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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.