Module on Light and Heavy weight Concrete

1. LIGHT AND HEAVY WEIGHT CONCRETE
MODULE
ME CIVIL (REGULAR)
(CONSTRUCTION TECHNOLOGY AND MANAGEMENT)
Course Coordinator:
Dr Hemant Sood
Submitted by:
Ankaj Kumar
Roll No- 202304

2. LIGHT WEIGHT CONCRETE
1.1 INTRODUCTION
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 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.
1.2 OUTCOME OF MODULE
 It will help in knowing about the importance of light weight concrete.
 It will help to know about the classification of light weight concrete.
 It will help to know about the applications and properties of light weight concrete.
 It will help to know about the advantages of using light weight concrete.
1.3 CLASSIFICATION OF LIGHT WEIGHT 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.

3. 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 Leca (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.

4. 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
1. Low Density Concrete
These are employing chiefly for insulation purposes. With low unit weight, seldom exceeding
800 kg/m³, heat insulation value are high. Compressive strength are low, regarding from about
0.69 to 6.89 N/mm2.

5. 2. Moderate Density Concrete
The use of these concrete requires a fair degree of compressive strength, and thus they fall
about midway between the structural and low density concrete. These are sometimes designed
as ‘fill’ concrete. Compressive strength are approximately 6.89 to 17.24 N/mm² and insulation
values are intermediate.
3. Structural Concrete
Concrete with full structural efficiency contain aggregates which fall on the other end of the
scale and which are generally made with expanded shale, clay, slates, slag, and fly-ash.
Minimum compressive strength is 17.24 N/mm².
Most structural LWC are capable of producing concrete with compressive strength in excess
of 34.47 N/mm².
Since the unit weight of structural LWC are considerably greater than those of low density
concrete, insulation efficiency is lower. However, thermal insulation values for structural LWC
are substantially better than NWC.
1.4 Characteristics of Light-Weight Concrete:
Following are the important characteristics of light weight concrete:
1. Low Density:
The density of this concrete varies from 300 to 1200 kg/m3. The lightest variety is suitable for
insulation purposes while the heavier variety is used for structural purposes. The low density
of cellular concrete makes it suitable for precast roofing and floor units. These units being
lighter are easy to handle and transport from factory to the site.
2. High Strength:
The compressive strength of cellular concrete is high in relation to its density. The compressive
strength of such concrete has been found to increase with the increase in its density. The tensile
strength of cellular concrete is about 15 to 20% of its compressive strength. The strength to
mass ratio of cellular concrete is much higher than normal concrete. Thus the weight of roof
slab and floor of the cellular concrete are about 25% of the normal reinforced concrete.
3. Durability:
Aerated concrete is slightly alkaline. Due to its porosity and low alkalinity it does not provide
any protection to the steel reinforcement as provided by the dense compacted concrete. Thus
the reinforcement used in cellular concrete needs special treatment for the protection against
corrosion.

6. 4. Thermal Insulation:
The insulation value of light weight concrete is about 3 to 4 times more than that of bricks and
about 10 times that of concrete. The degree of insulation of 20 cm thick wall of aerated concrete
of density of 800 kg/m3 is the same as that of 40 cm thick brick wall of 1600 kg/m3 density.
5. Fire Resistance:
The fire resistance properties of light weight concrete are excellent. Its low thermal
conductivity makes it suitable for the protection of other structures from the effect of fire.
6. Sound Insulation:
The sound insulation of cellular concrete is not as good as that of dense concrete.
7. Shrinkage:
The shrinkage of light weight concrete is small. The autoclaving of cellular concrete reduces
its dry shrinkage to l/5th i.e. 20% of that occurring during air curing.
8. Repairability:
The light weight concrete products can be easily cut, drilled, nailed and sawn. This property
makes the construction easier. The local repair of the structure can be attended as and when
required without affecting the rest of the structure.
9. Speed of Construction:
By adopting prefabrication of units, the structure can be designed on the concept of modular
coordination, which ensures a faster rate of construction.
10. Economy:
Due to the high ratio of strength to mass and light weight of cellular concrete products, their
use results in lesser consumption of steel. Composite floor construction using precast un-
reinforced cellular concrete blocks and reinforced concrete grid beams results in appreciable
saving in the consumption of cement and steel. This reduces the cost of construction of roofs
and floors considerably. Using this type of construction a saving of about 15-20% can be
effected in the construction of roofs and floors in comparison to conventional construction.
11. Quality Control:
With the use of light weight concrete products a better quality control can be exercised as these
units are factory made.
1.5 Properties of Light Weight Aggregate Concrete
Followings are some of the other properties of light weight aggregate concrete as compared to
normal weight concrete:

7. 1. For the same strength, the modulus of elasticity of light weight concrete is lower by 25 to
50% than normal concrete. Hence its deflections are greater.
2. Its resistance to freezing and thawing is greater than normal weight Concrete due to the
greater porosity of light weight aggregate, provided the aggregate is not saturated before
mixing.
3. Its fire resistance is greater as light weight aggregate have a lesser tendency to spall. Thus
concrete suffers a lesser loss of strength due to rise in temperature.
4. It is easy to cut to fix desired attachments.
5. For the same compressive strength its shear strength is lower by 15 to 25% and bond strength
is lower by 20 to 50%. Thus in the design of reinforced concrete beams these differences have
to be taken into account.
6. The tensile strain capacity of light weight aggregate is greater than normal weight aggregate.
Thus the tensile strain capacity of light weight aggregate concrete is about 50% greater than
normal weight concrete. Hence the ability to withstand restraint to movement i.e. due to internal
temperature gradient is greater for light weight concrete.
7. For the same strength the creep of light weight aggregate concrete is about the same as that
of normal weight concrete.
1.6Advantages of Light Weight Concrete
Following are the advantages of light-weight-concrete:
1. Light weight concrete reduces the dead load of the structure.
2. It increases the progress of construction of the structure.
3. It lowers the haulage and handling charges.
4. The weight of structure on the foundation is an important factor in design, specially in the
case of multi-story buildings and in weak soils. Heavier the dead load, deeper and thicker the
foundations involving higher cost.
5. In framed structures, columns and beams have to carry loads of walls and floors. If walls
and floor are made of light weight concrete, the foundations also will be lighter, resulting in
considerable economy in the construction.
6. The thermal conductivity of light weight concrete is relatively low, which dampens the heat
transfer from roof and walls, resulting lower inside temperature of the building. This lower
temperature provides comfort to the inhabitants. The thermal conductivity improves with
decrease in density.

8. 7. In case of buildings where air conditioning is to be installed, the use of light weight concrete
has been found advantageous from the point of view of thermal comfort and lower consumption
of power.
1.7 Applications of Light Weight Concrete
Light weight concrete can be used as follows:
1. As Load bearing masonry walls using cellular concrete blocks.
2. As precast floor and roof panels in all types of buildings.
3. As partition walls in all types of buildings as residential, industrial and institutional
buildings.
4. As insulating materials to exterior walls in all types of buildings, specially in office and
industrial buildings.
5. As a filler in the form of precast reinforced wall panels in multistoryed buildings.
6. As precast composite floor or wall panels etc.
1.8 REFERENCES
[1] https://theconstructor.org/concrete/lightweight-concrete/1670/
[2] https://www.civilknowledges.com/lightweight-concrete/
[3] CONCRETE TECHNOLOGY BY M L GAMBHIR

9. HEAVY WEIGHT CONCRETE
2.1 INTRODUCTION
Heavyweight concrete uses heavy natural aggregates such as barites or magnetite or
manufactured aggregates such as iron or lead shot. The main land-based application is for
radiation shielding (medical or nuclear). Offshore, heavyweight concrete is used for ballasting
for pipelines and similar structures. Heavyweight concrete as having an oven dry density
greater than 2600kg/m3.
The density achieved will depend on the type of aggregate used. Typically using barites the
density will be in the region of 3,500kg/m3, which is 45% greater than that of normal concrete,
while with magnetite the density will be 3,900kg/m3, or 60% greater than normal concrete.
Very heavy concretes can be achieved with iron or lead shot as aggregate, 5,900kg/m3 and
8,900kg/m3 respectively.
Cement contents and water/cement ratios are similar to those for normal concretes, but the
aggregate/cement ratios will be significantly higher, because of the higher density of the
aggregates. Heavyweight concrete can be batched, transported and placed using conventional
equipment, though there are obviously certain aspects, such as the amount that can be carried
by a ready-mixed truck that will be limited by the density. Because of the higher density,
formwork pressures will be increased. The rate of wear of mixers and pumps will also be
increased. Compaction will require more energy than normal concrete and poker vibrators will
have to be inserted at closer centres. There may be a greater tendency for the mix to bleed.
2.2 MODULE OUTCOME
 It help to know about the importance of heavy weight concrete.
 It help to know about the applications of heavy weight concrete.
2.3 APPLICATIONS AND PROPERTIES OF HEAVY WEIGHT
CONCRETE
Concretes made with heavyweight aggregates are used for shielding and structural purposes in
construction of nuclear reactors and other structures exposed to high intensity radiation (see
Art. 4.12). Heavyweight aggregates are used where heavyweight is needed, such as ship’s
ballast and encasement of underwater pipes, and for making shielding concretes because
absorption of such radiation is proportional to density, and consequently, these aggregates have
greater capacity for absorption than those ordinarily used for normal concrete. With such

10. aggregates, concrete weighing up to about 385 lb/ft3 can be produced.
Concrete made with limonite or magnetite can develop densities of 210 to 224 lb/ft3 and
compressive strengths of 3200 to 5700 psi. With barite, concrete may weigh 230 lb / ft3 and
have a strength of 6000 psi. With steel punchings and sheared bars as coarse aggregate and
steel shot as fine aggregate, densities of 250 to 288 lb/ft3 and strengths of about 5600 psi can
be attained. Generally, grading of aggregates and mix proportions are similar to those used for
normal concrete. The properties of heavyweight concrete are similar to those of normal-
weight concrete. Mixing and placing operations, however, are more difficult than those
for normal-weight concrete, because of segregation. Good grading, high cement content, low
W/C, and air entrainment should be employed to prevent segregation. Sometimes, heavyweight
aggregates are grouted in place to avoid segregation. Heavyweight concretes usually do not
have good resistance to weathering or abrasion.
2.4 REFERENCES
[1] https://www.civilengineeringx.com/construction/heavyweight-concrete/
[2] http://www.concrete.org.uk/fingertips-nuggets.asp?cmd=display&id=785