Light weight concrete-materials properties and types. Typical light weight concrete mix High density concrete and high performance concrete-materials,properties and applications, typical mix.

1. Light Weight Concrete
By
Dr. Vinay Kumar B M

2. Background
• Density of conventional concrete is 2200 to 2600 kg/m3.
• Hence structure is uneconomical.
• Reduction in self weight increases efficiency.
• Solution is Light weight concrete

3. Lightweight concrete
“Is a type of concrete which includes an expanding
agent in that it increases the volume of the mixture
while giving additional qualities such as nailibility and
lessened the dead weight”

4. Contd…..
• It is lighter than then conventional concrete with a dry
density ranges from 300 kg/m3 to 1840 kg/m3.
• 87 to 23% lighter.
• It was first introduced by the Romans.
• ‘The Pantheon’ has been constructed using pumice.

5. specialties of lightweight concrete
• low density and thermal conductivity.
• Reduction in dead load.
• faster building rates in construction.
• lower haulage and handling costs.
• Use of lighter materials results in economy

6. The Pantheon
still standing eminently in Rome until now for about 18

7. TYPES OF LIGHTWEIGHT CONCRETE
Lightweight concrete can be prepared
1. Injecting air in mortar.
2. Achieved by omitting the finer sizes of the
aggregate.
3. Replacing them by a hollow, cellular or porous
aggregate.

8. lightweight concrete can be categorized into
three groups:
1. No-fines concrete
2. Lightweight aggregate concrete
3. Aerated/Foamed concrete

9. NO-FINES CONCRETE
• No-fines concrete can be defined as a lightweight
concrete composed of cement and coarse aggregate.
• Uniformly distributed voids are formed throughout its
mass.
• lightweight concrete is it maintains its large voids

10. Mix Proportion
• Generally made with aggregate cement ratio 6:1 to 10:1.
• Aggregate used-Passing through 20mm and retained 10mm.
• Strength is dependent on w/c ratio.
• w/c ratio between 0.38 to 0.52.
No-fines concrete,
• conventional aggregate -1600 to 1900 kg/m3
• Light weight aggregate-360 kg/m3

11. No-fines Concrete

12. Contd….
• No-fines concrete usually used for both load bearing
and non-load bearing for external and partitions.
• The strength of no-fines concrete increases as the
cement content is increased.
• However, it is sensitive to the water composition
• Architects considers this is an attractive construction
material

13. LIGHTWEIGHT AGGREGATE CONCRETE
• Porous lightweight aggregate of low specific gravity is
used in this lightweight concrete instead of
conventional Aggregate.
The lightweight aggregate can be:
1. Natural aggregate such as pumice, scoria and all of
those of volcanic origin.
2. Artificial aggregate such as expanded blast-furnace
slag, vermiculite and clinker aggregate.

14. Typical Properties of LWC

15. Contd….
• The main characteristic of this lightweight aggregate is
its high porosity which results in a low specific gravity.
• The lightweight aggregate concrete can be divided
into two types according to its application:
1. Partially compacted lightweight aggregate concrete
2. The structural lightweight aggregate concrete

16. Partially compacted lightweight aggregate
concrete
1. Precast concrete blocks or Panels
2. Cast in-situ roofs and walls.
“Adequate strength and a low density to obtain the
best thermal insulation and a low drying shrinkage to
avoid cracking”

17. Structurally lightweight aggregate concrete
• Is fully compacted similar to that of the normal reinforced
concrete of dense aggregate.
• It can be used with steel reinforcement as to have a good
bond between the steel and the concrete.
• Should have compressive strength more than 17Mpa(28
days) .
• Unit weight should not exceed 1850kg/m3

18. workability
• Care should be taken on workability aspect of SLWC.
• High slump and over vibration-mortar goes down and
aggregates tend to float.
• Maximum slump limit is 100mm.
• Higher slump loss on account of Continous absorption of
water by aggregate.

19. Mix Design
• Mix design for conventional concrete cannot be followed.
• Lack of accurate value of absorption, sp.gravity, and free
moisture content makes difficult to apply w/c ratio.
• Mix design is usually established by trial mixes.
• The proportions of fine to coarse aggregate and cement and
water requirement based on previous experiences with
particular aggregate.

20. Lightweight Aggregate Concrete

21. AERATED CONCRETE
• Aerated concrete does not contain coarse aggregate, and
can be regarded as an aerated mortar.
• Aerated concrete is made by introducing air or other gas
into a cement slurry and fine sand.
In commercial practice,
• The sand is replaced by pulverized fly ash or other siliceous
material.
• Lime maybe used instead of cement

22. Methods to prepare the aerated concrete
• The first method is to inject the gas into the mix, during its
plastic condition by means of a chemical reaction.
• The second method, air is introduced either by mixing-in
stable foam or by whipping-in air, using an air-entraining
agent.

23. Aerated Concrete

24. Types and Grading of Lightweight Concrete

26. Advantages of Lightweight Concrete
• Rapid and relatively simple construction.
• Economical in terms of transportation as well as
reduction in manpower.
• Significant reduction of overall weight results in saving
structural frames, footing or piles.
• Most of lightweight concrete have better nailing and
sawing properties than heavier and stronger
conventional concrete

27. Disadvantages of Lightweight Concrete
• Very sensitive with water content in the mixtures.
• Difficult to place and finish because of the porosity
and angularity of the aggregate.
• Mixing time is longer than conventional concrete to
assure proper mixing

28. APPLICATION OF LIGHTWEIGHT CONCRETE
• The Pantheon’ where it used pumice aggregate in the
construction of cast in-situ concrete is the proof of its
usage.
• In USA and England, clinker was used in their construction
for example the ‘British Museum’ and other low cost
housing.
• Perlite with its outstanding insulating characteristics, used
for vessels, roof decks and other applications.

29. High Density concrete
• Density of normal concrete is -2400kg/m3.
• Density of lightweight will be less than 1900kg/m3.
• Density ,which is about higher than 50% of conventional
concrete. I,e 3350 to 3850 kg/m3.
• The high density concrete is normally used in construction
of radiation shields.
• Advent of nuclear energy industry, large production of
penetrating radiation and radioactive materials

30. Types of radiation
1. Electromagnetic waves
2. Nuclear Particles

31. Electromagnetic waves
• High energy and high frequency waves known as x-rays
and gamma rays which requires shielding.
• They are similar to light rays but of higher energy and
greater penetrating power.
• Hence it can be absorbed by providing appropriate
thickness of concrete shield.

32. Nuclear Particles
• Consist of nuclei of atoms and fragments thereof.
• Includes neutrons, protons, alpha and beta particles.
• Neutrons posses electric charge, if they are uncharged
they continue to interact with the nucleus.
• Protons, alpha and beta particles carry electrical charges
which interact with electric field, and loose their energy
considerably

33. Contd…..
• Hence the question of shielding resolves into protection
against x-rays, gamma rays, and neutron.
• Apart from the biological hazards, along with nuclear
reaction very high temperature is also generated.

34. Shielding ability of concrete
• Concrete posses needed characteristics for both neutrons and
gamma rays.
• Has satisfactory mechanical properties and has low initial and
maintenance cost.
• Aggregates whose sp.gravity is more than 3.5 is used for making
HDC.
• Some of the commercially available aggregate are: barite,
magnitite, ilminite, limonite, hematite etc.
• In general, heavyweight aggregate should be clean,strong,inert and
relatively free from deleterious materials

35. Concrete for radiation shielding
• Concrete should be highly dense and should have high
strength even at high temperature.
• w/c ratio, use of appropriate admixture and vibration for
good compaction is required.
• High modulus of elasticity, low thermal expansion and low
elastic and creep deformation are desired properties.

36. High Performance Concrete
Concrete is the most widely used construction material
in India with annual consumption exceeding 100 million
cubic metres.
Conventional Portland cement concrete is found
deficient in respect of:
• Durability in severe environs (Shorter service life and
require maintenance)
• Time of construction (longer release time of forms and
slower gain of strength)

37. Contd….
• Energy absorption capacity (for earthquake-resistant
structures)
• Repair and retrofitting jobs
High performance concrete (HPC) successfully meets
the above requirement.

38. Contd….
• HPC is an engineered concrete possessing the most
desirable properties during fresh as well as hardened
concrete stages.
• In the other words a high performance concrete is a
concrete in which certain characteristics are developed for
a particular application and environment.

39. Definition
HPC was defined as “concrete, which meets special
performance and uniformity requirements that cannot be
always be achieved routinely by using only conventional
materials and normal mixing, placing and curing practices”.

40. Methods for achieving High Performance
1. Reducing the capillary pore system such that no fluid
movement can occur is the first approach.
2. Creating chemically active binding sites which prevent
transport of aggressive ions such as chlorides is the
second more effective method.

42. Requirements for High-performance Characteristics
• Permeation is a major factor that causes premature
deterioration of concrete structures.
• The provision of high-performance concrete must
centre on minimizing permeation through
proportioning methods and suitable construction
procedures.
• Permeation can be divided into three distinct but
connected stages of transportation of moisture, vapour,
air, gases, or dissolved ions.

43. “Concrete takes in water by capillary suction. The rate
at which water enters is called sorptivity.”
“The ease with which fluid passes through concrete
usually under a pressure differential is referred to as
permeation.”
“Vapor or gas ions are sucked through concrete
under the action of ion concentration differential
known as diffusion.”
It is important to identify the dominant transport
phenomenon and design the Mix proportion

44. salient high-performance requirements

46. Parameter to be controlled for achieving the
required performance criteria
• Water/ (cement + mineral admixture) ratio.
• Strength.
• Densification of cement paste.
• Elimination of bleeding.
• Homogeneity of the mix

47. Contd….
• Particle size distribution.
• Stronger transition zone.
• Low free lime content.
• Very little free water in hardened concrete

48. Material Selection
• Cement
• Fine aggregate
• Coarse aggregate
• Water
• Mineral admixtures (fine filler and/or pozzolonic
supplementary cementitious materials)
• Chemical admixtures (plasticizers, superplasticizers,
retarders, air-entraining agents)

49. Cement
There are two important requirements for any
cement:
1. strength development with time.
2. facilitating appropriate rheological characteristics when
fresh

51. Coarse aggregate
• The important parameters of coarse aggregate that
influence the performance of concrete are its shape, texture
and the maximum size.
• Surface texture and mineralogy affect the bond between the
aggregates and the paste as well as the stress level at which
micro cracking begins.
• The use of larger maximum nominal size of aggregate
affects the strength in several ways.

52. Contd….
• It is generally suggested that 10 to 12 mm is the
appropriate maximum size of aggregates for making high
Performance concrete.
• However, adequate performance and economy can also be
achieved with 20 to 25 mm maximum size graded
aggregates.

53. Mineral admixtures
• Mineral admixtures form an essential part of the high-
performance concrete mix.
• Used for various purposes, depending upon their
properties.
• The fly ash (FA), the ground granulated blast furnace slag
(GGBS) and the silica fume (SF) has been used widely as
supplementary cementitious materials

54. Superplasticizers or HRWR
• The superplasticizers are extensively used in HPCs with very
low water cementitious material ratios.
• In addition to deflocculation of cement grains, it increases
the fluidity.

55. The following types of superplasticizers are
used:
• Naphthalene-based
• Melamine-based
• Lignosulphonates-based
• Polycarboxylate-based
• Combinations of above

56. Superplasticizer Dosage
• There is no a prior way of determining the required
superplasticizer dosage; it must be determined by trial and
error procedure.
• If strength is the primary criterion, then one should work
with the lowest w/c ratio.
• If the rheological properties of the HPC are very important,
then the highest w/c ratio.
• In general, some intermediate proportions must be found,
so that the combination of strength and rheological
properties are optimized.

57. Mix Proportion
• The main difference between mix designs of HPC and CC
is the emphasis laid on performance aspect also besides
strength, in case of HPC.
• whereas in design of CC mixes, strength of concrete is
an important criterion.

58. Mix design of HPC should be based on the following
considerations:
• The water-binder (w/b) ratio should be as less as possible,
preferably 0.3 and below.
• The workability of concrete mix should be enough to
obtain good compaction.
• The transition zone between aggregate and cement paste
should be strengthened.
• The microstructure of cement concrete should be made
dense and impermeable

59. Properties of Fresh Concrete
1. Workability
2. Rheological Properties
3. Curing

60. Workability
• workability of HPC is normally good, even at low slumps.
• HPC typically pumps very well, due to the ample volume
of cementing material.
• Due to reduced water-cementing material ratio no
bleeding occurs.
• The cohesiveness of concrete is much better as a result of
better dispersion of cement particles.

61. Rheological Properties
• The blended or composite cements with wider particle-size
distributions can achieve better rheological properties.

62. Curing
• The compressive strength of HPC is less sensitive to
temperature and relative humidity than the normal strength
concrete.
• The concrete containing very large quantities of ground
granulated blast furnace slag requires longer moist curing
times to develop adequate strength.
• The higher internal temperatures frequently found with high
early strength HPC can lead to a rapid strength gain in
concrete and consequent increase in elastic modulus.

63. Properties of Hardened concrete
1. Strengths
2. Modulus of elasticity
3. Shrinkage
4. Creep

64. Strengths
• Compressive, tensile and flexural strengths of high
performance concrete are much higher than those of the
normal concrete.
• The enhancement in the mechanical properties is generally
commensurate with reduction in water content when HRWR
is used.
• Strength – properties and proportions of the constituent
materials, degree of hydration, rate of loading, and method
of testing and specimen geometry.

65. Modulus of elasticity
• The elastic modulus of concrete increases with its
compressive strength.
• The modulus is greatly affected by the properties of the
coarse aggregate.
• The larger the amount of coarse aggregate with a high
elastic modulus, the higher would be the modulus of
elasticity of concrete.
• The concrete in wet condition has about 15 percent
higher elastic modulus than that in the dry condition

66. Shrinkage
• Little information is available on the shrinkage behavior of
High-Performance concrete.
• A relatively high initial rate of shrinkage has been reported.
• shrinkage of high-performance concrete is similar to that of
lower strength concrete.

67. Creep
• The creep of high-performance concrete made with high-
range water reducers is reported to be decreased
significantly.
• The maximum specific creep was less for high-strength
concrete than for lower-strength concrete loaded at the
same age.