Cement chemist notation

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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.

Contents

Abbreviations of oxides

The main oxides present in cement (or in glass and ceramics) are abbreviated in the following way:

CCNActual formulaName
CCaO Calcium oxide, or lime
SSiO2 Silicon dioxide, or silica
AAl2O3 Aluminium oxide, or alumina
FFe2O3 Iron oxide, or rust
TTiO2 Titanium dioxide, or titania
MMgO Magnesium oxide, or periclase
KK2O Potassium oxide
NNa2O Sodium oxide
HH2O Water
CCO2 Carbon dioxide
SSO3 Sulfur trioxide
PP4O10 Phosphorus pentoxide

Conversion of hydroxides in oxide and free water

For the sake of mass balance calculations, hydroxides present in hydrated phases found in hardened cement paste, such as in portlandite, Ca(OH)2, must first be converted into oxide and water.

To better understand the conversion process of hydroxide anions in oxide and water, it is necessary to consider the autoprotolysis of the hydroxyl anions; it implies a proton exchange between two OH−, like in a classical acid–base reaction:

OH−acid 1 + OH−base 2 → O2−base 1 + H2Oacid 2

or also,

2 OH− → O2− + H2O

For portlandite this gives thus the following mass balance:

Ca(OH)2 → CaO + H2O

Thus portlandite can be written as CaO · H2O or CH.

Main phases in Portland cement before and after hydration

These oxides are used to build more complex compounds. The main crystalline phases described hereafter are related respectively to the composition of:

Clinker and non-hydrated Portland cement

Four main phases are present in the clinker and in the non-hydrated Portland cement.
They are formed at high temperature (1,450 °C) in the cement kiln and are the following:

CCNActual formulaNameMineral phase
C3S3 CaO · SiO2Tricalcium silicate Alite
C2S2 CaO · SiO2 Dicalcium silicate Belite
C3A3 CaO · Al2O3 Tricalcium aluminate Aluminate or Celite
C4AF4 CaO · Al2O3 · Fe2O3Tetracalcium alumino ferrite Ferrite

The four compounds referred as C3S, C2S, C3A and C4AF are known as the main crystalline phases of Portland cement. The phase composition of a particular cement can be quantified through a complex set of calculation known as the Bogue formula.

To avoid the flash setting of concrete, due to the very fast hydration of the tricalcium aluminate (C3A), 2 – 5 wt. % calcium sulfate is interground with the cement clinker to prepare the cement powder. In cement chemist notation, CaSO4 (anhydrite) is abbreviated as CS, and CaSO4·2H2O (gypsum) as CSH2.

Similarly, in case of a limestone filler addition, CaCO3, or CaO·CO2, can be noted CC.

Hydrated cement paste

Hydration products formed in hardened cement pastes (also known as HCPs) are more complicated, because many of these products have nearly the same formula and some are solid solutions with overlapping formulas. Some examples are given below:

CCNActual formulaName or mineral phase
CH Ca(OH)2 or CaO · H2O Calcium hydroxide (portlandite)
C-S-H 0.6–2.0 CaO · SiO2 · 0.9–2.5 H2O, with variable composition within this range, and often also incorporating partial substitution of Al for Si Calcium silicate hydrate
C-A-H Phase more complex than C-S-HCalcium aluminate hydrate
C-A-S-H This is even more complex than C-S-H and C-A-HCalcium aluminate silicate hydrate
AFt C6AS3H32, sometimes with substitution of Fe for Al, and/or CO2−
3 for SO2−
4 		Calcium trisulfoaluminate hydrate, or ettringite
AFm C4ASH12, often with substitution of Fe for Al, and/or various other anions such as OH− or CO2−
3 for SO2−
4		Calcium monosulfoaluminate
C3AH6 3CaO · Al2O3 · 6 H2O Hydrogarnet

The hyphens in C-S-H indicate a calcium silicate hydrate phase of variable composition, while 'CSH' would indicate a calcium silicate phase, CaH2SiO4.

Use in ceramics, glass, and oxide chemistry

The cement chemist notation is not restricted to cement applications but is in fact a more general notation of oxide chemistry applicable to other domains than cement chemistry sensu stricto.

For instance, in ceramics applications, the kaolinite formula can also be written in terms of oxides, thus the corresponding formula for kaolinite,

Al2Si2O5(OH)4,

is

Al2O3 · 2 SiO2 · 2 H2O

or in CCN

AS2H2.

Possible use of CCN in mineralogy

Although not a very developed practice in mineralogy, some chemical reactions involving silicate and oxide in the melt or in hydrothermal systems, and silicate weathering processes could also be successfully described by applying the cement chemist notation to silicate mineralogy.

An example could be the formal comparison of belite hydration and forsterite serpentinisation dealing both with the hydration of two structurally similar earth -alkaline silicates, Ca2SiO4 and Mg2SiO4, respectively.

Calcium system
belite hydration:
Belite 2 Ca2SiO4 + water4 H2O → C-S-H phase3 CaO · 2 SiO2 · 3 H2O + portlandite Ca(OH)2

 

 

 

 

(Reaction 4a)

2 C2S + 4 H → C3S2H3 + CH

 

 

 

 

(Reaction 4b)

Magnesium system
forsterite serpentinisation:
Forsterite2 Mg2SiO4 + water3 H2O → serpentine Mg3Si2O5(OH)4 + brucite Mg(OH)2

 

 

 

 

(Reaction 4c)

2 M2S + 3 H → M3S2H2 + MH

 

 

 

 

(Reaction 4d)

The ratio Ca/Si (C/S) and Mg/Si (M/S) decrease from 2 for the dicalcium and dimagnesium silicate reagents to 1.5 for the hydrated silicate products of the hydration reaction. In other term, the C-S-H or the serpentine are less rich in Ca and Mg respectively. This is why the reaction leads to the elimination of the excess of portlandite (Ca(OH)2) and brucite (Mg(OH)2), respectively, out of the silicate system, giving rise to the crystallization of both hydroxides as separate phases.

The rapid reaction of belite hydration in the setting of cement is formally "chemically analogue" to the slow natural hydration of forsterite (the magnesium end-member of olivine) leading to the formation of serpentine and brucite in nature. However, the kinetic of hydration of poorly crystallized artificial belite is much swifter than the slow conversion/weathering of well crystallized Mg-olivine under natural conditions.

This comparison suggests that mineralogists could probably also benefit from the concise formalism of the cement chemist notation in their works.

See also

Related Research Articles

<span class="mw-page-title-main">Portland cement</span> Binder used as basic ingredient of concrete

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 was 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. The term portland in this context refers to a material or process, not a proper noun like a place or a person, and should not be capitalized.

<span class="mw-page-title-main">Calcium sulfate</span> Laboratory and industrial chemical

Calcium sulfate (or calcium sulphate) is the inorganic compound with the formula CaSO4 and related hydrates. In the form of γ-anhydrite (the anhydrous form), it is used as a desiccant. One particular hydrate is better known as plaster of Paris, and another occurs naturally as the mineral gypsum. It has many uses in industry. All forms are white solids that are poorly soluble in water. Calcium sulfate causes permanent hardness in water.

In inorganic chemistry, mineral hydration is a reaction which adds water to the crystal structure of a mineral, usually creating a new mineral, commonly called a hydrate.

<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.

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).

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">Calcium aluminoferrite</span> One of the four main mineral phases of the Portland cement clinker

Calcium aluminoferrite is a dark brown crystalline phase commonly found in cements. In the cement industry it is termed tetra-calcium aluminoferrite or ferrite. In cement chemist notation (CCN), it is abbreviated as C
4AF meaning 4CaO·Al
2O
3·Fe
2O
3 in the oxide notation. It also exists in nature as the rare mineral brownmillerite.

An AFm phase is an "alumina, ferric oxide, monosubstituted" phase, or aluminate ferrite monosubstituted, or Al2O3, Fe2O3 mono, in cement chemist notation (CCN). AFm phases are important hydration products in the hydration of Portland cements and hydraulic cements.

<span class="mw-page-title-main">Alkali–silica reaction</span> Chemical reaction damaging concrete

The alkali–silica reaction (ASR), also commonly known as concrete cancer, is a deleterious swelling reaction that occurs over time in concrete between the highly alkaline cement paste and the reactive amorphous silica found in many common aggregates, given sufficient moisture.

Calcium silicate hydrates are the main products of the hydration of Portland cement and are primarily responsible for the strength of cement-based materials. They are the main binding phase in most concrete. Only well defined and rare natural crystalline minerals can be abbreviated as CSH while extremely variable and poorly ordered phases without well defined stoichiometry, as it is commonly observed in hardened cement paste (HCP), are denoted C-S-H.

Friedel's salt is an anion exchanger mineral belonging to the family of the layered double hydroxides (LDHs). It has affinity for anions as chloride and iodide and is capable of retaining them to a certain extent in its crystallographical structure.

<span class="mw-page-title-main">Concrete degradation</span> Damage to concrete affecting its mechanical strength and its durability

Concrete degradation may have many different causes. Concrete is mostly damaged by the corrosion of reinforcement bars due to the carbonatation of hardened cement paste or chloride attack under wet conditions. Chemical damages are caused by the formation of expansive products produced by various chemical reactions, by aggressive chemical species present in groundwater and seawater, or by microorganisms. Other damaging processes can also involve calcium leaching by water infiltration and different physical phenomena initiating cracks formation and propagation. All these detrimental processes and damaging agents adversely affects the concrete mechanical strength and its durability.

Larnite is a calcium silicate mineral with formula: Ca2SiO4. It is the calcium member of the olivine group of minerals.

The pozzolanic activity is a measure for the degree of reaction over time or the reaction rate between a pozzolan and Ca2+ or calcium hydroxide (Ca(OH)2) in the presence of water. The rate of the pozzolanic reaction is dependent on the intrinsic characteristics of the pozzolan such as the specific surface area, the chemical composition and the active phase content.

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.

<span class="mw-page-title-main">Tacharanite</span> Calcium aluminium silicate hydrate mineral

Tacharanite is a calcium aluminium silicate hydrate (C-A-S-H) mineral of general chemical formula Ca12Al2Si18O33(OH)36 with some resemblance to the calcium silicate hydrate (C-S-H) mineral tobermorite. It is often found in mineral assemblage with zeolites and other hydrated calcium silicates.

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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