This PPT discusses the structure and properties of concrete making materials. This is followed by hydration of cement, porosity of cement pastes and a study of selected topics regarding fresh and hardened concrete behaviour. 1. To understand the different complex compounds in cement. 2. Study the behavior of concrete with the fundamental interactions between ingredients 3. Fundamental understanding of the mechanism governing concrete performance. 4. Demonstrating the porosity of cement paste and elastic modulus. 5. Dramatize the rheology of concrete in terms of Bingham’s parameter.

1. Advanced Concrete Technology
By
Dr. S.K
Introduction:Behaviour of fresh and
hardened concrete

2. CONTENTS
•Importance of bogue’s compounds,
•Structure of a hydrated cement paste,
•Volume of hydrated product,
•Porosity of paste and concrete, transition
zone, elastic modulus,
•Factors affecting strength and elasticity of
concrete,
•Rheology of concrete in terms of bingham’s
parameter.

3. • Concrete is a construction material composed of cement, fine
aggregates (sand) and coarse aggregates mixed with water which
hardens with time.
• Portland cement is the commonly used type of cement for production of
concrete. Concrete technology deals with study of properties of
concrete and its practical applications.
• There are different types of binding material is used other than cement
such as lime for lime concrete and bitumen for asphalt concrete which
is used for road construction. Various types of cements are used for
concrete works which have different properties and applications.
• Some of the types of cement are Portland Pozzolana Cement (PPC),
rapid hardening cement, Sulphate resistant cement etc. A cement is a
binder, a substance used for construction that sets, hardens, and
adheres to other materials to bind them together.
INTRODUCTION

4. CEMENT
• A cement is a binder, a substance used for construction that
sets, hardens, and adheres to other materials to bind them
together.
• Density: 3.15 g/cm³.
• Cement is seldom used on its own, but rather to bind sand
and gravel together.
• Cement mixed with fine aggregate produces mortar for
masonry, or Cement mixed with sand and gravel, produces
concrete.

5. Calcarious: Composed of or containing calcium or calcium
carbonate.
Argillaceous minerals: are minerals containing substantial
amounts of clay- like components.
Argillaceous components are alumino silicates, and more
particularly clay minerals such as kaolinite, montmorillonite-
smectite, illite, and chlorite. Clay
stone and shales are thus predominantly argillaceous

6. Strength Mechanism:
When water is added to cement, ingredients of cement
react chemically with water and form various complicated
chemical compounds. The chemical reaction that takes
place between cement and water is referred as hydration of
cement.
Anhydrous cement does not bind fine and course
aggregates. It acquire adhesive property only when water
is mixed.
The silicates (C3S,C2S) and aluminates of cement react
with water and form hydro silicates and hydro aluminates.
These products are thick and sticky. It is called gel.
Gel posses adhesive property and bind aggregate and sand
together. It also fill the voids between sand and aggregate.

7. Oxide Composition of Cement
The raw material used for the manufacturing of Ordinary
Portland cement contains mainly lime, silica, alumina, and
iron oxide.
These oxides interact with one another in the kiln at high
temperature to form more complex compounds.
The relative proportions of these oxide compounds are
responsible for various physical properties of cement. Rate
of cooling and fineness of grinding also affect the property
of cement.

8. Approximate composition limits of oxides
in portland cement
8
CHEMICAL REQUIREMENTS OF PORTLAND CEMENT
COMPONENTS PERCENTAGES
CaO 60-67
SiO2 21-22
AI2O3 4.0-5.0
Fe2O3 3.0-4.0
MgO 2.0-3.0
Gypsum 2.0-2.5
Free lime <1.0

9. 9
General Methodology
• Crush the materials and store them
• Blend the materials and grind them
• Store them and do final blending
• Wet, dry, and semi-dry processes
• Burn the materials
• Add 2to 3% of gypsum to Clinker

10. Fig.1 cement production process (Source: Internet)

11. 11
Fig.2 cement clinkers(Source: Internet)

12. Bogues Compounds: when water is added to cement it
react with the ingredients of the cement chemically &
results in the formation of complex chemical
compounds terms as BOGUES compounds. which are
not for simultaneously. .
1.Tri-Calcium Silicate (3CaO.SiO2 or C3S
2.Di-Calcium Silicate (2CaO.SiO2 or C2S)
3.Tri-Calcium Aluminate (3CaO.Al2O3 or C3A)
4.Tetra Calcium Alumino Ferrate (4CaO.Al2O3.Fe2O3
orC4AF)
Bogue’s Compounds

13. In addition to four major compound there exists minor
compounds, such as MgO, TiO2, Mn2O3, K2O, Na2O.
Two of the minor compounds of interest are K2O,
Na2O, known as alkalies.
They have been found to react with some aggregates,
the product of this reaction causing disintegration of
concrete, and also have been found to affect strength of
cement.

14. Bougue’s Compounds
Name Of The
Compound
Formula Abbreviate
d Formula
Percentag
e
Chemical
Crystal Name
Tri-Calcium
Silicate
3CaO.SiO2 C3S 40-65 Alite
Di-Calcium
Silicate
2CaO.SiO2 C2S 15-35 Belite
Tri-Calcium
Aluminate
3CaO.Al2O
3
C3A 10-18 Celite
Tetra
Calcium
Alumino
Ferrate
4CaO.Al2O
3.Fe2O3
C4AF 4-14 Felite

15. Properties of Bogue’s Compounds:
The properties of Bouge’s compounds are as under:
1. C3S:
It is responsible for early strength, First 7 days strength is due to C3S
It Produces more heat of Hydration
A cement with more C3S content is better for cold weather
concreting.
2. C2S:
The hydration of C2S starts after 7days. Hence, it gives strength after
7 days.
C2S hydrates and hardens slowly and provides much of the ultimate
strength.
It is responsible for the later strength of concrete.
It produces less heat of hydration.
e.g. hydraulic structures, bridges.

16. Properties of Bogue’s Compounds
3. C3A:
There action of C3A with water is very fast and may lead to an
immediate stiffening of paste, and this process is termed as flash set.
To prevent this flash set, 2 to 3% gypsum is added at the time of
grinding the cement clinkers.
The hydrate C3A do not contribute to the strength of concrete.
4. C4AF:
C4AF hydrates rapidly.
It does not contribute to the strength of concrete.
The hydrates of C4AFs have a comparatively higher resistance to
sulphate attack than the hydrates of C3A
Also responsible for grey colour of Ordinary
Portland Cement

17. Hydration process-C3S
17
Hydration process-C2S
(Source: Internet)
(Source: Internet)

18. Hydration process-C3A
18
Hydration process - C4AF
(Source: Internet)
(Source: Internet)

19. Characteristics of Hydration of the
Cement Compounds
19
(Source: Internet)

20. Hydration
“When Portland cement is mixed with water its
chemical compound constituents undergo a series of
chemical reactions that cause it to harden.”
20
(Source: Internet)
Fig.4 Ordinary Portland cement hydration
Fig.3 Hydration

21. 21
• Hydration starts as soon as the cement and water are
mixed.
• The rate of hydration and the heat liberated by the
reaction of each compound is different.
• Each compound produces different products when it
hydrates.

22. 22
Heat of Hydration
• The heat of hydration is the heat generated when water and
Portland cement react.
• Heat of hydration is most influenced by the proportion of C3S
and C3A in the cement. But is also influenced by water- cement
ratio, fineness and curing temperature.
• For usual range of Portland cements, about one-half of the total
heat is liberated between 1 and 3 days, about three- quarters in 7
days, and nearly 90 percent in 6 months.

23. Fig.5 Hydration of Cement
(Source: Internet)

24. Stages of Hydration of Cement
The five stages involved in the hydration of
cement are explained with respect to the figure-
2. There are Five stages of cement hydration:
1.Initial Hydrolysis
2.Induction Period or the Dormant Period
3.Acceleration
4.Deceleration
5.Steady State

25. Stage 1- Initial Hydrolysis: The initial dissolution of cement
will result in the sort release of heat shown by the first peak
in the calorimetry curve.
Stage 2 - Induction or Dormant Period: After the initial
dissolution process, the hydration products are precipitated
on the surface of each cement particle.
• The layer acts as a protective barrier and temporarily
delays the dissolution of the particle. This slows down the
reaction for a period of several hours. This is called as the
Dormant Period.
• The existence of the dormant period allows the concrete to
be transported to the construction site and placed and
finished in the forms.

26. Stage 3- Hydration Acceleration: The end of the dormant
period shows the beginning of the setting at which time the
cement starts to react more rapidly with water. This will
result in the formation of new hydration products.
Stage 4- Hydration Deceleration: This period will undergo
formation of hydration products but the rate of reaction and
the dissolution is very controlled and slow.
Stage 5 - Steady State: This is the stage that is for a longer
period that is equal to the age of the structure. The hydration
reaction carried out throughout this period at a very slow
rate.

27. Fig.6 Hydration of Cement Heat of Hydration - Calorimetry curve

28. 19
Structure of hydrated cement paste
• When the portland cement is dispersed in water-
liquid phase gets rapidly saturated.
• Interaction between calcium, sulphate,aluminate and
hydroxyl ions results in trisulfoaluminate hydrate-
“Ettrignite”.
• After some hours a large prismatic crystals of calcium
hydroxide and very small crystals of calcium silicate
hydrates begin to fill the empty space occupied by
waterand dissolving cement

29. 29
Fig.7 Structure of hydrated cement paste (source: Internet)

30. Solids in hydrated cement paste
Calcium silicate hydrate:
30
Fig.8 Structure of hydrated cement paste (source: Internet)

31. Calcium Hydroxide
• Constitute 20-25% of the volume of solids.
• Large crystals with a distinctive hexagonal prism
morphology.
31
Fig.9 Structure of hydrated cement paste
(source: Internet)

32. Calcium sulfoaluminates hydrates
32
Volume %:15 to 20
First:Ettringite, After:Monosulfate hydrated
Fig.10 Structure of hydrated cement paste
(source: Internet)

33. 33
Porosity of cement Paste
• In any material, Total Volume of the voids is called
porosity.
• In the case of hydrated cement paste different types
of voids are present.
Fig.11 Porosity of cement paste
(source: Internet)

34. 34
Fig.12 Solid dots represent gel particles; interstitial spaces are gel pores; spaces
such as those marked C are capillary pores.

35. Based on the studies pore structure of hardened cement paste into four parts:
1.Gel pores-(<10nm)
2,Small capillary pores(10-100nm)
3.Large capillarity pores (100-1000nm)
4.Air Holes(>several µm)
Many methods are applied to characterize the pore structure of hardened cement
paste or concrete
• Nitrogen absorption (NS) is based on the molecule adsorption of porous
volume –this is used to detect the smallest volume,i.e gel pores
• MIP-Mercury intrusion porosimetry permits detecting pores from 5nm to
several microns
Direct methods BY IMAGE ANALYSIS
• Xray computed tomography(XCT)
• Laser scanning confocal microscopy(LSCM)
• Scanning electron microscopy(SEM)

36. 36
Gel pores
No adverse effect on strength and permeability but some effect
on drying shrinkage and creep
Capillary Voids
>50nm –Detrimental to strength and impermeability
<50nm-important to drying shrinkage and creep
• During hydration the space is originally occupied by the
cement and water.
• And it is being replaced by the product of hydration.
• The space not filled by the product of
hydration consists of capillary voids

37. • The Properties of concrete
introducing intentional air voids.
can be altered by
• Both entrapped and entrained air voids are larger than the
capillary voids. Therefore these voids affect the strength and
impermeability of concrete composites
37
Air voids
Air voids
Entrapped air:Aprroximately 3 mm
Entrained air:50 to 200 Microns

38. 38
Fig.13 Microstructure of Concrete
(source: Internet)

39. 39
Porosity of Concrete
• Porosity of concrete depends on the porosity of the
paste and Interfacial Transition Zone(ITZ).
• Majority of the aggregates used to make a concrete is almost
impermeable.
• Therefore permeability of concrete is directly related to
properties of cement paste and ITZ.

40. 40
Interfacial Transition Zone
• Concrete and Mortar has three phases-Aggregate, Bulk paste
and the Transition zone.
• At macro level-aggregate particles are dispersed in a
matrix of cement paste.
• At micro level –complexities of the concrete begin to show
up, particularly in the vicinity of large aggregate size.

41. 41
Fig.14 Interfacial transistion of Concrete
(source: Internet)

42. 42
• The transition zone is the weak link in the composite system.
• Its presence is considerable for the overall elastic modulus and stress
distribution in the concrete material.
• The transition zone is a relatively more porous structure compared
with that of bulk paste and it may not be perfectly bonded to the
aggregate.
• In case of fresh concrete, water film form around the large particles.
Due to this the w/c ratio is higher at this zone.
• The crystalline product around the vicinity of the coarse
aggregates consists of relatively larger crystals. Therefore more
porous framework is formed compared to the bulk cement paste.
• The major factor responsible for the poor strength of ITZ in
concrete is the presence of micro cracks.

43. 43
Elastic Modulus
“Tendency to be deformed elastically when a force applied
to it”
Elastic modulus = Stress/Strain
• Concrete exhibits micro cracks even before application of the
load. Due to the cracks the concrete is deformed.
• The elastic characteristics of any material are the measure of its
stiffness.

44. 44
• Concrete shows elastic as well as inelastic strains on loading
and shrinkage strains on drying and cooling.
• The behavior of concrete is non linear under compressive loading. This
is due to progressive micro cracking in concrete under loading.
• The static modulus of elasticity of concrete under tension or
compression is calculated as the slope of stress-strain curve under
uniaxial loading.
• Since the curve is non linear in concrete three methods of
computing modulus are used.

45. Fig.14 Determination of Modulus of
Elasticity Concrete. (Source Internet)
Elastic Modulus of concrete

46. Stress-strain Relationship
46
Fig.15 Stress-strain Relationship(Source Internet)

47. 47
• Initial Tangent modulus is given by the slope of the line drawn
from the origin to any point in stress- strain curve.
• Secant modulus is given by the slope of the line drawn
tangent from origin to the specified point on the curve.
• Tangent modulus is given by the slope of the line drawn at any
point on stress- strain curve.
• It is the fact that stronger the concrete, higher is the modulus of
elasticity of concrete. Because stronger the gel lesser is the strain
for a given load and higher is the modulus of elasticity.

48. Different codes have prescribed some empirical relations to
determine the Modulus of Elasticity of Concrete. Few of them are
given below.
According to ACI 318-08 section 8.5,Modulus of elasticity for
concrete,
Ec=w1.50c×0.043√f′c MPa
This formula is valid for values of wc between 1440 and 2560
kg/m3.
For normal-weight concrete,
Ec=4700√f′c MPa
(in FPS unit Ec=57000√f′c psi)

49. 49
Factors affecting MOE
• Aggregate
• Cement Paste Matrix- w/c ratio, air content, admixture
and degree of hydration
• Transition zone-capillary voids, micro cracks, calcium
hydroxide crystal
• Testing Parameter-wet or dry condition of concrete, rate of loading

50. 50
Strength of Concrete
• The strength of concrete depends on ability to resist stress
without failure. The failure can be identified by the appearance
of the cracks.
• Compressive strength is the important specification in concrete
design and quality control.
• Many Properties of the concrete are directly related to the
compressive strength.
Factors affecting the strength of concrete
• Characteristics and Proportions of Materials.
• Curing conditions
• Testing Parameters

51. 51
Characteristics and Proportions of Materials.
1. Water to Cement ratio
2. Air Entrainment - High strength concrete suffers
considerable strength loss as compared to low strength
concrete.
3. Cement Type - Depends on grades.
4. Aggregate – size, shape, surface texture and
grading.
5. Mixing Water – impurities in water
6. Admixtures – chemical and Mineral.

52. 52
Curing Conditions
1. Time-Strength increases with the time.
2. Humidity- strength of concrete increases in humid
condition compared to dry.
3. Temperature-Higher temperature results in higher
hydration(till the age of 28 days).
4. Low temperature curing forms a more uniform microstructure
accounts for higher strength.

53. Specimen Parameters
• Some countries specify cylinders and some cubes for
compression test as per corresponding codes.
• It is an established fact that in case of cylinder, larger the
diameter lower will be the strength.
• Specimen geometry- height to diameter ratio influences the
strength of concrete. Greater the ratio lower will be the strength.
• The strength of concrete cube would be 10 to 15% higher than
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54. 54
Rheology of concrete
“Is a science of deformation and flow of materials”.
• It is concerned with relationships between stress,
strain, rate of strain and time.
• Rheological Principles and techniques as applied to
concrete include:
• Deformation of the hardened concrete
• Handling and Placing of fresh concrete and its behavior

55. The determination of rheological characteristics or
parameters of fresh concrete are based on the assumption
that:
1.The concrete as a multi phase material is a continuum. This
means, a material with no discontinuity between any two
points on it
2.The concrete as a multi phase material is a homogeneous
mix. This means a material with uniform composition
throughout.
3.The concrete as a multi phase material is an isotropic
material. This means, material of the same properties in all
directions

56. 56
The Rheology of Fresh Concrete includes parameters
like:Stability, Mobility, Compactability
Stability
Defined as the “condition in which aggregate are held in homogenous
dispersion by a matrix” and the sampling shows the same particle size
distribution during transportation, Placing and Compaction .
• This is measured by bleeding and segregation characteristics of
concrete.
Mobility
Defined as “ its ability of flow under momentum.”
• The flow is restricted by the cohesive, viscous and frictional forces.
• The relative mobility characteristics at the construction site can be
measured by Vee-bee test and compaction factor test.

57. 57
Compactability
“Measures the ease with which the concrete is Compacted”.
• Compacting consists of expelling the entrapped air and
repositioning the aggregate particles in dense mass without
causing segregation.

58. 58
Bingham’s Parameter
• Concrete in its fresh state can be thought of as a fluid, Provided
that a certain degree of flow can be achieved with homogenity.
• The description of flow of fluid uses concepts such as shear stress
and shear rate.
• Concrete as a fluid, is most often assumed to behave like a
Bingham fluid.

59. 59
Bingham Fluid
“Is a fluid that acts as a rigid body at low shear stress
and flow like a viscous fluid at high shear”.
• Bingham Model for Rheology of Concrete
• Concrete is a non-Newtonian fluid whose rheological properties
is represented by Bingham model.
• When we relate with the concrete material, the constant is related
to the shear rate at which concrete is measured and the shear
history of the same.

60. 60
Bingham Model
• In Bingham model, the flow is defined by two
parameters: yield stress and plastic viscosity.
Ԏ = Ԏo + µϒ
Where,
Ԏ = is the shear stress applied to the materials
Ԏo= is the yield stress.
µ = is the Plastic viscosity
ϒ = is the shear strain rate.

61. Fig.16 Shear Stress- Rate of shear Relationship (Source Internet)

62. • When the concrete is studied at a lower shear stress value, that
is the practical case of fresh concrete,
• it is observed that, the linear curve obtained when drawing
shear stress to strain curve do not pass through the
origin.Instead, it starts at a particular value from the x-axis as
shown.
• This intercept formed at the x-axis is the minimum stress value
below which the concrete will not flow.

63. Fig.17 Shear Stress- Rate of shear
Relationship (Source Internet)

64. Any questions ?

65. THANK YOU