite - C4AF are commonly calculated using the Bogue calculation. This calculation uses assumed pure mineral compositions and requires the bulk analysis of the clinker for CaO, SiO2, Al2O3 and Fe2O3, and the unreacted lime in the cement ('free lime').

For more information, see: www.understanding-cement.com/bogue.html

Cohesiveness A concrete mix that is cohesive does not segregate or bleed to any significant extent. See bleeding and segregation.

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Concrete A synthetic rock containing sand and gravel aggregate, bonded in a cementitious matrix.

Conversion Applied to concrete made from calcium aluminate cements, this is the process of conversion of one form of calcium aluminate hydrate to another. The principal component of CAC - calcium aluminate or CA - hydrates to form calcium aluminate hydrate (CAH10). This is very strong, but also unstable at normal temperatures. It slowly, over a period of months or years depending on the concrete mix and ambient conditions, converts to C3AH6 plus aluminium hydroxide and water. Conversion results in some loss of strength of the concrete because the porosity of the cement paste increases. How significant this strength loss is, depends on the particular circumstances of the case.

See also calcium aluminate cement.

Creep (of concrete) The increase in strain while under a stress maintained over a long period of time.

C-S-H C-S-H represents calcium silicate hydrate in cement chemistry notation. The '-' are important and indicate that no exact stoichiometric proportions are intended.

Delayed Ettringite A particular form of sulfate attack which may occur in concrete Formation (DEF) cured at high temperatures. Does not require additional sulfate –the sulfate originally in the cement is sufficient to produce DEF. See also TSA.

For more information, see: www.understanding-cement.com/sulfate.html

EDX Energy-dispersive X-ray microanalysis (sometimes also known as EDS: Energy-dispersive X-ray Spectroscopy and EDAX.)

For more information, see: www.whd.co.uk

EN-196 European standard for methods of testing cement.

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EN-197 European standard for the composition, specifications and conformity criteria for common cements.

CEM I – Portland cement CEM II – Portland-composite cements CEM III - Blastfurnace cements CEM IV - Pozzolanic cements CEM V - Composite cements

Suffixes are used to indicate the proportion and nature of other constituents, and the strength class of the cement. Eg: a cement classified as: CEM II/A-LL 42,5 N is a Portland composite cement (CEM II) containing a low proportion (A) (6%-20%) of the second constituent. The second constituent is limestone (L), in this case a high-purity limestone (LL). The cement strength class is 42,5 –ie: normal strength development.

Ettringite See cement hydration products and AFt.

European cement See standard specifications for cement. standards

False setting (false- False setting can occur as concrete or mortar is being mixed. It setting, plaster set) happens if there is an excess of soluble sulfate available in the cement pore fluid (mix water). This results in the formation of crystals of gypsum (calcium sulfate dihydrate) and these crystals cause the mix to stiffen. The gypsum crystals may re- dissolve, so it may be possible to mix through a false set and restore workability.

For more information, see: www.understanding-cement.com/variability.html

Ferrite Impure tetracalcium aluminoferrite. Typically comprises 5%- 10% of Ordinary Portland Cement. Black or dark grey in colour, ferrite gives cement the characteristic grey colour.

For more information, see: www.understanding-cement.com/clinker.html

Fine filler effect The physical effect of the incorporation of fine powder (of cement fineness or finer) in concrete mixes can have a beneficial effect on the concrete. These small particles act as additional nucleation sites on which cement hydrates can form, resulting on more rapid cement hydration and a more uniform, denser, microstructure giving higher strengths.

The fine filler effect is a physical effect and separate from any chemical reactions in which the fine particles may participate.

Ground limestone is a typical example of a material that can act as a fine filler.

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Flash setting Flash setting occurs if insufficient sulfate is available in the pore fluid (mix water) to control the hydration of the aluminate (C3A) phase in the cement. The aluminate phase is the most reactive phase in cement and reacts quickly with water to produce calcium aluminate hydrates. These crystals bond particles together in the mix and reduce workability. In the extreme case, they can form an interlocking mass which produces a solid mix. Unlike false setting, flash setting cannot be mixed through, as the calcium aluminate hydrates do not re-dissolve.

For more information, see: www.understanding-cement.com/variability.html

Free lime Unreacted lime (, CaO) in Portland cement clinker; usually less than about 2%.

Freeze-thaw Damage caused to concrete by frost action is common; repeated cycles of freezing followed by thawing cause spalling (flaking) at the surface and, possibly, vertical cracks extending into the concrete. Dense concrete made with a low water/cement ratio and hence low permeability is resistant to freeze-thaw action; air entrained concrete is also resistant. Damage is caused by the formation of an ice front extending into the concrete from the surface.

Grindability A descriptive term, usually applied to clinker but also to raw materials and coal, indicating the ease with which the material can be ground to the required fineness.

Grindability can be quantified by procedures based on grinding a quantity of material for a fixed time and assessing the degree of comminution of the material. The Hardgrove Test is a widely- used test.

Factors which may adversely affect clinker grindability include: low nodule porosity; increasing proportion of flux phases, especially ferrite and the presence of numerous, large, belite clusters. Improving the homogeneity of the raw feed is likely to improve clinker grindability.

Grout A fine material typically used to fill gaps and joints eg: between floor or wall tiles. Grouts may be cementitious (eg: containing cement, fine sand, water and admixtures) or based on other materials such as resin.

Gypsum Calcium sulfate dihydrate (CaSO4.2H2O).

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Hydraulic The ability to react with water to form a solid.

A ‘latently hydraulic’ material is one that reacts with water to form a solid if a small amount of activator is added. Typical activators are cement or lime, or other alkaline material such as sodium hydroxide.

Ground granulated blastfurnace slag (=GGBFS, GBFS) is a latently hydraulic material. When mixed with Portland cement, GBFS is activated by the alkaline environment provided by the cement.

Hydrogarnet Hydrated mineral of variable composition: often referred to as C3AH6 but this is only one end member of a solid solution series bounded by C3AH6,C3FH6, C3AS3,C3FS3. Occurs in concrete in sites formerly occupied by ferrite phase. Also a significant phase in autoclaved concrete products especially when made using pulverised fuel ash (PFA).

In-situ hydration product See cement hydration products

Kiln See rotary kiln.

Lime Saturation Factor An important parameter in cement clinker composition. Given (LSF) by:

CaO / (2.8SiO2 + 1.2 Al2O3 + 0.65Fe2O3)

Where CaO, SiO2, Al2O3 and Fe2O3 are the relevant oxide contents of the clinker.

For more information, see: www.understanding-cement.com/parameters.html

Litre weight of clinker Bulk density of clinker, usually determined on a particular nodule size fraction by weighing a litre of clinker. Underburned clinker is porous and has a higher litre weight compared with harder-burned clinker. The litre weight is therefore a very approximate rough-and-ready assessment of the clinker burning regime. By way of illustration, a litre weight of 1.4 kg may indicate good combination, while 1.1 kg-1.3 kg may suggest underburning or poor combination due to other causes. The actual optimum values will vary between clinkers from different sources and also depend on the size fraction used.

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Loss on ignition (LOI) A test involving heating the sample to be tested to drive off volatile material. In the context of cement, a cement sample is heated at 1000 ºC; the LOI shows the extent that the cement has hydrated and carbonated through exposure to air. In cement, the LOI mainly detects hydrated and carbonated free lime (CaO) and free magnesia (MgO), but any hydration of the main clinker minerals will also be detected. The LOI is limited by standard specifications for cement.

LSF See Lime Saturation Factor

Mac A “mac” is a minor additional constituent; macs are permitted inclusions up to 5% by mass of the cement under the European cement standard EN197-1. Macs are: - inorganic natural mineral materials, or - inorganic mineral materials derived from the clinker production process, or - other constituents, but not those already included as main constituents in the cement. Under the standard, a cement containing a mac must comply with the same performance and compositional criteria as would apply to that cement if the mac were not present. Typical examples of macs are fine limestone, dust and PFA.

Metakaolin Metakaolin is produced by heating (china clay). This results in a highly reactive pozzolan.

Inclusion of metakaolin in a concrete mix can result in a beneficial effect on concrete properties, including strength and durability.

Microsilica (silica fume) By-product of production. As used in concrete, it has a small particle size (typically about 0.1µm across) and a high surface area. It is a very reactive pozzolan, usually mixed in concrete as a slurry.

Inclusion of microsilica in a concrete mix can result in a beneficial effect on concrete properties, including strength and durability.

Monosulfate phase See cement hydration products

National Standards See standard specifications for cement.

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Newton SI unit of force, symbol N. Defined as the force that causes a mass of one kilogram to accelerate by one metre per second per second. Concrete compressive strength measurements are often given in units of N mm-2 (Newtons per square millimeter). The “per square millimeter” is often omitted for brevity, thus: “60 Newton concrete” means concrete that has a compressive strength of 60 N mm-2. Measurements in Newtons per square millimeter are measurements of pressure or stress; the SI unit of pressure is the Pascal (symbol Pa). One Pascal is equivalent to a force of one Newton exerted over one square metre. One N mm-2 is therefore equivalent to 1 MPa (one megapascal).

Optical microscopy of Examining cement or cement clinker using optical microscopy is cement and clinker a powerful technique in troubleshooting cement production problems. Is also used on many cement plants (=cement works) as a kiln control technique.

For more information, see: www.whd.co.uk

Pascal (Pa) Derived SI unit of pressure and stress, defined as one Newton per square metre. Concrete strengths may be given in MegaPascals (MPa).

Periclase , MgO. Periclase crystals form in Portland cement clinker if the clinker MgO content is greater than about 2%. Below 2% the MgO can be accommodated within the crystal structures of the clinker minerals. Excessive amounts of periclase can lead to expansion of hardened concrete, as the periclase hydrates to form magnesium hydroxide. For this reason, the MgO content of cement is limited by national standards.

PFA (Pulverised Fuel Ash) PFA is the fused non-combustible mineral component in pulverized coal, separated from the flue gas. In the flame, the mineral assemblages fuse to form a molten blob, which is spherical in shape due to the surface tension of the liquid. The molten material usually solidifies before impacting any hard surface, so PFA is largely composed of small glassy spheres, typically 100µm to sub-micron in diameter.

Partial replacement of cement by PFA can result in a beneficial effect on concrete properties, including strength, durability and resistance to chemical attack.

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Portland cement There are various types of Portland cement. The most common is the typical ‘grey cement.’ Usually made by heating limestone and clay at about 1450 C and grinding the resulting clinker with a little gypsum to control the setting process.

For more information, see: www.understanding-cement.com/basic.html

Pozzolan - Pozzolanic Pozzolanic materials are predominantly siliceous and do not react with water alone, but react with lime and water to produce calcium silicate hydrate. When mixed with Portland cement, they can contribute significantly to calcium silicate hydrate formation and therefore to strength development.

Pozzolanic materials mixed with lime also form calcium silicate hydrate and such mixtures are an effective hydraulic cement. Hydraulic lime was produced in this way by the Romans and is still produced today.

Pozzolanic materials include: pulverized fuel ash (PFA); metakaolin, ground fired clay-eg:bricks and microsilica (silica fume).

Pre-calciner Dry process type of kiln with an additional burner in the preheater tower. Most new kilns are of the pre-calciner type as it is the most energy-efficient of the different types of cement kiln.

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Quarry (noun) Place where rock or other raw material is extracted from the ground to make cement or other products. (verb) To extract raw materials from the ground on an industrial scale.

Raw meal Raw (unburned) material as it is fed to the kiln, comprising ground raw materials mixed in the correct proportions.

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Raw meal Raw materials for making cement (limestone, shale, clay, sand etc.) that have been crushed, milled and blended into the desired proportions. The fineness is often controlled by the residue on a sieve with a 90µm aperture mesh; the ‘90µm residue’ is typically 9%-15%.

UNDERSTANDING CEMENT GLOSSARY OF CEMENTITIOUS TERMS

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Reactions in the cement Typically those of: calcination (loss of from kiln limestone); formation of intermediate products (part of the process of combining the raw materials but intermediate products are not present in the final clinker); and clinkering (formation of nodules from raw meal as liquid forms, combination of belite and free lime to form alite).

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Rotary kiln Almost all Portland cement clinker is produced in a rotary kiln. In essence, the rotary kiln is a long cylinder with a flame at one end. The kiln is inclined at a small angle, with the flame (burner) end being slightly lower. Kiln feed is introduced at the cool end and, due to the rotating motion of the kiln, gradually passes down the kiln towards the burner. Cement clinker is formed in the burning zone, near the flame, and finally the clinker passes out of the kiln and cools.

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Segregation The process of partial separation of aggregate, cement and water while concrete is in a plastic state. Coarser aggregate moves downwards under gravity, displacing water and fine particles –particularly cement –which move upwards. Segregation is undesirable as it may impair both strength and durability. The more cohesive the mix, the less segregation occurs.

SEM Scanning Electron Microscope; also Scanning Electron Microscopy.

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Silica fume See microsilica.

Silica Ratio (SR) An important parameter in cement clinker composition. Given by:

SiO2 / (Al2O3 + Fe2O3)

Where SiO2, Al2O3 and Fe2O3 are the relevant oxide contents of the clinker.

For more information, see: www.understanding-cement.com/parameters.html

UNDERSTANDING CEMENT GLOSSARY OF CEMENTITIOUS TERMS

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Slag Slag used as a partial cement replacement material in concrete is blastfurnace slag, a by-product of iron production. In the iron-smelting process, limestone is added to the iron ore to react with impurities –mainly these are rich in alumina and silica. The slag is a liquid at about 1500 ºC and is typically tapped off and rapidly cooled with water to form a solid with a high glass content (typically 90%-95%). When ground to cement fineness, the slag is latently hydraulic. Formerly referred to as Ground Granulated Blast Furnace Slag (GGBFS) but ground granulated blastfurnace slag (gbs) is now the standard abbreviation.

Partial replacement of Portland cement by slag can result in beneficial effects on concrete properties, including strength, durability and resistance to chemical attack.

Slump An empirical test of concrete workability. Concrete is placed in a conical container, which is then lifted off the concrete. The degree to which the cone of wet concrete subsides under its own weight is termed ‘slump.’

Set or hardened concrete will have a zero slump. The higher the slump, the ‘runnier’ or sloppier’ the concrete.

e Sodium equivalent Equivalent , Na2O =Na2O+0.66K2O: convenient way of combining sodium and into a single number to represent the alkali content of a cement or a concrete mix. Of particular importance concerning alkali-silica reaction.

SR See Silica Ratio

Standard specifications There are two principal standards for the specification of for cement cement: the European EN-197 and the ASTM C150 used mainly in the United States. BS12, for many decades the British Standard, is now superseded in Britain by BS EN-197 but remains the basis for the national cement standard in some countries.

Stratlingite An AFm phase with an aluminosilicate anion, composition C2ASH8.

UNDERSTANDING CEMENT GLOSSARY OF CEMENTITIOUS TERMS

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Strength “Concrete strength” typically means the compressive strength of concrete. Concrete is strong in compression but weak in tension. Strength depends on a number of factors, including:

 porosity (which in turn depends on compaction, water- cement ratio, air entrainment and any other factors relating to voids)  aggregate grading (particle size distribution of the aggregate)  age  aggregate-paste bond  aggregate strength  admixture-related factors  cement content  curing regime  cement type (including replacement materials, eg: PFA, slag)  other cement-related factors, including cement fineness, alite content, soluble alkali content, alite and belite reactivity.

Strengths are typically measured in Newtons per square millimeter (N mm-2), MegaPascals (MPa), or pounds per square inch (psi); these are therefore measurements of pressure or stress. 1 N m-2 = 1 Pa = ~145x10-6 psi.

Sulfate attack (sulphate Concrete made from Portland cement is susceptible to attack by attack) solutions that contain sulfate. There are different forms of sulfate attack. A typical form might be where, for example, sulfate-containing groundwater reacts with concrete foundations. Concrete suffering from sulfate attack typically contains much ettringite and, possibly, gypsum, although the symptoms of sulfate attack vary widely.

For more information, see: www.understanding-cement.com/sulfate.html

Sulfate-resisting Portland Portland cement made with a low aluminate (C3A) content. Cement (SRPC, Type V Hydration products of the aluminate phase make concrete more cement) susceptible to sulfate attack.

Suspension preheater Part of a dry process type of kiln in which raw feed is fed from the top of a tower –the preheater tower –downwards through a series of cyclones and then into the kiln at the bottom of the tower. Heat is transferred from the hot kiln gases passing upwards through the cyclones, to the raw meal as it passes downwards.

For more information, see: www.understanding-cement.com/kiln.html

UNDERSTANDING CEMENT GLOSSARY OF CEMENTITIOUS TERMS

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Syngenite Portland cement hydration product composed of alkalis and sulfates. Typically found in air-set cement, such as in old bags of cement, where syngenite has formed at the points of contact of the cement grains. This results in a loss of flowability of the powder, or the formation of ‘lumps’ of cement in more severe cases.

Syngenite has the formula:

K2Ca(SO4)2.H2O

Syngenite may also form during normal cement hydration in a concrete or mortar mix. See also air setting.

Thaumasite (TSA) Thaumasite formation is a particular type of sulfate attack ('TSA' - thaumasite form of sulfate attack) in which thaumasite -(Ca3Si(OH)6(SO4)(CO3).12H2O) - forms through a combination of sulfate attack and carbonation. TSA can attack the surface regions of concrete foundations but more commonly is found in masonry and render. Usually thought to require cold conditions to form.

For more information, see: www.understanding-cement.com/sulfate.html

Tobermorite Tobermorite (strictly, 1.1nm tobermorite) is the main constituent of autoclaved aerated concrete and of calcium silicate bricks. It is a calcium silicate hydrate. When produced from a mixture of lime and silica sand, it has the idealized composition C5S6H5.

When produced from mixes including cement and, especially, pulverized fuel ash or slag, tobermorite also contains aluminium. These tobermorites tend to be ‘anomalous tobermorites.’ Another form of tobermorite, 1.4nm tobermorite, occurs as a natural mineral. On heating above 55 ºC it converts to 1.1nm tobermorite.

Type I cement See ASTM C150 Type II cement Type III cement Type IV cement Type V cement

Undesignated product See cement hydration products

UNDERSTANDING CEMENT GLOSSARY OF CEMENTITIOUS TERMS

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Water cement ratio Water/cement ratio (w/c) is defined as the weight of water in a mix divided by the weight of cement. Eg: a mix containing 400 kg cement and 180 kg water per cubic metre of concrete has a water/cement ratio of 180/400 = 0.45.

For more information, see: www.understanding-cement.com/hydration.html

Wet process kiln The original type of rotary cement kiln, in which the raw meal is fed as slurry into the kiln. This is the simplest type of rotary kiln, but it is not energy-efficient. The water has to be driven off and the process of heat transfer from the hot kiln gases to the raw meal is inefficient. Because the process is so thermally inefficient, wet process kilns have to be longer than dry process kilns.

For more information, see: www.understanding-cement.com/kiln.html

White Portland cement White cement is Portland cement that contains very little ferrite phase. Normal cement is grey due to the presence of ferrite. White cement is made using raw materials of very low iron content so that ferrite does not form, or forms in very small amounts only. White cement clinker is burned under reducing conditions so that Fe3+ is reduced to Fe2+, in which form it substitutes for calcium. Used in specialized architectural applications.

Workability A general descriptive term describing the rheology of fresh concrete –how easily it can be mixed, placed, compacted etc.. In layman’s terms, the ‘runnier’ or ‘sloppier’ the concrete,the better the workability.

Adding water to improve concrete workability generally results in a more porous concrete of lower strength and more susceptible to damage by, for example, frost or chemical attack.

UNDERSTANDING CEMENT GLOSSARY OF CEMENTITIOUS TERMS

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X-ray diffraction (XRD) A powerful analytical technique used for a wide variety of materials. Used to analyse both hydrated and unhydrated cementitious materials. Usually used to analyse powders. Gives a structural analysis based on crystal lattice spacings. XRD only works with crystalline material, hence cannot detect, for example, calcium silicate hydrate in normal concrete except as a broad ‘amorphous hump.’

Can be used to identify defects in concrete such as sulfate attack by determining the presence of salts such as ettringite or thaumasite.

Can be used with cement or clinker to identify mineral phases; can be used quantitatively by a skilled operator.

Routinely used to analyse clinker free lime contents during cement manufacture.

X-ray Fluorescence (XRF) Analytical technique for determining the bulk elemental analysis of a material.

An incident beam of X-rays excites characteristic elemental X- rays within the specimen; these are then collected by an X-ray detector and used to quantify the proportions of each element.

This is a compositional technique, not structural, therefore the crystallinity of the sample does not matter (unlike X-ray diffraction).

Widely used to analyse cement raw materials, clinker and cement.

UNDERSTANDING CEMENT GLOSSARY OF CEMENTITIOUS TERMS

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