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KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY
INSTITUT DES SCIENCES ET TECHNOLOGIE DE KIGALI
Avenue de lArme, BP3900 Kigali- Rwanda
FACULTY OF ENGINEERING
DEPARTMENT OF CIVIL ENGINEERING AND ENVIRONMENTAL
TECHNOLOGY
A PROJECT REPORT
ON
Submitted by:
MANIRAFASHA Amos (REG. NO: GS20050571)
Under the guidance of
Mr.And NGARAMBE
Submitted in partial fulfillment of requirements for the award of
BACHELOR OF SCIENCE DEGREE IN CIVIL ENGINEERING AND
ENVIRONMENT TECHNOLOGY
SEPTEMBER, 2009
ANALYSIS OF THE USES OF LIGHT CONCRETE, NORMAL COCRETE
AND HEAVY CONCRETE IN RWANDA
PROJECT ID: CEET/O9/02
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KIGALI INSTITUTE OF SCIENCE AND TECHNOLOGY
INSTITUT DES SCIENCES ET DE TECHNOLOGIE DE KIGALI
Avenue de l'Arme, B.P. 3900 Kigali, Rwanda
FACULTY OF ENGENEERING
DEPARTMENT OF CIVIL ENGINEERING AND ENVIRONMENTAL
TECHNOLOGY
C E R T I F I C A T E
This is to certify that the Project Work entitled ANALYSIS OF THE USES OF
LIGHT CONCRETE, NORMAL COCRETE AND HEAVY CONCRETE IN
RWANDA is a record of the original work done by MANIRAFASHA Amos
(REG.No: GS20050571) in partial fulfillment of the requirement for the award of
Bachelor of Science Degree in Civil Engineering and Environmental Technology of
Kigali Institute of Science and Technology during the Academic Year 2008.
..
Andr NGARAME G. Senthil KUMARAN
Project Supervisor HEAD, Dept. of CE&ET
Submitted for the Project Examination held at KIST on September 2009
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DECLARATION
I,MANIRAFASHA Amos hereby declare that this research ANALYSIS OF THE
USES OF LIGHT CONCRETE, NORMAL COCRETE AND HEAVY
CONCRETE IN RWANDA for the award of Bachelor of Science Degree in Civil
Engineering and Environmental Technology is my original work and has never been
presented anywhere else for the same purpose. All sources I have used and quoted have
been acknowledged as complete references.
.. ..
MANIRAFASHA Amos Andr NGARAME
REG NO 20050571 Project Supervisor
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DEDICATION
This research project is dedicated to:
Almighty God,
My beloved father KANYANZIRA Flicien,
My beloved mather MUKARUZIMA Spciose
My Brothers and sisters,
All my Colleagues,
All my friends.
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ACKNOWLEDGEMENT
I am deeply intended to almighty God who has guided me through the whole period of
my studies. My sincere thanks are due all friends and colleagues who helped me in one-
way or another. I am very grateful to all members of my family for their support and
advice.
My special thanks are addressed to the Government of Rwanda for its appreciable policy
of promoting education at all levels.
Again my sincere acknowledgements go to entire administration of KIST and the whole
academic staff.
My sincere gratitude goes to my supervisor, Mr. Andr NGARAMBE for his technical
and wise advice, suggestions and corrections that made this research project fruitful.
Finally I express my gratitude to each one who directly and indirectly contributed to
make my studies successful today.
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ABSTRACT
Ttis project is the study of the light concrete, normal concrete and heavy concrete which
are used in different construction in RWANDA. The uses of lightweight aggregate and
heavy concrete in concreting are possible in construction to day in RWANDA.
A systematic imvestigation was undertaken to determe the availability of lightweight
aggregate, normal weight aggregate and heavy weight aggregate; their application and the
advantages of uses light concrete, normal concrete and heavy concrete.
To identify the characteristics of lightweight aggregate, normal weight aggregate and
heavy aggregate; and to know why normal concrete is more popular compare to other
types of concrete.
After, characterize the lightweight aggregate, normal weight aggregate and heavy
aggregate; then compare the uses of light concrete, normal concrete and heavy concrete
in RWANDA.
Therefore the results show that the normal concrete is more useful because of more
frequent of normal weight aggregate.
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TABLE OF CONTENTS
C E R T I F I C A T E .......................................................................................................... i
DECLARATION ................................................................................................................ ii
DEDICATION ................................................................................................................... iii
ACKNOWLEDGEMENT ................................................................................................. iv
ABSTRACT ........................................................................................................................ v
TABLE OF CONTENTS ................................................................................................... vi
LIST OF ABBREVIATIONS ............................................................................................ ix
NOMENCLATURES AND SYMBOLS LIST .................................................................. x
LIST OF TABLES ............................................................................................................. xi
LIST OF FIGURES ........................................................................................................... xi
Chapter1. GENERAL INTRODUCTION .......................................................................... 1
1.1 Introduction ............................................................................................................... 1
1.2Problem statement ..................................................................................................... 1
1.3 Objectives of the project ........................................................................................... 2
1.4 Scope of the project .................................................................................................. 2
1.5 Justification of the project ......................................................................................... 2
1.6 Methodology ............................................................................................................. 3
Chapter 2. LITERATURE RIVIEW ................................................................................... 4
2.1 History of concrete .................................................................................................... 4
2.2 Properties of Concrete............................................................................................... 5
2.3 Applications of Concrete .......................................................................................... 7
2.4 Types of cement ........................................................................................................ 8
2.5 Admixtures ................................................................................................................ 9
2.6 Types of aggregate .................................................................................................. 11
2.6.1 Lightweight aggregate ..................................................................................... 11
2.6.2 Normal weight aggregate ................................................................................. 12
2.6.3 Heavyweight aggregate .................................................................................... 12
2.6.3.1 Characteristics of heavy aggregate ............................................................... 13
2.7 Fresh concrete ......................................................................................................... 14
2.7.1 Introduction ...................................................................................................... 14
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2.7.2 Workability ...................................................................................................... 14
2.7.3 Shrinkage ......................................................................................................... 15
2.7.4 Creep ................................................................................................................ 16
2.7.5 Advantages and disadvantages of concrete ...................................................... 16
2.8 Behavior of hardened concrete ............................................................................... 17
2.8.1 Strength ............................................................................................................ 17
2.9 Light concrete ......................................................................................................... 21
2.9.1 Definition ......................................................................................................... 21
2.9.2 Quality control ................................................................................................. 22
2.9.3 Concrete Strength............................................................................................. 22
2.9.4 Moisture Contents ............................................................................................ 23
2.9.5 Production considerations ................................................................................ 23
2.10 Normal concrete .................................................................................................... 24
2.10.1 Characteristics of normal concrete ................................................................. 24
2.10.2 Advantages & the disadvantages of normal concrete .................................... 25
2.11 Heavy concrete ...................................................................................................... 25
2.11.1 Characteristics of heavy concrete .................................................................. 25
2.11.2 Compressive strength ..................................................................................... 26
2.11.3 Mixing and curing .......................................................................................... 26
2.12 Concrete in road pavements ...................................................................................... 27
Chapter 3. MATERIALS AND ANALYSIS.................................................................... 28
3.1 Materials ............................................................................................................... 28
3.1.1 Ordinary Portland cement ................................................................................ 28
3.1.2 Aggregate ......................................................................................................... 28
3.1.4 Water ................................................................................................................ 29
3.1.5 Admixture ........................................................................................................ 30
3.2 ANALYSIS ............................................................................................................. 31
3.2.1 Ligh concrete ................................................................................................... 31
3.2.2 Normal concrete ............................................................................................... 33
3.2.3 Heavy concrete................................................................................................. 33
3.2.4 Comparison of light , narmal and heavy concrete ........................................... 34
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Chapter 4. RESULTS AND DISCUSSION ..................................................................... 36
4.1 Comparison of uses of lightweight concrete, normal concrete and ........................ 38
heavy concrete in RWANDA ................................................................................. 38
4.2 Discussion ............................................................................................................... 38
Chapiter. CONCLUSION AND RECOMMENDATION ................................................ 39
CONCLUSION ............................................................................................................. 39
RECOMMENDATION ................................................................................................ 40
REFERENCES ................................................................................................................. 41
APPANDICES .................................................................................................................. 42
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LIST OF ABBREVIATIONS
ASTM: American Society for Testing and Materials
PCC: Portiland Cement Concrete
BS: British Standard
CA: Coarse Aggregate
FA: Fine Aggregate
CIMERWA: Cimenterie du Rwanda
ELECTROGA: Etablissement Public de Production de Transport et de Distribution
dEau et de Gaz
KIST: Kigali Institute of Science and Technology
OPC: Ordinary Portland Cement
RWF: Rwandan franc
SFAR: Student Financing Agency in Rwanda
W/C: Water Cement ratio
L.C: Light concrete
N.C: Normal concrete
H.V: Heavy concrete
Aggr.:Aggregate
SCC: Self-consolidating concrete
Fe3O4: Magnetite
BaSO4: Barites
AASHO:
V : volume
P : maximum load applied on a single aggregate
h : distance
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NOMENCLATURES AND SYMBOLS LIST
kg: kilogram
g: gram
m3: cubic meter
MPa: Mega Pascal
KN: kilo Newton
Me: Fineness Modulus
22: mean compressive strength of aggregate
W/B: Water binder ratio
E :Modulus of Elasticity
&: and
%: percentage
t: Temperature
OC: Degree celcius
mm: millimeter
mm2: millimeter square
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LIST OF TABLES
Table2.1 Common types of concrete admixtures ............................................................. 10
Table 3.1 Quality of aggregate ......................................................................................... 29
Table.3.1 Comparison of light , normal and heavy concrete ............................................ 35
Table 4.1 Availability of aggregate in Rwanda ................................................................ 36
Table 4.2 Availability of concrete in RWANDA ............................................................. 37
LIST OF FIGURES
Figure 2.1 The effect of the aggregate type on compressive strength .............................. 19
Figure. 2.2 Stress-strain relationship for concrete ........................................................... 20
Figure 2.3 Different modulus of alacticity ........................................................................ 20
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do the analysis of the uses of all three types of concrete in RWANDA, and to know why
some types of concrete are not used.
Also, another problem is that may be in RWANDA we use normal concrete only because
the other types of concrete are not known, this analysis will discover why.
1.3 Objectives of the project
Main objectives
The main objective of this project is to do the analysis of the normal concrete, light
concrete, and heavy concrete used in RWANDA.
Specific objectives
To know the uses of normal concrete. To know the uses of light concrete. To know the uses of heavy concrete. To compare the availability of normal, light and heavy concrete.
1.4 Scope of the project
My project is based on the analysis of the uses of normal, light and heavy concrete.
The contents required for each type of concrete:
Cement
Aggregate
Water and
Admixture.
1.5 Justification of the project
This project will be helpful to the Government of RWANDA through the authorities in
charge of infrastructure to improve the uses of concrete in construction.
Also to conduct another research regarding any other type of concrete used in
RWANDA.
And helpful to any other who want to use any type of concrete.
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Finally this project is very helpful in such a way that it helps me to increase my
knowledge in concrete.
1.6 Methodology
The methodologies used to achieve the intended objectives of this work are:
Documentation: Library and internet Field investigation and Questionnaire.
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Chapter 2. LITERATURE RIVIEW
2.1 History of concrete
Concrete is a material used in building construction, consisting of a hard, chemically inert
particulate substance, known as an aggregate (usually made from different types of sand
and gravel), that is bonded together by cement and water.
The Assyrians and Babylonians used clay as the bonding substance or cement. The
Egyptians used lime and gypsum cement. In 1756, British engineer, John Smeaton made
the first modern concrete (hydraulic cement) by adding pebbles as a coarse aggregate and
mixing powered brick into the cement. In 1824, English inventor, Joseph Aspdin
invented Portland Cement, which has remained the dominant cement used in concrete
production. Joseph Aspdin created the first true artificial cement by burning ground
limestone and clay together. The burning process changed the chemical properties of the
materials and Joseph Aspdin created a stronger cement than what using plain crushed
limestone would produce.
The other major part of concrete besides the cement is the aggregate. Aggregates include
sand, crushed stone, gravel, slag, ashes, burned shale, and burned clay. Fine aggregate
(fine refers to the size of aggregate) is used in making concrete slabs and smooth
surfaces. Coarse aggregate is used for massive structures or sections of cement.
Concrete that includes imbedded metal (usually steel) is called reinforced concrete or
ferroconcrete. Reinforced concrete was invented (1849) by Joseph Monier, who received
a patent in 1867. Joseph Monier was a Parisian gardener who made garden pots and tubs
of concrete reinforced with an iron mesh. Reinforced concrete combines the tensile or
bendable strength of metal and the compressional strength of concrete to withstand heavy
loads. Joseph Monier exhibited his invention at the Paris Exposition of 1867. Besides his
pots and tubs, Joseph Monier promoted reinforced concrete for use in railway ties, pipes,
floors, arches, and bridges. [7]
The use of concrete dates to many ancient civilizations. The Romans, in particular, used
concrete for everything from buildings to the cores of aqueducts. The Romans were also
among the first to experiment with mixing additives into their concrete. They understood
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that mixing it with certain things would make it more water-resistant and less likely to
crack under pressure.
Self-consolidating concrete (SCC) has arrived, but vibration still prevails and still follows
principles described in a two-part series from March-April 1959. Explaining the
fundamentals is never outmoded; the subject of this "primer" was reprised in a June 2002
Concrete Basics column titled "To Improve Placement, Understanding Vibration Is Key."
Concrete is still known today for its durability and longevity. As with any building
material, it does have its share of completely acceptable alternatives. Wood is often
designed to be load-bearing, particularly in foundations, and can be treated to
withstand the negative effects of moisture and termites. Steel is both sturdy and cost-
effective, and can be ideal in areas infested by insects. Insulated steel panels are also
often used instead of concrete in the construction of walls. [4]
2.2 Properties of Concrete
After learning briefly about the history of concrete, let us focus upon the properties of
concrete. Concrete is an artificial building material whose production differs from
application to application. Amongst general properties of concrete, we must understand
that concrete should possess certain physical and chemical properties, tensile strength,
low-level of permeability to avoid moisture and retain chemical and volume stability.
Concrete essentially has a high level of compress ional strength, while the tensile strength
of concrete is relatively very weak. As concrete can crack under its own weight, it needs
to be reinforced. It is generally reinforced using steel bars or fibre and iron mesh. To
reduce the tensile strength of concrete, it is also pre-stressed with the use of steel cables.
The deciding factor for strength is also inherently related to the proportion and ratio of
water and cement, the type of cement used and the strength of used aggregate.
Generally, concrete made using lower water-cement ratio makes a stronger concrete than
when higher ratios are used. It is noticed that concrete made out of rough broken rock
pieces is much stronger than concrete made using smooth pebbles. The reason is that the
material should not result into more surface bondage area as this will increase the
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quantity of bondage, which is cement, resulting in weaker concrete. It is known that
limestone possesses higher bonding properties than conventionally used gravel.
Normally, a 28-day compressive strength testing is done to achieve desired workability.
The 28-day test for compressive strength is achieved by determining the right quantity of
cement required in water cement ratio. In structures like arches, vaults where shapes and
structures with internal forces require concrete.
Workability of concrete means the ability of a concrete to fill the mould appropriately,
producing the desired work without plummeting the quality of concrete. Concrete
workability is achieved with the water ratio, shape and size of aggregate and the level of
hydration. It is observed that workability can be considerably improved by increasing the
quantity of water, or with usage of plasticizer.
More water content can lead to bleeding and segregation, which can result in poor quality
concrete formation.
Curing is a process that keeps the concrete intact by providing an appropriate
environment. It is considered that good curing ensures a moist environment for hydration.
This steady hydration results in low level of permeability, thus increasing concrete
strength and quality. Concrete also needs to be protected from shrinkage. As concrete has
low thermal expansion co-efficient, this means that it cannot handle repetitive expansion
and shrinkage.
If there is no external force used for expansion, it can result in sizeable force acting
against it, resulting in shrinkage and cracking of structure. As concrete grows older, it
goes on shrinking due to internal forces caused within the material.
Cracking of concrete begins at micro level. Normally, concrete is kept in a wet state to
allow easy moulding when required. Hydration and hardening of concrete can lead to
shrinkage and cracking when it has not yet developed the tensile strength. It is important
to reduce stress before curing. Freezing of concrete before the curing is complete can
seriously hamper the process of hydration. This can also decrease the concrete strength
and weaken and damage the concrete.
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Creeping is described as constant deformation of a material owing to internal stress
taking place in the material. The amount of reinforcement of concrete structures ensures
minimal shrinkage, creep and cracking.
These general concrete properties of concrete are taken care of during building of
concrete. Depending upon the end application, concrete is accordingly treated for
maximum strength and durability.
Good concrete has to satisfy performance requirement in plastic or green state and also
the hardened state.
The concrete should be workable and free segregation and bleeding.
In its hardened state concrete should be strong, durable, and impermeable.
It should have minimum dimensional changes.
The properties and performance of concrete are dependent to a large extend on the
characteristics and properties of the aggregates themselves. In general, an aggregate to be
used in concrete must be clean, hard, strong, properly shaped and well graded.
The aggregate must possess chemical stability, resistance to be abrasion, and to freezing
and thawing. They should not contain deterious material which may cause physical or
chemical change, such as cracking, swelling, softening or leaching.
One of the most popular concrete used is Portland cement, mineral aggregates and water.
Concrete often solidifies as the cement hydrates and glues all the other components
together. It has a high compressive strength and general uses of concrete include
pavements, fences, gates, walls and more. In old times, concrete was often referred to as
liquid stone. Sometimes external stabilizers are included to concrete to give it desired
characteristics. [6]
2.3 Applications of Concrete
Concrete has been used for construction since ancient times. Modern day concrete
application include dams, bridges, swimming pools, homes, streets, patios, basements,
balustrades, plain cement tiles, mosaic tiles, pavement blocks, kerbs, lamp-posts, drain
covers, benches and so on?. It is interesting to note that over six billion tons of concrete is
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produced each year, and is the second most widely used substance. Concrete is specific to
different applications like rebuilding, mending and construction. Concrete building
components in different sizes and shapes are also made before hand and later applied.
They include wall panels, doorsills, beams, pillars and more. Post-tensioned slabs is a
preferred method for industrial, commercial and residential floor slab construction. Ready
mixed concrete is durable and hard wearing and is used for variety of applications owing
to its crack-resistance and durability. Situ concrete is cast in place, on site. Precast
concrete finds application in concrete certain walls, exterior cladding and structural walls,
as it monolithic and can be easily used for two-way structural systems. It is also
adjustable to post tensioning and easily adapts to any building shape.
Controlled-density fill is used as structural fill, foundation pillar, pavement base an pipe
bedding. It is also known as flowable mortar.
The life expectancy of concrete flooring materials is much more than other flooring
material. It is used to enhance concrete applications and to add colour and texture to
interiors, driveways, pathways and patios.
Fiber cement is made using a mixture of sand, cellulose fibers and cement. It has a wood-
like appearance, is durable and used for decorative shapes and trim application.
Vegetative roofs are used in residential societies, office buildings, hospitals, schools,
recreational facilities, shopping centers and airports.
Concrete is used to provide prolonged building benefits by functioning as thermal mass,
acoustical barrier and durable structure.
Other Applications
Beams, drain tiles, piers, steps, Post, Beam and Deck ,Pilasters and round column forms
Brickledge application, High Performance Admixtures ,Masonry ,Soil solidification. [9]
2.4 Types of cement
1. Ordinary Portland cement Ordinary Portland cement 33 Grade-Is 269: 1989 Ordinary Portland cement 43 Grade-Is 8112: 1989 Ordinary Portland cement 53 Grade-Is 12269: 1987
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2. Rapid Hardening Cement -Is 8041: 19903. Extra Rapid hardening Cement - _4. Sulphate Resisting Cement -Is 12330: 19885. Portland Slag Cement -Is 455: 19896. Quick Setting Cement -Is _7. Super Sulphated Cement -Is 6909: 19908. Low Heat Cement -Is 12600: 19899. Portland Pozzolana Cement -Is 1489 (Part I) 1991 (fly ash based)
-Is 1489 (part II) 1991 (Calcined Clay
based)
10.Air Entraining Cement - _11.coloured Cement: White Cement -Is 8042: 198912.Hydrophobic Cement -Is 8043: 199113.Masonry Cement -Is 3466: 198814.Expansive Cement - _15.Oil Well Cement -Is 3466: 198816.Rediset Cement - _17.Concrete Sleeper grade Cement -IRS-T 40: 198518. High Alumina Cement -Is 6452: 198919.Very High Strength Cement [1]2.5 AdmixturesAdmixture are the materials other than the basic ingredients of concrete cement,water,
and aggregate; added to the concrete mix immediately before or during mixing to modify
one or more of the specific properties of concrete in the fresh or hardened state. [2]
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Table2.1 Common types of concrete admixtures
Admixture Function Typical compound Applications Disadvantages
Accelerator i. More rapid
gain of strength
ii. More rapid
stting
Calicium chloride
Sodium sulphate
Sodium aluminate
Sodium silicate
Sodium carbonate
Potassium hydroxide
i. Normal rate of
strength at low t
ii. Shorter
stripping times.
iii. Plugging of
pressure leaks
iv. sprayed
concreting
i. possible
cracking due to
heat evolution.
ii. Possibility of
corrosion of
embedded
reinforcement
Set-retarders Detalyed setting Hydroxylatedcarboxylic
acids, sugers
i. Maintain
workability at
high tii. Reduce rate of
heat evolution
iii.Extend placing
times
May promote
bleeding
Water-reducing
accelerator
Increased
workability with
faster gain of
strength
Mixture of calcium
chloride and
lignosulphonate
Water-reducers
with faster
strength
development
Risk of
corrosion
Water-reducing
Retarders
Increased
workability and
delayed setting
Mixture of sugers or
Hydroxylatedcarboxylic
acids and
lignosulphonate
Water-reducers
with slower loss
of workability.
Air-entraining
agents
Entrainment of
air into concrete
Wood resins, fasts,
lignosulphonate
Increase
durability of frost
without
increasing cement
content, cellular
concrete
Carefull contol of
air content and
mixing time
necessary
Water-proofers i. prevention of
water from
entering
capillaries of
concrete
Potash soaps,
butylstearate petroleum
waxes
Reduce
permeability,
Reduce surface
staining,
Watertighteness
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ii. Reduced
permeability of
concrete
of structures
without using
very low w/c ratio
plasticizers
(Water-reducing)
Increased
workability
Calcium and sodium
lignosulphonate
i. Higher
workability withstrength
unchanged
ii. Higher strength
with workability
unchanged
iii.Less cement
for same strength
and workability
Retardation at
high dosagesTendency to
segregate
Premature
stiffening under
certain conditions
Super plasticizers
Super-water-
redusers
Geatly
increseased
workability
Sulphonate
malamineformaldehyde
resin, Sulphonated
naphthalene-
formaldelyde resin,
Mixtures of saccharates
and acid amides
i. Water-reducers,
but over a wide
range
ii. Facilitae
production of
flowing concrete
Tendency to
segregate
May increase rate
of loss of
workability
2.6 Types of aggregate
2.6.1 Lightweight aggregate
The lightweight aggregates having unit weight up to 12KN/m3
are used to manufacture
the structural concrete and masonry blocks for reduction of self-weight of structure.
Light weight aggregate can be classified into two categories namely natural light weight
aggregates and artificial light weight aggregates. [2]
Natural lightweight aggregate:
Pumice
Datomice
Scoria
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Volcanic cinders
Sawdust
Rice husk
Artificial light weight aggregate:
Artificial cinders
Coke breeze
Foamed slag
Bloated clay
Expanded shale and slate
Sintered fly ash
Exfoliated vermiculite
Expanded partite
Thermo Cole beads
2.6.2 Normal weight aggregateThe commonly used aggregates; sand and gravels, crushed stone which have specific
gravities between 2.5 to 2.7 produced concrete with unit weight ranging from 23 to 26
KN/m3 and crushing strength at 28 days between 15 to 40 Mpa. [2]
2.6.3 Heavyweight aggregate
Some heavyweight aggregate having specific gravities ranging from 2.8 to 2.9 and unity
weights from 28 to29 KN/m3 such as magnetite (Fe3O4), and barites(BaSO4) and scarp
iron are used in the manufacture of heavy weight concrete which is more effective as
radiation shield. Concrete having unit weight of about 30KN/m3, 36KN/m3
and56KN/m3 can be produced by using magnetite, barites and scarp iron, respectively.
The compressive strength of these concrete is of the order of 20 to25 Mpa. The cement-aggregate ratio varies 1:5 to 1:9 with a water-cement ratio between 0.5 to 0.6. The
produce dense and crack-free concrete. The main drawback with these aggregates is that
they are not suitably graded and hence it is difficult to have adequate workability without
segregation.
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2.6.3.1Characteristics of heavy aggregate Structural properties like strength and stiffness Resist to abrasion With the aggregate react with the hydrated Portland cement paste. The thermal conductivity of the aggregate might be an issue in lightweight
concrete used for insulation, and the coefficient of thermal expansion of the
aggregate also is issue of the pcc will be subjected to a large range of service
temperature.
The roughness or smoothness of the aggregate plays a role in the workability offresh pcc.
The gradation of the aggregate is also of some importance.
According to size of aggregate are divided into two types as follows:
a. Fine aggregate
It is the aggregate most of which passes through a 4.5 mm IS sieve and contains only so
much coarse material as is permited by the specifications. Sand considered to have a
lower size limit of about 0.07mm. For increased workability and for economy as
reflected by use of less cement, the fine aggregate should have a rounded shape. The
purpose of the fine aggregate is to fill the voids in the coarse aggregate and to act as a
workability agent. .
b. Coarse aggregate
The aggregate most of which are retained on the 4.75 mm IS sieve and contain only so
much of fine materials ar is permitted by the the specifications are termed coarse
aggregates. As with fine aggregate, for increased workability and economy as reflected
by the use of less cement, the coarse aggregate should have a rounded shape. Even
though the definition seems to limit the size of coarse aggregate, other considerationsmust be accounted for. When properly proportioned and mixed with cement, these two
groups yield an almost voidless stone that is strong and durable. In strength and
durability, aggregate must be equal to or better than the hardened cement to withstand the
designed loads and the effects of weathering. It can be readily seen that the coarser the
aggregate, the more economical the mix. [2]
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2.7 Fresh concrete
2.7.1 Introduction
The performance requirements of hardened concrete are more or less well defined with
respect to shape and strength. To achieve these objectives economically, the fresh
concrete, in addition to have suitable composition in terms of quality and quantity of
cement, aggregate and admixtures, should satisfy a number of requirement form the
mixing stage till is transported, placed in formwork and compacted. The requirement may
be summarized as follows.
(i) The mix should be able to produce a homogeneous fresh concrete from theconstituent materials of the batch under the action of the mixing forces.
(ii) The mix should be stable, in that it should not segregate duringtransportation and placing when it is subjected to forces during handling
operations limited nature
(iii) The mix should be cohesive and sufficiently mobile to be placed in theform around the reinforcement and should be able to cast into require
shape without losing continuity or homogeneity under the available
techniques of placing the concrete at a particular job.
(iv) The mix should be amenable to proper and thorough compaction into adense, compact concrete with minimum voids under the existing facilities
of compaction at the site.
2.7.2 Workability
The diverse requirements of mixability, stability, transportability, placeability and
compactibility of fresh concrete are referred to as workability. The workability of fresh
concrete is thus a composite property. We can define workability as that property of
freshly mixed concrete or mortar which determines the homogeneity with which it can be
mixed, placed, and compacted. Every job requires a particular workability. The concrete
which is considered workable for mass concrete foundation is not workable for concrete
to be used in roof construction and vice-versa.
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Sometimes the terms consistency and plasticity are used to denote the workability of a
concrete mix. The consistency of the mix really means the wetness of the mix, and a
wetter mix need not have all the above desired properties.
Factor affecting workability:
Water content: Water content in a given volume of concrete, will significant influences
on the workability. The higher the water content per cubic meter of concrete, the higher
will be the fluidity of concrete, which is one of the important factors affecting
workability.
Mixing proportion: Aggregate/cement ratio is an important factor influencing
workability. The higher agg/cement ratio, the leaner is the concrete.
Size af aggregate: The bigger the size of the aggregate, the less in the surface area and
hence less amount of water is required for wetting the surface and less matrix or paste is
required for lubricanting the surface to reduce internal friction.
Shape of aggregate: The shape of aggregates influences workability in good mesure.
Surface texture: The influence of surface texture on workability is again due to the fact
that the total surface area of rough textured aggregate is more than the surface area of
smoof rounded aggregate of same volume.
Grading of aggregate: This is one of the factors which will have maximum influence on
workability. A well graded aggregate is the one which has least amount of voids in a
given volume.
Use of admixtures: Of all the factor mentioned above, the most important fact which
affects the workability is the use of admixture.[1]
2.7.3 Shrinkage
The concrete is always subjected to changes in volume which affect long-term strengthand durability, this change in volume cause cracks in concrete. One of the important
factors that contribute to the cracks in concrete is that due to shrinkage.
Two types of shrinkage are recognized, namely plastic and drying shrinkage.
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-Plastic Shrinkage: the hydration of cement causes a reduction in the volume of system of
cement plus water to an extent of about 1 per cent of volume of dry cement. This
contraction is plastic shrinkage
-Drying Shrinkage: the shrinkage that takes place after the concrete has set and hardened
is called drying shrinkage and most of it takes place in the first few months.
2.7.4 Creep
The increase in strain in concrete with time under sustained stress is termed creep. The
shrinkage and creep occur simultaneously and they are assumed to be additive for
simplicity. When the sustained load is removed, the strain decreases immediately by an
amount equal to elastic strain at the given age. This instantaneous recovery is then
followed by gradual decrease in strain, called creep recovery which is a part of total creep
strain suffered by the concrete.
The rate of creep decreases with time and time the creep strains attained at a period of
five years are usually taken as terminal values. While 80 to 85 per cent shrinkage strains
occur in six months, only about 75 per cent of creep strains occur in twelve months. All
the factors which influence shrinkage influence creep also in similar way.
2.7.5 Advantages and disadvantages of concrete
a. advantages:
Concrete is economical in the long run as compare to other engineering materials.
Concrete possess a high compressive strength, and the corrosive and the weathering
effects are minimal.
Concrete can even be sprayed on and filled into fine cracks for repairs by the granting
process.The concrete can be pumped and hence it can be laid in the difficult positions
also. It is durable and fire resistant and requires very little maintenance.b.Disadvantages:
Concrete has low tensile strength and hence cracks easily. Therefore concrete is to be
reinforced with steel or meshes.
Fresh concrete shrinks on drying and hardened concrete expands on wetting.
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Concrete under sustained loading undergoes creep resulting in the reduction of prestress
in the prestressed concrete construction.
Concrete expands and contracts with the change in temperature.
Concrete is not entirely impervious to moisture and contains soluble salts which may
cause efflorescence.
Concrete is liable to disintegrate by alkali and sulphate attack.
Lack of ductility inherent in concrete as material is disadvantageous with respect to
earthquake resistant design. [2]
2.8 Behavior of hardened concrete
The behavior of hardened concrete can be characterized in terms of its short-term
(essentially instantaneous) and long-term properties. Short-term properties include
strength in compression, tension, bond, and modulus of elasticity. The long-term
properties include creep, shrinkage, behavior under fatigue, and durability characteristics
such as porosity, permeability, freeze-thaw resistance, and abrasion resistance
2.8.1 Strength
The strength of concrete depends on a number of factors including the properties and
proportions of the constituent materials, degree of hydration, rate of loading, method of
testing and specimen geometry.
The properties of the constituent materials which affect the strength are the quality of fine
and coarse aggregate, the cement paste and the paste-aggregate bond characteristics
(properties of the interfacial, or transition, zone). These, in turn, depend on the macro-
and microscopic structural features including total porosity, pore size and shape, pore
distribution and morphology of the hydration products, plus the bond between individual
solid components. Concrete composition limits the ultimate strength that can be obtained
and significantly affects the levels of strength attained at early ages. Two dominant
constituent materials that are considered to control maximum concrete strength are coarse
aggregate and paste characteristics. The important parameters of coarse aggregate are its
shape, texture and the maximum size. Since the aggregate is generally stronger than the
paste, its strength is not a major factor for normal strength concrete; However, the
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aggregate strength becomes important in the case of higher-strength concrete or
lightweight aggregate concrete. Surface texture and mineralogy affect the bond between
the aggregates and the paste as well as the stress level at which microcracking begins.
The surface texture, therefore, may also affect the modulus of elasticity, the shape of the
stressstrain curve and, to a lesser degree, the compressive strength of concrete. Since
bond strength increases at a slower rate than compressive strength. Tensile strengths may
be very sensitive to differences in aggregate surface texture and surface area per unit
volume. Using the aggregates for the mix proportions of high strength concretes, they
also found close correlations between the mean compressive strengths of the aggregates
and the compressive strength of the concretes, ranging from 35 to 75 MPa (5,000 to
10,700 psi), at both 7 days and 28 days of age. The mean compressive strength of the
aggregate is calculated as:
22is the mean compressive strength of aggregate
V is the volume of a single aggregate determined using Archimedes's principle after the
over dried weight is measured
Pis the maximum load applied on a single aggregate
his the distance between the two opposite load points of P
In a study by Lindgard and Smeplass [1993] six aggregate types with different strength
and rigidity were tested: dehydrated bauxite, quartzite, quartz-diorite (as reference),
gneiss/granite, basalt and limestone. All the aggregates except gneiss/granite were
crushed. Fig. 2.1. shows the effect of the aggregate type on compressive strength. The
difference between the highest and the lowest strengths is approximately 40%. The
authors noted, however, that the bauxite and the basalt aggregates were porous and
capable of absorbing significant amounts of mixing water, thus reducing the effective
W/CM from 0.30 to 0.24 and 0.27 respectively.
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Figure. 2.2 Stress-strain relationship for concrete
An equation representing the stress and stain curve completely should satisify the
following conditions:
i. at=0, =0 iii.at=f, =uii.at=o, =o
Figure 2.3 Different modulus of alacticity
Strain
Initial
tangent
A Tangent
B
Secant
strain
o o
fo
ff
Stress
Stress
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2.9 Light concrete
2.9.1 Definition
There are differing definitions for concretes that can be produced with lightweight
aggregates. Low-density concrete generally is produced with partite or vermiculite
aggregates, rarely exceeds (800 kg/m3). Structural lightweight concretes are typically
produced with expanded shales, clays, slates and slag. They can also be made with
pumice or scoria, which are naturally occurring volcanic aggregates. By definition,
structural lightweight concretes have a minimum compressive strength of (17.2 Mpa) and
an air-dried unit weight of (1,440 to 1,850 kg/m3). Moderate strength concretes fall
somewhere in between low-density and structural lightweight concrete. For comparison,
normal-weight concretes have a typical dry unit weight of (2,300 to 2,400 kg/m3).
Advantages of using lightweight aggregates
The primary advantage of using lightweight aggregates to precasters is the reduction of
product weight. Reduction in weight can lead to improved economy of structural
components because there will be less dead load for the structure to support.
Also, as mentioned previously, this may significantly affect the way in which products
can be shipped..
Another reason to consider using lightweight aggregates is that sometimes the dead load
of a product is near or above the capacity of the crane being used at a plant.
With lightweight aggregates, it may be possible to reduce the weight of the product so
that special cranes would not be necessary, or to produce larger sections than would be
possible with normal-weight concrete. Also, a reduction in crane movements may be
realized since longer reaches are possible with lighter loads.
Lightweight aggregates can also provide unique and potentially useful properties to
concrete besides reduced weight.
Lightweight concrete is thermally efficient. With warmer walls, there is less risk of
condensation. Lightweight concrete is fire-resistant. Because lightweight aggregates have
already been pre-fired, they are stable and do not decompose in high temperatures. This is
ideal for building components or refractory products.
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Lightweight concrete absorbs energy well. With the addition of fiber reinforcement and
even foaming agents, an extremely lightweight concrete could be produced and used for
such products as highway impact attenuators or sacrificial blast-resistant barriers.
With reduced weight, lightweight concrete will have a correspondingly reduced
hydrostatic pressure on formwork. This is useful when casting large, custom products.
Also, water that has been absorbed into the porous structure of lightweight aggregates is
said to provide additional water for internal curing. [5]
2.9.2 Quality control
To assure uniform quality, manufacturers should ensure that gradations and dry, loose
unit weight of the lightweight aggregates are consistent. Reports including this data can
usually be obtained from the aggregate supplier. If this is not the case, plant personnel
should do the tests themselves. Variation in either the aggregate gradations or the dry,
loose unit weight generally requires adjustments to the mix proportions in order to
produce uniform concrete. In addition, both unit weight and slump testing of the fresh
concrete should be performed frequently in order to verify consistency of the mix
constituents and the concrete itself. Slumps should be as low as possible while remaining
sufficiently easy to place, consolidate and finish. [5]
2.9.3 Concrete Strength
Lightweight concretes generally have what is called a strength ceiling. This is the
maximum compressive or tensile strength a certain mix can obtain despite improvements
to the cementations materials. This limiting strength is dependent on the strength of the
lightweight coarse aggregate and/or the quality of the contact zone and bond between the
aggregate and the surrounding cement paste. It is possible to achieve a slight increase in
strength by reducing the maximum size of coarse aggregates. Given that these limits
exist, it should be noted that structural lightweight concrete strengths compare favorably
with that of normal-weight concretes in the 3,000 to 5,000 psi-range. [5]
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2.9.4 Moisture Contents
Highly absorptive lightweight aggregate should be wetted at least 24 hours prior to use,
allowing time for the porous aggregate to become fully saturated. Wetting aggregate may
be a logistical challenge depending on the weather, with freezing a possibility in cold
weather and moisture loss in the hot weather. However, one benefit of wetting is that it
helps keep the aggregate particles from segregating during handling.
It is not recommended that dry lightweight aggregate be directly batched and mixed
because the aggregate particles can continue to absorb water from the mix. This can
cause the mix to segregate or stiffen before it can be placed.
Because of the high variability of aggregate moisture contents, water-cement ratios are
generally not specified for lightweight concretes. Calculation of water-cement ratios is
hampered by the uncertainty of the total amount of water contained in the aggregates. [5]
2.9.5 Production considerations
It may be necessary to extend mix times for lightweight concrete compared with
conventional concrete to ensure that all of the mix constituents are properly mixed.
Greater variations in workability should be expected, compared with conventional
concrete with the same slump. Along those same lines, the amount of air-entraining
admixture necessary to produce a constant amount of air content could also vary widely.
Consult your admixture supplier for more information.
Depending on the porosity and the degree of the aggregate angularity, the concrete could
be more difficult to place and finish. In some cases it is possible for the aggregate and the
other mix constituents to separate, allowing the lightweight aggregate particles to float
toward the concrete surface. Overworking the concrete can also cause the mix to
segregate. This situation can be remedied by adjusting the aggregate gradation to reduce
the size of the larger aggregates, adding natural sand or other filler materials. Although
this is the opposite problem encountered with self-consolidating concrete, where the goal
is to keep aggregates suspended in the mix, it is likely that similar rheological mix
enhancements can help stabilize the mix.
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As with other conventional concrete mixes, ease of placement can be enhanced by
including air entrainment if not already a part of the mix design. Air entrainment also
reduces bleeding and segregation and improves durability.
Finally, lightweight concretes may have an increased tendency to experience drying
shrinkage and creep (strain increase over long periods of time with a constant load).
Steam curing effectively reduces the likelihood of both drying shrinkage and creep.
The decision to use lightweight aggregates in order to economize transportation costs is
one that requires you to take into account many variables. Although not every project is a
good candidate for the use of lightweight aggregate, some projects definitely are. In
addition, some of the more unique properties that lightweight aggregates offer could
enhance specialized products, whether they are fire-resistant, blast-resistant or other
insulating products. Its good to keep your options open and be ready to take advantage
of opportunities that allow you to boost your plants income. Ultimately, only you can
decide if your products should lose some weight. As with our own diet, if you wish to
lose weight, you must be patient and should expect some trial-and-error in finding the
right combination of what works best. [5]
2.10 Normal concrete
2.10.1 Characteristics of normal concrete
Normal concrete or ordinary concrete is a mixture of fine aggregate, water, cement and
coarse aggregate. All components of ordinary concrete are mixed together until they
become a paste, which surrounds the voids in aggregate during its fresh concrete.
Compressive strength depends upon water, the cement ratio and the quality of the cure
cycle. According to the ACI code, the compressive strength of the concrete is obtained
from the standard test cylinder 6-in(150mm) diameter by 12-in(300mm) high measured at
7,14 and 28 days of age before testing. After 28 days of water curried or placed in aconstant temperature room to obtain 100% of humidity.
For normal weight concrete, the value of shrinkage is 0.003 when the specimen after
casting is submerged in water not less than 7 days. To avoid high shrinkage in the
concrete, we have to consider proportional size of aggregate, water-cement ratio and
humidity.[4]
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2.10.2 Advantages & the disadvantages of normal concrete
As a construction material Concrete has the following advantages:
1. Concrete can handle the compression stresses 10 times more than the tension and the
most of loads in our life is compression.
2. Concrete is a brittle material which gives the advantage to make a rigid structure.
3. Easy to handle over specially now there is plants that give you ready mix concrete.
Disadvantages:
1. Concrete is weak in handling tension.
2. Because concrete is a brittle material the strength upon shear must be checked.
3. Needs another material to reinforce it against excessive shear and tension. [5]
2.11 Heavy concrete
2.11.1 Characteristics of heavy concrete
A heavy material such as concrete is capable of buffering a large part of the free heat
gains, such as solar radiation and heat. Concrete can therefore decrease energy
consumption as well as improve thermal comfort. A taskforce of three principal
organisations related to concrete construction has investigated and documented the
advantages of heavy buildings. Energy balance calculations were undertaken for
buildings of heavy and lightweight construction in various European climates, for both
residential and office circumstances. The results show that a solid residential building
requires 2-7% less bought energy for heating compared to a building of lightweight
construction. This has significant economical and environmental impacts. Where cooling
is required, the energy savings are even larger and cooling facilities can be avoided
altogether in many heavy buildings. The advantages are further increased if the effect of
thermal mass is actively taken into account in the building design. An information
database of the role of concrete in energy efficient buildings including a portfolio of
energy efficient concrete buildings has been compiled. [9]
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2.11.2 Compressive strength
The inclusion of heavy aggregate in concrete does not increase the concrete strength as
previously expected to reflect their characteristics of higher strength and density. This
can attribute to the cracking types, which takes place as the crack propagating in the
paste. This can observed by testing results of compressive strengths that an increase of
iron ore and iron shot amount makes a little growth in concrete strength. In fact an
inclusion of 40% of heavy aggregate in volume only raises the compressive strength up to
5% higher than the strength of regular concrete.
To investigate the effect of metallic aggregate on the mechanical properties of heavy
concrete, the mixture of concrete are designed with a unique water to cement ratio W/C
equal to 0.48, and 0%,1o%, 20%, 40% and 48.8% of metallic aggregate in volume in the
testing program. The latest mixture has been used in same nuclear power plants. It is
noted that the amount of iron shot is fixed at 9.2% for all mixture while the iron ore is
varied, therefore the unity weight of concrete increase with the increase of metallic
aggregate content. And it is noted that some admixtures such as water reducers and
superplastizer and not advisable in the mixture of heavy concrete in order to ascertain to
the minimum requirement of water which supplies sufficient amount of hydrogen atoms.
[9]
2.11.3 Mixing and curing
The procedure for mixing heavy concrete is similar to ordinary concrete. In a typical
mixing procedure, iron shot are mixed first, followed by cement and then water, as some
as mixing of regular concrete. However due to higher specific gravities of both iron ore
and iron shot, too much compacting vibration that can lead to segregation has to be
avoided. Trial mix for each mixture has been engaged until a good workability and
sufficient strength gain achieved. In the mean time air content for each mix, which could
provide useful data to figure out the amount of voids. All concrete specimens were cast in
molds for one day and then placed in water for 28 days prior to testing; the specimens for
cracking analysis were placed in air for another three days before the process of pre-
cracking and dying. [10]
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2.12 Concrete in road pavements
Some pavement designers assume "average concrete" properties in their calculations
without any information about which aggregates, cement, pozzolans, or mixture
proportions that the con- tractor will use later on the job. Concrete properties of particular
importance to pavement design are: E (Modulus of Elasticity), strength, thermal
expansion, shrinkage, creep, heat generation, and durability (physical and chemical
reactivity). A good pavement designer should also be a concrete expert.
At the AASHO Road Test, there were two distinctive failure modes. The very thin
pavements failed with continuous edge pumping that caused edge cracking that coalesced
into a longitudinal edge crack. The thicker pavements failed by joint pumping that caused
transverse cracking starting particularly in the traffic leave side of the joints. The data
from both were averaged together in the road test analysis to develop a performance
equation. Even so, of the 84 pavement test sections greater than 8 in (200 mm) in
thickness, only seven sections had a serviceability index of less than 4.0 at the end of the
testing. In fact, only three sections could actually be considered as having failed. Hence,
one can conclude that even though the AASHO data is the best that we have, it hardly
predicts failure of the thicknesses of pavement that are now being built. [10]
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Chapter 3. MATERIALS AND ANALYSIS
3.1 Materials
3.1.1 Ordinary Portland cement
The OPC used in this project was manufactured at MASHYUZA in CEMERWA factory,
BAMBURI in KENYA and HIMA in UGANDA. This kind of cement from
MASHYUZA made with three basic raw materials such as: lime stone, quartz and clay.
The two first are found at MASHYUZA quarry, the raw pulps concentration is: 70% of
lime stone; 155 of quartz and 5% of clay soil.
The cement samples produced was tested in national laboratory to determine its physical
properties such us fineness, setting time, standard consistency, soundness, density and
compressive strenght. The role of Ordinary Portland Cement is to bind materials together.
3.1.2 Aggregate
The aggregates are used primarily for the purpose of providing bulk to concrete, to
increase the density of the resulting mix. The aggregate is frequently used in two or more
sizes. The most important function of the fine aggregate is to assist the mixture, in
producing workability and uniformity to fresh concrete. It also assists the cement paste to
hold the coarse aggregate, particles in suspension.
The source of aggregate is not difficult in this country. That sand was free from deterious
materials.
Take a sample of different aggregate from different area in RWANDA and results from
national laboratory are: GIHARA, BUGESERA, GITI CYINYONI, KARONGI,
MUKUNGWA, GATUMBA, MUSANZE and RUSINE River.
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Table 3.1 Quality of aggregate
Aggregate Specific gravity Water
absorption (%)
bulk density
(g/m3)
uncompacted
bulk density
(g/m3
)GIHARA 2.71 0.4 1.64 1.48
BUGESERA 2.67 0.14 1.62 1.48
GITI
CYINYONI
2.64 0.32 1.61 1.45
KARONGI 2.92 0.52 1.71 1.51
MUKUNGWA 2.70 1.62 1.57 1.4
GATUMBA 2.89 0.3 1.64 1.52
MUSANZE 2.97 0.2 1.75 1.52
According to their unit weight are classified flowing:
Normal weight aggregate, Lightweight aggregate and Heavy weight aggregate.
AndAccording to size of aggregate are divided into two types as follows:
fine aggregate and coarse aggragate.
3.1.4 Water
Water is used in concrete to react with cement and thus causing it to set and harden, also
facilitates mixing, placing and compacting of fresh concrete. It is also used for washing
the aggregates and for curing purposes. Water used for both mixing and curing should be
free from injurious amount of deterious materials. The quality of water is important
because impurities in it may interface with setting of the cement may adversely affect the
strength of concrete or cause staining of its surface. And the quality of water is covered
by clause saying that water should be fit for drinking. The source of that water used in
this project was water distributed by ELECTROGAZ
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3.1.5 Admixture
3.1.5 1.Definition
Admixture are the materials other than the basic ingredients of concrete, cement, water
and added to the concrete mix immediately before or during mixing one or more of the
specific properties of concrete in the flesh or hardened state. [2]
3.1.5 2 Sika latex
Sika latex is generally added to the clean mixing water within the range 1:1-1:4. for all
application a part from sprayed on renders a bonding coat of sika latex: water(1:1) mixed
with fresh cement and sand (1:1) should be brushed into the prepared surface. Sub
sequent mortar application must be carried out whilst the bonding coat is still wet.
Application and limitation
Rendering, floor toppings should be allowed to cure correctly. Protect the appliedmortar from frost exposure.
Avoid excessive air-entrainment through over mixing. Do not use neat sika latex or sika latex with water as bonding agent. Especially
always add cement and sand.
Minimum application temperature is +5 C Clean all tools and application equipment with water immediately after use.
3.1.5 3. Sikatop
Designed for use on concrete, mortar, and masonry substates. Easily applied by brush,
roller, or spray equipment. This fine textured, abrasion-resistant coating is used for
protection against deicing salts and for damp proofing/water proofing.
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3.2 ANALYSIS
3.2.1 Ligh concrete
3.2.1.1 Properties of structural
Concrete can be produced with density which are 25 to 40 percent lower but with
strengths equal to the maximum normally achieved by ordinary concrete.
Characteristics of lightweight concrete
Low density: the density of the concrete varies from 300 to 1200 kg/m3.
High strength: cellular concrete has high compressive strength in relation to its density.
The strength of aerated cellular concrete is about 15 to 20 percent of its compressive
strength. Due to much higher strength to mass ratio, the cellular concrete floor and roof
slabs are approximately one quarter the weight of normal reinforced concrete slabs.
Thermal insulation: the insulation value of light weight concrete is about 3 to 6 times that
of bricks and about 10 times that of other concrete. A 200 mm thick and wall of aerated
concrete of density 800kg/m3has the same degree of insulation as a 400 mm thick brick
wall of density 1600kg/m3.
Fire resistance: light weight has excellent fire resisting properties. Its thermal
conductivity makes its suitable for protecting other structures from the effects of fire.
Shrinkage: light weight concrete is subjected to shrinkage but to a limited extend.
Sound insulation: sound insulation in cellular concrete is normal not as good as in dense
concrete.
Repairability: light weight products can be easily sown, cut drilled or nailed. This makes
construction easier.Speed of construction: with the adoption of prefabrication is possible to design the
structure on the concept of molecular which ensure of faster rate of construction.
Economy: due to light weight and high strength to mass ratio of cellular concrete
products, their use results in lesser consumption of steel.
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Quality control: a better quality control is exercised in construction of structure with light
weight concrete products owning to the use of factory made units.
3.2.1.2 Applications of lightweight concrete
Different uses of light weight concrete can summarized as follows:
As load bearing masonry wall using cellular concrete blocks As precast floor and roof panels in all types of buildings As a filler wall in the form of precast reinforced wall panels in multistoried
building.
As partition walls in residential, institutional and industrial building. As in situ composite roof or floor slabs with reinforced concrete grid beams. As precast composite wall or floor panels, and As insulation cladding to exterior walls of all types of buildings, particularly in
office and industrial building.
These are many advantages of having low density.
-It helps in reduction of dead load
-It increases the progress of building and lowers haulage and handling costs.
-It will result in considerable economy.
-Lower thermal conductivity
And one of the disadvantages of conventional concrete is the high self weight of
concrete.
Basically there is only one method for making concrete light.
This is achieved in actual practice by 3 different ways.
By replacing the usual mineral aggregate by cellular porous or light weightaggregate.
By introducing gas or air bubbles in mortar. This known as aerated concrete. By omitting sand fraction from aggregate. This is called no-fines concrete.
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3.2.2 Normal concrete
Normal concrete or ordinary concrete is a mixture of fine aggregate, water, cement and
coarse aggregate. Density of normal concrete is in the order of 22 to 26 KN/m3.
Application of normal concrete
As load bearing masonry wall using concrete blocks As precast floor and roof panels in all types of buildings As a filler wall in the form of precast reinforced wall panels in multistoried
building.
As partition walls in residential, institutional and industrial building. As in situ composite roof or floor slabs with reinforced concrete grid beams. As precast composite wall or floor panels.
3.2.3 Heavy concrete
Heavy concrete having unit weight of about 30KN/m3
to 57KN/m3
and produced by using
heavy weight aggregate.
Application of heavy concrete
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The most common use of high-strength concrete is for construction of high-rise
buildings. At 969 ft (295 m), Chicago's 311 South Wacker Drive uses concrete with
compressive strengths up to 12,000 psi (83 MPa) and is the tallest concrete building in
the United States. [7]
Heavy aggregate is some times desired when structure such as pcc walls and floor are
constructed and radiation shielding is important. One common example is in hospitals
where X-Ray facilities might be enclosed in heavy weight pcc walls so that the radiation
used there in does not escape and pose a threat to other building occupants. A few
examples of heavy weight aggregate are iron slugs and steel bar bearings.
3.2.4 Comparison of light , narmal and heavy concrete
By definition lightweight concrete is lighter ther normal-weight concrete. This 25 to 35%
weight reduction affords architects and engineers considerable design flexibility and
substantial cost savings to the owner. The reduction in unit weight provides less dead
load, resulting in improved seismic structural response and permits the use of longer
spans, thinner sections, and smaller size structural members, less reinforcing steel and
less costly foundations. Because lightweight concrete has greater tire resistance than
normal-weight concrete, required tire ratings are achieved with thinner floor sections,
further reducing the dead load and enhancing the advantages. All of this adds up to more
efficient structural systems with less material being used, which in turn improves the
long-term sustainability of the concrete industry and the environment.
Concrete is made lighter primarily by replacing the "heavy" normal weight aggregate
with lightweight aggregate and by maintaining air entrainment at about 6%.
The primary difference between high-strength concrete and normal-strength concrete
relates to the compressive strength that refers to the maximum resistance of a concrete
sample to applied pressure. Although there is no precise point of separation between
high-strength concrete and normal-strength concrete, the American Concrete Institute
defines high-strength concrete as concrete with a compressive strength greater than 6000
psi (41 MPa)
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Table.3.1 Comparison of light , normal and heavy concrete
Light concrete Normal concrete Heavy concrete
Compressive
strength N/mm2on cubic samples
9 to 88 10 to 60 Greater than
60 up to 115
Density(KN/m3) 14.40 to 18.4 22.4-24.0 Greater than 25
Cost Cheap Medium Expensive
Aggreagate Lightweight aggr. Normal weight aggr. Heavy weight aggr.
Transport Easly (low weight) Difficult Difficult
Some reasons of
use
Insulation, and
reduction of the dead
load of structure
Normal use Protection against
eradiation, rigid
pavement of roads.
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Chapter 4: RESULTS AND DISCUSSION
Table 4.1 Availability of aggregate in Rwanda
Types of aggregates Quantity Examples Sources
Lightweight
aggregate
Medium Volcanic cinders,
Sawdust and
Rice husk
Northern province,
Western province,
carpentry workshop,
southern province
and eastern province
Normal weight
Aggregate
High Sand, gravel,
crushed stone,
coarse aggregate,
In all province
In all rivers
Heavy weight
aggregate
Low Crushed rock with
high density.
All province
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Table 4.2 Availability of concrete in RWANDA
Types of
concrete
availability Compressive
strength
Aggregates
used
Observation
Lightweight
concrete
Low - Volcanic
cinders
Some dont know
the different of
L.C and N.C and
they confuse plain
concrete& L.C.
Normal weight
concrete
More 99% 16.5 -25 Mpa Sand, Gravel,
crushed stone,
coarse
aggregate.
It has observed
that normal
concrete are more
used in all
province.
Heavy weight
concrete
low - crushed stone
(dolerite)
We need other
cement for
making heavy
concrete.
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4.1 Comparison of uses of lightweight concrete, normal concrete and
heavy concrete in RWANDA
I found that 99% of concrete used in RWANDA are normal concrete because of
availability of normal aggregate in all region of country, and is known by many people,
and are not very expansive. And other concrete are not known by many people and they
confuse plain concrete and light concrete. By example lightweight aggregate are available
in RWANDA but are not used in all construction use only in construction of road. But
they are an absence of cement used in heavy concrete in RWANDA. When you want to
use them there is one way of getting that cement, is to import in other countries have
successful for production of that cement or CIMERWA should produce cement that have
strength grade more than 32.5 especially for highter grade concretes, it means the use of
heavy concrete are very expensive.
4.2 Discussion
Data received from different companies show that they dont know the difference
between Lightweight concrete, Normal weight concrete and Heavy concrete. They name
concrete according to the quantity of cement used in mixing ratio of cement and
aggregate; when they use low quantity of cement in cement/aggregate ratio the concrete
produced is Lightweight concrete. And when they use more quantity of cement means
that concrete produced is Heavy concrete.
By example:
Lightweight concrete 1:3:5 Normal concrete 1:2:4 Heavy concrete 1:1:2
But all types of concrete used are Normal concrete, because they use normal weight
aggregate with at different mixing ratio and differents size;
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Chapiter 5 CONCLUSION AND RECOMMENDATION
5.1 CONCLUSION
The research conducted during this work has increasing our understanding in several
areas related to the lightweight concrete, normal concrete and heavy concrete .
The conclusions that could be made from the results are:
Some site dont know the difference between light concrete, normal concrete and heavy
conrete.
They know that the type of concrete depends on the mixing ratio of cement and
aggregates; when use more quantity of cement means that heavy concrete, and when use
low quantity is lightweight concrete.
Lightweight concrete should be used in different areas in our contry because of
availability of lightweight aggregate in all area of RWANDA and are not expensive and
the compressive strength is not as great as ordinary concrete, but it weathers just as well.
Among its advantages are less need for structural steel reinforcement, smaller foundation
requirements, better fire resistance and most importantly, the fact that it can serve as an
insulation material!
Als heavy concrete should be used in our contry because of their advantages by example
some time they dont need to be reinforced,
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5.2 RECOMMENDATION
Analysis of light concrete, normal concrete and heavy concrete it helps different clients
to differenciate these three types of concrete and facilitate the selection of type of
concrete used.
It is recommended the Ministry of education to encourage the final year students by
helping them executing what they have discovered in order to improve our technology in
Rwanda.
It is recommended to the government authorities to sensitive the population on the use of
Light concrete as new building material for making walling blocks on the market
industry, since it might be cheap and easily made in the country.
In view of the following on some special concrete its recommended to be used in
development contries like RWANDA such us heavy concrete in order to reduce the
damaged roads cause damage to vehicles, reduce their fuel efficiency and lead to
passenger discomfort. The rigid pavements or the concrete roads, on the other hand,
provide smooth drive consistently over long period of time The bitumen roads, although
incur lower initial cost, end up costing more in comparison with concrete roads, on
account of higher maintenance requirements. The concrete roads offer special
advantages in city in terms of their capacity to withstand heavy traffic loads, long service
life and minimum maintenance costs.
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REFERENCES
[1]M.S SHETTY and S.CHAND(2005), Concrete Technology Theory and
Practice, Technical Advisor, MC Bauchemie Pvt Ltd
[2]ML GAMBHIR (1995),Concrete Technology, Second edition
[3]Neville A.M. (1963), Properties of Concrete Technology, Sir Isaac and Pitman sons
Ltd London.
[4]www.wikipedia.org/wiki/compressive strength (2007)
[5]e- mail [email protected]
[6]htt:/// www.cement.org/bosic/concrete products_histrenght.asp
[7]http://cr4.globalspec.com/thread/42583/Concrete-beams-for-ceiling
[8]http://www.tfhrc.gov/structur/hpc/hpc2/ack.htm[9]http://www.tfhrc.gov/pubrds/julaug98/concrete.htm
[10]http://www.spancrete.com/products.php
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APPANDICES
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