Strength Properties of M 25 Concrete with Partial Replacement of
Cement with Fly Ash and Coarse Aggregate with Coconut Shell
Neetesh Kumar
Abhinav Singh
Research Scholar
Research Scholar
Civil Engg. Department
Civil Engg. Department
M.M.M.U.T. Gorakhpur
M.M.M.U.T. Gorakhpur
niteshmmmec@gmail.com
abhinavsinghbaghel@gmail.com
Abstract: An effort has been made to study the suitability of replacing the 25% of fly ash
obtained from N.T.P.C. Tanda Uttar Predesh is common for all mixes with cement and
simultaneously by replacing 10%, 20% and 30% of coconut shell as coarse aggregate for
concrete of grade M 25. Check strength characteristics such as compressive strength of
concrete mix are found for 7 days, 14 days, 28 days of curing period and results are analyzed
and compared with the regular (conventional) mix. Test for grade as per specified procedure
of IS codes. The materials are proportioned by their weight. The water cement ratio is
obtained by conducting workability tests. The results found were comparable with that of
conventional mix. The proportion used in this study is 1:1.49:3.03 and water cement ratio is
0.47.
Keywords: Coarse aggregate, fine aggregate, coconut shell, compressive strength, concrete,
fly ash, slump, compaction factor.
INTRODUCTION
The word “sustainable” is becoming very common worldwide. The fashion goes beyond the
practice of design and construction, since the consciousness of the current population is a
crucial factor for the success of this tendency. Sustainable building systems can have a direct
implication on the betterment of livelihood conditions of communities. Unfortunately, the
extraction of natural aggregates has led to establishing human made quarries that have drastic
environmental impact on the nature and surroundings.
Sustainable materials are currently widely considered and investigated in construction
engineering research. Some examples of sustainable research worldwide are the use of
recycled concrete aggregates, coal fly ash, ground clay brick and pervious paver block
system. Further, substantial research work has been conducted on fiber-reinforced concrete
which is a concrete primarily made of a mix of hydraulic cement, aggregates, water and
reinforcing fibers.
The high demand for concrete in the construction using normal weight aggregates such as
gravel and granite drastically reduces the natural stone deposits and this has damaged the
environment thereby causing ecological imbalance. Therefore, there is a need to explore and
to find out suitable replacement material to substitute the natural stone. In developed
countries, the construction industries have identified many artificial and natural lightweight
aggregates (LWA) that have replaced conventional aggregates thereby reducing the size of
structural members. However, in Asia the construction industry is yet to utilize the advantage
of LWC in the construction of high rise structures. Coconut Shell (CS) are not commonly
used in the construction industry but are often dumped as agricultural wastes.
The aim of this study is to spread awareness of coconut fibres as a construction material.
Typical concrete is a mixture of fine aggregates, coarse aggregates, cement and water.
Because of its convenient use, it is not only used in building construction but also in other
areas roads, harbors, bridges and many more. The usage of concrete is very wide. It is one of
the most important constituent materials. It is comparatively economical, easy to make offers
continuity solidity and indeed it lays the role of developing and improving our modern
society. Coarse aggregates not only constitute the bulk of concrete but also contribute the
most towards its compressive strength through high particle strength and close particle
interlock. But, the construction industry worldwide is facing a shortage of this natural
resource. The recycling of demolished masonry rubble as coarse aggregate in concrete is an
interesting possibility due to its environmental benefits. It is not only a viable alternative to
natural coarse aggregate but also solves the major problem of disposal of demolition of
waste. Recycling construction and demolition waste into aggregate would ultimately lead to
fewer quarries and landfills.
DESCRIPTIONS OF MATERIALS
Cement: Cement must develop the appropriate strength. It must represent the appropriate
rheological behaviour. Generally same types of cements have quite different rheological and
strength characteristics, particularly when used in combination with admixtures and
supplementary cementing materials. Ordinary Portland cement 43 grade brand name ACC
cement was used conforming to IS 8112 – 1989 and physical property was given below:
S.N.
Physical property
Test result
1.
Compressive Strength(MPa)
48.35
2.
Fineness (%)
6
3.
Specific Gravity
3.06
Fly Ash:
The burning of harder, older anthracite and bituminous coal typically produces Class F fly
ash. This fly ash is pozzolanic in nature, and contains less than 20% lime (CaO).
S.N.
Physical property
Test result
1.
Specific Gravity
2.37
2.
Bulk Density(kg/m3)
1050
Fine aggregate
Fine aggregate normally consists of natural, crushed, or manufactured sand. Natural sand is
the usual component for normal weight concrete. In some cases, manufactured light weight
particles used for lightweight concrete and mortar. The maximum grain size and size
distribution of the fine aggregate depends on the type of product being made. Sand
conforming to Zone-III was used as the fine aggregate, as per I.S 383-1970. The sand was air
dried and free from any foreign material, earlier than mixing.
S.N.
Physical property
Test result
3.
Fineness modulus
2.45
4.
Specific Gravity
2.64
5.
Bulk Density(kg/m3)
1530-1600
6.
Water Absorption (%)
0.80
Coarse aggregate
As coarse aggregates in concrete occupy 35 to 70% of the volume of the concrete. It may be
proper to categories the properties into two groups: exterior features (maximum size, particle
shape, textures) and interior quality (strength, density, porosity, hardness, elastic modulus,
chemical mineral composition etc.). Smaller sized aggregates produce higher concrete
strength. Particle shape and texture affect the workability of fresh concrete. The transition
zone between cement paste and coarse aggregates, rather than the properties of the coarse
aggregates itself.
Usually an aggregate with specific gravity more than 2.55 and absorption less than 1.5%
(except for light weight aggregates) can be regarded as being of good quality. Where
aggregates strength is higher, concrete strength is also higher. Crushed granite was used as
coarse aggregate of size 20 mm and 10 mm both.
S.N.
Physical property
Test result
1.
Maximum Size (mm)
20
2.
Fineness modulus
7.25
3.
Specific Gravity
2.70
4.
Bulk Density(kg/m3)
1480-1610
5.
Water Absorption (%)
.12
6.
Aggregate Crushing Value (%)
16.60
7.
Aggregate Impact Value (%)
11.01
Coconut Shell: In this work coconut shell was used as partial replacement of coarse
aggregate which is crushed granite. Coconut shells were unruffled from the local temple after
that it was cleaned, sun dried, removed fibers to evaluate its properties. Coconut shell needs
no pre treatment, except for water absorption. Coconut shell has very high water absorption.
Due to this property, before use coconut shells were soaked in potable water for 24 hours.
S.N.
Physical property
Test result
1.
Maximum Size (mm)
20
2.
Fineness modulus
6.48
3.
Specific Gravity
1.56
4.
Bulk Density(kg/m3)
510-600
5.
Water Absorption (%)
23
6.
Aggregate Crushing Value (%)
2.49
7.
Aggregate Impact Value (%)
8.55
8.
Moisture Content (%)
4.2
9.
Shell Thickness(mm)
3-6
Fly Ash: Fly ash has been used extensively in concrete for many years. Fly ash much more
variable than silica fumes in both their physical and chemical characteristics. In general, fly
ash is used at about 15-25% of the cement content.
Because of the variability of the fly ash produced even from the single plant, quality control
is very important. This involves determination of the blain specific surface area, as well as
the chemical composition. It is also very important to check the degree of crystallinity.
The compressive strength of 150×150×150 mm3 cubes and flexural strength of 150×150×700
mm3 was measured according to IS 516:1959 [179].
Compressive Strength Test
For compressive strength test cubes of size 150×150×150 mm3 made. Test was done on the
hydraulic testing machine. Compressive strength is defined as resistance of concrete to axial
loading. Cubes are put in the machine and after tighten its wheel start button is pressed as
pressure is begin to apply. Reading of meter is note down when cracks are there on cubes.
Compressive strength is calculated by following formula:
Compressive Strength =
P
A
Where P is load and A is area of cube
Fig: Compressive Testing Machine
Workability Test
The word ‘workability’ signifies much wider and deeper meaning than the other terminology
“consistency” often used loosely for workability. Consistency is to indicate the degree of
fluidity or degree of mobility. A concrete which has high consistency and which is more
mobile, need not be of right workability for a particular job. Every job requires a particular
workability. There are several factors which affect the workability:
i.
Water content
ii.
Mix proportions
iii.
Shape of aggregates
iv.
Size of aggregates
v.
Surface texture of aggregates
vi.
Grading of aggregates
vii.
Use of admixtures
Measurement of Workability
Some of tests measures the parameters very close to workability and provide useful
information. The following tests are commonly employed to measure workability.
1. Slump test
2. Compacting factor test
3. Flow test
4. Vee Bee consistometer test
Slump test
It is most commonly method used to measure consistency or workability of concrete. It is not
an appropriate method for very wet and for very dry concrete. It neither measures all the
factors that contributing to workability, nor always show placability of the concrete. It is used
for the reason of the consistency of freshly mixed concrete, in which the maximum size of the
coarse aggregate used does not exceed 38 mm. Workability of concrete is generally affected
by consistency i.e. mixture with extra water will be extra workable than drier mixes, however
concrete of the same consistency may differ in workability. It is also used to find out
consistency between batches to batches. The apparatus used for conducting the slump test
consists of a metallic mould in form of a frustum of a cone. The size of the slump cone is
diameter at top 10 cm, 20-cm diameter base and 30 cm height. Repeated batch of the same
mix, brought to same slump, will have the same water content ratio provided the weights of
aggregate, cement and admixtures are uniform and aggregate grading is within acceptable
limits. The deformation shows the characteristics of concrete with respect to tendency for
segregation The mould is filled in four layers, each approximately ¼ of height of the mould.
To compact each layer concrete after mixture fills ¼ is tamped 25 times by the rod it should
be noted that blows should vary entire surface area. Types of slump are as follows.
Collapse: In a collapse slumps the concrete collapses completely.
Shear: If one half of the cone slides down then it is called shear slump.
True: If concrete slumps evenly it is called true slump
Compaction factor test
Compacting factor of fresh concrete is done to determine the workability of fresh concrete by
compacting factor test as per IS: 1199 – 1959. It is more precise and sensitive than slump test
and is particularly useful for concrete mixes of very low workability as are normally used
when concrete is to be compacted by vibration. This test gives behaviour of concrete in the
action of external forces. By this the compactability of concrete, by measuring the level of
compaction. This test is best for mixes having low and medium workabilities i.e. compaction
factor in between 0.91 to 0.81, but it is not suitable for concretes which have very low
workabilities, i. e. the compaction factor below 0.71.
The apparatus, which is commercially available, consist of a rigid frame that supports two
conical hoppers vertically aligned above each other and mounted above a cylinder. The top
hopper is slightly larger than the bottom hopper, while the cylinder is smaller in volume than
both hoppers. To make this test, the top hopper is filled with mixture without compacted. The
flap on the bottom of this top hopper is opened and now concrete is permitted to fall into the
lower hopper. Once all the mixture has fallen from the top hopper to the bottom hopper, the
door located on the lower hopper is now opened to allow the concrete to fall into the bottom
cylinder. To force down cohesive concretes from the hoppers a tamping rod can be used. The
excess concrete is carefully removed from the top of the cylinder and the weight of the
mixture in the cylinder is recorded. This weight measured is compared to the weight of the
fully compacted mixture in the same cylinder achieved by tampering from rod. The
compaction factor is defined as the ratio of the weight of mixture in the cylinder under
gravity force to the fully compacted mixture in that cylinder with rod. The standard test
apparatus, described here, is appropriate for maximum aggregate sizes of up to 20 mm. A
larger apparatus is available for concretes with maximum aggregate sizes of up to 40 mm.
The compaction factor test provides us the workability more accurate than slump test.
CASTING OF CONCRETE CUBES
The moulds of size 150×150×150 mm3 are kept ready before mixing. Total 36 cubes are
casted. The bolts of the moulds carefully tightened because if bolts are not kept tight the
concrete mixture coming out of the mould when vibration takes place. Then moulds are
cleaned and oiled on all contact surfaces of the moulds and place the moulds on vibrating
table. The concrete is filled into moulds in layers and then vibrated. The top surface of
concrete is struck off level with a trowel. The number and date of casting are put on the top
surface of the cubes.
TESTS FOR CONCRETE
Test for Compressive strength of concrete cubes
To calculate the compressive strength of concrete cubes the universal testing machine (UTM)
having capacity of 2000 KN was used. In this test the strength obtained in KN. The measured
compressive strength of the specimen shall be calculated by dividing the maximum load
applied to the specimen during the test by the cross sectional area calculated from mean
dimensions of the section and shall be expressed to the nearest N/mm2. Compressive strength
is defined as resistance of concrete to axial loading. Cubes are put in the machine and after
tighten its wheel start button is pressed as pressure is begin to apply. Reading of meter is note
down when cracks are there on cubes. Compressive strength is calculated by following
formula:
Compressive Strength =
P
A
Where P is load and A is area of cube
Days
Conventional
10%CS and
25% fly ash
20%CS and
25% fly ash
30%CS and
25% fly ash
7
29.78
26.08
24.54
22.89
14
31.56
28.13
26.23
25.36
28
36.44
33.56
32.75
29.39
Fig: Testing of cubes
Workability test results
S.N
Slump (mm)
1
Conventional
84
2
10%CS and 25% fly ash
35
3
20%CS and 25% fly ash
41
4
30%CS and 25% fly ash
47
Compaction Factor
1
Conventional
0.912
2
10%CS and 25% fly ash
0.916
3
20%CS and 25% fly ash
0.917
4
30%CS and 25% fly ash
0.922
CONCLUSIONS
1. The slump of the concrete increased when the percentage of coconut shell increases
and decrease as comparison with the conventional concrete.
2. The compaction factor increased when the percentage of coconut shell increases and
increased as comparison with the conventional concrete.
3. The specific gravity of coconut shell is lower than to the coarse aggregate and the
water absorption is higher for coconut shell than coarse aggregate so the strength
decreased as comparison with the conventional concrete.
4. 25% fly ash when replaced with cement and coconut shell as 10%, 20%, and 30%
when replaced with coarse aggregate it is found that compressive strength of concrete
is lower when compared to conventional concrete.
5. The compressive strength of the cubes reduced as the replacement with coconut shell
increased.
6. The cube compressive strength of concrete at the age of 7 days resulted in marginal
reduction with 10% and 20% replacement of coarse aggregate with coconut shell.
FURTHER SCOPE OF WORK
1. The study can be carried out with varying percentage substitution of the material for
specific low cost housing applications.
2. The properties like water absorption, light weight concrete and study on economic
aspects can be carried out.
3. The effect of temperature on the concrete developed can be studied.
4. The study can be extended to assess the durability aspects of the concrete with
varying replacement proportions.
5. Many other waste materials can be also used in low cost constructions.
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