Compressive strength and Flexural of Hardened Concrete | Jameel Academy

#Jameel_Academy_Concrete_Tests

1. University of Duhok
College of Engineering
Civil Department
Concrete Technology – Practical
Concrete Laboratory



A Report About :


Compressive and Flexural strength of
hardened Concrete





Submitted By : Jameel Masoud Jameel

Lab. No. : 9 & 10
Group Name : B1

Testing Date : 12 / 1 / 2018
Submitting Date : 16 / 1 / 2018

Supervised By : Youkhanna

2017 – 2018

2. References :



1) ASTM C 39/C 39M – 01
2) BS 1881 - 116: 1983
3) ASTM C78
4) BS 1881 - 118




Introduction :

Flexural Strength : or (modulus of rupture), is one of the material property, Which
is the stress in a material just before Failure due to flexure test. The Flexural test
used to determine the tension indirectly using prisma Shape and its apparatus.

Compressive Strength: The most commonly used test in construction which is the
Ability of material (Concrete) to resist axially directed Compression forces. When
the limit of compressive strength is reached, the material can't resist any force, then
the materials are crushed (damaged). The cube of concrete that used in test, which
its dimensions are (150mm × 150mm × 150mm), The compressive strength is used
to determine the hardness of cubical specimens of cement mortar. And to know the
ability of cement mortar to resist a load.

3. Purpose :


This test method is used to determine flexural and compressive strength of
specimens prepared and cured in accordance with ASTM and BS standards
respectively.


Materials :

1) O.P.C.
2) Water.
3) Sand (fine aggregate).
4) Gravel (coarse aggregate)
5) Oil.


Equipment :



1) Universal Compression Machine.
2) Standard Cylinders (150mm dia. ×300 mm height).
3) Standard Cubes (150×150×150) mm.
4) Tamping rod: (a round straight rod, 16mm in diameter rod used to
compact cylindrical samples) or (square steel rod having a cross-sectional
area of 1”×1” used to compact cubical samples).
5) Curing bath.
6) Mechanical pan mixer.
7) Balance.
8) Trowel and Scoop and Plastic grooves.
9) Loading apparatus (use three point loading).
10) Standard prisms (150×150×500) mm or (100×100×400) mm.

4. Sketches :









Mixer Testing machine Sensitive balance












Standard Cubes and Prism Loading apparatus for Flexural Strength

`








hand Cover Curing Bath Trowel and Tamping rod

5. Procedures for Flexural Strength :

1) Clean the prisms and coat the inside faces with oil, then place on a clean,
level and firm surface.
2) Weigh the cement, sand, gravel and water, according to mix design for
(????????????− =24 MPa) (1:1.8:3.5:0.45) with a required slump of (50-75) mm.
3) Mix the materials in order to produce a homogeneous fresh concrete in a
manner similar to procedures followed in test#10.
4) Perform the slump test as described in test#10 in order to check the required
slump (50-75) mm.
Using a scoop, place the freshly mixed concrete into the mold in two
layers. Compaction is achieved in two layers, each layer being compacted
by 64 strokes using the 16 mm dia. steel rod with a rounded end).
1. After completing the compaction of all samples, strike off excessive
concrete from surface of the molds to make a smooth and a level surface,
and store the specimens in a moist room in order to prevent evaporation of
water from the specimens.
2. De-mold specimens after 24 hrs. Then place in the water basin of
temperature (20±2 Co) for curing until time of testing (3, 7, 28, 90) days.
3. At the time of testing bring out the specimens from the curing basins, then
insure that the specimens are in SSD conditions prior testing.
4. Place the specimens under compression machine in a direction Normal to
the direction of casting. The rate of loading is sets to be (ASTM: 0.0143
and 0.020 MPa/sec, BS: 0.04 and 0.06 MPa/sec).
5. Start the test and apply the load to the specimens until the specimen is
broken into two parts exactly when the first crack is occurred at bottom
fibre of the beam. Record the load and then compute the flexural strength
and compute the average.

6. Procedures for Compressive Strength :

1) Clean the cylinders or cubes and coat the inside faces with oil, then place on a
clean, level and firm surface.
2) Weigh the cement, sand, gravel and water, according to mix design for (????????????− =24
MPa) (1:1.8:3.5:0.45) with a required slump of (50-75) mm.
3) Mix the materials in order to produce a homogeneous fresh concrete in a manner
similar to procedures followed in test#9.
4) Perform the slump test as described in test#10 in order to check the required
slump (50-75) mm.
5) Using a scoop, place the freshly mixed concrete into the mold in layers.
Compaction is achieved in three layers, (for cylinders, each layer being
compacted by 25 strokes using the 16 mm dia. steel rod with a rounded end), and
(for cubes, each layer being compacted by 35 strokes using square steel rod of
1”×1” ).
6) After completing the compaction of all samples, strike off excessive concrete
from surface of the molds to make a smooth and a level surface, and store the
specimens in a moist room in order to prevent evaporation of water from the
specimens.
7) De-mold specimens after 24 hrs. Then place in the water basin of temperature (20±2
Co) for curing until time of testing (3, 7, 28, 90) days.
8) At the time of testing bring out the specimens from the curing basins, then insure that
the specimens are in SSD conditions prior testing.
9) For cubes, place the specimens under compression machine in a direction perpendicular
to the direction of casting. For cylinders, place the specimens normal to the direction
of casting (after being capped). The rate of loading is sets to be (ASTM: 0.15-.34
MPa/sec, BS: 0.2-0.4 MPa/sec).
10) Start the test and apply the load to the specimens until the load indicator shows that the
load is decreasing and the specimen displays a well-defined fracture pattern as shown
in figure below.

7. Calculations and Results :


For Compressive Strength :

- We will determine the compressive strength of Cubes by using this Formula :

??????��������??????� ��������=
�????????????��??????� ��??????�
??????����−�������??????� ??????��??????


Area of each cubes : A = 150mm × 150mm = 22500m�
??????


With different Cube we have different Load :

For Example: Compressive strength For Cube (1)=
Load
Area
=
757100 N
????????????�????????????��
??????
= 33.64
??????
��
??????


For more details :
Cube Area (mm
2
) Load (kN) Compressive Strength (MPa)
1 22500 757.1 33.64
2 22500 751 33.38
3 22500 784 30.84
4 22500 752 33.42
Average 32.8 MPa


For Flexure Strength :

Moment of Inertia of cross section (I) =
bh
3
12
=
100×100
3
12
=8.33 (10
6
) mm
4

Center of Cross-section (C) =
100 mm
2
=50 mm
Maximum Moment (M) =
P×L
4
=
10.61 (10
3
)×400
4
= 61 (10
6
) N.mm
Stress (??????) =
M×C
I
=
6.1 (10
7
)×50
8.33 (10
6
)
=366.2 N/mm
2


Flexure Strength (One Point) :
Flexural Strength =
3PL
2bd
2
=
3 × 10.61 (10
3
) ×400
2 ×100 ×100
2
=�.� �????????????

8. Discussion and Conclusion :

In this test we determine the compressive and flexural Strength of
Hardened Concrete, finally we got a result after doing all procedure
accurate, the average of all cubes For Compressive strength is (32.8
MPa) and flexural strength of our Prism is (6.4 MPa). Our cubes that
applied compressive strength was mixed with an proportion that must be
resist 24 MPa or greater, it shown that its created with best quality, but
the less flexure strength in concrete (6.4 MPa) doesn’t mean that our
prism was fail in flexure test because concrete doesn’t resist high tension
load and compressive strength of 3 to 4 times greater than Flexure
Strength. But the error that maybe we did are the aggregate doesn’t
absorb water sufficient, and some of cubes doesn’t compacted fully
…etc.

In conclusion the purpose of this test is to know what's thee tension and
compression strength and determine the resistance of concrete from
compression and tension load, finally we got the result, and the our
concrete that is used in test can be used in any construction project and
it can be used for resist 30 MPa of compression Strength and 6 MPa for
Flexural Strength.