This presentation gives overview of different Lightweight aggregates and its influence in concrete

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2. LIGHTWEIGHT AGGREGATES AND
ITS INFLUENCE IN CONCRETE
Dr.R.Gopi, ME, Ph.D.
Associate Professor, Department of Civil Engineering,
Marri Laxman Reddy Institute of Technology & Management,
Dundigal, Hyderabad.
Mail id – gopir@mlritm.ac.in
RECENT TRENDS IN CIVIL ENGINEERING
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3. Overview of the Presentation
• Lightweight concrete – Introduction
• Materials for lightweight concrete
• Advantages & Disadvantages
• Applications
• Lightweight aggregate – Introduction
• Types
• Properties
• Internal curing using lightweight aggregate
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4. Lightweight concrete – Introduction
• Lightweight concrete is a special type of
concrete which weighs lighter than
conventional or normal concrete. Density of
light weight concrete is conventionally low.
Generally 300 kg/m³ to 1900 kg/m³ and thus
normal concrete has density between 2300
kg/m³ to 2600 kg/m³.
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5. Methods of producing lightweight
concrete
• There are three different methods available.
1. By using porous lightweight aggregate of low specific gravity, i.e.
lower than 2.6. This type of concrete is known as lightweight
aggregate concrete.
2. By introducing large voids within the concrete. These voids should
be clearly distinguished from the extremely fine voids produced
by air entrainment. Foaming agents are added like aluminum
powder to create the aeration effect. This types of concrete is
variously knows as aerated, cellular, foamed or gas concrete.
3. By removing the fine aggregate from the mix so that a large
number of voids are present; normal weight coarse aggregate is
generally used. This concrete as no-fines concrete.
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6. Advantages
• It reduces the dead load of the building.
• Easy to handle and hence reduces the cost of transportation
and handling.
• Improves the workability.
• Lightweight concrete has a lower thermal conductivity.
• Good resistance to freezing & thawing action when compared
to conventional concrete.
• The use of light weight concrete gives an outlet for industrial
wastes such as fly ash, clinkers, slag etc, which create problem
for disposal.
• It offers great fire resistance.
• Light weight concrete gives overall economy
• Reduces the foundation cost
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7. Disadvantages
• Lightweight concrete is generally very sensitive with
water content in the mixture.
• Difficult to place and finish because of porosity and
angularity of the aggregate, hence skilled labours are
required.
• In some cases may separate the aggregates and make it
float on the surface.
• Mixing time is comparatively longer than conventional
concrete, so as to assure proper mixing of concrete.
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8. Applications
• Since the strength of LWC is low, it is used in the construction
of roof slabs, small houses with load bearing walls etc.
• It is also used in the construction of stairs, windows, garden
walls, etc.
• In large building construction this is used in the construction
of partition walls.
• These are moulded in the form of slabs and used as thermal
insulators inside the building.
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9. Lightweight Aggregate (LWA) -
Introduction
• Lightweight aggregates are used to produce
lightweight concrete when the weight of
aggregates, ranges from 400 to 1150 kg/m3.
• Properties of LWA:
1. Porous in nature
2. Low density
3. High water absorption & Retention (majorly
used in Horticulture for growing plants)
4. High insulating property
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11. Types of LWAs
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12. Pumice aggregate
Pumice stone is a natural lightweight aggregate which is formed by the
sudden cooling of molten volcanic matter. Pumice is formed during the
volcanic eruption of viscous magma. Pumice is notably one of the most
common and the oldest of naturally occurring aggregates utilized lightweight
coarse aggregates used for the production of concrete for construction
industry. Their lightness is due to the escaping of gas from the molten lava
when erupted from deep beneath the earth’s crest. It having density around
600 kg/m3.
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14. Diatomite
It is derived from the remains of microscopic
aquatic plants called diatoms. The deposit of
aquatic plants are formed beneath the deep
ocean bed. The bulk density about 450 kg/m3. It
also used as a pozzolanic material.
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16. Sawdust
Sawdust refers to the tiny sized and powdery waste
produced by the sawing of wood. It is used as lightweight
aggregate in flooring and in the manufacture of precast
products. The density of saw dust is 210kg/m3.
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17. Scoria
Scoria is porous, reddish or black in color, lightweight and strong enough
to be used as light weight aggregate. Concrete produced using scoria
aggregates can insulate heat five to seven times better than the concrete
produced using conventional aggregate. The scoria is therefore, suitable
as a thermal insulating material and has the potential to be utilized in
manufacturing heat-insulating concrete and building blocks. The density of
scoria is 1100kg/m3.
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19. Light Expanded Clay Aggregate (LECA)
LECA is a special type of light aggregates that has been
pelletized and fired in a rotary kiln at a very high
temperature. As it is fired, the organic compounds are
burn off forcing the pellets to expand and become
honeycombed. The resulting pellets are lightweight,
porous and have a high crushing resistance. Density of
LECA ranges from 400 to 800 kg/m3
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23. Expanded shale and slate
• Expanded Shale is mined, crushed and fired
under high temperatures around 1100⁰ C in a
rotary kiln, producing a clean, inert, porous, and
light material. Density ranges from 400 to 800
kg/m3
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25. Sintered fly ash aggregate
Above 90% fly ash mixed with water and in some cases a small volume of
additives. After agglomeration and pelletizing, the green pellets are
sintered at high temperature (the process of fusing particles together into
one solid mass by using a combination of pressure and heat without
melting the materials.), producing light weight aggregate whose
characteristics are similar to natural aggregates.
• Typical Physical Characteristics:
• Aggregate Size : 5 – 16 mm
• Bulk Density : 650 – 950 kg/m3
• Particle Density : 1250 – 1450 kg/m3
• Aggregate Strength : >= 5.0 MPa
• Water Absorption : <= 22%
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27. Perlite
Perlite is an amorphous volcanic glass that has
relatively high water content (2-5%). It occurs naturally
and has the unusual property of greatly expanding
when heated sufficiently. It is an industrial mineral and
a commercial product useful for its light weight after
processing. Density of perlite around 30–150 kg/m3.
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29. Exfoliated Vermiculite
Vermiculite is a naturally-occurring mineral composed of shiny
flakes resembling Mica. It is produced in different grades or
sizes. When heated to high temperature, vermiculite flakes
expand 8-30 times their original size (a process called
exfoliation) and loses weight. Mostly, exfoliated vermiculite is
used in different markets namely horticultural, agricultural,
construction and industry. Density around 200 kg/m3
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31. Foamed slag
The lightweight cellular material obtained by
controlled processing of molten blast-
furnace slag with water, or with water and other
agents such as steam or compressed air or both.
Density range from 800 kg/m3 to 1040 kg/m3.
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33. Spectrum of lightweight aggregates
(ACI 213R-87)
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34. Internal curing using lightweight
aggregates
The American Concrete Institute (ACI) defines internal curing as
“a process by which the hydration of cement continues because of the
availability of internal water that is not part of the mixing water.” This is
accomplished by replacing some of the fine or intermediate aggregate
with prewetted lightweight aggregate. We call it curing from the inside
out.
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36. Internal curing using lightweight
aggregates
• The strength of the concrete is increased as the bond between the
light weight aggregate and the hydrated cement becomes
continuous due to decrease in permeability.
• Advantages of internal curing:
1. Achieve good bonding between cement paste & aggregate
2. Considerable water saving, suitable for water scarcity areas. (1 m3
of concrete required 3 m3 of water for mixing and curing purpose)
3. Reduces the shrinkage cracking
4. Reduces permeability
5. Provide greater durability
6. Increases the early age strength
7. Improved rheology
8. Manpower for curing not required
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37. References
• ASTM C 330 - Standard Specification for Lightweight
Aggregate for Structural Concrete
• ASTM C 1761 - Standard Specification for Lightweight
Aggregate for Internal Curing of Concrete
• https://www.escsi.org/internal-curing/technical-docs/
• IS 6042 (1969): Code of practice for construction of
lightweight concrete block masonry
• IS 9142 (1979): Specification for Artificial Lightweight
Aggregates for Concrete Masonry Units
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