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Lecture No. 03

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C3A C4AF Hydration of Cement Slide 31 Hydration Reactions Chemical composition and Fineness of Cements Relative Reactivity of Cement compounds Relative volume ... – PowerPoint PPT presentation

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Title: Lecture No. 03


1
Lecture No. 03
  • Subject
  • Cement Types and
  • Characteristics of Cements

2
Objectives of Lecture
  • Explain briefly the various types of Portland
    cement.
  • Explain the chemical compounds in Portland cement.

3
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.

4
Type Name
Type I Normal
Type IA Normal, air-entraining
Type II Moderate sulfate resistance
Type IIA Moderate sulfate resistance, air-entraining
Type III High early strength
Type IIIA High early strength, air-entraining
Type IV Low heat of hydration
Type V High sulfate resistance
5
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.

6
Application of Type I Cement
7
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.

8
Application of Type II Cement
9
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.

10
Application of Type III Cement
11
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.

12
Application of Type IV Cement
13
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.

14
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.

15
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.

16
Application of White Cement
17
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.

18
Blended Cements
19
  • 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).

20
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

21
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).

22
Special Cements (Not covered by ASTM)
Type Uses
Oil-well cements For sealing oil wells
Waterproof Portland cements For reducing capillary water transmission
Plastic cements For making plaster and stucco (coating exterior surfaces)
23
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)

24
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.

25
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.

26
2. C2S
  • Hydrates and hardens slowly.
  • Contributes largely to strength increase at ages
    beyond one week.

27
Alite (C3S) and Belite (C2S)
28
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.

29
C4AF
  • Does not play any significant role on hydration.

30
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.

31
  • 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

32
Hydration Reactions
33
Chemical composition and Fineness of Cements
34
Relative Reactivity of Cement compounds
35
Relative volume of major compounds in hydrated
cement paste
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