Lecture No' 03

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Lecture No. 03

• Subject
• Cement Types and
• Characteristics of Cements

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Objectives of Lecture

• Explain briefly the various types of Portland
  cement.
• Explain the chemical compounds in Portland cement.

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Types of Portland Cement

• Different types of Portland cement are
  manufactured to meet the requirements for
  specific purposes.
• The American Society for Testing and Materials
  (ASTM) C150 specifies the following eight types
  of Portland cement.

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Type I cement

• It is a general-purpose cement used in concrete
  for making pavements, floors, reinforced concrete
  buildings, bridges, tanks, pipes, etc.
• It is for all uses where the special properties
  of other cement types are not required, such as
  sulfate attack from soil and water, or to an
  objectionable temperature rise.

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Application of Type I Cement
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Type II cement

• It is used where precaution against moderate
  sulfate attack is important, as in drainage
  structures, which may be subjected to a moderate
  sulfate concentration from ground waters. It has
  moderate sulfate resistance because it contains
  no more than 8 tricalcium aluminate (C3A).
• It usually generates less heat of hydration at a
  slower rate than Type I cement and therefore can
  be used in mass structures such as large piers,
  heavy abutments, and retaining walls.
• Due to less heat generation it can be preferred
  in hot weather.

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Application of Type II Cement
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Type III cement

• It is chemically and physically similar to Type I
  cement, except that its particles have been
  ground finer.
• It provides high early strengths at an early
  period, usually a week or less.
• It is used when forms need to be removed as soon
  as possible or when the structure must be put
  into service quickly.
• It is preferred in cold weather for reduction in
  the curing period.

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Application of Type III Cement
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Type IV cement

• It is used where the rate and amount of heat
  generated from hydration must be minimized.
• It develops strength at a slower rate than other
  cement types.
• It is most suitably used in massive concrete
  structures, such as large gravity dams, where the
  temperature rise resulting from heat generated
  during hardening and must be minimized to control
  the concrete cracking.

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Application of Type IV Cement
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Type V cement

• It is used only in concrete exposed to severe
  sulfate action principally where soils or
  ground waters have a high sulfate content.
• Its high sulfate resistance is due to its low C3A
  content of about 4.
• It is not resistant to acids and other highly
  corrosive substances.

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Air-Entraining Portland Cements(Types IA, IIA,
and IIIA)

• These cements have same composition as Types I,
  II, and III, respectively, except that small
  quantities of air-entraining material are
  inter-ground with the clinker during manufacture.
• These cements produce concrete with minute,
  well-distributed and separated air bubbles which
  improve the resistance to freeze-thaw action and
  to scaling caused by chemicals applied for snow
  and ice removal.

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White Portland Cement

• It has composition same as Type I or Type III
  cement, except that it has a white color instead
  of gray color.
• It is made of selected raw materials containing
  negligible amounts of iron and magnesium
  oxides-the substances that give cement its gray
  colors.
• It is used primarily for architectural purposes.

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Application of White Cement
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Blended Hydraulic Cements

• These cements are produced by intimately and
  uniformly blending the Portland cement and the
  by-product materials, such as blast-furnace slag,
  fly ash, silica fume and other pozzolans.

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Blended Cements
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• ASTM C 596 recognizes five classes of blended
  cements
• Portland blast-furnace slag cement-Type IS.
• Portland pozzolan cement-Type IP and Type P.
• Pozzolan-modified Portland cement-Type I(PM).
• Slag cement-Type S.
• Slag-modified Portland cement-Type I(SM).

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SPECIAL CEMENTS

• Masonry Cements
• These cements are used in mortar for masonry
  construction.
• ASTM C 91 classifies masonry cements as Type N,
  Type S, and Type M

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Expansive Cements

• These cements are primarily used in concrete for
  shrinkage control.
• ASTM C 845 classifies expansive cements asType
  E-1(K), Type E-1(M), Type E-1(S).

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Special Cements (Not covered by ASTM)
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Chemical Compounds in Portland Cement

• As indicated earlier the burning operation of the
  raw materials results into the reaction between
  the oxides and four compound compositions are
  formed in the final cement product, as follows
• C3S 3CaO.SiO2 (Tricalcium silicate)
• C2S 2CaO.SiO2 (Dicalcium silicate)
• C3A 3CaO.Al2O3 (Tricalcium aluminate)
• C4AF 4CaO. Al2O3.Fe2O3 (Tetracalcium
  aluminoferrite)

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In general

• C3S Constitutes 50 to 70 of the clinker.
• C2S Constitutes 15 to 30 of the clinker.
• C3A Constitutes 5 to 10 of the clinker.
• C4AF Constitutes 5 to 15 of the clinker.

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Role of Compound Composition

• C3S
• Hydrates and hardens rapidly and is largely
  responsible for initial set and early strength.
• Early strength of cement is higher with increased
  percentages of C3S.

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2. C2S

• Hydrates and hardens slowly.
• Contributes largely to strength increase at ages
  beyond one week.

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Alite (C3S) and Belite (C2S)
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3. C3A

• Liberates a large amount of heat during the first
  few days of hydration and hardening.
• Also contributes slightly to early strength
  development.
• Gypsum added to the cement slows down the
  hydration rate of C3A.
• Cements with low percentages of C3A are
  especially resistant to soils and waters
  containing sulfates.

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C4AF

• Does not play any significant role on hydration

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Hydration of Cement

• In the presence of water the cement compounds
  chemically combined with water (hydrate) to form
  new compounds that are the infrastructure of the
  hardened cement paste in concrete.
• Both C3S and C2S hydrate to form calcium
  hydroxide and calcium silicate hydrate (CSH).
  Hydrated cement paste contains 15 to 25
  Calcium hydroxide and about 50 calcium silicate
  hydrate by mass. The strength and other
  properties of hydrated cement are due primarily
  to calcium silicate hydrate.

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• C3A reacts with water and calcium hydroxide to
  form tetracalcium aluminate hydrate.
• C4AF reacts with water and calcium hydroxide to
  form calcium aluminoferrite hydrate.
• For all the Portland cement compound hydration
  reactions see Table 2-5

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Hydration Reactions
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Chemical composition and Fineness of Cements
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Relative Reactivity of Cement compounds
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Relative volume of major compounds in hydrated
cement paste