FRESH CONCRETE AND HARDEN CONCRETE

1. UNIT–IV
FRESHANDHARDENPROPERTIESOFCONCRETE

2. Concrete is referred to as fresh when the setting and hardening process has not yet started. Fresh
concrete can be deformed and poured which means it can be transported or pumped and used to fill
moulds and formwork. When concrete is in plastic stage it is called fresh concrete
Fresh concrete has two fundamental properties:
MOULDABILITY (Which means it can assume any shape)
WORKABILITY
The characteristics of the structure and the concrete placement techniques determine the composition of
the concrete whose consistency is then adjusted on the basis of the Abrams cone slump test.
FRESH CONCRETE

3. Requirements of Fresh Concrete
The basic requirements of fresh concrete used in construction are:
1.Mixability
2.Stability
3.Mobility or Flowability
4.Compactibility
5.Finishability
Mixability of Concrete
The mix should be able to produce homogeneous fresh concrete from the constituent materials of the
batch under the action of the mixing forces. A less mixable concrete mix requires more time to produce a
homogeneous and uniform mix. This property is called as mixability.
Stability of Concrete
The mix should be stable such that it should not segregate during transportation and placing, when it is
subjected to forces during handling operation. The Tendency of hardening should be minimum.
Mobility/Flowability of Concrete
The mix should be cohesive and sufficiently mobile to be placed in the form around the reinforcement and
should be able to cast into the required shape. This property is called as Flowability or Mobility.

4. Compactability of Concrete
The compatibility is the property which ensures the dense and the compacted concrete with minimum voids.
Finishability of Concrete
The concrete must be possible to attain a satisfactory surface finish without honeycombing or the blowing
of the holes from the formwork. This capability of concrete is called as finishability.

5. Properties of Fresh Concrete
•Workability
•Temperature
•Water Cement Ratio
•Segregation
•Bleeding
•Plastic shrinkage
•Setting Time
•Hydration

18. https://youtu.be/IJMSIu7B8ko

19. COMPACTION FACTOR
TEST
https://youtu.be/gxjfiRcPcoU

20. https://youtu.be/KN-
nKeSqDPU

21. VEE BEE
CONSISTOMTER
https://youtu.be/B8va6peUJqE

22. KELLY BALL TEST OF CONCRETE
Kelly Ball Test for Concrete || Test for Workability of
Concrete #6 - YouTube

23. SEGGREGATION AND BLEEDING
There are hard effects of segregation and bleeding on the workability and strength of concrete. So
before the job frequently we are asked in the interview or on-site, that how to avoid segregation or how to
avoid bleeding in concrete.
At that time can only answer it, if you really know the definition or difference between segregation and
bleeding. So, a friend here I have described them in detail.

24. What is Segregation?
It can be defined as separating out the ingredients of the concrete mix so that the mix is no longer in a
homogeneous condition. It Separates out of coarser particles from the rest of the matrix Like Cement
(cement slurry), Sand, etc.
Cause of Segregation
1) Segregation depends upon handling, transportation, and placing
2) More workability i.e. slump value means susceptible to segregation.
3) Dropping concrete from heights will result in segregation
4) Insufficient mixed concrete with excess water is prone to segregation.
5) Excess vibration i.e. vibration for long time results ins in segregation.
6) Segregation may also occur when we use a vibration needle to spread a heap of concrete.
Disadvantages of segregation?
1) It reduces the lifespan of concrete structures.
2) It makes the structure weak.
3) It makes the structure unstable due to eccentric loading caused by unequal distribution of
concrete materials.
4) It generates the extra cost of labor and materials to repair and maintenance of segregated
concrete.
5) It spoils the appearance of the concrete structure.

25. How to avoid segregation?
Avoid excessive compaction in concrete.
Use the suitable size of aggregate in concrete.
The dropping of aggregate in form-work should not be greater than 1.5 meters.
There should be an excessive gap between steel bars to enter the concrete slurry in it.

26. BLEEDING
It is a form of segregation in which some of the water in the mix tends to rise to
the surface of freshly placed concrete. This is caused by the inability of a solid
constituent of the mix to hold all the mixing water when they settle down during
compaction.
Effect and remedies of Bleeding
1) It causes the formation of the porous, weak & nondurable concrete
layer at the top of placed concrete.
2) Bleeding may be reduced by proper proportioning, uniform & complete
controlled compaction.
3) It also can be reduced by the use of pozzolanic materials and air-
entraining agents.
4) According to ASTM code 232, Bleeding is expressed in terms of the
amount of accumulated water as % of the net mixing water sample.
5) Bleeding causes lack of water in concrete so, It decreases the strength
of concrete due to not proper hydration.

42. TEST ON HARDEN CONCRETE
COMPRESSIVE STRENGTH https://youtu.be/t4RDdn6rOwU
FLEXURAL STRENGTH TEST OF
CONCRETE
https://www.youtube.com/watch?v=wI5
hFajlrrM
SPLIT TENSILE STRENGTH TEST OF
CONCRETE
https://youtu.be/C5h9nfufG9Y

43. Concrete Resitivity Test
Principle & Procedure
Corrosion is an electrochemical process. For corrosion of steel reinforcement to occur in
concrete, an ionic current (a flow of ions) must pass between anodic and cathodic regions of
the concrete. The electrical resistivity of the concrete affects the ionic flow and the rate at
which corrosion can occur; a higher concrete resistivity decreases the current flow. An
empirical relationship between corrosion rate and concrete resistivity has been derived from
measurements on actual structures
The resistivity of a given structure exposed to chloride load gives information about the risk of
early corrosion damage, because generally a low concrete resistivity is correlated to rapid
chloride penetration and to a high corrosion rate.
The electrical resistivity of concrete is a materials property that may be useful for monitoring
and inspection of concrete structures with regard to reinforcement corrosion. Generally a low
concrete resistivity is correlated to rapid chloride penetration and to a high corrosion rate. In
addition resistivity mapping may show the most porous spots, where chloride penetration is
likely to be fastest and future corrosion rates will be highest.

44. Four probes
Concrete electrical resistivity can be obtained by applying a current into the concrete and
On-site electrical resistivity of concrete is commonly measured using four probes in a Wenner
probes is the same as in the laboratory method – to overcome contact errors. In this method four
applied to the specimen in a line. The two outer probes induce the current to the specimen and
the resulting potential drop. The probes are all applied to the same surface of the specimen and
suitable for measuring the resistivity of bulk concrete in situ.

49. https://youtu.be/OJ2pe9zSYHg