General concepts such as workability, aggregate properties, problems with concrete components, admixtures Note:- The information contained in the document may be incomplete i.e. it may not cover each topic in its entirety

1. Roles
Coarse Agg.
Fine Agg.
Cement
Water
Admixture
• Provide
Abrasion
resistance
• Soundness
increase
• Inert filler
• Allow mix
to be
workable
• Cementatio
n–
Adhesion
and
cohesion
• Workability
in fresh
state
• Strength in
hardened
state
• Reaction of
water with
cement
leads to
cementatio
n
• Workability
• Enhance
properties

3. How to?
Strength
Economy
Durability
• Good quality paste –
Low w/c ratio and
appropriate
cementitious material
• Good Quality Agg. –
Appropriate gradation
and strength
• Dense concrete – Low
permeability
• Proper placing and
compaction
•
•
•
•
•
• Low w/c ratio
• Use of pozzolans
• Appropriate air
entrainment
• Inert agg.
• Adequate gradation –
max size
• Strong agg.
• Appropriate cements
• Proper handling ,
placing and
compaction
Proper mix design
Low w/c cement ratio
Use of pozzolans
Max. aggregate size
Efficient handling,
placing and
compacting

4. Durability
• Weathering resistant
• Wear resistant
• Chemical attack resistant
• Water tight
• Sound – low volume changes

5. Cement manufacture
1.
2.
3.
4.
5.
Quarried limestone and clay
Primary Crusher
Blending
Preheating
Heating in kiln ( water driven out and fusion to
form clinker)
6. Addition of Gypsum
7. Secondary Crushing
8. Packing and distribution

6. Cement composition (in
decreasing % age)
• C3S
• C2S
• C3A
• C4AF
• CASO4
• Calcite CC’
• Na2O K20
• MgO

8. Cement Types

10. CSH vs CH
CSH
CH
High specific surface area (400 – 700
m^2/g)
Lower Specific surface area
Indefinite Stoichiometry
Definite Stoichiometry
Amorphous to poorly crystalline
structure, Chemical bonds of Van Der
Waals forces
Crystalline – elongated generally
Layered structure
Platy to nondescript
50 – 60 % of HCP
20 -25 % of HCP
Strength imparting Phase
Contribution to strength is insignificant

11. Water in HCP
S no.
Description
1
Capillary water – present in capillary
voids, also called free water
2
Interlayer water – Water present
between CSH layers
3
Chemically combined water - non
evaporable water
4
Physically adsorbed water – water
molecules form hydrogen bonds with
other HP and cling to their surfaces.

12. Shrinkage types
Shrinkage
Plastic
Decription
•
Loss of water from fresh concrete or plastic
concrete
• Occurs usually with water close to the
concrete surface
• Crack formation on surface
•
Drying Shrinkage
Loss of water from hardened concrete
• Free water evaporation does not produce
significant volume changes but gel pore water
loss does
Autogenous Shrinkage
• Volume change resulting from chemical
reactions within the concrete without transfer
of water to the surrounding environment
Carbonation shrinkage
•
CO2 reacts with water and CH to produce
CaCO3 which occupies less volume than CH
and thus causes shrinkage of the concrete

13. Admixtures
• Chemical (water soluble compounds) and mineral
(finely ground solids)
• Any ingredient besides water, aggregates, cement
and firber reinforcement added to the concrete mix
either before or immediately after mixing
• An addition is any substance that is added to
cement during the manufacturing process to aid in
manufacturing or alter properties of the cement.

14. FA
SF
Slag
Non reactive minerals or
natural Pozzolans
Pozzolanic reaction
React with CH to produce
CSH
Pozzolanic reaction
Hydraulic cement react with
H2O to produce CSH and CH
Finely ground limestone,
Hydrated lime or silica flour
is a byproduct of the
combustion of
pulverized coal in electric
power generating plants.
This byproduct is a result of
the manufacture of silicon
or ferrosilicon alloy.
By product of the extraction
of iron from Iron ore….
Molten Slag cooled rapidly
and pelletized
Primarily an Aluminosilicate
(F) or Calcium
Aluminosilicate (C)
Essentially silicon dioxide in
a non crystalline form
Consists mostly of CaO with
alumina and silica in lesser
quantities
15 – 40 % of total mass
Cementitious material
5 – 10 % of total mass
cementitious material
30 – 40 % by mass
420 m2/g
20000 m2/g
400 m2/g
Slower reaction
Quicker reaction
Slower reaction
Cheap (relative to OPC)
Expensive
Comparable
Air entrainment
requirement increases but
not significantly
Air entrainment
requirement increases
significantly
Variable effects on air
entrainment requirement
Improves workability and
reduces permeability
Reduces workability but
reduces permeability
Highly fine GGBS increases
workability and reduces
permeability
Increase in long term
strength
Increase in long term
strength
Increase in long Term
Strength

15. Chemical Admixtures
• Enhance properties of concrete mix
• Include water reducing or plasticizing admixtures,
Set controlling admixtures and air entraining
admixtures
• Must be kept in controlled conditions
• Must be added in an appropriate amount
• Must be handled carefully
• Must be clearly defined in terms of effects on
performance of mix (both good and bad effects)

16. Air entrainers
• Air entrainment is beneficial because it:
• Increases Freeze thaw resistance of concrete
• Aids in workability as air voids reduce internal friction
between concrete components (ball – bearing effect)
• Reduce water needed to attain a certain slump
• Air entrainment reduces long term strength
• Different from entrapped air which occupies more
space and is irregularly distributed.
• Alkylbenzene Sulfonates, Sulfonated Hydrocarbon
salts, Wood resin salts

17. Air entrainment affected by:
• Use of pozzolans
• Use of other admixtures, Water reducing
admixtures reduce air entrainment
• Fines content
• Placing and compaction

18. LRWR and HRWR or SP
• SP are more efficient in interaction and reducing bleeding
than LRWR
• SP reduce wc by 15 – 30 % where as LRWR reduce wc by 5 –
10 %
• WR and SP benefits:
• Reduce water demand and increase slump for a constant w/c ratio,
workability increase
• Increase long term strength due to the decreased w/c ratio
• Decrease high early heat evolution and prevent thermal cracking
• Bleeding decreased due to low w/c ratio.
• Disadvantages:
• Reduce air entrainment
• Slump decrease accelerated
• SP can be incompatible with cements and can reduce of their mixes
workability

19. Examples
• SP : Sulfonated naphthalene formaldehyde
condesates, S melamine FC,
• LRWR: lignosulfates , Hydroxylated Carboxylic acids
• Set retarders : Lignosulfates , sugars
• Set accelerators : CaCl2 (causes corrosion, increase
in drying shrinkage and scaling and creep potential,
darkening of concrete) , Na2CO3, TEA (flash
setting), Calcium Formate,

20. How Ps work?
• Flocculation – Alumina and silica particles have
opposite charges and lock in water which becomes
adsorbed on their surfaces
• Plasticizers cause dispersion – Electrostatic or Steric
Stabilization; dispersion means alumina and silica
develop like charges and water is freed for
increasing workability.

21. Aggregate properties preferred
• Well graded
•
•
•
•
Rounded agg.
Max Agg size
Optimum contents of both fine and coarse
Better bond with softer , porous , mineralogically heterogenous
agg.
• Rough texture agg. more strong then Smooth
• Shape controls flexural strength
• Texture controls compressive strength
• Cement slurry percolation preferred
• Modulus of elasticity and thermal expansion similar to cement
paste
• Min impurities (organic loam, humus), min Coatings (fine agg,
salts ) and min. unsound particles (coal,mica,shale)

22. ASR
• Use of high alkali cement, Siliceous agg.
(Sandstone, Opaline shales, Chalcedonic Cherts)
• Alkali silica gel created that swells when it absorbs
water.
• Cracking occurs
• Prevention:
• Use of low alkali cements
• Use of lithium based admixtures
• Use of Pozzolans

23. ACR
• Carbonate rich agg. (dolomitic limestone)
• Rare
• Is an expansive reaction

24. Less fines?
• Increase water demand
• Affect bond of coarse agg. with paste
• Increase in Plastic shrinkage
Bulking of fines:
Increase in vol of fines due to moisture content
increase, surface tension of water prevents fines
from interacting or interlocking.

25. Workability
• The ability of mix to be handled ,placed ,compacted
and finished with minimum effort and loss in
homogeneity of the mix.
• Three components ; Flowability, Consistency and
compactibility
• Internal friction b/w particles of mix and surface
friction b/w concrete and formwork is present

27. Tests
• Slump Test for consistency
• Compacting factor for compactibility
• Vebe Test for flowability

28. Segregation
• Separation of agg. from mix or Settlement of heavy
agg. to the bottom of mix.
• Water rise to surface of mix; bleeding
• Causes:
•
•
•
•
•
Large size agg.
Improper placing, handling, compaction
Too wet or too dry mix
A decreased amount of fines
Perfectly rounded agg.

29. Bleeding
• Heavy laitance accumulation giving an unsightly
appearance
• Plane of weakness on concrete surface
• Corrosion of rebar
• Increase in porosity of concrete, chemical attacks
• Weakening of bond between agg and paste
• Delay in finishing and cost increase

30. Control
• Proper mix design
• Proper placement, handling and compaction
• Use of pozzolans
• Use of highly fine cement
• Air entrainment
• Use of WR admixtures

31. A = 96.5MPa (14,000 lb/in2)
B = may be taken to be about 4 (depends
on the type of cement)