Light weight concrete

Light weight concrete
Civil Department Page 1 East WestPolytechnic
Chapter :01
Introduction to concrete

Introduction to concrete
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.
In a building construction, concrete is used for the construction of foundations, columns,
beams, slabs and other load bearing elements.
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 type of cement are Portland Pozzolana Cement (PPC), rapid
hardening cement, Sulphate resistant cement etc.
Materials are mixed in specific proportions to obtain the required strength. Strength of mix is
specified as M5, M10, M15, M20, M25, M30etc… where M signifies Mix and 5, 10, 15 etc.
as their strength in kN/m2. In United States, concrete strength is specified in PSI which is
Pounds per Square Inch.
What is Grade of concrete
Grade of concrete denotes its strength required for construction. For example, M30 grade
signifies that compressive strength required for construction is 30MPa. The first letter in
grade “M” is the mix and 30 is the required strength in MPa.
The strength is measured with concrete cube or cylinders by civil engineers at construction
site. Cube or cylinders are made during casting of structural member and after hardening it is
cured for 28 days. Then compressive strength test is conducted to find the strength.
Regular grades of concrete are M15, M20, M25 etc. For plain cement concrete works,
generally M15 is used. For reinforced concrete construction minimum M20 grade of concrete
are used.

Advantages of concrete
Ingredients of concrete are easily available in most of the places.
Unlike natural stones, concrete is free from defects and flaws.
Concrete can be manufactured to desired strength with an economy.
The durability of concrete is very high.
It can be cast to any desired shape.
The casting of concrete can be done in the working site which makes it economical.
Maintenance cost of concrete is almost negligible.
The deterioration of concrete is not appreciable with age.
Concrete makes a building fire-safe due to its non-combustible nature.
Concrete can withstand high temperatures.
Concrete is resistant to wind and water. Therefore, it is very useful in storm shelters.
As a soundproofing material cinder concrete could be used.
They are some special types of concrete
1. Ordinary concrete
2. Self-compacting concrete
3. Reinforced cement concrete
4. Precast concrete
5. Prestressed concrete
6. Pervious concrete
7. Light weight concrete
8. Fibre reinforced concrete
1.Ordinary concrete
It is one of the most commonly used types of concrete. In this type of concrete, the essential
constituents are cement, sand and coarse aggregates designed and mixed with a specified
quantity of water.
The ratio of essential constituents may be varied within wide limits. A very commonly used
mix design, commonly known as Nominal Mix Design is 1:2:4.
Plain concrete is mostly used in the construction of pavements and in buildings, where very
high tensile strength is not required. It is also used in the construction of Dams.
Among the most important properties of ordinary concrete, the following may be mentioned.
 Density: 2200 – 2500 Kg/meter. Cube.
 Compressive Strength: 200 – 500 Kg/centimeter.square.
 Tensile Strength: 50 – 100 Kg/centimeter.square.
 Durability: Very Satisfactory.

2.Self-compacting concrete
The defects in concrete in Japan were found to be mainly due to high water-cement ratio to
increase workability. Poor compaction occurred mostly because of the need for speedy
construction in the 1960s and 1970s. Hajime Okamura envisioned the need for concrete
which is highly workable and does not rely on the mechanical force for compaction. During
the 1980s, Okamura and his Ph.D. student Kazamasa Ozawa at the University of Tokyo
developed self-compacting concrete (SCC) which was cohesive, but flowable and took the
shape of the formwork without use of any mechanical compaction. SCC is known as self-
consolidating
concrete in the United States.
SCC is characterized by the following:
 extreme fluidity as measured by flow, typically between 650–750 mm on a flow table,
rather than slump (height)
 no need for vibrators to compact the concrete
 easier placement
 no bleeding, or aggregate segregation
 increased liquid head pressure, which can be detrimental to safety and workmanship
SCC can save up to 50% in labour costs due to 80% faster pouring and reduced wear and
tear on formwork.
In 2005, self-consolidating concretes accounted for 10–15% of concrete sales in some
European countries. In the precast concrete industry in the U.S., SCC represents over 75% of
concrete production. 38 departments of transportation in the US accept the use of SCC for
road and bridge projects.
This emerging technology is made possible by the use of polycarboxylates plasticizer instead
of older naphthalene-based polymers, and viscosity modifiers to address aggregate
segregation.
3.Reinforced cement concrete
Reinforced concrete (RC) (also called reinforced cement concrete or RCC) is a composite
material in which concrete's relatively low tensile strength and ductility are counteracted by

the inclusion of reinforcement having higher tensile strength or ductility. The reinforcement
is usually, though not necessarily, steel reinforcing bars (rebar) and is usually embedded
passively in the concrete before the concrete sets. Reinforcing schemes are generally
designed to resist tensile stresses in particular regions of the concrete that might cause
unacceptable cracking and/or structural failure. Modern reinforced concrete can contain
varied reinforcing materials made of steel, polymers or alternate composite material in
conjunction with rebar or not. Reinforced concrete may also be permanently stressed
(concrete in compression, reinforcement in tension), so as to improve the behaviour of the
final structure under working loads. In the United States, the most common methods of doing
this are known as pre-tensioning and post-tensioning.
For a strong, ductile and durable construction the reinforcement needs to have the following
properties at least:
 High relative strength
 High toleration of tensile strain
 Good bond to the concrete, irrespective of pH, moisture, and similar factors
 Thermal compatibility, not causing unacceptable stresses (such as expansion or
contraction) in response to changing temperatures.
 Durability in the concrete environment, irrespective of corrosion or sustained stress for
example.
4.Precast concrete
Concrete makes a building fire-safe due to its noncombustible nature.

5.Prestressed concrete
Prestressed concrete is a form of concrete used in construction that is "prestressed" by being
placed under compression prior to supporting any loads beyond its own dead weight. This
compression is produced by the tensioning of high-strength "tendons" located within or
adjacent to the concrete volume and is done to improve the performance of the concrete in
service. Tendons may consist of single wires, multi-wire strands or threaded bars and are
most commonly made from high-tensile steels, carbon fibre or aramid fibre The essence of
prestressed concrete is that once the initial compression has been applied, the resulting
material has the characteristics of high-strength concrete when subject to any
subsequent compression forces and of ductile high-strength steel when subject to tension
forces. This can result in improved structural capacity and/or serviceability compared with
conventionally reinforced concrete in many situations.In a prestressed concrete member, the
internal stresses are introduced in a planned manner so that the stresses resulting from the
superimposed loads are counteracted to the desired degree.
Prestressed concrete is used in a wide range of building and civil structures where its
improved performance can allow for longer spans, reduced structural thicknesses, and
material savings compared with simple reinforced concrete. Typical applications
include high-rise buildings, residential slabs, foundation
systems, bridge and dam structures, silos and tanks, industrial pavements and nuclear
containment structures.
6.Pervious concrete
Pervious concrete (also called porous concrete, permeable concrete, no fines concrete and
porous pavement) is a special type of concrete with a high porosity used for
concrete flatwork applications that allows water from precipitation and other sources to pass
directly through, thereby reducing the runoff from a site and allowing groundwater recharge.
Pervious concrete is made using large aggregates with little to no fine aggregates. The
concrete paste then coats the aggregates and allows water to pass through the concrete slab.
Pervious concrete is traditionally used in parking areas, areas with light traffic,
residential streets, pedestrian walkways, and greenhouses.[1][2] It is an important application
for sustainable construction and is one of many low impact development techniques used by
builders to protect water quality.
7.Fibre reinforced concrete
Fibre reinforced concrete is concrete containing fibrous material which increases its
structural integrity. It contains short discrete fibers that are uniformly distributed and
randomly oriented. Fibers include steel fibers, glass fibers, synthetic fibers and natural
fibres– each of which lend varying properties to the concrete. In addition, the character of

fibre-reinforced concrete changes with varying concretes, fibre materials, geometries,
distribution, orientation, and densities.
Fibers are usually used in concrete to control cracking due to plastic shrinkage and to drying
shrinkage. They also reduce the permeability of concrete and thus reduce bleeding of water.
Some types of fibers produce greater impact–, abrasion–, and shatter–resistance in concrete.
Generally fibers do not increase the flexural strength of concrete, and so cannot
replace moment–resisting or structural steel reinforcement. Indeed, some fibers actually
reduce the strength of concrete.
The amount of fibers added to a concrete mix is expressed as a percentage of the total
volume of the composite (concrete and fibers), termed "volume fraction" (Vf). Vf typically
ranges from 0.1 to 3%. The aspect ratio (l/d) is calculated by dividing fibre length (l) by its
diameter (d). Fibers with a non-circular cross section use an equivalent diameter for the
calculation of aspect ratio. If the fibre's modulus of elasticity is higher than the matrix
(concrete or mortar binder), they help to carry the load by increasing the tensile strength of
the material. Increasing the aspect ratio of the fibre usually segments the flexural strength
and toughness of the matrix. However, fibers that are too long tend to "ball" in the mix and
create workability problems.
Some recent research indicated that using fibers in concrete has limited effect on the impact
resistance of the materials This finding is very important since traditionally, people think that
ductility increases when concrete is reinforced with fibers. The results also indicated that the
use of micro fibers offers better impact resistance to that of longer fibers.
The High Speed 1 tunnel linings incorporated concrete containing 1 kg/m³ of polypropylene
fibers, of diameter 18 & 32 μm, giving the benefits noted below.
8.Light weight concrete
Lightweight concrete mixture is made with a lightweight coarse aggregate and sometimes a
portion or entire fine aggregates may be lightweight instead of normal aggregates. Structural
lightweight concrete has an in-place density (unit weight) on the order of 90 to 115 lb / ft³
(1440 to 1840 kg/m³).
Normal weight concretes a density in the range of 140 to 150 lb/ft³ (2240 to 2400 kg/m³). For
structural applications the concrete strength should be greater than 2500 psi (17.0 MPa).
Lightweight aggregates used in structural lightweight concrete are typically expanded shale,
clay or slate materials that have been fired in a rotary kiln to develop a porous structure.
Other products such as air-cooled blast furnace slag are also used.

There are other classes of non-structural LWC with lower density made with other aggregate
materials and higher air voids in the cement paste matrix, such as in cellular concrete.
Uses of Lightweight Concrete
Screeds and thickening for general purposes especially when such screeds or thickening and
weight to floors roofs and other structural members.
Screeds and walls where timber has to be attached by nailing.
Casting structural steel to protect its against fire and corrosion or as a covering for
architectural purposes.
Heat insulation on roofs.
Insulating water pipes.
Construction of partition walls and panel walls in frame structures.
Fixing bricks to receive nails from joinery, principally in domestic or domestic type
construction.
General insulation of walls.
Surface rendered for external walls of small houses.
It is also being used for reinforced concrete.

Chapter:02
Literature review

1.MATERIALS, PROPERTIES AND APPLICATION REVIEW
OF LIGHTWEIGHT CONCRETE
Jihad Hamad Mohammed and Ali Jihad Hamad
15/10/2014
1. Lightweight concrete (LWC) is considered as a versatile material that has created great
interest and large industrial demand in recent years in a wide range of construction projects.
It has been made lighter than conventional (normal weight aggregate) concrete (El Zareef,
2010; Babu, 2008). LWC has an oven dry density range of about 300 to not exceed 2000
kg/m3, with a compressive strength for a cube of about 1 to more than 60 MPa, thermal
conductivities of 0.2 to 1.0 W/mK. These values can be compared to those for normal weight
concrete with approximately 2100–2500 kg/m3, 15 to greater than 100 MPa and 1.6–1.9
W/mK (Newman and Choo, 2003). Lightweight concrete can be classified according to:
A. The production methods
The types of LWC classified according to the method of production. These types are: a)
Using lightweight aggregate of low specific gravity in place of the normal weight aggregate,
specific gravity of lightweight aggregate is lower than 2.6. This type of concrete is well
known as lightweight aggregate concrete. b) Inducing bubble voids within the concrete or
mortar mass. This type of concrete is known as aerated, cellular, foamed, or gas concrete. c)
Eliminating the fine aggregate from the mix so the coarse aggregate of ordinary weight is
generally used. This concrete is known as no-fines concrete (Neville and
Materials, properties and production of lightweight concrete
Lightweight aggregate concrete
Lightweight aggregates are used to produce lightweight concrete when the weight of
aggregates, lower than 1120 kg/m3 (Mehta and Monteiro, 2006). Lightweight aggregates
have many sources: natural materials such as shales, clays, pumice, diatomite, volcanic
cinders, and slates or artificial materials (by products) such as iron blast furnace slag, clay,
sintered fly ash, and shale (Neville, 2000; ACI 213R-87; Milled et al., 2004). Figure 2 shows
the sorts of the lightweight aggregate (Shetty, 2006). Properties of lightweight aggregate
concrete depend on type of lightweight aggregate in the concrete (ACI 213R-87), structural
lightweight aggregates can produce concretes with compressive strengths in excess of 35
MPa, a limited number of lightweight aggregates can be used in concretes that develop
cylinder strengths from 48 to more than 69 MPa (Wal raven, 2002). Also, the Figure 3
shows the spectrum of lightweight aggregates, classification of lightweight aggregate

concrete into three categories depending on the air dry unit weight of the lightweight
aggregate concrete (ACI 213R-87). The ASTM C330, ASTM C331 and ASTM C 332
specifications was covering the lightweight aggregates for use in structural concrete,
production of masonry units and insulating concrete.
Classification of aerated lightweight concrete.
The foam agent used to obtain foamed concrete. It is defined as an air entraining agent. The
foam agent is the most essential influence on the foamed concrete. Foam agents when added
into the mix water, it will produce discrete bubbles cavities which become incorporated in
the cement paste. The properties of foamed concrete are critically dependent upon the quality
of the foam (Brady, Watts and Jones, 2001; Byun, Song and Park, 1998; Gelim, 2011).
Foamed concrete is produced either by preforming method or mixed foaming method. The
pre-foaming method involves the separate production of a base mix cement slurry (cement
paste or mortar) and a stably preformed aqueous (foam agent with water) and then the
thorough blending of this foam into a base mix. In mixed foaming, the surface-active agent is
mixed with the base mixture ingredients and during the process of mixing, foam is produced
resulting in cellular structure in concrete (Sulaiman, 2011; Zulkarnain and Ramli, 2011;
Nambiar and Ramamurthy, 2007). Aluminum powder is usually used to obtain autoclaved
aerated concrete (AAC) by a chemical reaction generating a gas in fresh mortar, so that when
it sets it contains a large number of gas bubbles (Salman, M.M. and Hassan, S.A., 2010).
Aluminum is used as a foaming agent in AAC production worldwide and it is widely proven
as the best solution for its purpose. Aluminum is added usually at about 0,2% to 0,5% by dry
weight of cement to the mixing ingredients (Boggelen). The materials which are suitable for
autoclaved aerated concrete are fine grading materials. Silica or quartz sand, lime, cement
and aluminum powder are the main raw materials for producing AAC. Silica sand’s

percentage is higher than the other aggregates in aerated concrete mix. Both silica and quartz
sand are mineral based aggregates which can be obtained from broken rocks or granites. At
the same time fly ash, slag, or mine tailings can be used as aggregates in combination with
silica (Somi, 2011). The aerated concrete combines insulation and structural capability in one
material for walls, floors, and roofs. Its light weight/cellular properties make it easy to cut,
shave, and shape, accept nails and screws readily, and allow it to be routed to create chases
for electrical conduits and small-diameter plumbing runs. This gives its design and
construction flexibility, and the ability to make easy adjustments in the field. The aerated
concrete features in durability and dimensional stability. Autoclaved aerated concrete resists
water, rot, mold, mildew, and insects. Also, the aerated concrete is excellent to fire resistance
.
CONCLUSION
The lightweight concrete is different conventional concrete in certain materials and
applications. The features of lightweight concrete are higher strength to weight ratio as
compared with conventional concrete, enhanced in thermal and sound insulation, reduced
dead load in the structure result reduce structural elements and minimize the steel
reinforcement. The lightweight concrete is classified into three types lightweight aggregate
concrete, aerated concrete and no-fines concrete. The lightweight aggregate concrete can be
development in the strength to obtain structural concrete by dominate the percentages of
lightweight aggregates. Aerated concrete is unlike other types of lightweight concrete in
coarse aggregate elimination, these gives more homogeneity and distribution of the voids
within concrete. The no-fines concrete feature from other types in eliminate of sand (fine
aggregate) and this gives no segregation between ingredient.
2.STUDY OF LIGHT WEIGHT CONCRETE
T. Divya Bhavana Senior Asst. Professor, Civil Engineering Department,
Auroras Engineering College, Bhongir, Telangana, India
Rapolu Kishore Kumar, S. Nikhil, P. Sairamchander
U.G Student, Civil Engineering Department, Auroras Engineering College,
Bhongir, Telangana, India
Lightweight concrete is a type of concrete contains expanded light weight aggregates which
increase the volume of the mixture while giving additional qualities such as lowering the
dead weight. Lightweight concrete maintains its large voids and not forming laitance layers
or cement films when placed on the wall. This research was based on the performance of
light weight concrete using expanded clay aggregate. However, sufficient water cement ratio
is vital to produce adequate cohesion between cement and water. Lightweight concrete is

usually chosen for structural purpose where its use will lead to a lower overall cost of a
structure than normal weight concrete This research report is prepared to show the activities
and progress of the lightweight concrete research project. The performance of lightweight
concrete such as compressive strength tests, water absorption and density and supplementary
tests and comparisons has been made with nominal concrete.
Used materials
Cement
Silica fume
Expanded clay aggregate
Coarse aggregate
Poly vinyl alcohol [PVA]
Water
Experimental procedure
The experimental investigation is carried based on volume proportions and the cement
content was taken to be 394.1kg/m3. Water/cement ratio (w/c) was taken to be 0.45 from

previous studies and from various trial mixes. Mix proportion pertaining to 0%, 25%,
50%, 75% and 100% replacement of expanded clay aggregate is considered to carry out
investigation. Aggregate sizes ranging from 16 mm - 20 mm were used to prepare the
samples of various mix proportions.
Compressive Strength
In this investigation, different concrete mix of ECA replacements is considered to
perform the test by-weight basis with 10% of cement replaced by silica fume and 1.6%
PVA solution. A 150x150 mm concrete cube was used as test specimens to determine the
compressive strength of concrete cubes. The constituents of concrete were thoroughly
mixed till uniform consistency was achieved. The cubes were properly compacted. All
the concrete cubes were de-molded within 24 hours after casting. The demolded test
specimens were properly cured in water available in the laboratory at an age of 7 and 28
days. Compression test was conducted on a 2000KN capacity universal testing machine.
Table 1 compressive strength for 28 days for various mix proportions
Figure 1 compressive strength of different mixes

Flexural Strength
In this investigation, different concrete mix of ECA replacements as mentioned above is
considered to perform the test by-weight basis with 10% of cement replaced by silica
fume and 1.6% PVA solution. A 700mm x 150mm x 150mm concrete beam was used as
test specimens to determine the flexural strength of concrete beams. The ingredients of
concrete were thoroughly mixed till uniform consistency was achieved. The beams were
properly compacted. All the concrete beams were de-molded within 24 hours after
casting. The demolded test specimens were properly cured in water available in the
laboratory at an age of 7 and 28 days. Flexural test was conducted on a -KN capacity
flexural testing machine.
Table 2 flexural strength for 28 days for various mix proportions
Figure 2 flexural strength of different mixes

Density
The density of both fresh and hardened concrete is of interest to the parties involved for
numerous reasons including its effect on durability, strength and resistance to permeability.
Hardened concrete density is determined either by simple dimensional checks, followed by
weighing and calculation or by weight in air/water buoyancy methods.
Table 3 Density 28 days for various mixes
Figure 3 density of different mixes
CONCLUSION
The compressive strength of light weight concrete is lower than the ordinary
conventional concrete. Therefore this light weight concrete can be used in places
where the external force acting on the structure is minimum. This light weight
concrete is only capable to carry its self weight
The workability of light weight concrete is not good when it is compared to the
ordinary conventional concrete. This workability can be improved by introducing
microscopic air bubbles into this concrete or air entrainment
From the above compressive strength results, it is observed that as the percentage of
ECA is increasing the compressive and flexure strength is decreasing since, the
density of concrete is reduced by addition of ECA

The partially light weight concrete may also be used as structural concrete on some
cases because it is having the compressive strength value which is suitable for
structural.
This light weight concrete has low thermal conductivity and has an ability to absorb
sound. So, it can be used for acoustic structures.

Chapter:03
Study area

Lightweight Concrete
Lightweight concrete mixture is made with a lightweight coarse aggregate and sometimes a
portion or entire fine aggregates may be lightweight instead of normal aggregates. Structural
lightweight concrete has an in-place density (unit weight) on the order of 90 to 115 lb / ft³
(1440 to 1840 kg/m³).
Normal weight concrete is a density in the range of 140 to 150 lb./ft³ (2240 to 2400 kg/m³).
For structural applications the concrete strength should be greater than 2500 psi (17.0 MPa).
Lightweight aggregates used in structural lightweight concrete are typically expanded shale,
clay or slate materials that have been fired in a rotary kiln to develop a porous structure.
Other products such as air-cooled blast furnace slag is also used.
There are other classes of non-structural LWC with lower density made with other aggregate
materials and higher air voids in the cement paste matrix, such as in cellular concrete.
Types of Lightweight Concrete
1. Lightweight Aggregate Concrete
In the early 1950s, the use of lightweight concrete blocks was accepted in the UK for load
bearing inner leaf of cavity walls. Soon thereafter the development and production of new
types of artificial LWA (Lightweight aggregate) made it possible to introduce LWC of high
strength, suitable for structural work.

These advances encouraged the structural use of LWA concrete, particularly where the need
to reduce weight in a structure was in a structure was an important consideration for design
or for economy.
Listed below are several types of lightweight aggregates suitable for structural
reinforced concrete: -
1. Pumice – is used for reinforced concrete roof slab, mainly for industrial roofs in
Germany.
2. Foamed Slag – was the first lightweight aggregate suitable for reinforced concrete
that was produced in large quantity in the UK.
3. Expanded Clays and Shales – capable of achieving sufficiently high strength for
prestressed concrete. Well established under the trade names of Aglite and Lecia
(UK), Haydite, Rocklite, Gravelite and Aglite (USA).
4. Sintered Pulverised – fuel ash aggregate – is being used in the UK for a variety of
structural purposes and is being marketed under the trade name Lytag
2. Aerated Concrete
Aerated concrete has the lowest density, thermal conductivity and strength. Like timber it can
be sawn, screwed and nailed, but there are non-combustible. For works in-situ the usual
methods of aeration are by mixing in stabilized foam or by whipping air in with the aid of an
air entraining agent.
The precast products are usually made by the addition of about 0.2 percent aluminums
powder to the mix which reacts with alkaline substances in the binder forming hydrogen
bubbles.
Air-cured aerated concrete is used where little strength is required e.g. roof screeds and pipe
lagging. Full strength development depends upon the reaction of lime with the siliceous
aggregates, and for the equal densities the strength of high pressure steam cured concrete is
about twice that of air-cured concrete, and shrinkage is only one third or less.
Aerated concrete is a lightweight, cellular material consisting of cement and/or lime and sand
or other silicious material. It is made by either a physical or a chemical process during which
either air or gas is introduced into a slurry, which generally contains no coarse material.
Aerated concrete used as a structural material is usually high-pressure steam-cured. It is thus
factory-made and available to the user in precast units only, for floors, walls and roofs.
Blocks for laying in mortar or glue are manufactured without any reinforcement.

Larger units are reinforced with steel bars to resist damage through transport, handling and
superimposed loads. Autoclaved aerated concrete, which was originally developed in Sweden
in 1929, is now manufactured all over the world.
3. No Fines Concrete
The term no-fines concrete generally means concrete composed of cement and a coarse (9-
19mm) aggregate only (at least 95 percent should pass the 20mm BS sieve, not more than 10
percent should pass the 10mm BS sieve and nothing should pass the 5mm BS sieve), and the
product so formed has many uniformly distributed voids throughout its mass.
No-fines concrete is mainly used for load bearing, cast in situ external and internal wall, non
load bearing wall and under floor filling for solid ground floors (CP III: 1970, BSI). No-fines
concrete was introduced into the UK in 1923, when 50 houses were built in Edinburgh,
followed a few years later by 800 in Liverpool, Manchester and London.
This description is applied to concrete which contain only a single size 10mm to 20mm
coarse aggregate (either a dense aggregate or a light weight aggregate such as sintered PFA).
The density is about two-third or three quarters that of dense concrete made with the same
aggregates.
No-fines concrete is almost always cast in situ mainly as load bearing and non load bearing
walls including in filling walls, in framed structures, but sometimes as filling below solids
ground floors and for roof screeds.
No-fines concrete is thus an agglomeration of coarse aggregate particles, each surrounded by
a coating of cement paste up to about 1·3 mm (0·05 in.) thick. There exist, therefore, large
pores within the body of the concrete which are responsible for its low strength, but their
large size means that no capillary movement of water can take place.
Although the strength of no-fines concrete is considerably lower than that of normal-weight
concrete, this strength, coupled with the lower dead load of the structure, is sufficient in
buildings up to about 20 storeys high and in many other applications.
Types of Lightweight Concrete Based on Density and Strength
LWC can be classified as :-
1. Low density concrete
2. Moderate strength concrete
3. Structural concrete

Uses of Lightweight Concrete
1. Screeds and thickening for general purposes especially when such screeds or
thickening and weight to floors roofs and other structural members.
2. Screeds and walls where timber has to be attached by nailing.
3. Casting structural steel to protect its against fire and corrosion or as a covering for
architectural purposes.
4. Heat insulation on roofs.
5. Insulating water pipes.
6. Construction of partition walls and panel walls in frame structures.
7. Fixing bricks to receive nails from joinery, principally in domestic or domestic type
construction.
8. General insulation of walls.
9. Surface rendered for external walls of small houses.
10. It is also being used for reinforced concrete.
Advantages of Lightweight Concrete
1. Reduced dead load of wet concrete allows longer span to be poured un-propped. This
save both labor and circle time for each floor.
2. Reduction of dead load, faster building rates and lower haulage and handling costs.
The eight of the building in term of the loads transmitted by the foundations is an
important factor in design, particular for the case of tall buildings.
3. The use of LWC has sometimes made its possible to proceed with the design which
otherwise would have been abandoned because of excessive weight. In frame
structures, considerable savings in cost can be brought about by using LWC for the
construction floors, partition and external cladding.
4. Most building materials such as clay bricks the haulage load is limited not by volume
but by weight. With suitable design containers much larger volumes of LWC can haul
economically.
5. A less obvious but nonetheless important characteristics of LWC is its relatively low
thermal conductivity, a property which improves with decreasing density in recent
years, with the increasing cost and scarcity of energy sources, more attention has been
given the formerly to the need for reducing fuel consumption while maintaining, and
indeed improving, comfort conditions buildings. The point is illustrated by fact that a
125 mm thick solid wall of aerated concrete will give thermal insulation about four
times greater than that of a 230 mm clay brick wall.

Durability of Lightweight Concrete
Concrete makes a building fire-safe due to its non-combustible nature.
Factors Affecting Durability of Lightweight Concrete and its
Remedies
Lightweight concrete has many applications and hence its significant to know its durability
properties and resistance in different environmental conditions. That is why the durability of
lightweight concrete is discussed in the following sections.
Lightweight concrete according to American code is defined as concrete that its air-dry
density is smaller than 1810 Kg/m3.
The definition of lightweight concrete in other counties might slightly be different, for
instance, according to Norway Code the concrete is assumed to be lightweight concrete if its
saturated surface dry density is equal or greater than 1800 Kg/m3 and its compression
strength should not surpass 85 MPa.
Lightweight concrete is produced by blending cement, water, fine aggregate, and lightweight
coarse aggregate for instance clay materials, slate materials, and expanded shale.

Following are the different durability properties of lightweight concrete and its
remedies:
 Freezing and thawing resistance
 Lightweight aggregate resistance against chemical attack
 Abrasion resistance
 Carbonation
 Corrosion resistance of reinforced lightweight concrete
Freezing and Thawing Resistance of Lightweight Concrete
The resistance of lightweight concrete against freezing and thawing effect is based on
number of factor such as types of aggregates, proportions of concrete mixture, aggregate
moisture content, and the percentage of air entrainment.
It is demonstrated through tests that, the durability of non-air entrained lightweight concrete
under freezing and thawing condition is better than then non-air entrained normal weight
concrete, specifically if natural fines are utilized. This is true for most of lightweight
aggregate regardless of whether the aggregate is in pre-soaked or airdried situation.
Regarding air entrained performance under freezing and thawing conditions, the ability of
lightweight concrete that is produced with lightweight aggregate in air dry condition is
considerably greater than that of normal weight concrete.

The performance of both lightweight concrete made with lightweight aggregate in pre-soaked
concrete and normal weight concrete are similar and do not show significant differences.
Freezing and thawing resistance of high strength lightweight concrete, which its compressive
strength ranges between 54 and 73 MPa, is exceptional and substantially great.
Lightweight Aggregate Resistance Against Chemical Attack
Lightweight coarse aggregates are not likely to react with alkalis, therefore, chemical attacks
might not influence lightweight concrete the same way as normal weight concrete.
Lightweight concrete matrix usually has high cement content a d low free water to cement
ratio which make the penetration difficult.
Dense fines are applied in the production of the majority of structural grades of lightweight
aggregate concrete, that is why such concrete need to be investigated for possible reactivity.
Abrasion Resistance of Lightweight Concrete
Lightweight concrete resistance against abrasion is based on strength, hardness, toughness
characteristics of aggregate and cement paste, and the bond between aggregate and cement
paste. The resistance of lightweight concrete is enhanced as the properties are improved.
Lightweight aggregate resistance to abrasion is decreased substantially if the aggregate
particles are exposed. So, it is recommended to blend low density coarse aggregate and
natural fine aggregate, to provide concrete surface protection through surface treatments, and
enhance matrix quality.
It is reported that, the resistance of lightweight concrete used in the construction of bridge
deck subjected to hundred million crossings of vehicles show similar resistance to that of
normal weight concrete.
It is advised to undertake certain level of restrictions in commercial utilization where steel
wheeled industrial vehicles are employed although surface protection is usually provided in
such applications.
Carbonation of Lightweight Concrete
Carbonation is the reaction between calcium hydroxide produced because of cement
hydration and carbon dioxide in the atmosphere. This will create calcium carbonate that lead
to reduce alkalinity, which naturally protect embedded reinforcement from corrosion in
concrete.

Concrete protection degradation may be anticipated through PH in concrete and it is
detrimental when it is reduced to around 9 from 13, because the reinforcement protection will
be eliminated and steel bars are considerably vulnerable to corrosion.
Most of lightweight aggregates are porous that makes lightweight concrete more previous
and permits gas diffusion for instance carbon dioxide.
This problem can be tackled provided that a good aggregate distribution is obtained and
continuous paths though particles to the steel reinforcement is avoided to decrease
carbonation rate.
The ability of lightweight concrete to withstand carbonation can be improved by providing
thick concrete cover and increase the amount of cement content. It is shown through tests that
the depth of carbonation is quite small if the amount of cement content is larger than 350
Kg/m3
light weight concrete mix proportioning
Step 1. choice of concrete slump
Step 2. choice of max. aggregate size
Step 3. Estimation of mixing water & Air content
Step 4. Water cement ratio
Step 5. calculation of the amount of cement
Step 6. estimation of coarse aggregate

Step 7. calculation of fine aggregate
factors affecting concrete strength
• Concrete porosity
– the more porous the concrete, the weaker it will be
• Water/cement ratio
– In mixes where the w/c is greater than approximately 0.4, all the cement can, in
theory, react with water to form cement hydration products.
– At higher w/c ratios it follows that the space occupied by the additional water above
w/c=0.4 will remain as pore space filled with water, or with air if the concrete dries
out.
• Soundness of aggregate
– if the aggregate in concrete is weak, the concrete will also be weak
• Aggregate-paste bond
– the integrity of the bond between the paste and the aggregate is critical.
– If there is no bond, the aggregate effectively represents a void; which are a source
of weakness in concrete.
• Cement composition related parameters

– alite (Ca3SiO5 = C3S ) content: more alite should give better early (7d) strengths
– alite and belite (Ca2SiO4 = C2S ) reactivity
– cement sulfate content: both the clinker sulfate and added gypsum, retards the
hydration of the aluminate phase
– cement surface area and particle size distribution
• Curing temperature
-Higher curing temperatures promote an early strength gain in concrete but may
decrease its 28-day strength.
Mixing and placing
In general, procedures for mixing lightweight structural concrete are similar to those for
regular weight concretes, but some of the more absorptive aggregates may require prewetting
prior to addition of other mix ingredients.
Water added at the batching plant should be sufficient to provide the specified slump at the
building site; slump at the batching plant will probably be appreciably higher. Adequate
workability, as indicated by the concrete slump, is necessary in order to realize all of the
desired properties of the hardened concrete. Slump for floor concretes is generally limited to
4 inches, but a lower slump of 3 inches, 1 and 2 may be better for maintaining cohesiveness
of the mix and preventing lighter coarse particles from working up through the mortar to the
surface during finishing. With certain aggregates deficient in minus No. 301 3 sieve material,
finish ability can be improved by using a portion of natural sand to supplement the
lightweight fines. A well-proportioned lightweight mix can generally be placed, screeded and

floated with less effort than that required for normal weight concrete. Surface preparation
prior to troweling is best done with aluminum or magnesium screeds and floats to minimize
surface tearing and pullouts of aggregate. Vibrating screeds may be advantageous, but over
vibration and over working may cause finishing problems. Too much finishing effort can
drive the heavier mortar away from the surface where it is needed and bring an excess of the
lighter course aggregate to the surface.

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