TABLE OF CONTENT

CONTENT PAGE

1. Title 1

2. Introduction 2-3

3. Objective 4

4. Apparatus and Materials 4-5

5. Procedure 6-7
A） Compression Test
B） Flexural Test

6. Results 8-9

7. Discussion 10 - 12

8. Conclusion 13

9. Reference 14

10. Appendix 15 - 24

1. TITLE

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C5 – Mechanical Properties of Hardened Concrete Based

2. INTRODUCTION

Mechanical properties of concrete refer to the physical properties of the concrete

when there is load acting on it. Example of mechanical properties are compressive
strength, tensile strength and flexural strength. Compressive strength of a concrete is a
very crucial property as it shows the ability of the concrete to carry loads without cracks
or damages. Some of the factors that affect compressive strength are water-cement
ratio, compaction of concrete and aggregate-cement ratio. Compressive strength
formula is load applied at a point to the cross-sectional area of the hardened concrete.

Compressive Strength=Load / Cross-sectional area

Concrete has relatively high compressive strength, but significantly lower tensile
strength. As a result, without compensating, concrete would almost always fail from
tensile stresses – even when loaded in compression. The practical implication of this is
that concrete elements subjected to tensile stresses must be reinforced with materials
that are strong in tension. The elasticity of concrete is relatively constant at low stress
levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete
has a very low coefficient of thermal expansion, and as it matures concrete shrinks. All
concrete structures will crack to some extent, due to shrinkage and tension. Concrete
which is subjected to long-duration forces is prone to creep. The density of concrete
varies, but is around 2,400 kilograms per cubic metre ( Jones, Katrina, 1999 )

Concrete is used for structural purposes such as beams and floors. With the variety
of uses of concrete, the concrete must be capable in taking the loads applied. It is crucial
to check the quality of the concrete for safety, financial and convenience purposes.

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Therefore, Cube Test of Concrete is carried in order to determine if the target
compressive strength is achieved or if the concrete is suitable to be used or not. After
24 hours these cubes are removed from the mould and cured under water. The edges
must be smooth before they are inserted in water for curing ( Team WFM, 2017 ). The
purpose of doing the cube test is determining the strength of concrete, or whether or not
it is suitable to be used at all. With the huge variety of uses for concrete, it’s important
to fully aware of the quality of mixture, for both safety, financial and convenience
reasons ( What is The Concrete Cube Test?, n.d. )

Mixing of concrete is done first before it is poured into the moulds. After the fresh
concrete is poured into the moulds, the concrete is let sit for 24 hours. Then, the moulds
will be removed and the specimens will be put in water for curing. After 28 days, the
cubes are removed from curing tank and are dried. The test is then carried because the
rate of compressive strength is at its maximum during the first 28 days then it will slows
down. The concrete strength achieves 99% at 28th day which almost achieve the final
strength and so the concrete are reliable. The result is used as the base for the design.
Calibrated compression machine is used to test it. The machine exerts a strong force
onto the cube until the cube fails or cracks. The rate of loading at failure is the maximum
strength of the concrete ( Gopal Mishra, n.d. )

The factors that affecting the strength of concrete is affected by many factors, such
as quality of raw materials, water/cement ratio, coarse/fine aggregate ratio, age of
concrete, compaction of concrete, temperature, relative humidity and curing of concrete
( Gopal Mishra, n.d. ).

3. OBJECTIVE

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To test mechanical properties of hardened concrete based on concrete samples made in
C4 to determined strength required for a particular project.

4. APPARATUS

Compression Machine, flexural test machine, Curing Tank, Blanket.

MATERIALS

Test specimens ( Cubes and Beam ).

Figure Apparatus and Materials

Figure 1 shows compression

machine that used to test the
compressive strength of specimens.

Figure 1: Compression Machine

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 Figure 2 shows flexural test machine
that used to test the flexural strength
of specimens.

Figure 2: Flexural Test Machine

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 5. PROCEDURE

A) COMPRESSION TEST

The compression test of cube is carried out according to BS 1881 :

Part 116 : 1983 : The Compressive Strength of Cubic Concrete Specimens ( refer to
Appendix 1 Procedure III ).

Some modification have been made in this test is the cylinder does not use in this
test.

The compressive strength of the specimens are calculated using the

formula :-
𝐹𝑎𝑖𝑙 𝑙𝑜𝑎𝑑 ( 𝑁 )
𝐶𝑜𝑚𝑝𝑟𝑒𝑠𝑠𝑖𝑣𝑒 𝑠𝑡𝑟𝑒𝑛𝑔𝑡ℎ =
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑎𝑟𝑒𝑎 ( 𝑚𝑚2 )

Figure 3 : Compressive test of specimen

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 B) FLEXURAL TEST

The compression test of cylinder is carried out according to BS 1881 :

Part 116 : 1983 : Method for determination of flexural strength ( refer to Appendix 2 ).
The flexural strength of the specimen is calculated using the following
equation:-
𝐹× 𝑙
𝐹𝑐𝑓 =
𝑑1 × 𝑑2 2

Where:
F = breaking load ( in N )
d1 and d2 = lateral dimensions of the cross – section ( in mm )
l = distance between the supporting rollers

Figure 4 : Flexural test of specimen

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 6. RESULT

A) COMPRESSION TEST

Cube Dimensions Weight Volume Fail Load Strength

( mm ) ( kg ) ( mm3 ) ( kN ) ( N/mm2 )

1 150 x 150 x 7971.0 3.375x106 408.78 18.168

150
2 150 x 150 x 7722.0 3.375x106 443.80 19.725
150
3 150 x 150 x 7801.0 3.375x106 413.05 18.358
150

Average Compressive 18.168 + 19.725 + 18.358

=
Strength of Cube 3
= 18.75 N/mm2

Average Maximum Load 408.78 + 443.80 + 413.05

Applied = 3

= 18.75 N/mm2

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CALCULATIONS

CUBE 1
408.78 x 103 N
Compressive strength =
150mm x 150mm
= 18.168 N/mm2
CUBE 2
650.45 x 103 N
Compressive strength =
150mm x 150mm
= 19.725 N/mm2

CUBE 3
413.05 x 103 N
Compressive strength =
150mm x 150mm
= 18.358 N/mm2

B) FLEXURAL TEST

Dimensions Weight Distances Fail Load Strength

( mm ) ( kg ) ( mm ) ( kN ) (N/mm2)
Beam 500 x 100 x 11742.0 300 12.30 3.69
100

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CALCULATIONS:

𝐹× 𝑙
Flexural strength, Fcf =
𝑑1 × 𝑑2 2

12.30 x 103 N x 300 mm

=
100 mm x 1002 mm

= 3.69 N/mm2

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 7. DISCUSSION :

From the results, the average compressive strength of 3 cubes for 28 days that
we obtained are 18.75 N/mm2 . The characteristic strength that we used in mix design
form is 25 N/mm2 at 28 days but the actual average compressive strength that we
obtained in the result is 18.75 N/mm2. Therefore, our samples are failed.

The factors that cause our compressive strength do not achieve the
characteristics strength in the mix design form are the concrete do not evenly compacted
in the mould causes our compressive strength of hardened concrete at 28 days became
lower and do not achieved the strength required. Besides, the water cement ratio is high
causes the concrete becomes more wet. The higher the water cement ratio cause the
concrete has less strength but the workability of this concrete increase and our concrete
has undergo bleeding process. After the compressing test, we found out that there is
many hole in our concrete.

Figure 5

Furthermore, the uneven surface of concrete when the surface of the concrete is
been compressed also cause compressive strength to decrease.

To make sure the concrete increase in strength after 24 hours, curing process is
needed. Concrete will gain in strength but the hydration process is still continues so the
concrete need to put inside the curing tank. Higher strength of concrete is produced
when the period of time for curing increases. One of the factor that cause our concrete
does not reach the required strength is improper curing for example the curing tank does
not fully filled with water cause our concrete did not fully cured.

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 In the curing tank, our cubes and beams are placed inside bottom of the curing
tank because of that there are external loads such as concrete cubes, columns and beams
from the other groups will placed above our concrete. This cause our concrete need to
sustain extra loads from other concrete and a small reduction in volume of our concrete.
A concrete that deform elastically when subjected to an external load is called creep.
Due to mechanical stress like other concrete are placed on our concrete in the curing
tank, our concrete will deform slowly. The deformation will increase with time if the
loading increases. Therefore, we can conclude that the reduction in volume of cubes
and beams is because of the creep.

The flexural strength of beam for 28 days is 3.69 N/mm2. From the theory, the
flexural test is used to determine the tensile strength of concrete. The tensile strength
of concrete is normally weaker than the compressive strength. Our compressive
strength results in 28 days is higher than flexural strength in 28 day. Hence our
experiment is successful because the strength of the samples is follow according to the
theory. Our flexural strength is very small if compared to other groups. The main reason
is do not evenly compacted in the mould causes our compressive strength of hardened
concrete at 28 days became lower and do not achieved the strength required. Besides,
the water cement ratio is high causes the concrete becomes more wet.

There are some sources of error in this experiment. First, the sensitivity of
compression testing machine and flexural testing machine is not sensitive cause the
accuracy of the result to be reduced. Besides, the scale of the electronic balance do not
start from zero cause weight of cubes and beams is slightly different.Finally is when
getting the coarse aggregate from large bucket with water, we does not clear the
remaining water in our bucket .

There are some precautionary steps that are needed to be taken in this
experiment. First, the cubes and beams should be placed correctly inside the
compression machine and flexural test machine so that the testing can be done
accurately. Besides, parallax error should be avoided when taking the dimension of the
concrete after the concrete is removed out from the curing tank.

There are some factors that will affect the compressive strength of hardened
concrete such as aggregates, water/cement ratio and others. The fineness modulus of

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the aggregates will affect the compressive strength of the concrete. A change of fineness
modulus of mixed aggregates cause the compressive strength of concrete change.
Rough surface texture and angular shape of coarse aggregate will increase the
compressive strength of concrete than the smooth and rounded coarse aggregate at the
same water/cement ratio.

Water/cement ratio also can affect the compressive and flexural strength of
concrete. With the increase of water/cement ratio, the compressive strength decrease.
This is because diluted paste will be produced when more water to be added that cause
concrete more weaker and shrinkage. Adding more water also cause concrete to be
more porous and this will reduce compressive strength.

Figure 6 : Porous is observed

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8. CONCLUSION :

In this experiment, the mechanical properties of hardened concrete based on

concrete samples made in C4 to determine strength is tested. Based on the results,
The characteristic strength that we used in mix design form is 25 N/mm2 at 28 days
but the actual average compressive strength that we obtained in the result of cube
is 18.75 N/mm2 and for beam is 3.69 N/mm2. Thus, our samples failed. First, the
concrete do not evenly compacted in the mould causes our compressive strength of
hardened concrete at 28 days low and do not achieved the required strength.
Secondly, the higher the water cement ratio cause the concrete has less strength but
the workability of this concrete increase. Moreover, the uneven surface of concrete
when the surface of the concrete is been compressed also cause compressive
strength to decrease due to mechanical stress like other concrete are placed on our
concrete in the curing tank causes our concrete will deform slowly. Therefore, many
factors affect the compressive strength of the concrete.

1. REFERENCE :

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Mishra, G. Factors Affecting Strength of Concrete, Why We Test Concrete
Compressive Strength after 28 Days?

Retrieved from
https://theconstructor.org/concrete/factors-affecting-strength-of-concrete/6220/
https://theconstructor.org/concrete/why-we-test-concrete-strength-after-28-
days/6060/

What is The Concrete Cube Test? - EasyMix Concrete UK Ltd

Retrieved from

www.easymixconcrete.com

Team WFM, 2017 Concrete Cube Test to Determine the Comprehensive Strength of
Concrete

Retrieved from

https://www.wfm.co.in/what-is-cube-test-of-concrete/

Jones, Katrina (1999). "Density of Concrete"

Retrieved from

The Physics Factbook.

2. APPENDIX

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Appendix 1

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Appendix 2

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