2. STRENGTH BEHAVIOUR OF SELF CURING FLY
ASH CONCRETE USING STEEL FIBRES
Seminar report submitted
In partial fulfillment of requirements
For the award of degree of
Master of Technology
In
Department of CIVIL ENGINEERING
By
SATISH BABU.B
(14202001)
Under the guidance of
DR. SHASHI KUMAR GUPTA
PROFESSOR
Department of civil engineering
K L UNIVERSITY
Greenfields,, Vaddeswaram, Guntur District, Vijayawada, Andhra Pradesh 522502
2014-2015
3. CERTIFICATE
This is to certify that the seminar Report entitled “STRENGTH BEHAVIOUR OF SELF
CURING FLY ASH CONCRETE USING STEEL FIBRE” that is being submitted by Mr.
SATISH BABU.B
in partial fulfillment of the requirement for the award of the Degree of M.Tech. In civil
engineering 2014-2015 to K.L.University, Vijayawada is a record of bonafide work carried out
by him under my Guidance and supervision
Supervisor Head of the Department
4. ACKNOWLEDGEMENT
This acknowledgement is intended to be thanks giving gesture to all those people who have been
involved directly or indirectly with my dissertation work. Fir s t and foremos t, I would l ike
to expres s my thanks and indebtednes s to my guide. DR. SHASHI KUMAR
GUPTA, PROFESSOR, and DR. K RAMESH head of the department, Department of Civil
Engineering, K L UNIVERSITY, for his deep involvement, invaluable and continuous
motivation throughout this work. I am highly obliged to him for being there always whenever I
needed him.
I would like to express my deep sense of gratitude and sincere thanks to the staff
of K L UNIVERSITY, for their support and providing access to data/documents/processes
needed during the project. I wish to extend my sincere thanks for their benign help and
continuous interest taken throughout the project work.
Finally, I would like to dedicate this project work to my parents, who have always
been a great source of support and encouragement, especially in all of my academic endeavours.
5. ABSTRACT
Concrete usage around the world is second only to water. Ordinary Portland cement (OPC) is
conventionally used as the primary binder to produce concrete. The environmental issues
associated with the production of OPC are well known. The amount of the carbo n dioxide
released during the manufacture of OPC due to the calcinations of limestone and combustion of
fossil fuel is in the order of one ton for every ton of OPC produced. In addition, the extent of
energy required to produce OPC is only next to steel and aluminum.
On the other hand, the abundant availability of fly ash worldwide creates opportunity to
utilize this by-product of burning coal, as a substitute for OPC to manufacture cement products.
When used as a partial replacement of OPC, in the presence of water and in ambient temperature,
fly ash reacts with the calcium hydroxide during the hydration process of OPC to form the
calcium silicate hydrate (C-S-H) gel. The development and application of high volume fly ash
concrete, which enabled the replacement of OPC up to 60% by mass is a significant
development.
In 1978, Davidovits proposed that binders could be produced by a polymeric reaction of
alkaline liquids with the silicon and the aluminum in source materials of geological origin or by-product
materials such as fly ash and rice husk ash. He termed these binders as geopolymers.
In this project, fly ash-based geopolymer is used as the binder, instead of Portland or
other hydraulic cement paste, to produce cement mortar. The fly ash-based geopolymer paste
binds the loose fine aggregates and other un-reacted materials together to form the geopolymer
mortar, with or without the presence of admixtures. The manufacture of geopolymer concrete is
carried out using the usual concrete technology methods.
The silicon and the aluminum in the fly ash react with an alkaline liquid that is a
combination of sodium silicate and sodium hydroxide solutions to form the geopolymer paste
that binds the aggregates and other un-reacted materials.
6. Contents
1. INTRODUCTION ..........................................................................................................................8
1.2 Need for Self–curing ..................................................................................................................8
1.3 Potential Materials for IC ...........................................................................................................9
1.4 Chemicals to Achieve Self–curing ...............................................................................................9
1.5 Super-absorbent Polymer (SAP) for IC.........................................................................................9
1.6 Means of Providing Water for Self–curing Using LWA ................................................................ 11
1.7 Water Available from LWA for Self–curing ................................................................................ 11
2. LITERATURE REVIEW .............................................................................................................. 12
3. METHODS OF SELF CURING .................................................................................................... 15
2.1 Definition of Internal Curing (Ic) ............................................................................................... 15
2.2 Mechanism of Internal Curing: ................................................................................................. 15
2.3 Significance of Self–Curing: ...................................................................................................... 15
2.4 Potential Materials for Internal Curing (Ic): ............................................................................... 16
2.5 Advantages of Internal Curing .................................................................................................. 16
2.6 Polyethylene Glycol: ................................................................................................................ 16
4. MATERIALS ................................................................................................................................... 17
4.1 Cement................................................................................................................................... 17
4.2 Fine Aggregate ........................................................................................................................ 17
4.3 Coarse Aggregate .................................................................................................................... 17
4.4 Fly Ash .................................................................................................................................... 17
4.5 Silica Fume.............................................................................................................................. 17
4.6 Water ..................................................................................................................................... 17
4.7 Super Absorbent Polymer ........................................................................................................ 17
4.8 Fiber ....................................................................................................................................... 17
5. MIX PROPORTIONS ................................................................................................................... 19
5.1 Requirements Of Concrete Mix Design ..................................................................................... 20
5.2 Types of Mixes ........................................................................................................................ 20
5.2.1. Nominal Mixes ................................................................................................................ 20
5.2.2. Standard Mixes ................................................................................................................ 20
5.2.3 Designed Mixes ................................................................................................................ 21
5.3 Factors Affecting The Choice Of Mix Proportions ....................................................................... 21
7. 5.3.1. Compressive Strength....................................................................................................... 21
5.3.2. Workability ..................................................................................................................... 21
5.3.3. Durability......................................................................................................................... 22
5.3.4. Maximum Nominal Size Of Aggregate .............................................................................. 22
5.3.5. Grading And Type Of Aggregate....................................................................................... 22
5.3.6. Quality Control ................................................................................................................ 22
5.4 Mix Proportion Designations .................................................................................................... 23
5.5 Factors to Be Considered For Mix Design .................................................................................. 23
6. PREPARATION OF TEST SPECIMENS ...................................................................................... 25
6.1 Optimum Sap Content ............................................................................................................. 25
6.2 Slump Cone Test...................................................................................................................... 25
6.3 Procedure To Determine Workability Of Fresh Concrete By Slump Test ...................................... 25
6.4 Compression Test .................................................................................................................... 26
6.5 Splitting Tensile Strength Test .................................................................................................. 27
6.6 Flexural Strength Test .............................................................................................................. 28
6.7 Modulus of Elasticity ............................................................................................................... 29
7. RESULTS AND DISCUSSION..................................................................................................... 31
8. CONCULSION ............................................................................................................................ 34
9. REFERENCES ................................................................................................................................. 35
8. 1. INTRODUCTION
The advances in construction industry have contributed tremendously for the new
developments in construction chemicals. The use of various chemicals in concrete alters the
properties of strength and durability. A durable concrete is one that performs satis factorily in the
working environment during its anticipated exposure conditions during service. Due to the vast
construction activities different grades of concrete with natural and artificial in gradients are in
use. It is observed during construction even though supervision is given importance proper care
is not taken in the curing and other operations. As an alternative to water curing, different other
methods are also available including membrane curing, polymer curing etc. Curing is the process
of controlling the rate and extent of moisture loss from concrete during cement hydration. By
proper curing only we can attain desirable strength properties. In practical good curing is not
always possible, while poor curing process will affect the strength properties, self-curing
methods are developed. By adding self-curing agents an internal water reservoir is created in the
fresh concrete. Once the initial free water has been consumed, the water absorbed by the SAP
will be gradually released to maximize the heat of hydration.
1.1 Self Curing
Proper curing of concrete structures is to meet performance and durability requirements.
In conventional curing this is achieved by external curing applied after mixing, placing and
finishing. Self curing and internal curing is a technique that can be used to provide additional
moisture in concrete for more effective hydration of cement and reduced self-desiccation.
1.2 Need for Self–curing
When the mineral admixtures react completely in a blended cement system, their demand
for curing water (external or internal) can be much greater than that in a conventional ordinary
Portland cement concrete. When this water is not readily available, due to depreciation of the
capillary porosity, for example, significant autogenously deformation and (early-age) cracking
may result. Due to the chemical shrinkage occurring during cement hydration, empty pores are
created within the cement paste, leading to a reduction in its internal relative humidity and also
to shrinkage which may cause early-age cracking. This situation is intensified in HPC (compared
to conventional concrete) due to its generally higher cement content, reduced water/cement (w/
9. c) ratio and the pozzolanic mineral admixtures (fly ash, silica fume). The empty pores created
during self-desiccation induce shrinkage stresses and also influence the kinetics of cement
hydration process, limiting the final degree of hydration. The strength achieved by IC could be
often specially in HPC, it is not easily possible to provide curing water from the top surface at
the rate required to satisfy the ongoing chemical shrinkage, due to the extremely low
permeability’s often achieved.
1.3 Potential Materials for IC
The following materials can provide internal water reservoirs:
Lightweight Aggregate (natural and synthetic, expanded shale),
LWS Sand (Water absorption =17 %)
LWA 19mm Coarse (Water absorption = 20%)
Super-absorbent Polymers (SAP) (60-300 mm size)
SRA (Shrinkage Reducing Admixture) (propylene glycol type i.e. polyethylene-glycol)
Wood powder
1.4 Chemicals to Achieve Self–curing
Some specific water-soluble chemicals added during the mixing can reduce water evaporation
from and within the set concrete, making it ‘self-curing.’ The chemicals should have abilities to
reduce evaporation from solution and to improve water retention in ordinary Portland cement
matrix.
1.5 Super-absorbent Polymer (SAP) for IC
The common SAPs are added at rate of 0–0.6 wt % of cement. The SAPs are covalently
cross- linked. They are Acryl amide/acrylic acid copolymers. One type of SAPs are suspension
polymerized, spherical particles with an average particle size of approximately 200 mm; another
type of SAP is solution polymerized and then crushed and sieved to particle sizes in the range of
10. 125–250 mm. The size of the swollen SAP particles in the cement pastes and mortars is about
three times larger due to pore fluid absorption. The swelling time depends especially on the
particle size distribution of the SAP. It is seen that more than 50% swelling occurs within the
first 5 min after water addition. The water content in SAP at reduced RH is indicated by the
sorptionisotherm.
SAPs are a group of polymeric materials that have the ability to absorb a significant amount of
liquid from the surroundings and to retain the liquid within their structure without dissolving.
SAPs are principally used for absorbing water and aqueous solutions; about 95% of the SAP
world production is used as a urine absorber in disposable diapers. SAPs can be produced with
water absorption of up to 5000 times their own weight. However, in dilute salt solutions, the
absorbent
Linked poly acrylates and copolymerized poly acryl amides/ poly acrylates. Because of
their ionic nature and interconnected structure, they can absorb large quantities of water without
dissolving. From a chemical point of view, all the water inside a SAP can essentially be
considered as bulk water. SAPs exist in two distinct phase states, collapsed and swollen. The
phase transition is a result of a competitive balance between repulsive forces that act to expand
the polymer network and attractive forces that act to shrink the network. The macromolecular
matrix of a SAP is a polyelectrolyte, i.e., a polymer with ionisable groups that can dissociate in
solution, leaving ions of one sign bound to the chain and counter- ions in solution. For this
reason, a high concentration of ions exists inside the SAP leading to a water flow into the SAP
due to osmosis. Another factor contributing to increase the swelling is water salvation of
hydrophilic groups present along the polymer chain. Elastic free energy opposes swelling of the
SAP by a refractive force.cy of commercially produced SAPs is around 50 g/g. They can be
produced by either solution or suspension polymerization, and the particles may be prepared in
different sizes and shapes including spherical particles. The commercially important SAPs are
covalently cross
SAPs exist in two distinct phase states, collapsed and swollen. The phase transition is a result of
11. a competitive balance between repulsive forces that act to expand the polymer network and
attractive forces that act to shrink the network.
1.6 Means of Providing Water for Self–curing Using LWA
Water/moisture required for internal curing can be supplied by incorporation of saturated-surface
dry (SSD) lightweight fine aggregates (LWA).
1.7 Water Available from LWA for Self–curing
It is estimated by measuring desorption of the LWA in SSD condition after exposed to a
salt solution of potassium nitrate (equilibrium RH of 93%). The total absorption capacity of the
LWA can be measured by drying a Saturated Surface Dry (SSD) sample in desiccators.
12. 2. LITERATURE REVIEW
The properties of hardened concrete, especially the durability, are greatly influenced by
curing since it has a remarkable effect on the hydration of the cement. The advancements in the
construction and chemical industry have paved way for the development of the new curing
techniques and construction chemicals such as Membrane curing compounds, Self-curing agents,
Wrapped curing, Accelerators, Water proofing compounds etc. With the growing scale of the
project conventional curing methods have proven to be a costly affair as there are many practical
issues and they have been replaced by Membrane curing compounds and Self-curing agents up to
some extent as they can be used in inaccessible areas, Vertical structures, Water scarce areas etc
.It is most practical and widely used curing method. In this review paper effort has been made to
understand the working and efficiency of curing methods which are generally adopted in the
construction industry and compared with the conventional water curing method. Conventional
water curing is the most efficient method of curing as compared to Membrane curing, Self-curing,
Wrapped curing and Dry air curing methods. Using Membrane curing and Self-Curing
methods one can achieve 90% of efficiency as compared to Conventional Curing method. Self
Curing method is most suitable for high-rise buildings especially in columns and inaccessible
areas. Membrane curing compounds are most practical and widely used method it is most
suitable in water scarce area. Wrapped curing is less efficient than Membrane curing and Self-
Curing it can be applied to simple as well as complex shapes. Dry-Air curing should be avoided
at the construction sites because designed design strength is not achieved by this method. The
average efficiency of the curing compound increases with curing age initially by reduces at later
age. Application of the curing compound is significantly dependent on the time of application of
the compound.
Most of the concrete that is produced and placed each year all over the world already
does self-cure to some extent. Some of it is not intended to have anything done to its exterior
surface, except perhaps surface finishing. Yet the concrete’s ability to serve its intended purpose
is not significantly reduced.―Curing is the maintaining of a satisfactory moisture content and
temperature in concrete during its early stages so that desired properties (of concrete) may
develop. Curing is essential in the production of concrete that will have the desired properties.
The strength and durability of concrete will be fully developed only if it is cured. No action to
13. this end is required, however, when ambient conditions of moisture, humidity, and temperature
are sufficiently favorable to curing. Otherwise, specified curing measures shall start as soon as
required. Most of the concrete in the world is placed in quantit ies that are of sufficient thickness
such that most of the material will remain in satisfactory conditions of temperature and moisture
during its early stages. Also, there are cases in which concrete has been greatly assisted in
moving toward a self-curing status either inadvertently or deliberately through actions taken in
the selection and use of materials. To achieve good cure, excessive evaporation of water from a
freshly cast concrete surface should be prevented. Failure to do this will lead to the degree of
cement hydration being lowered and the concrete developing unsatisfactory properties. Curing
can be performed in a number of ways to ensure that an adequate amount of water is available
for cement hydration to occur. However, it is not always possible to cure concrete without the
need for applying external curing methods. Most paving mixtures contain adequate mixing water
to hydrate the cement if the moisture is not allowed to evaporate. It should be possible to develop
oil, polymer, or other compound that would rise to the finished concrete surface and effectively
seal the surface against evaporation new developments in curing of concrete are on the horizon
as well. In the next century, mechanization of the placement, maintenance, and removal of curing
mats and covers will advance as performance-based specifications quantify curing for acceptance
and payment. In addition, effective sealants and compounds that prevent the loss of water and
promote moist curing conditions will be in high demand. Self-curing concrete should become
available in the not-too-distant future. (Tarun R. Naik et al.)
Proper curing of concrete structures is important to ensure that they meet their intended
performance and durability requirements. Curing plays a major role in developing the concrete
microstructure and pore structure. Self curing distributes the extra curing water throughout the
entire 3-D concrete microstructure so that it is more readily available to maintain saturation of
the cement paste during hydration, avoiding self-desiccation and reducing autogenously
shrinkage. The scope of the research included characterization of super absorbent polymer for
use in self curing. Experimental measurements were performed on to predict the compressive
strength, split tensile strength and flexural strength of the concrete containing Super Absorbent
Polymer (SAP) at a range of 0%, 0.2%, 0.3%, and 0.4% of cement and compared with that of
cured concrete. The grade of concrete selected was M40. Addition of SAP leads to a significant
increase of mechanical strength (Compressive and Split tensile) Maximum compressive stress
14. develop in M-40 grade self curing concrete by adding sap 0.3% of cement. Split tensile strength
of self curing concrete for dosage of SAP 0.3% of cement was higher than non self curing
concrete. Flexural strength of self curing concrete for dosage of SAP 0.3% of cement was higher
than non self curing concrete. Performance of the self-curing agent will be affected by the mix
proportions mainly the cement content and the w/c ratio.
15. 3. METHODS OF SELF CURING
Currently, there are two major methods available for internal curing of concrete. The first
method uses saturated porous lightweight aggregate (LWA) in order to supply an internal source
of water, which can replace the water consumed by chemical shrinkage during cement hydration.
The second method uses poly-ethylene glycol (PEG) which reduces the evaporation of water
from the surface of concrete and also helps in water retention.
2.1 Definition of Internal Curing (Ic)
The ACI-308 Code states that “internal curing refers to the process by which the
hydration of cement occurs because of the availability of additional internal water that is not part
of the mixing Water.” Conventionally, curing concrete means creating conditions such that water
is not lost from the surface i.e., curing is taken to happen ‘from the outside to inside’. In contrast,
‘internal curing’ is allowing for curing ‘from the inside to outside’ through the internal reservoirs
(in the form of saturated lightweight fine aggregates, superabsorbent polymers, or saturated
wood fibers) Created. ‘Internal curing’ is often also referred as ‘Self–curing.’
2.2 Mechanism of Internal Curing:
Continuous evaporation of moisture takes place from an exposed surface due to the
difference in chemical potentials (free energy) between the vapors and liquid phases. The
polymers added in the mix mainly form hydrogen bonds with water molecules and reduce the
chemical potential of the molecules which in turn reduces the vapors pressure, thus reducing the
rate of evaporation from the surface.
2.3 Significance of Self–Curing:
When the mineral admixtures react completely in a blended cement system, their demand
for curing water (external or internal) can be much greater than that in a conventional ordinary
Portland cement concrete. When this water is not readily available, significant autogenously
Deformation and (early-age) cracking may result. Due to the chemical shrinkage
occurring during cement hydration, empty pores are created within the cement paste, leading to a
16. reduction in its internal relative humidity and also to shrinkage which may cause early-age
cracking.
2.4 Potential Materials for Internal Curing (Ic):
The following materials can provide internal water reservoirs:
Lightweight Aggregate (natural and synthetic, expanded shale)
Super-absorbent Polymers
Polyethylene glycol
2.5 Advantages of Internal Curing
Internal curing (IC) is a method to provide the water to hydrate all the cement,
accomplishing what the mixing water alone cannot do.
Provides water to keep the relative humidity (RH) high, keeping self-desiccation from
occurring.
Eliminates largely autogenously shrinkage.
Maintains the strengths of mortar/concrete at the early age (12 to 72 hrs.) Above the
level where internally & externally induced strains can cause cracking.
Can make up for some of the deficiencies of external curing, both human related (critical
period when curing is required in the first 12 to 72 hours) and hydration.
2.6 Polyethylene Glycol:
Polyethylene glycol is a condensation polymer of ethylene oxide and water with the general
formula H(OCH2CH2)nOH, where n is the average number of repeating ox ethylene groups
typically from 4 to about 180. The abbreviation (PEG) is termed in combination with a numeric
suffix which indicates the average molecular weights. One common feature of PEG appears to be
the water-soluble nature. Polyethylene glycol is non-toxic, odorless, neutral, lubricating, non-volatile
and non-irritating and is used in a variety of pharmaceuticals.
17. 4. MATERIALS
4.1 Cement
Ordinary Portland cement of 43 grade (IS 8112:1989). The total quantity of cement
required was approximately estimated, brought and stored in an air tight container.
4.2 Fine Aggregate
Locally available river bed sand having specific gravity 2.61 and fineness modulus of
3.32 was used.
4.3 Coarse Aggregate
Locally available crushed granite chips having specific gravity 2.6 and fineness modulus
of 3.59 was used. The particle size varies from 10 to 20mm was used.
4.4 Fly Ash
Fly Ash collected from Neyveli Lignite Corporation, Neyveli, Tamil Nadu confirms to
IS: 3812-1981 is a Class C Fly Ash (High Calcium Fly Ash). The properties of Fly Ash are
having 2.41 and fineness of 1.24 M2/g.
4.5 Silica Fume
Silica fume obtained from Moon traders, Madurai, India. The properties of silica fume
are specific gravity 2.20 and fineness 20000 M2/kg.
4.6 Water
Potable water available in the college campus was used for preparing concrete in the
entire experimental investigation.
4.7 Super Absorbent Polymer
The absorbing speed of SAP is 30 to90 sec.
4.8 Fiber
18. Double end hooked steel fibers with an aspect ratio of 50 were used.
19. 5. MIX PROPORTIONS
The process of selecting suitable ingredients of concrete and determining their relative
amounts with the objective of producing a concrete of the required, strength, durability, and
workability as economically as possible, is termed the concrete mix design. The proportioning of
ingredient of concrete is governed by the required performance of concrete in 2 states, namely
the plastic and the hardened states. If the plastic concrete is not workable, it cannot be properly
placed and compacted. The property of workability, therefore, becomes of vital importance.
The compressive strength of hardened concrete which is generally considered to be an
index of its other properties, depends upon many factors, e.g. quality and quantity of cement,
water and aggregates; batching and mixing; placing, compaction and curing. The cost of concrete
is made up of the cost of materials, plant and labour. The variations in the cost of materials arise
from the fact that the cement is several times costly than the aggregate, thus the aim is to produce
as lean a mix as possible. From technical point of view the rich mixes may lead to high shrinkage
and cracking in the structural concrete, and to evolution of high heat of hydration in mass
concrete which may cause cracking.
The actual cost of concrete is related to the cost of materials required for producing a
minimum mean strength called characteristic strength that is specified by the designer of the
structure. This depends on the quality control measures, but there is no doubt that the quality
control adds to the cost of concrete. The extent of quality control is often an economic
compromise, and depends on the size and type of job. The cost of labour depends on the
workability of mix, e.g., a concrete mix of inadequate workability may result in a high cost of
labour to obtain a degree of compaction with available equipment
20. 5.1 Requirements of Concrete Mix Design
The requirements which form the basis of selection and proportioning of mix ingredients are:
a) The minimum compressive strength required from structural consideration
b) The adequate workability necessary for full compaction with the compacting
equipment available.
c) Maximum water-cement ratio and/or maximum cement content to give adequate
durability for the particular site conditions
d) Maximum cement content to avoid shrinkage cracking due to temperature cycle in
mass concrete.
5.2 Types of Mixes
5.2.1. Nominal Mixes
In the past the specifications for concrete prescribed the proportions of cement, fine and
coarse aggregates. These mixes of fixed cement-aggregate ratio which ensures adequate
strength are termed nominal mixes. These offer simplicity and under normal
circumstances, have a margin of strength above that specified. However, due to the
variability of mix ingredients the nominal concrete for a given workability varies widely
in strength.
5.2.2. Standard Mixes
The nominal mixes of fixed cement-aggregate ratio (by volume) vary widely in strength and may
result in under- or over-rich mixes. For this reason, the minimum compressive strength has been
included in many specifications. These mixes are termed standard mixes.
IS 456-2000 has designated the concrete mixes into a number of grades as M10, M15, M20,
M25, M30, M35 and M40. In this designation the letter M refers to the mix and the number to
the specified 28 day cube strength of mix in N/mm2. The mixes of grades M10, M15, M20 and
M25 correspond approximately to the mix proportions (1:3:6), (1:2:4), (1:1.5:3) and (1:1:2)
respectively.
21. 5.2.3 Design Mixes
In these mixes the performance of the concrete is specified by the designer but the mix
proportions are determined by the producer of concrete, except that the minimum cement content
can be laid down. This is most rational approach to the selection of mix proportions with specific
materials in mind possessing more or less unique characteristics. The approach results in the
production of concrete with the appropriate properties most economically. However, the
designed mix does not serve as a guide since this does not guarantee the correct mix proportions
for the prescribed performance.
For the concrete with undemanding performance nominal or standard mixes (prescribed in the
codes by quantities of dry ingredients per cubic meter and by slump) may be used only for very
small jobs, when the 28-day strength of concrete does not exceed 30 N/mm2. No control testing
is necessary reliance being placed on the masses of the ingredients.
5.3 Factors Affecting the Choice of Mix Proportions
The various factors affecting the mix design are:
5.3.1. Compressive Strength
It is one of the most important properties of concrete and influences many other describable
properties of the hardened concrete. The mean compressive strength required at a specific age,
usually 28 days, determines the nominal water-cement ratio of the mix. The other factor affecting
the strength of concrete at a given age and cured at a prescribed temperature is the degree of
compaction. According to Abraham’s law the strength of fully compacted concrete is inversely
proportional to the water-cement ratio.
5.3.2. Workability
The degree of workability required depends on three factors. These are the size of the section to
be concreted, the amount of reinforcement, and the method of compaction to be used. For the
narrow and complicated section with numerous corners or inaccessible parts, the concrete must
have a high workability so that full compaction can be achieved with a reasonable amount of
22. effort. This also applies to the embedded steel sections. The desired workability depends on the
compacting equipment available at the site.
5.3.3. Durability
The durability of concrete is its resistance to the aggressive environmental conditions. High
strength concrete is generally more durable than low strength concrete. In the situations when the
high strength is not necessary but the conditions of exposure are such that high durability is vital,
the durability requirement will determine the water-cement ratio to be used.
5.3.4. Maximum Nominal Size of Aggregate
In general, larger the maximum size of aggregate, smaller is the cement req uirement for a
particular water-cement ratio, because the workability of concrete increases with increase in
maximum size of the aggregate. However, the compressive strength tends to increase with the
decrease in size of aggregate.
IS 456:2000 and IS 1343:1980 recommend that the nominal size of the aggregate should be as
large as possible.
5.3.5. Grading and Type of Aggregate
The grading of aggregate influences the mix proportions for a specified workability and water-cement
ratio. Coarser the grading leaner will be mix which can be used. Very lean mix is not
desirable since it does not contain enough finer material to make the concrete cohesive.
The type of aggregate influences strongly the aggregate-cement ratio for the desired workability
and stipulated water cement ratio. An important feature of a satisfactory aggregate is the
uniformity of the grading which can be achieved by mixing different size fractions.
5.3.6. Quality Control
The degree of control can be estimated statistically by the variations in test results. The variation
in strength results from the variations in the properties of the mix ingredients and lack of control
of accuracy in batching, mixing, placing, curing and testing. The lower the difference between
the mean and minimum strengths of the mix lower will be the cement-content required. The
factor controlling this difference is termed as quality control.
23. 5.4 Mix Proportion Designations
The common method of expressing the proportions of ingredients of a concrete mix is in the
terms of parts or ratios of cement, fine and coarse aggregates. For e.g., a concrete mix of
proportions 1:2:4 means that cement, fine and coarse aggregate are in the ratio 1:2:4 or the mix
contains one part of cement, two parts of fine aggregate and four parts of coarse aggregate. The
proportions are either by volume or by mass. The water-cement ratio is usually expressed in
mass
5.5 Factors to Be Considered For Mix Design
The grade designation giving the characteristic strength requirement of concrete.
The type of cement influences the rate of development of compressive strength of
concrete.
Maximum nominal size of aggregates to be used in concrete may be as large as possible
within the limits prescribed by IS 456:2000.
The cement content is to be limited from shrinkage, cracking and creep.
The workability of concrete for satisfactory placing and compaction is related to the size
and shape of section, quantity and spacing of reinforcement and technique used for
transportation, placing and compaction.
The concrete mix was designed for M30 grade as per IS 10262-2009 and mix proportion arrived
as 1: 1.269: 2.57 with w/c 0.42. Cement replacement of 40% with fly ash and 10% with silica
fume (totally 50%) by weight was considered. Totally 6 types of concrete mixes were prepared.
The quantities of aggregates, water content, cement and the additives are given in table 3.1
M1- Conventional Concrete
M2- 50% Cement + 40% Fly Ash + 10% Silica fume
M3- Self-curing Fly Ash concrete (50% Cement + 40% Fly Ash + 10% Silica fume+ SAP)
M4- 50% Cement + 40% Fly Ash + 10% Silica fume + SAP + 1% steel fiber
25. 6. PREPARATION OF TEST SPECIMENS
The specimens were casted in steel moulds and compacted on a table vibrator. 150mm
cube specimens, 100mm diameter x 200mm long cylinder specimens, 100 x 100 x 500mm beam
specimens and 150mm diameter x 300mm long cylinder specimens were cast for the
determination of compressive strength, split tensile strength, flexural strength and modulus of
elasticity of concrete respectively.
6.1 Optimum Sap Content
SAP content was varied as 0.1% to 0.5% and the optimum amount of SAP was found by
compression test at the age of 7 days. By test results 0.3% was found as optimum.
6.2 Slump Cone Test
Slump test is used to determine the workability of fresh concrete. Slump test as per IS:
1919 – 1959 is followed. The apparatus used for doing slump test are Slump cone and tamping
rod.
6.3 Procedure To Determine Workability Of Fresh Concrete By Slump Test.
i) The internal surface of the mould is thoroughly cleaned and applied with a light coat of oil.
ii) The mould is placed on a smooth, horizontal, rigid and nonabsorbent surface.
iii) The mould is then filled in four layers with freshly mixed concrete, each approximately to
one-fourth of the height of the mould.
iv) Each layer is tamped 25 times by the rounded end of the tamping rod (strokes are distributed
evenly over the cross section).
v) After the top layer is rodded, the concrete is struck off the level with a trowel.
vi) The mould is removed from the concrete immediately by raising it slowly in the vertical
direction.
26. vii) The difference in level between the height of the mould and that of the highest point of the
subsided concrete is measured.
viii) This difference in height in mm is the slump of the concrete.
In case of a dry sample, slump will be in the range of 25-50 mm that is 1-2 inches. But in
case of a wet concrete, the slump may vary from 150-175 mm or say 6-7 inches. So the value of
slump is specifically mentioned along the mix design and thus it should be checked as per your
location. Slump depends on many factors like properties of concrete ingredients – aggregates etc.
Also temperature has its effect on slump value. So all these parameters should be kept in mind
when deciding the ideal slump. Once the cone is filled and topped off [excessive concrete from
top is cleared] raise the cone within 5-10 seconds.
Workability for fresh concrete was found out by slump cone test. Higher slump value
gives good workability. The slump values for each mix were given in table 3.1.
6.4 Compression Test
Out of many test applied to the concrete, this is the utmost important which gives an idea
about all the characteristics of concrete. By this single test one judge that whether Concreting has
been done properly or not. For cube test two types of specimens either cubes of 15 cm X 15 cm
X 15 cm or 10cm X 10 cm x 10 cm depending upon the size of aggregate are used. For most of
the works cubical moulds of size 15 cm x 15cm x 15 cm are commonly used.
This concrete is poured in the mould and tempered properly so as not to have any voids.
After 24 hours these moulds are removed and test specimens are put in water for curing. The top
surface of this specimen should be made even and smooth. This is done by putting cement paste
and spreading smoothly on whole area of specimen.
These specimens are tested by compression testing machine after 7 days curing or 28 days
curing. Load should be applied gradually at the rate of 140 kg/cm2 per minute till the Specimens
fails. Load at the failure divided by area of specimen gives the compressive strength of concrete.
Three cubes were crushed at each age to get the average value.
27. 6.5 Splitting Tensile Strength Test
The split tensile strength was determined by subjecting 100mm diameter x 200mm long
cylinders to diametric compression so as to induce uniform lateral tension on the perpendicular
plane. At the end of each age of the specimen, the test was conducted as per IS: 5816-1999.
28. 6.6 Flexural Strength Test
The flexural strength tests were carried out on beam specimen of size 100 x 100 x 500mm under
two standard point loading at the end of each age of the specimen, flexural testing was conducted
under uniform rate of loading of 180kg/cm2/min. and the procedure was followed according to
IS: 516-1959. All the test results reported in this paper represent the average value obtained from
29. 6.7 Modulus of Elasticity
Cylinders of 150mm diameter x 300mm long specimens were cast and tested at the age of
28days in a compression testing machine. Deformation was measured using 250mm gauge
length compress meter fixed on the surface of the cylinder. Readings were taken at regular
intervals of load increment. Considering the stress level at twenty five percent of ultimate stress,
secant modulus of elasticity was calculated and the variation was shown in fig 4.5
31. 7. RESULTS AND DISCUSSION
Workability and strength properties of conventional concrete (M1), fly ash concrete
(M2),self-curing fly ash concrete (M3), self- curing fly ash concrete with 1% steel fiber
(M4),self- curing fly ash concrete with 1.5% steel fiber (M5), self- curing fly ash concrete
with2% steel fiber (M6) were compared at the age of 7, 28 and 60 days.
Fig 7.1 Compressive Strength for optimum SAP content
Fig.7.2Compressive Strength of varies mixes
32. Fig 7.3 Split Tensile Strength of varies mixes
Fig 7.4 Flexural Strength of varies mixes
33. 1
Fig 7.5 Modulus of Elasticity of varies mixes at the age of 28 days
34. 8. CONCULSION
By the above testing results following conclusions are made:
By varying the SAP content as 0.1% to 0.5% the optimum amount of SAP was
Found as 0.3% by compression test at the age of 7 days.
Self-curing Fly ash Concrete (M3) gives high Compressive Strength, Tensile
Strength and Flexural Strength when compared to externally cured Fly ash Concrete.
When Steel Fiber is added to the Self-Curing Fly Ash Concrete the strength
Properties go on increasing for 1% and 1.5% addition.
When 2% Steel Fiber is added the Strength properties suddenly decreases.
All the Self-curing Fly Ash concrete mixes with steel fibers (M4, M5, M6) give
High Strength compared to normal curing mix.
Addition of 1.5% Steel Fiber in Self-curing Fly Ash concrete gives high strength than
conventional concrete.
35. 9. REFERENCES
DURABILITY OF ‘SELF-CURE’ CONCRETE RK. Dhir’, P.C. Hewlett and
T.D. Dyer*Cement and Concrete Research, Vol. 25. No. 6, pp. 1153-1158.1995
Self-curing concrete: Water retention, hydration and moisture transport A.S. El-
Dieb *Department of Structural Engineering, Faculty of Engineering, Ain Shams
University, 1 El- Sarayat St., Abbasia 11517, Cairo, Egypt 19 February 2006
Bibliography of Self curing concrete: Ambily P.S, Scientist, and Rajamane N P,
Deputy Director and Head, Concrete Composites Lab Structural Engineering
Research Centre, CSIR, Chennai NBMCW July 2007
STRENGTH CHARACTERISTICS OF SELF-CURING CONCRETE
M.V.Jagannadha Kumar, M.Srikanth, Dr.K.Jagannadha Rao, volume 1 IJRET
SEP 2012
A.S. El-Dieb, T.A. El-Maaddawy and A.A.M. Mahmoud, “Water-Soluble
Polymers as Self-Curing Agent in Silica Fume Portland Cement Mixes”, ACI
Material JournalVol.278 (2011) 1-18.
FLY ASH GENERATION AND UTILIZATION - AN OVERVIEW Tarun R. Naik,
Ph.D., P.E. Department of Civil Engineering and Mechanics College of
Engineering and Applied Science the University of Wisconsin-Milwaukee, June
1993.
