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:

1. The volume of concrete needed for the tests was calculated

= 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 22⁰C 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 21⁰C 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

= 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 à 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

πDL

Where, P = Cylinder Splitting Load (kN) L

D = Diameter (mm)

L = Height of Cylinder (mm)

= 2(124.988)

π (150)(300)

= 1.768 x 10^-3 kN/mm²

= 1.768 N/mm²

Flexural Strength of Beam

Modulus of Rupture f_b = 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 f_b = 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.