This document discusses fresh concrete and factors that affect its workability. It describes workability as the ease with which concrete can be mixed, placed, and compacted. Key factors that influence workability include water content, aggregate size and shape, admixtures, aggregate surface texture, and aggregate grading. Common tests to measure workability are the slump test, compacting factor test, and VeeBee consistometer test. The document also covers segregation and bleeding of concrete, their causes, and methods to prevent them.

1. FRESH CONCRETE
CONTENT
1. WORKABILITY
2. FACTORS AFFECTING WORKABILITY
3. MEASUREMENT OF WORKABILITY
4. SEGREGATION
5. BLEEDING

2. WORKABILITY
• The property of concrete which determines the amount of useful interval work, necessary
to produce to full compaction. So workability is the amount of energy to overcome friction
while compacting.
• Also defined as the relative ease with which concrete can be mixed, transported, moulded
and compacted.

3. FACTORS AFFECTING WORKABILITY

4. WATER CONTENT
Workability of concrete increases with increase in water content. Higher the water content per
cubic meter of concrete, the higher will be the fluidity of concrete, which is one of the
important factors affecting workability.
Adding excess of water to concrete also has some disadvantages –
i. Strength of concrete may reduced.
ii. Increased quantity of water may cause bleeding in concrete.
iii. Cement slurry also escapes through the joints of formwork

5. AGGREGATE SHAPE AND SIZE
Size –
• The bigger the size of the aggregate, less is the surface area and hence less amount of
water is required for wetting the surface and less paste is required for lubricating the
surface to reduce internal friction.
• Hence, smaller aggregate are less workable compared to larger size aggregate.

6. Shape -
• Angular, flaky and elongated aggregate reduces the workability.
• Round/sub rounded aggregate have the following advantage-
I. For a given volume/weight, it has less surface and void, so excess paste is available to give
better lubricating effect.
II. Due to rounded shape it has less friction resistance.
Because of these reasons rounded aggregate show a high workability as compared to angular,
flaky or elongated aggregate.
Angular Round

7. ADMIXTURE
• The most important factor which affect the workability of concrete is admixture.
• Plasticizers and superplasticizers greatly improve the workability.
• Air entraining agents are also used to increase the workability.
• Air entraining agents create a large number of very small bubbles. These bubbles get
distributed thoroughly the mass of concrete and acts as a roller and increase
workability.
• Pozzolanic materials are also used to improve workability are also used.

8. SURFACE TEXTURE OF AGGREGATE
• The influence of surface texture on workability is due to fact that rough aggregate has more
surface area than smooth aggregate of same volume.
• Rough textured aggregate will show poor workability and smooth/glassy textured aggregate
will give better workability.
• Less friction resistance offered by smooth aggregates also contribute to higher workability.

9. GRADING OF AGGREGATE
• Grading of aggregate has max influence on workability.
• The better the grading less amount of void in it. When total void are less, excess
paste is available to give better lubricating effect.
• With excess amount of paste the mixture becomes cohesive and fatty which
prevents segregation of particle and least amount of compacting effort is
required.

10. MEASUREMENT OF WORKABILITY
It is done by following methods –
1. Slump test
2. Compacting factor test
3. Vee bee consistence test

11. SLUMP TEST
• It is most commonly method of measuring consistency of concrete which can be employed
either in laboratory or at site.
• A slump cone (bottom diameter- 20cm, top diameter- 10cm, height- 30cm) is filled with
concrete.
• Each layer is temped for 25 times by a standard tamping rod of 16mm diameter and 60 cm
length.
• The slump is kept inverted on ground and removed immediately, the subsidence of concrete
under gravity is slump, and measured in mm.

12. COMPACTING FACTOR TEST
Compacting factor = (weight of partially compacted concrete/weight of
fully compacted concrete)
• It gives fairly good results for concrete with low workability.
Quality Value
Very low workability 0.7-0.8
Low workability 0.8-0.85
Medium workability 0.85-0.95
High workability Greater than 0.95

13. VEE BEE CONSISTOMETER TEST
• It is a laboratory test to measure workability.
Procedure –
I. Placing concrete inside the conical mould.
II. Then removing the conical mould and vibrating the base of concrete with
machine.
III. The time required for the shape of concrete to change from slump cone
shape to cylindrical shape in seconds is known as vee bee degree.
SUITABILITY – for dry concrete having low workability.
Workability Time
Very low workability More than 20 sec
Low workability 6-12 sec
Medium workability 3-6 sec
High workability 0-3 sec

14. SEGREGATION
• It is defined as the separation of the constituent material of concrete.
Segregation may be done by three type-
i. The coarse aggregate separating out or setting down from the rest of matrix.
ii. The paste/matrix separating away from coarse aggregate.
iii. Water separating out from rest of material being a material of lowest specific gravity.
 In a good concrete all concrete. Aggregate are evenly coated with sand and cement past and
form a homogeneous mass.
 During handling, transporting and placing, due to jerk and vibration. The paste of cement and
sand get separated from coarse aggregate.
 If concrete segregates during transit it should be remixed properly before depositing.

15. CAUSES OF SEGREGATION
1. Use of high water-cement ratio in concrete.
2. Excessive vibration of concrete with mechanical needle vibration make
heavier particle settle down and light cement sand past on top.
3. When concreting is done from height in case of underground
foundations and raft, which causes concrete to segregate.

16. PREVENTION OF SEGREGATION
Following methods are used in preventing segregation –
1. By maintaining a proper proportioning in the mix, segregation can be controlled.
2. By using air entraining agents, admixtures and pozzolanic material in the mix
segregation can be controlled to some extent.
3. By careful handling, placing, transporting, compacting and finishing.
4. Whenever depth of concreting is more than 1:5 meter it should be placed through
temporary inclined chutes. The angle of inclination should be between 1:3 to 1:2.
So that the concrete from top of chutes travel smoothly to bottom, use of small quantity
of free water from top at interval helps in lubricating the path of flow of concrete to
bottom smoothly.

17. BLEEDING
It is form of segregation in which water present in
concrete mix is pushed upwards due to this water
tends to move upwards . Bleeding ordinarily occurs
in the wet mix of concrete.
• Prime factor of bleeding in concrete is high
dosage of water cement ratio. Higher water
cement ratio weakens concrete and lends to
excessive bleeding.
• Bleeding is not harmful, if the rate of evaporation
of water Is equal to rate of bleeding. Normal
bleeding is quite good, and it enhances the
workability of concrete.

18. PREVENTION OF BLEEDING
1. Bleeding in concrete is controlled by adding minimum water content in
concrete mix.
2. Encouraging use of air-entraining admixture.
3. By adding more cement in mix.