Post on 19-Mar-2020
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CHAPTER 5
FRESH AND HARDENED PROPERTIES OF
CONCRETE WITH MANUFACTURED SAND
5.1 GENERAL
The material properties, mix design of M 20, M 30 and M 40
grades of concrete were discussed in the previous chapter. In this chapter, the
fresh concrete property such as workability and the hardened properties such
as compressive strength, splitting tensile strength, modulus of rupture,
modulus of elasticity and Poisson’s ratio of concrete are studied.
5.2 TEST DETAILS
5.2.1 Workability
Workability is one of the important parameters of measuring the
consistency of the fresh concrete. Slump test is the most commonly used
method of measuring the consistency of the concrete. In this research work,
the workability of the M 20, M 30 and M 40 grades of concrete with different
proportions of manufactured sand varying from 0 to 100% as the increments
of 10% in the order of A to K are measured by the slump cone apparatus as
per IS: 1199 – 1959.
5.2.2 Compressive Strength
In most structural applications, concrete is employed primarily to
resist the compressive stresses. Therefore, concrete making properties of
various ingredients of mix are usually measured in terms of the compressive
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strength. Compressive strength is also used as a qualitative measure for other
properties of hardened concrete. The compressive strength of concrete cube
was determined based on IS: 516 –1959. Three cubes of size 150mm x
150mm x 150mm were tested for each trial mix combination at the age of 7,
28, 56, 90 and 365 days of curing using a compression testing machine.
5.2.3 Splitting Tensile Strength
This is an indirect test to determine the tensile strength of the
cylindrical specimens of size 150mm diameter and 300mm height. Splitting
tensile strength was determined in accordance with IS: 5816-1970. The test
was carried out by placing a cylindrical specimen horizontally between the
loading surface of a compression testing machine and the load was applied
until the failure of the cylinder, along the vertical diameter. In order to reduce
the magnitude of the high compressive strength near the point of loading,
narrow packing of plywood was placed between the specimen and the loading
plates of the machine.
5.2.4 Flexural Strength
Flexural strength of the concrete was measured by the prism
specimens of size 100mm x 100mm x 500mm and tested as per IS: 516-1959.
The bed of the testing machine was provided with two steel rollers of 38mm
in diameter on which the specimen was supported, and these rollers were
mounted at the distance of 40mm from center to center. The system of loading
was symmetrical two point loading.
5.2.5 Modulus of Elasticity and Poisson’s Ratio
Concrete is not a perfectly elastic material. The modulus of
elasticity was determined as per IS: 516 –1959, subjecting the cylinder to uni
- axial compression and measuring the deformations by means of dial gauges
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fixed between the certain gauge length which is shown in Figure 5.1. The
stress–strain curve was established from the readings. The modulus of
elasticity was calculated from the stress–strain curve.
Poisson’s ratio is calculated from the cylinder subjected to uni -
axial compression and measuring the change in dimensions in longitudinal
and lateral directions by means of dial gauges fixed on both the directions.
Poisson’s ratio was calculated as the ratio between the lateral and longitudinal
strain.
Figure 5.1 Modulus of elasticity test set up
5.3 DISCUSSION OF TEST RESULTS
5.3.1 Workability
Figure 5.2 shows the slump values of M 20, M 30 and M 40 grades of
concrete with various replacement levels of manufactured sand from 0 to 100%.
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Figure 5.2 Slump values of M 20, M 30 and M 40 grade concrete with MS
From the Figure 5.2, it is observed that the slump values are
reduced while increasing the replacement levels of manufactured sand for all
the three grades of concrete. The shape and surface texture of the
manufactured sand have a significant effect on the water requirement of the
mix. The round shape and smooth surface texture of natural sand reduces the
inter particle friction in the fine aggregate component, so that the workability
is high in natural sand. Manufactured sand is angular in shape and the rough
surface texture improves the internal friction in the mix, which reduces the
workability of the concrete. The results indicate very low slump values in
80 %, 90 % and 100 % of manufactured sand due to the presence of a large
amount of fines in it.
5.3.2 Compressive Strength
Figures 5.3(a), (b) and (c) show the compressive strength of M 20,
M 30 and M 40 grades of concrete. The rate of increase in strength of M 20,
M 30 and M 40 grades of concrete are given in Figures 5.4 (a), (b) and (c).
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Figure 5.5 shows the comparison between the compressive strength of M 20,
M 30 and M 40 grades of concrete with MS.
(a) M 20 grade concrete
(b) M 30 grade concrete
(c) M 40 grade concrete
Figure 5.3 Compressive strength of M 20, M 30 and M 40 grade
concrete with MS
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(a) M 20 grade concrete
(b) M 30 grade concrete
(c) M 40 grade concrete
Figure 5.4 Compressive strength achievements of M 20, M 30 and M 40grade concrete with MS
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Figure 5.5 Comparison between the compressive strength of M 20,M 30 and M 40 grade concrete with MS
From Figures 5.3(a), (b) and (c), it is observed that the compressive
strengths are increased with the increase in percentage of manufactured sand
for all the three grades of concrete. This is due to the rough surface and
angular particles of the manufactured sand crates better interlocking between
the aggregate and the hydrated cement paste.
From Figures 5.4 (a), (b) and (c), it is noticed that the rate of
increase of strength at 7 days is higher for M 30 and M 40 grades of concrete
when compared to the M 20 grade concrete due to the high cement content
and less w/c ratio.
Figure 5.5 indicates that there is no significant change for the
proportions H and K. It states that even though the strength is increased for
100% manufactured sand, there is no significant improvement in the strength
achievement beyond 70% of manufactured sand due to the large amount of
fine particles present in 80, 90 and 100% of manufactured sand
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5.3.3 Splitting Tensile Strength
The tensile strength achievements of M 20, M 30 and M 40 grades
of concrete are depicted in Figures 5.6(a) , (b) and (c).
(a) M 20 grade concrete
(b) M 30 grade concrete
(c) M 40 grade concrete
Figure 5.6 Tensile strength achievements of M 20, M 30 and M 40grade concrete with MS
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Figure 5.7 Comparison between the splitting tensile strength of M 20,M 30 and M 40 grade concrete with MS
Figures 5.6 (a), (b) and (c) show the tensile strength achievements
of M 20, M 30 and M 40 grades of concrete with various proportions of
manufactured sand from 0 to 100% at various curing periods. From the
Figures, it is noticed that the splitting tensile strength achievement of the
concrete is increased when the percentage of manufactured sand is increased
up to 70%. The strength achievement is higher at an early period and it is
also noted that it is increased for M 40 grade concrete when compared to the
M 20 and M 30 grades of concrete due to the high cement content and less
water content.
Figure 5.7 shows the comparison between the splitting tensile
strengths of M 20, M 30 and M 40 grades of concrete with the proportions of
A, H and K. From the Figure, it is found that there is no significant change for
the proportions H and K. It indicates that beyond 70% of manufactured sand,
there is no improvement in the strength due to the presence of large amount of
fines in the remaining proportions of manufactured sand.
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5.3.4 Flexural Strength
The flexural strength of M 20, M 30 and M 40 grades of concrete
are shown in Figures 5.8(a), (b) and (c).
(a) M 20 grade concrete
(b) M 30 grade concrete
(c) M 40 grade concrete
Figure 5.8 Flexural strength of M 20, M 30 and M 40 grade concretewith MS
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Figure 5.9 Comparison between the flexural strength of M 20, M 30and M 40 grade concrete with MS
Figures 5.8 (a), (b) and (c) show the flexural strengths of M 20, M
30 and M 40 grades of concrete with various proportions of manufactured
sand from 0 to 100% during the various curing periods. From the Figures, it is
found that the flexural strengths are increased with the increase in percentage
of manufactured sand up to 70%. The flexural strength achievements are
80%, 137% and 144% at 7 days, 56 days and 365 days respectively, when
compared to the conventional concrete of 28 days strength in M 20 grade
concrete. For M 30 and M 40 grades of concrete, the strength achievements
are increased at an early period and reduced at a later period.
Figure 5.9 shows the flexural strengths of A, H and K proportions
of three grades of concrete. From the Figure, it is clearly understood that there
is no improvement in the flexural strength beyond 70% of manufactured sand.
This is because beyond 70% the manufactured sand has a large amount of fine
particles in it.
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5.3.5 Modulus of Elasticity and Poisson’s Ratio
The modulus of elasticity of M 20, M 30 and M 40 grades of
concrete with various proportions of manufactured sand at 28 days is shown
in Figure 5.10.
Figure 5.10 Modulus of elasticity M 20, M 30 and M 40 grade concretewith MS
Figure 5.11 Comparison between the modulus of elasticity of M 20, M 30and M 40 grade concrete with MS
From the Figure 5.10, it is clearly understood that the modulus of
elasticity is increased with the increase in proportions of manufactured sand
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up to 70%. Beyond 70% of manufactured sand, the elasticity values are
reduced due to the presence of large amount of fine particles that reduce the
filling of cement content in the voids. Figure 5.11 shows the modulus of
elasticity of proportions A, H and K of all the three grades of concrete. It
states that the modulus of elasticity is high for proportion H due to the
presence of less amount of fines in it. Poisson’s ratio values are
experimentally determined as 0.15 to 0.16 for all the three grades of concrete
with various proportions of manufactured sand.
5.3.6 Relationship Between the Mechanical Properties of the Concrete
The relationship between the mechanical properties of the concrete
are given in Figures 5.12 and 5.13.
Figure 5.12 Splitting tensile strength Vs Compressive strength
Figure 5.13 Flexural strength Vs Compressive strength
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The compressive strength and the splitting tensile strength results
are plotted as a graph, shown in Figure 5.12. Based on these results, an
analytical equation was developed for determining the relationship between
these two as follows:
ft = 0.395 fck (5.1)
whereas for normal concrete as per ACI 318 - 89, ft = 0.32 to 0.36 fck.
Hence the splitting tensile strength slightly increases for concrete with
manufactured sand due to the angular particles in it.
The flexural strength and compressive strength test results are plotted
as a graph, and given in Figure 5.13. An analytical equation for the relationship
between these two was derived from the test results as given below:
fr = 1.041 fck (5.2)
whereas for normal concrete as per IS 456 – 2000, fr = 0.7 fck.
Hence the flexural strength slightly increases for concrete with manufactured
sand due to the angular particles of the manufactured sand.
The relationship between the modulus of elasticity and compressive
strength was calculated from the experimental results as,
E = 5100 fck (5.3)
whereas for normal concrete as per IS 456 – 2000, E = 5000 fck. Hence the
modulus of elasticity slightly increases for concrete with manufactured sand
due to the angular particles of the manufactured sand.
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5.4 CONCLUDING REMARKS
The conclusions from the experimental investigations are as
follows:
Concrete with manufactured sand significantly improves the
strength properties of the concrete. The rough texture and angular particles of
manufactured sand create better interlocking between the particles and the
cement paste which improves the strength properties of concrete just as the
less w/c ratio increases the strength of the concrete.
Blending of 70% manufactured sand with 30% natural sand has
higher strength properties. The presence of small amount of fines in 70%
manufactured sand increases the strength and elasticity properties of the
concrete. Due to the presence of large amount of fines in 80, 90 and 100% of
manufactured sand, there is no improvement in the strength development. The
relationship between the compressive strength with splitting tensile strength,
flexural strength and modulus of elasticity are higher than the standards set
forth by IS specifications.