The document discusses workability of concrete and factors that affect it. It defines workability as the ease with which concrete can be mixed, compacted, transported, placed and finished. Workability is important for achieving full compaction of concrete and high strength. The key factors that affect workability include water content, aggregate properties, aggregate-cement ratio, presence of admixtures, cement fineness, time and temperature. The document also discusses segregation, bleeding, and various tests used to measure workability including slump test, compacting factor test, Vebe test, flow table test and ball penetration test.
2. ٢٠٠
Long
Long-
-term properties of hardened concrete such as strength, volume
term properties of hardened concrete such as strength, volume
stability, and durability, are seriously affected by degree
stability, and durability, are seriously affected by degree of
of
compaction. Therefore, concrete should be easily compacted,
compaction. Therefore, concrete should be easily compacted,
transported, placed, and finished without segregation; it must
transported, placed, and finished without segregation; it must be
be
consistent or workable.
consistent or workable.
Definition of Workability
Definition of Workability
Workability Definition
Workability Definition : Ease with which concrete can be easily
: Ease with which concrete can be easily
mixed, compacted, transported, placed, and finished.
mixed, compacted, transported, placed, and finished.
Another Definition: It is the amount of useful internal work ne
Another Definition: It is the amount of useful internal work necessary to
cessary to
produce full compaction; to overcome friction forces between
produce full compaction; to overcome friction forces between
aggregate particles. In addition, additional energy is needed to
aggregate particles. In addition, additional energy is needed to overcome
overcome
friction with Formwork. Without segregation.
friction with Formwork. Without segregation.
Strength =
Strength = f
f (full compaction)
(full compaction)
3. ٢٠١
To achieve high density, concrete must be compacted properly; mo
To achieve high density, concrete must be compacted properly; more
re
voids in concrete reduces the density and greatly reduces the st
voids in concrete reduces the density and greatly reduces the strength.
rength.
Example, 5% voids can lower concrete strength by 30%.
Example, 5% voids can lower concrete strength by 30%.
Two Types of Voids:
Two Types of Voids:
Bubbles of Entrapped air: governed by fine particles grading
Bubbles of Entrapped air: governed by fine particles grading
and wetness of the mix.
and wetness of the mix.
Space left after excess water has been removed: This depends
Space left after excess water has been removed: This depends
on the
on the w/c
w/c ratio
ratio
There is no optimum water content, since the later depends on
There is no optimum water content, since the later depends on
the amount of compaction.
the amount of compaction.
4. ٢٠٢
A.
A. Water Content :
Water Content : increase water content , increase workability ,
increase water content , increase workability ,
and decrease strength
and decrease strength
Water
Water
Interparticle
Interparticle lubrication
lubrication
space left after excess water has been removed
space left after excess water has been removed
Density
Density
Factors Affecting Workability :
5. ٢٠٣
B. Aggregate type and grading
B. Aggregate type and grading
Finer aggregate
Finer aggregate Water
Water
Irregular shape and Rough texture
Irregular shape and Rough texture
Water
Water
Porosity or absorption
Porosity or absorption Water
Water
Factors Affecting Workability depends on :
6. ٢٠٤
C.
C. Aggregate:Cement
Aggregate:Cement Ratio:
Ratio: Constant W/C ratio
Constant W/C ratio
aggregate content
aggregate content Workability
Workability
CA:FA
CA:FA Segregation
Segregation Workability
Workability
CA:FA
CA:FA Workability
Workability
Less Durable
Less Durable
Concrete
Concrete
Harsh Mix: Not Easily Finished
Harsh Mix: Not Easily Finished
Factors Affecting Workability depends on :
7. ٢٠٥
D. Presence of admixtures
D. Presence of admixtures
E. Cement Fineness
E. Cement Fineness has a minor influence on workability
has a minor influence on workability
Air entertainment
Air entertainment Water Requirements
Water Requirements
Fineness
Fineness Water
Water
Factors Affecting Workability depends on :
For a given workability
For a given workability
8. ٢٠٦
F. Time and Temperature
F. Time and Temperature
Time or Temperature
Time or Temperature Stiffening (not setting)
Stiffening (not setting)
workability
workability
Water is removed by evaporation,
Water is removed by evaporation,
absorption of aggregate, and some by
absorption of aggregate, and some by
initial reaction.
initial reaction.
Factors Affecting Workability depends on :
9. ٢٠٧
Absence of Segregation
Absence of Segregation →
→
→
→
→
→
→
→ Full compaction (Mix cohesive)
Full compaction (Mix cohesive)
Segregation:
Segregation: Separation of the constituents
Separation of the constituents
of a heterogeneous concrete mixture so that
of a heterogeneous concrete mixture so that
their distribution is no longer uniform. In
their distribution is no longer uniform. In
concrete, it is the difference in particle size or
concrete, it is the difference in particle size or
difference in the specific gravity of the mix
difference in the specific gravity of the mix
constituents that could cause segregation;
constituents that could cause segregation;
but its extent can be controlled by:
but its extent can be controlled by:
•
•Choice of suitable grading
Choice of suitable grading
•
•Care in handling.
Care in handling.
Cohesion and Segregation
Cohesion and Segregation
10. ٢٠٨
Segregation Forms :
Segregation Forms :
•
• Segregation resulting from coarse particles that travel along a
Segregation resulting from coarse particles that travel along a
slope or settle more than finer particles (occurs mostly in dry
slope or settle more than finer particles (occurs mostly in dry
mixes).
mixes).
•
• Separation of grout (cement + water) (occurs mostly in wet mixe
Separation of grout (cement + water) (occurs mostly in wet mixes)
s)
To prevent or Reduce Segregation
To prevent or Reduce Segregation
Good Grading
Good Grading
Appropriate handling and placing
Appropriate handling and placing
Proper vibration; needed to achieve good compaction:
Proper vibration; needed to achieve good compaction:
not under nor over vibration
not under nor over vibration.
.
Using of air entrainment
Using of air entrainment
-
-
Close specific gravities for coarse and fine aggregate
Close specific gravities for coarse and fine aggregate
Cohesion and Segregation
Cohesion and Segregation
11. ٢٠٩
Segregation Measurement
Segregation Measurement
Measuring cohesion: evaluated by flow Table Test, or
Measuring cohesion: evaluated by flow Table Test, or
Over vibrating a cube or cylinder for 10 minutes, then observe
Over vibrating a cube or cylinder for 10 minutes, then observe
segregation extent .
segregation extent .
Difficult to measure quantitatively, but easily to detect.
Difficult to measure quantitatively, but easily to detect.
Could be evaluated by :
Could be evaluated by :
Cohesion and Segregation
Cohesion and Segregation
12. ٢١٠
Form of segregation in which some of the water in the mix tends
Form of segregation in which some of the water in the mix tends to
to
rise to the surface of freshly placed concrete, caused by the in
rise to the surface of freshly placed concrete, caused by the inability
ability
of the solid constituents of the mix to hold all the mixing wate
of the solid constituents of the mix to hold all the mixing water when
r when
they settle down. Creating a weak and non
they settle down. Creating a weak and non-
-durable surface
durable surface →
→ it
it
should be removed by brushing the surface carefully.
should be removed by brushing the surface carefully.
Bleeding
Bleeding
Bleeding depends on:
Bleeding depends on:
A. Water Content
A. Water Content
Water
Water bleeding
bleeding
B. Temperature
B. Temperature
Temperature
Temperature Rate of bleeding
Rate of bleeding
13. ٢١١
C. Properties of cement (largely affects bleeding)
C. Properties of cement (largely affects bleeding)
Calcium Chloride
Calcium Chloride
high alkali content
high alkali content
C
C3
3A
A
Fineness
Fineness
bleeding
bleeding
bleeding
bleeding
bleeding
bleeding
bleeding
bleeding
D. Rich mixes are less prone to bleeding
D. Rich mixes are less prone to bleeding
E. Addition of
E. Addition of Pozzolan
Pozzolan and Aluminum powder
and Aluminum powder bleeding
F. Air entrainment
F. Air entrainment bleeding
Bleeding
Bleeding
14. ٢١٢
Workability Tests
Workability Tests
There is no acceptable test which measures directly the workabil
There is no acceptable test which measures directly the workability.
ity.
Slump Test
Slump Test
Compacting Factor Test
Compacting Factor Test
Vebe
Vebe Test (From V
Test (From V Bahrner
Bahrner)
)
Flow Table Test
Flow Table Test
Ball Penetration Test
Ball Penetration Test
Comparison of Tests
Comparison of Tests
15. ٢١٣
The slump is insensitive to low workability mixes (dry ones).
The slump is insensitive to low workability mixes (dry ones).
The slump is sensitive to variation in workability of rich mix.
The slump is sensitive to variation in workability of rich mix.
The slump test is unreliable for lean mixes:
The slump test is unreliable for lean mixes:
True slump could easily changed to Shear slump
True slump could easily changed to Shear slump or
or Collapse slump.
Collapse slump.
In general, slump measurement bears no unique relation t
In general, slump measurement bears no unique relation to the
o the
workability; mixes with different aggregates could have the sam
workability; mixes with different aggregates could have the same
e
slump, yet their
slump, yet their workabilities
workabilities are different.
are different.
Routine test
Routine test for checking variation and consistence of concrete
for checking variation and consistence of concrete
mixes.
mixes.
1. Slump Test
1. Slump Test
Is a measure of consistency of freshly mixed concrete
Is a measure of consistency of freshly mixed concrete
Apparatus : frustum of cone
Apparatus : frustum of cone
16. ٢١٤
For each job requirement there is a certain value of slump
For each job requirement there is a certain value of slump
requirement.
requirement.
Slump is
Slump is not
not a measurement of the quality of the concrete
a measurement of the quality of the concrete
Slump values (mm)
Degree of workability
0-25
Very low
25-50
Low
50-100
Medium
100-175
High
17. ٢١٥
Slump Test
Slump Test
the cone is filled with concrete in three
the cone is filled with concrete in three
layers. Each layer is tamped 25 times
layers. Each layer is tamped 25 times
with a standard 16 mm diameter steel
with a standard 16 mm diameter steel
rod.
rod.
19. ٢١٧
It reflects the degree of compaction achieved by a standard amou
It reflects the degree of compaction achieved by a standard amount of
nt of
work.
work.
Degree of compaction or compacting factor =
Degree of compaction or compacting factor =
Density (achieved)
Density (achieved)
Density (fully compacted)
Density (fully compacted)
2. Compacting Factor Test
2. Compacting Factor Test
Full compaction is achieved by filling the cylinder (shown)
Full compaction is achieved by filling the cylinder (shown)
with concrete of four compacted or tamped layers.
with concrete of four compacted or tamped layers.
21. ٢١٩
Table 1 : Correlation between compacting factor and slump
Table 1 : Correlation between compacting factor and slump
Use for which concrete is
Use for which concrete is
suitable
suitable
Compacting
Compacting
factor
factor
Slump
Slump
(mm)
(mm)
Degree of
Degree of
Workability
Workability
Roads: Vibrated by power
Roads: Vibrated by power-
-operated
operated
machines.
machines.
0.78
0.78
0
0-
-25
25
Very low
Very low
Roads: Vibrated by hand
Roads: Vibrated by hand-
-operated
operated
machines.
machines.
0.85
0.85
25
25-
-50
50
Low
Low
-
- Flat slabs: Manually compacted
Flat slabs: Manually compacted
-
- Heavily Reinforced: Vibrated
Heavily Reinforced: Vibrated
0.92
0.92
25
25-
-100
100
Medium
Medium
-
- Congested reinforcement
Congested reinforcement
(No Vibration)
(No Vibration)
0.95
0.95
100
100-
-175
175
High
High
22. ٢٢٠
Compacting factor test yields, in general, reliable results, but
Compacting factor test yields, in general, reliable results, but
the size of the apparatus represents limitation when to be
the size of the apparatus represents limitation when to be
used in the field.
used in the field.
Notes:
Notes:
Compacting factor is more sensitive than slump for low
Compacting factor is more sensitive than slump for low
workability mixes.
workability mixes.
The compacting factor does not reflect the amount of work
The compacting factor does not reflect the amount of work
needed to achieve full compaction; leaner mixes needs more
needed to achieve full compaction; leaner mixes needs more
work than rich ones.
work than rich ones.
23. ٢٢١
3.
3. Vebe
Vebe Test ( From V
Test ( From V Bahrner
Bahrner)
)
The input of energy required for full compaction is a
The input of energy required for full compaction is a
measure of workability of the mix, and this is expressed in
measure of workability of the mix, and this is expressed in
Vebe
Vebe seconds.
seconds.
Time Correction: the measured
Time Correction: the measured vebe
vebe time is to the corrected
time is to the corrected
to consider the change in volume before and after vibration
to consider the change in volume before and after vibration
thus;
thus;
after
before
V
V
*
t
t measure
corrected =
It is:
It is:
(a) A good test for very dry mixes.
(a) A good test for very dry mixes.
(b) Simulate to some extent the way of which the
(b) Simulate to some extent the way of which the
concrete is handled and placed.
concrete is handled and placed.
Note:
Note:
25. ٢٢٣
4. Flow Table Test
4. Flow Table Test
Place the concrete in the frustum cone, tamp with a wooden tampe
Place the concrete in the frustum cone, tamp with a wooden tamper,
r,
clean the surrounding , wait 30sec, then remove slowly the mold.
clean the surrounding , wait 30sec, then remove slowly the mold. After
After
that, lift the table , drop it 15 times, each cycle should take
that, lift the table , drop it 15 times, each cycle should take 4 sec.
4 sec.
2
2
1 D
D
D
+
=
D1 and D2
D1 and D2 are diameters parallel to the two wooden edges
are diameters parallel to the two wooden edges .
.
Medium workability = 400 mm
Medium workability = 400 mm
High workability = 500 mm
High workability = 500 mm
For this test to be credible, concrete should appear cohesive,
For this test to be credible, concrete should appear cohesive,
otherwise, test is considered inappropriate; it offers an i
otherwise, test is considered inappropriate; it offers an indication
ndication
of cohesiveness of mix.
of cohesiveness of mix.
28. ٢٢٦
5. Ball Penetration Test (Kelly Ball Test)
5. Ball Penetration Test (Kelly Ball Test)
Alternative to slump test
Alternative to slump test
Measured depth of sinking of the ball in concrete, under it own
Measured depth of sinking of the ball in concrete, under it own
weight reflecting workability
weight reflecting workability
Used for routine checking of consistence for control purpose.
Used for routine checking of consistence for control purpose.
Simpler and quicker than slump test
Simpler and quicker than slump test
Applied to concrete in forms.
Applied to concrete in forms.
Avoid boundary effects that is:
Avoid boundary effects that is:
Depth of concrete > 200mm
Depth of concrete > 200mm
Least lateral dimension> 460mm
Least lateral dimension> 460mm
30. ٢٢٨
6. Comparison of Tests
6. Comparison of Tests
No unique relation between the results of various tests should b
No unique relation between the results of various tests should be
e
expected, because each test measures the behavior of conc
expected, because each test measures the behavior of concrete
rete
under different conditions.
under different conditions.
The relation between the compacting factor and
The relation between the compacting factor and Vebe
Vebe time must not
time must not
be assumed to be generally applicable since it depends on facto
be assumed to be generally applicable since it depends on factors
rs
such as : the shape and texture of aggregate, and presence
such as : the shape and texture of aggregate, and presence of
of
entrained air, as well as mix proportions.
entrained air, as well as mix proportions.
For specific mixes, the relation between compacting factor an
For specific mixes, the relation between compacting factor and
d
slump has been obtained , but such a relation is also a functio
slump has been obtained , but such a relation is also a function of the
n of the
proportions of the mix.
proportions of the mix.
As already stated, the ideal test for workability has yet to
As already stated, the ideal test for workability has yet to be devised.
be devised.
In general, experience is necessary, once it has been acquired,
In general, experience is necessary, once it has been acquired, the
the “
“
by eye
by eye”
” test, particularly for the purpose of checking uniformity, is
test, particularly for the purpose of checking uniformity, is
both rapid and reliable.
both rapid and reliable.
