During filtration, the clear water passes through filters that have different pore sizes and are made of different materials (such as sand, gravel, and charcoal). These filters remove dissolved particles and germs, such as dust, chemicals, parasites, bacteria, and viruses.

1. Concrete Technology
4th Sem BE
Civil Engineering
Lec 11: Fresh concrete Workability

2. Covered so far
Materials for Concrete Making
– Cement
– Aggregates
– Water
Fresh Concrete: Types of concretes

3. This lecture
Property of Fresh Concrete:
Workability

4. Two properties
"consistency“ is a general term to indicate
the degree of fluidity or the degree of
mobility. A concrete which has high
consistency and which is more mobile,
need not be of right workability for a
particular job.
“workability”

5. workability
"the property of concrete which determines
the amount of useful internal work
necessary to produce full compaction.“
Another definition "ease with which
concrete can be compacted hundred per
cent having regard to mode of compaction
and place of deposition.“

6. workability
Workability is often referred to as the ease with
which a concrete can be transported, placed and
consolidated without excessive bleeding or
segregation. It is obvious that no single test can
evaluate all these factors. In fact, most of these
cannot be easily assessed even though some
standard tests have been established to
evaluate them under specific conditions (not
always similar to that occurring on site).

7. The workability of concrete is, in practice,
influenced by even small changes in any
relevant parameter:
– Physical and chemical properties of each
individual constituent material
– Relative proportions of the constituent
materials
– Mixing procedure of material used
– Temperature
– Time

8. Parameters
Cement
Water
Aggregates
Chemical admixtures
Supplementary cementitious materials
Mixing procedure
Temperature and time

9. factors affecting workability
Water Content
Mix Proportions
Size of Aggregates
Shape of Aggregates
Surface Texture of Aggregate
Grading of Aggregate
Use of Admixtures

10. (a) Water Content
Workability α water content
Strength α 1/ water content

11. If water is required for the workability,
sometimes, the excess water is vacuumed
out from the surface.

12. b) Mix Proportions
Aggregate/cement ratio influences
workability.
Leaner Concrete: Ag/C ration is more,
Mobility of concrete is less, hence it is less
workable
Rich Concrete: Enough cement paste is
available for covering the aggregate
particles.

13. (c ) Size of Aggregate
Bigger the size of the aggregate, the less
is the surface area and hence less amount
of water is required for wetting the surface
and less matrix
Paste is required for lubricating the
surface to reduce internal friction.
For a given quantity of water and paste,
bigger size of aggregates will give higher
workability.

14. (d ) Shape of Aggregates
Angular, elongated or flaky aggregate
makes the concrete very harsh when
compared to rounded aggregates or
cubical shaped aggregates.
Rounded aggregate: for the given volume
or weight it will have less surface area and
less voids than angular or flaky aggregate.
Frictional resistance is also greatly
reduced.

15. Particle Shape and Texture
Deviation from spherical shape requires higher paste volume to
enable rotation without particle interference

16. (e ) Surface Texture
total surface area of rough textured
aggregate is more than the surface area of
smooth rounded aggregate of same
volume.
smooth or glassy textured aggregate will
give better workability.
A reduction of inter particle frictional
resistance offered by smooth aggregates
also contributes to higher workability.

17. (f ) Grading of Aggregates
will have maximum influence on
workability.
A well graded aggregate is the one which
has least amount of voids in a given
volume.
Other factors being constant, when the
total voids are less, excess paste is
available to give better lubricating effect.

18. With excess amount of paste, the mixture
becomes cohesive and prevents
segregation of particles.
Aggregate particles will slide past each
other with the least amount of compacting
efforts.
The better the grading, the less is the void
content and higher the workability.

19. (g ) Use of Admixtures:
Admixture: Additional material added to
concrete
It enhances the properties of concrete like
workability
May also reduce slump faster

20. Next Lecture
Tests for Workability

21. Thank You