CONCRETE TECHNOLOGY UNIT IV

G.GUNA SRVEC 1
DEPARTMENT OF CIVIL ENGINEERING
CE 6002 – CONCRETE TECHNOLOGY
G.GUNA S.R.V.E.C

3
Requirement of Fresh Concrete
Workability is the property of concrete which
determine the amount of useful internal work necessary to
produce full compaction.
G.GUNA SRVEC

G.GUNA SRVEC 4
Factors affecting Workability
Measurement of Workability
Slump Test
Compacting Factor Test
Flow Test
Kelly Ball Test
Vee Bee Test

6G.GUNA SRVEC
Concrete is filled in top hopper
1 meter high
Allowed to drop in second
hopper
Concrete is dropped from
second hopper into cylinder
and leveled
Weighed and emptied
Filled with fully compacted
concrete and weighed again
Ratio of fallen weight to fully
compacted concrete is
compacting factor

7G.GUNA SRVEC
 Slump cone test
is performed in a
closed cylinder
of 300 mm dia.
 Perspex plate is
placed on top.
 Vibration are
applied at
standard rate till
plate is fully in
contact.
Time in
second to
achieve state
of concrete
shown below
is called
Vee Bee

G.GUNA SRVEC 8
Conical mould is filled with concrete and placed in
centre of board.
Board is raised and dropped 15 times
Spread of concrete is measured and is called
Flow

9G.GUNA SRVEC
Setting Time Of Concrete
Setting of concrete is caused by water cement reaction.
Setting time of cement and concrete do not coincide.
Initial and final setting times are arbitrarily defined by method of
penetration of needle
Final set of concrete do not mean complete loss of workability.
Initial set represent time after which concrete can not be mixed
placed and compacted properly.

G.GUNA SRVEC 10
Properties of fresh and hardened concrete
The potential strength and durability of concrete
of a given mix proportion is very dependent on the degree
of its compaction. It is vital, therefore, that the
consistency of the mix be such that the concrete can be
transported, placed, and finished sufficiently early
enough to attain the expected strength and durability.
Properties of Fresh Concrete:
 The first 48 hours are very important for the performance of
the concrete structure.
 It controls the long-term behavior, influence f'c (ultimate
strength), Ec (elastic modulus), creep, and durability.
Properties at Early Ages :
• Workability
• Slump Loss
• Segregation/Bleeding
• Plastic Shrinkage
• Time of Set
• Temperature

G.GUNA SRVEC 11
Workability :
Definition: Effort required to manipulate a concrete mixture with a minimum of
segregation.
It is not a fundamental property of concrete.
I) consistency (slump)-- easy to flow
II) cohesiveness --tendency to bleed and segregate
Slump Test:
Slump test is a test conducting before concrete to
be used for casting. The purpose of slump test
Is to determine the water content in concrete and its workability
Consistency:
Consistency or fluidity of concrete is an important component of
workability and refers in a way to the wetness of the concrete.
However, it must not be assumed that the wetter the mix the more workable it is.
If a mix is too wet, segregation may occur with resulting honeycomb, excessive
bleeding, and sand streaking on the formed surfaces.
On the other hand, if a mix is too dry it may be difficult to place and compact,
and segregation may occur because of lack of
cohesiveness and plasticity of the paste.

G.GUNA SRVEC 12
PROPERTIES OF
HARDENED CONCRETE
 The principal properties of hardened concrete which are of
practical importance can be listed as:
1) Strength
2) Permeability & durability
3) Shrinkage & creep deformations
4) Response to temperature variations
Of these compressive strength is the most important
property of concrete.
Of the abovementioned hardened properties compressive
strength is one of the most important property that is often required,
simply because;
1) Concrete is used for compressive loads
2) Compressive strength is easily obtained
3) It is a good measure of all the other properties.

G.GUNA SRVEC 13
 The strength of a concrete specimen prepared, cured
and tested under specified conditions at a given age
depends on:
1. w/c ratio
2. Degree of compaction
Compressive Strength is determined by loading properly
prepared and cured cubic, cylindrical or prismatic
specimens under compression.
 Permeability is important because:
1. The penetration of some aggresive solution may result in
leaching out of Ca(OH)2 which adversely affects the
durability of concrete.
2. The moisture penetration depends on permeability & if
concrete becomes saturated it is more liable to frost-action.
3. In some structural members permeability itself is of
importance, such as, dams, water retaining tanks.

G.GUNA SRVEC 14
DURABILITY
A durable concrete is the one which will withstand in a
satisfactory degree, the effects of service conditions to which it will be
subjected.
Factors Affecting Durability:
External → Environmental
Internal → Permeability, Characteristics of ingredients, Air-Void
System...
SULFATE ATTACK
Ground water in clayey soils containing alkali sulfates may affect
concrete.
These solutions attack CH to produce gypsum. Later, gypsum and
calcium alumina sulfates together with water react to form
“ettringite”.
Formation of ettringite is hardened cement paste or concrete leads
to volume expansion thus cracking.
Moreover, Magnesium sulfate may lead to the decomposition of the
C-S-H gel.

G.GUNA SRVEC 15
CORROSION
Electrochemical reactions in the steel rebars of a R/C structure
results in corrosion products which have larger volumes than
original steel.
Thus this volume expansion causes cracks in R/C. In fact, steel
is protected by a thin film provided by concrete against corrosion.
However, that shield is broken by CO2 of air or the Cl- ions.

CONCRETE TECHNOLOGY UNIT IV

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CONCRETE TECHNOLOGY UNIT IV