Concrete Technology

1. Concrete technology
COURSE COORDINATOR:
DR. VIBHA VENKATARAMU
BMSIT&M
DEPT. OF CIVIL ENGINEERING
18CV44

2. Topics covered
• Manufacturing of cement
• Chemical composition
• Hydration of cement
• Types of cement
• Testing of cement
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3. Process inside the rotary kiln
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4. Chemical composition
Cement
Alumina
Magnesia
Iron
Oxide
Calcium
Sulphate
Sulphur
dioxide
Alkalies
Silica
Lime
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5. Process inside the rotary kiln
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Anton H. (2020)

6. Chemical compounds present
Sl
No
Chemical Name Chemical Formula Notation % by weight
1 Tricalcium Silicate (Belite) 3CaO.SiO2 C3S 50
2 Dicalcium Silicate (Alite) 2CaO.SiO2 C2S 25
3 Tricalcium Aluminate (Aluminate) 3CaO.Al2O3 C3A 12
4 Tetracalcium Aluminoferrite
(Ferrite)
4CaO.Al2O3.Fe2O3 C4AF 8
5 Gypsum 2CaSO4. H2O 3.5
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7. How to control the chemistry?
Control ratios!!
• Lime saturation factor (LSF)
• Silica Ration (SR)
• Alumina Ratio (AR)
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LSF =
C
2.8S +1.2 A + 0.65 F
SR =
S
S+F
AR =
A
F
LSF > 100 => free lime present High SR => High C3S, less C3A High AR => High C3A

8. Bogue’s equation for compound composition
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9. Hydration of cement
• Hydraulic hardening of Portland cements is primarily due to the hydration of calcium silicates
(C3S and C2S) – Other phases like aluminates also participate in the process.
• The products of cement hydration gradually fill the space between aggregate particles to give a
continuous matrix.
• The cement paste sets and hardens as the hydration proceeds after contact with water.
• Setting is the sudden loss of plasticity of the paste and conversion to solid material
• Hardening denotes the development of hardness and strength following the setting of cement
paste.
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10. Hydration reactions
• C3A and C4AF phases have the highest rates of reaction, followed by C3S, and
C2S is the slowest to react.
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1. Calcium silicate hydrates (C-S-H)
2. Calcium hydroxide (Ca(OH)2)
3. Calcium Aluminate Hydrates (C-A-H)

11. Stages of
hydration
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12. Cement hydration products
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Mehta & Monteiro, 2000

13. Hydration of cement
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14. Hydration of cement –
Rate of heat evolution vs time
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15. rEFERENCES
• M S SHETTY, CONCRETE TECHNOLOGY THEORY AND PRACTICE, 2012
• MEHTHAAND MONTEIRO, PROPERTIES AND MICROSTRUCTURE OF
CONCRETE, 2000
• NEVILLE, PROPERTIES OF CONCRETE, 2002
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16. Types of cement
TYPES OF
CEMENT
Portland
cement
Non portland
cement
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• OPC
• Rapid hardening cement
• Sulphate resistant cement
• Portland slag cement
• Super sulphated cement
• Low heat cement
• Portland pozzolana
cement
• Coloured cement
• High alumina cement
• High strength cement

17. IS (OPC)
33 Grade 43 Grade 53 Grade
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ASTM
Type 1
cement
Type II
Cement
Type III
Type IV, V
etc

18. TESTS ON CEMENT
• Field Testing
• Based on experience and vague
• Lab testing
• Fineness test
• Setting time test
• Strength test
• Soundness test
• Heat of Hydration test
• Chemical composition test
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19. Fineness of cement
• Sieve test
• Air permeability method
• Sieve test
– Not more than 10% should be retained on No
9 Sieve (90 microns)
– Not very accurate

20. Air permeability method
• To determine specific surface or total surface area in m²/kg
• Principle: Relation between air flow through cement bed of
known thickness or the air permeability of bed of given porosity
• Cement bed thickness 1 cm and dia 2.5 cm
• The porosity of cement bed is maintained at 0.475
• Methods: Blain’s air permeability / Lea and Nurse Air
permeability

21. Standard consistency test, Initial and Final setting
time
• Standard Consistency: “The consistency which
will permit a Vicat plunger having a diameter of
10mm and 50 mm length to penetrate to a depth
of 33- 35 mm from the top of the bed of cement
paste”
• Initial setting: Time elapsed between addition
of water to cement and a point where paste start
to loose its plasticity” ~30 mins
• Final setting: Time elapsed between addition of
water to cement and point where cement paste
has completely lost its plasticity and attains
sufficient firmness to resist a certain pressure”
~not more than 10 hours

22. Compressive strength of cement
• Directly reflects the quality of cement
• Not performed on neat cement paste
• Conducted on mortars cubes of specific mix ratio (1:3),having water content as
per std. consistency test
• 7 and 28 day strength is recorded

23. Soundness of cement
• To ascertain the expansion
• Unsoundness is due to presence of excess CaO, MgO OR Calcium
sulphate
• Causes – inadequate burning or grinding of raw materials
• Test method : Le Chatelier’s soundness test

24. Other tests
• Heat of Hydration – Vacuum flask method, Adiabatic calorimeter
• Chemical composition – Titration method or XRF

26. Chemical Admixtures
• A chemical admixture is any chemical additive to the concrete mixture that
enhances the properties of concrete in the fresh or hardened state.
• It does not typically include paints and protective coatings (for steel or concrete).
• ACI 116R defines the term admixture as “a material other than water, aggregates,
hydraulic cement, and fiber reinforcement, used as an ingredient of concrete or
mortar, and added to the batch immediately before or during its mixing.”
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27. Classification
• Air Entrainers
• Set Controllers
• Water reducers
• Normal (5 – 8 %)
• Mid Range (8 – 15%)
• High Range water reducers (HRWR) (15- 25%)
• Specialty Admixtures
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28. Uses
Water reducers can be used in three ways:
1.For a given workability, they can reduce the water demand, thus resulting in higher
strength and durability.
2.For a given w/c and strength, they can increase the workability.
3.For a given w/c, strength and workability, the quantity of cement can be reduced.
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29. Water reducers
They belong to a group of chemicals known as ‘dispersants’. The action of the dispersant
is to prevent the flocculation of fine particles of cement. These dispersants are basically
surface-active chemicals consisting of long-chain organic molecules, having a polar
hydrophilic group (water-attracting, such as –COO-, -SO3-, -NH3+) attached to a non-
polar hydrophobic organic chain (water-repelling) with some polar groups (-OH). As
shown in the Figure 1, the polar groups in the chain get adsorbed on the surface of the
cement grains, and the hydrophobic end with the polar hydrophilic groups at the tip point
outwards from the cement grain. The hydrophilic tip is able to reduce the surface tension
of water, and the adsorbed polymer keeps the cement particles apart be electrostatic
repulsion. With the progress of hydration, the electrostatic charge diminishes and
flocculation of the hydrating product occurs.
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30. Fig 1
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31. Fig 2
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32. Examples
• Common normal water reducers:
• Lignosulphonate salts (sodium salts of sulphonated lignin)
• Hydroxycarboxylic acids – Citric, gluconic acid
• Carbohydrates – Corn syrup, dextrin
The dosage of normal WRs is 0.3 – 0.5% by weight of cement. At higher dosages, there
is danger of excessive retardation and bleeding. Also, returns diminish, and excessive
air entrainment can occur.
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33. Common high-range water reducers (or Superplasticizers):
1st generation: Lignosulphonates at high dosages
2nd generation: Polysulphonates
Sulphonated melamine formaldehyde (SMF)
Sulphonated naphthalene formaldehyde (SNF)
3rd generation:
• Polycarboxylates
- Polyacrylates
- Monovinyl alcohols
Typical dosage: 0.7 – 1.0% by weight of cement.
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34. Set controlling admixtures
Set controlling chemicals are used to lengthen or shorten the setting time of concrete in
order to suit the concrete to a specific casting condition. For example, when early strengths
are desired, or when the temperature is low, accelerators may be added to the concrete.
Conversely, when casting is done in hot weather, and there is a chance of increased
transportation time of the concrete, retarders may be used.
Type I: Gypsum
Type II: Calcium chloride, calcium nitrate
Type III: Potassium and sodium carbonate, sodium silicate
Type IV: Gluconates, Lignosulphonates and sugars, sodium salts of carboxylic acids, Zn
and Pb salts
Type V: Salts of formic acid and triethanol amine (TEA)
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35. The same chemical can sometimes act either as a
retarder or an accelerator based on its concentration
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36. Classification
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37. Mechanism of action
• An accelerator should promote the dissolution of both cations and anions. Since several
anions are present, the accelerator should promote the dissolution of that anion which
has the lowest dissolving rate, i.e., silicate.
• A retarder impedes the dissolution of Ca ions and aluminates.
• Organic retarders: Lignosulphonates, hydroxycarboxylic acids (citric, gluconic),
carbohydrates (corn syrup, dextrin). These are the same chemicals as normal water
reducers.
• Inorganic retarders: Borates, phosphates, Zn and Cu compounds. These are not
generally used because of their high costs and low solubility.
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38. Sequence of addition of set-controlling admixtures:
• Accelerators and retarders are added to the concrete either separately or with the
mix water, soon after the cement and water come in contact. It must be noted that it
is absolutely essential to pay particular attention to dosage – the same chemical may
behave as accelerator or retarder depending on concentration (as described in the
earlier discussion).
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39. Air entraining Admixtures
• Air entraining agents are used in concrete to generate air bubbles within the concrete,
which help protect against damage due to freezing and thawing. They also help in
reducing bleeding and segregation, and improve the workability of concrete, since the
air bubbles act in a manner similar to ball bearings.
• Air-entraining agents are also surface-active chemicals. Unlike the water-reducing
surfactants, the hydrocarbon chain does not have any polar groups, and is entirely
hydrophobic. The hydrophilic polar groups are similar to water reducers. The mode of
action of these chemicals is depicted in Figure 4. The polar group sticks outward, lowers
the surface tension of water and promotes bubble formation. However, the polar ions get
adsorbed on the cement surface with the hydrophobic chain sticking out.
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41. • Air bubbles are generated during the agitation and mixing of the concrete. The air-
entraining agents simply helps to stabilize these bubbles by the above action. Some
common chemicals used as air entrainers are neutralized vinsol resin, derivatized
pine rosin, and fatty acids (detergents). Air entrainers are added to the concrete
mixture either early in the process – with the sand and coarse aggregate – or after
the cement has been added along with some of the mix water. Air entraining
chemicals should never be mixed with any other chemical additives.
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42. Entrapped air and entrained air !!!
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43. Reference
• The materials from theconcreteportal.com is extensively used to prepare this
study materials
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