C1 FRESH AND HARDENDED CONCRETE TEST
1.0
INTRODUCTION
The suitability of a
concrete for any task is initially assessed whilst that concrete is still in
its freshly mixed state before setting occurs. The test should give the answer
on the concrete workability, will it pump, segregate, air entrainments and
bleeds. Well established tests are used to categories fresh concrete properties.
Concrete is tested during
its fresh and hardened state mainly to ensure that concrete mix satisfies the
specification of works.
In its fresh state,
concrete is tested for its consistency so as to achieve the desired
workability. Workability is an important property in concrete since a workable
mix will produce concrete, which can be well compacted, transported and placed
without segregation. A well-compacted concrete will produce a good strength
concrete.
Tests to be conducted on fresh
concrete to measure its workability consist of:
1.
Slump
Test
2.
Compacting
Factor Test
3.
Vebe
Test
Hardened concrete tests to destruction
consist of:
1.
Compression
Test
2.
Indirect
Tension Test Methods
3.
Flexural
strength of concrete
2.0 OBJECTIVES
The objectives of the test are to
determine the properties of concrete as follows:
1.
Workability
of fresh concrete
2.
Strength
of hardened concrete
3.0 APPARATUS
FRESH CONCRETE TEST (WORKABILITY)
Slump Test:
1.
Mould
consisting of the frustum of a cone
2.
Standard
16 mm diameter steel rod, 600 mm long
3.
Measuring
scale
4.
Rigid
metal sheet
Compacting Factor Test:
1. Two
conical hoppers and a cylinder.
2. Weighing
machine
Vebe Time Test:
1.
An
open-ended cylinder
2.
A
vibrating table
3.
Glass
plate rider
4.
Metal
cone
5.
Stop
watch
6.
Standard
iron rod
HARDENED CONCRETE TEST
Compression Test:
1.
Standard
steel cube mould, 150 x 150 x 150 mm
2.
Standard
steel rod, 25 mm square
Indirect Tension Test Methods
(Cylinder Splitting Tension Test):
1.
Standard
steel mould, 150 mm diameter, 300 mm long
2.
Standard
steel rod, 16 mm diameter
Flexural
Strength of Concrete:
1.
Standard
beam measuring 100 x 100 x 500 mm long
2.
Standard
steel rod, 25 mm square
4.0 PROCEDURES
Preparation of concrete mix:
= volume of (3 cubes (150 x 150 x 150mm)
+
2 cylinders
(150mm dia. x 300mm) +
1 beam (100 x 100 x 500mm) +
test for workability)
= 0.0257 + 25% contingencies
= 0.032 m3
2.
Standard
mix-ST5 was selected from Table 3 BS 5528
3.
The
mix proportion was determined as given in Table 5 to produce concrete of 0.032
m3.
Example:
Standard mix ST5
Slump: 75 mm
Nominal Maximum size of aggregate:
20 mm
|
Constituent
|
From
Table 5: BS 5528 ( 1m3 concrete )
|
Test
requirement
(
0.032m3 )
|
|
Cement
|
340 kg
|
340 kg x
0.032 = 10.88 kg
|
|
Fine
aggregate
|
0.35 x
1830 kg = 640 kg
|
640 kg x
0.032 = 20.48 kg
|
|
Course
aggregate
|
(1830 –
640) kg = 1190 kg
|
1190 kg x
0.032 = 38.08 kg
|
|
Water (w/c
= 0.5)
|
0.5 x 340
kg = 170 kg
|
170 kg x
0.032 = 5.44 kg
|
4.
Cement,
fine and course aggregate were mixed in mixer for 1 minute.
5.
Water
was added in and mixes approximately for another 1 minute.
6.
When
the mix is ready, proceeds with the workability tests.
Slump Test
1.
The
cone was placed on a smooth, flat and clean surface.
2.
The
mould was filled with 3 layers of concrete approximately of the same thickness
each.
3.
Each
layer of concrete was compacted by tamping it 25 times with the standard steel
rod.
4.
The
top surface of the concrete was leveled with a trowel.
5.
Slowly
the cone was lifted vertically to allow concrete to subside.
6.
The
difference in level between the height of the mould and that of the highest
point of the subsided concrete were measured. This difference in height in mm
is taken as slump of concrete.
Compacting Factor Test
1.
The
apparatus were assembled vertically. Then the bigger hopper was placed
uppermost, the smaller hoper in the middle and the cylinder at the bottom.
2.
All
inside surface of hoppers were cleaned thoroughly to reduce friction.
3.
Each
hopper has hinged door (trap-door) at the bottom. Make sure that this door is
closed before commencing the test.
4.
The
upper hopper was filled up with concrete to the brim.
5.
The
door was released to let the concrete falls into the lower hopper.
6.
The
door of the second hopper was released to let the concrete falls into the
cylinder.
7.
Excess
concrete from the top of the cylinder was cut off by sliding it across with two
floats.
8.
The
net weight of the concrete was determined. This weight is known as “weight of
partially compacted concrete”.
9.
The
cylinder was emptied and refilled with the concrete from the same sample in
three layers. Each layer was tamped 25 times with standard steel rod.
10. The top surface of the cylinder was
leveled off and weighed it to the nearest 10gm. This weight is known as “weight
of fully compacted concrete”.
11. The compacting factor of concrete was
calculated as shown below:
|
|
Weight of fully
compacted concrete
|
|
Weight of
partially compacted concrete
|
|
The Compacting factor =
Vebe Test
1.
The
slump cone was placed inside the cylindrical pot of the Vebe apparatus.
2.
The
cone was filled with concrete as in the slump test.
3.
The
cone was removed and the glass plate rider was placed gently on top of the
concrete.
4.
The
vibrating table was switched on and a stopwatch was started simultaneously.
5.
The
vibration was continued until conical shape oft the concrete was assumed as a
cylindrical shape. This can be judge by observing the glass disc from the top
for disappearance of transparency. During this state, stopwatch was switched
off.
6.
The
time required from the shape of concrete to change from slump cone shape to
cylindrical shape is known as Vebe degree (time).
HARDENED CONCRETE TEST
Compression Test
1.
Three
moulds of size 150 mm x 150 mm x 150 mm were prepared.
2.
The
interior surfaces of the assembled mould were thinly coated with mould oil to
prevent adhesion of concrete.
3.
Each
mould was filled with three layers of concrete and each layer was tamped 35
times with a 25 mm square steel rod.
4.
The
top surface was finished with a trowel and the date of manufacturing was record
on the surface of the concrete.
5.
The
cube was stored undisturbed for 24 hours at a temperature of 18 to 22 0C
and a relative humidity of not less than 90%. The concrete was covered with wet
gunnysacks to ensure the condition above.
6.
The
mould was striped after 24 hours. After that, it was cured by immersing them in
water at temperature 19 to 21 0C until the testing date.
7.
The
cubes were tested at the age of 7 days.
8.
The
cube was positioned in the compressive machine with the cast faces in contact
with the platens.
9.
Load
at the rate of 15MN/m2/min was applied to cubes.
10. The maximum load was recorded to the
nearest 0.5 N/mm2.
Indirect Tension Test
1.
Two
moulds of cylinder measuring 150mm diameter by 300mm long were prepared.
2.
The
mould was coated inside with mould oil.
3.
Each
mould was filled with three layers of concrete and each layer was stamped 35
times with a 16mm diameter steel rod.
4.
The
date was recorded on the surface of the concrete.
5.
The
cylinder was cured. Method of curing is similar as for the cubes.
6.
The
cylinder was tested at the age of 7days.
7.
The
cylinder was placed with its axis horizontal between the platens of the testing
machine.
8.
A
narrow strip of plywood was placed at the top of and bottom between the platens
and the cylinder.
9.
Load
at the rate of 1.6 MN/m2/min was applied.
Flexural Strength of
Concrete
1.
A
mould of beam was prepared using measuring 100x100x500mm long.
2.
The
mould was coated inside with mould oil.
3.
The
mould was filled with 3 layers of concrete and each layer was tamped 35 times
with a 25 mm square steel rod.
4.
The
beam was cured. The method of curing is similar as for the cubes.
5.
The
beam was test at the age of 7 days.
6.
The
beam is positioned for testing with a span of 400mm i.e.50 mm from each end.
7.
The
beam was imposed with a two point loading system.
8.
Load
at the rate of 1.6 MN/m2/min was applied.
9.
Position
of the crack from the support was measured.
10. The modulus of rupture was calculated
using formulae below:
Modulus of rupture = PL / bd2 if a > L/3
or
= 3Pa / bd2 if a < L/3
Where,
P = maximum load
L
= span of beam (400 mm)
b
= width of beam
d = depth
of beam
a = position of
fracture from near support
5.0 DATA AND CALCULATION
Slump
Test
|
Slump of Concrete (mm)
|
170 mm
|
|
Types of Slump
|
Collapse Slump
|
Figure C1.1 Collapse Slump
Compacting
Factor Test
|
Weight
of Partially Compacted Concrete
|
= 15.9 – 4.8
= 11.1 kg
|
|
Weight
of Fully Compacted Concrete
|
= 16.4 – 4.8
= 11.6 kg
|
Compacting
Factor = 11.1
11.6
= 0.957 Ã High Workability
|
Workability
Category
|
Slump
(mm)
|
Compacting
Factor
|
Vebe Time
(sec)
|
Applications
|
|
Extremely
Low
|
0
|
0.65-0.7
|
Over
20
|
Lean
mix concrete for roads (compacted by vibrating roller); precast paving slab.
|
|
Very
Low
|
0-10
|
0.7-0.75
|
12-20
|
Roads
compacted by power operated machines.
|
|
Low
|
10-30
|
0.75-0.85
|
6-12
|
High-quality
structural concrete, mass concrete compacted by vibration.
|
|
Medium
|
30-60
|
0.85-0.95
|
3-6
|
Normal
purposes – reinforced concrete compacted by vibrating poker or manually.
|
|
High
|
60-180
|
0.95-1.0
|
0-3
|
Areas
with congested reinforcement, concrete for placing under water.
|
Table C1.1 Workability
categories: Properties and Applications
Cube
Test
Compressive
strength of cube = Load at
failure
Surface Area
|
Sample
|
1
|
2
|
3
|
|
Load,
kN
|
597.131
|
531.553
|
527.631
|
|
Area,
mm2
|
22500
|
|
Compressive
Strength of Cube, kN/mm2
|
0.0265
|
0.0236
|
0.0235
|
|
Mean
Compressive Strength of Cube
|
0.0245
kN/mm2
|
Indirect Tensile Strength
ITS =
2P D
Ï€DL
Where, P = Cylinder Splitting
Load (kN) L
D = Diameter (mm)
L = Height of Cylinder
(mm)
=
2(124.988)
Ï€ (150)(300)
= 1.768 x 10-3 kN/mm2
= 1.768 N/mm2
Flexural Strength of Beam
Modulus
of Rupture fb = PL if a > 5.33”
bd 2
f
b = 3PL if a < 5.33”
bd
2
a = 7”
50mm 200mm 200m 50mm
Modulus
of Rupture fb = PL if a >5.33”
bd
2 7” > 5.33”
= (13.385)(400)
100(100)2
= 5.354 X 10-3 kN/mm2
=5.353 N/mm2
6.0 RESULT
Fresh
Concrete Test
Slump of Concrete = 170mm
Compaction factor = 0.957
V-B Time = 3 second
Hardened Concrete Test
Strength Test at the age 14 day
Mean
Compressive = 24.50 N/mm2
Strength of Cube
Indirect
Tensile = 1.768 N/mm2
Strength
Flexural
Strength = 5.353 N/mm2
7.0 DISCUSSION
Based on the result, the slump of
concrete is 170 mm and mode of slump is collapse slump. The concrete is
collapse slump will be affected by:-
- Moisture of aggregates.
·
The
fine and coarse aggregates are exposed to rain a day before test. Hence, there
must have excess moisture (the aggregates is wet dry) content which makes the
aggregates wet and collapse slump happen.
- Compaction during do the test.
·
Since
compaction using man power, the compaction must not perfect as compaction using
machine. Hence, there still have void in the concrete mix.
- Slump mould not pulled up
carefully.
Besides
that, the workability of concrete is high and the vebe test time range between
0-3second. The application for this concrete suitable to apply at the area with
congested reinforcement and also for underwater area.
Result
of the strength test, From the test result, we obtain high workability concrete
sample because the compressive strength of cubes is 24.50 N/mm2,
indirect tensile strength is 1.765 N/mm2 and flexural strength of
beam is 5.354 N/mm2.
Compressive Strength of Cubes
|
|
Indirect Tensile Strength
|
|
Flexural Strength of Beam
|
|
2Compare the results of the strength with the target mean strength.
Discuss on the results
From Table 3: BS5528, the
characteristic compressive strength at 28 days for the standard mix for ST5 is
25N/mm2. Thus, the characteristic compressive strength at 14 days is
24.5 N/mm2 which is about the same with standard mix.
Concrete that satisfied
these conditions are said to have high workability. The desired workability for
an ideal concrete would depend on the means of the compaction available. The
characteristic compression strength we got during experiment satisfying the
standard mix shows that the concrete was well compacted.
8.0 CONCLUSIONS
In
conclusion, this concrete mix of (1:2:4) suitable to be apply for concrete that
have a lot of reinforcement. It also suitable concrete that compacted without
vibration and when compaction work difficult to do. The collapse slump happen
because the concrete mix is wet due to wet dry aggregates used and produced the
quality of concrete.
9.0 REFERENCES
i.
Concrete
Technology Theory and Practice, M.S Shetty, TA681.S53.2006.
ii.
Materials
in Construction, An Introduction, G.D. Taylor, TA403,T396.2000.
APPENDIX
Coarse
Aggregate Fine Aggregates Cement
Slump
Set Compacting Factor Vebe
Concrete Compression and Flexural Machine
yang penting enjoy sbb dpt bercuti dlm bulan Disember, Yay! Sekian bye!
Opss, minggu sebelum tu, pegi Legoland. Masuk percuma atas sbb tertentu. hehehe. 
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