Concreteee-and-Reinforced-Concreteee.ppt

CONCRETE AND
REINFORCED
CONCRETE

What is Concrete?
Concrete is a rock-like
material that can be
easily prepared by
mixing binding material
(lime or cement), fine
aggregate (sand) and
coarse aggregate
(crushed stone or brick),
and water in the
required proportion.

Brief History
 The ancient Romans accidentally discovered a
silica- and alumina- bearing mineral on the
slopes of Mount Vesuvius that, when mixed with
limestone and burned, produced a cement that
exhibited a unique property

Advantages of Concrete
 Availability of materials
 Easy handling and molding
 Easy transportation
 Resistant to wind and water
 Can withstand high temperatures

Disadvantages of Concrete
 Low tensile strength
 Low ductility
 May contain soluble salts
 Require proper curing

Concrete Ingredients
Concrete has been used as a building material
for thousands of years. The main ingredients
have been the same, but new admixture
technologies allow designers and engineers to
finely tune the final properties of the full set
concrete.

Types of Concrete Chemicals
(Admixtures)
 Retarding admixtures
 Accelerating admixtures
 Air-entraining admixture
 Pozzolanic Admixtures
 Damp-proofing admixtures

Retarding admixtures
 Retarding admixtures slow down the hydration
of cement, lengthening set time. Retarders are
beneficially used in hot weather conditions in
order to overcome accelerating effects of
higher temperatures and large masses of
concrete on concrete setting time. Because
most retarders also act as water reducers,
they are frequently called water-reducing
retarders.

Accelerating admixtures
 Accelerators shorten the set time of concrete,
allowing a cold-weather pour, early removal of
forms, early surface finishing, and in some
cases, early load application. Proper care
must be taken while choosing the type and
proportion of accelerators, as under most
conditions, commonly used accelerators cause
an increase in the drying shrinkage of
concrete.

Air-entraining admixtures
 Air-entraining agents entrain small air bubbles
in the concrete. The major benefit of this is
enhanced durability in freeze-thaw cycles,
especially relevant in cold climates. While
some strength loss typically accompanies
increased air in concrete, it generally can be
overcome by reducing the water-cement ratio
via improved workability (due to the air-
entraining agent itself) or through the use of
other appropriate admixtures.

Pozzolanic or mineral
admixtures
 The proper addition of pozzolanic admixtures
to cement enhances many qualities of
concrete, such as lowering the heat of
hydration, increasing the water tightness,
reducing the alkali–aggregation reaction,
resisting sulphate attack, improving
workability, etc.

Damp-proofing admixtures
 They have the property of filling pores or being
water repellents. The prime materials in pore-
filling admixtures are silicate of soda,
aluminum and zinc sulphates, and aluminum
and calcium chloride. These are also more
active and render the concrete more
impervious and accelerates the setting time.

Types of Concrete
 Plain Cement Concrete (CC)
 Reinforced Cement Concrete (RCC)
 Pre-stressed Cement Concrete
 Light-weight Cement Concrete
 Precast Cement Concrete
 Lime Concrete (LC)

Classification of Concrete
 The terms of the mixing of concrete
 Bulk density of the concrete
 The type of binder
 The consistency of the fresh concrete
 Concrete class
 The purposes of concrete and other.

The terms of the mixing of
concrete
 The first category of concrete (B.I), which can
be mixed without the previous tests, but amount
of cement determined by Article 26 of the
Rulebook on technical norms for concrete and
reinforced concrete must be used
 The second categories of concrete (B.II) with
concrete class MB 30 or more, as well as
concretes with special properties and
transported concrete of all concrete classes

Bulk density of the concrete
 Lightweight concretes, whose bulk density
does not exceed 1900 kg/m3.
 Classic concrete with bulk density from 1900
kg/m3 to 2500 kg/m3
 Heavy-weight concrete with bulk density of
higher than 2500 kg/m3.

Concrete Class
 For the construction of concrete blocks the
following concrete classes (MB) are used:
10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60.

Mixing the materials for
concrete
 Is the process of
measuring concrete
mix ingredients by
either mass or
volume and
introducing into the
mixer.
BATCHING PLANT

Consolidation of Concrete
 Consolidation is the process of inducing a
closer arrangement of the solid particles in
freshly mixed concrete or mortar during
placement by the reduction of voids, usually by
vibration, centrifugation, rodding, tamping, or
some combinations of these actions
 The process of consolidation
1. Hand compaction
2. Compaction by vibration
3. Bleeding of concrete

Hand Compaction
 Hand compaction is adopted for pavements ,
narrow and deep members. Compact must be
and concrete must reach to the concerns of
the formwork
Methods of hand compaction
Ramming Tamping
Rodding

Compaction by Vibration
 In the case of high-strength concrete, the
water-cement ratio is too low and concrete is
too stiff to compact by hand. To compact such
types of concrete, mechanically operated
vibratory equipment must be used.
 Vibration reduces the friction between concrete
ingredients gives them time to settle down in a
compacted mass of concrete.

VIBRATORS
Internal vibrators are popular in
the precast industry and consist
of a power source, a shaft and a
vibrating head. Internal vibration
is a manual procedure requiring
hard work and careful attention,
but don’t give in to the
temptation to give the task to the
newest worker.
External vibrators
Internal vibrators
External vibrators are often called
form vibrators, but it’s important to
understand that while they are
attached to formwork, they are
designed to vibrate concrete.

Systematic Vibration
CORRECT
Vertical penetration a few inches
into previous lift (which should not
yet be rigid) of systematic regular
intervals will give adequate
consolidation
INCORRECT
Haphazard random penetration of
the vibrator at all angles and
spacings without sufficient depth will
not assure intimate combination of
the two layers

Bleeding of Concrete
 Bleeding is the tendency of water to rise to the
surface of freshly placed concrete.

Curing of Concrete
 Curing is the operation by which moist
conditions are maintained on finished concrete
surface, to promote continued hydration of
cement.
 If proper curing is not done, complete hydration
of cement will not take place, with the result that
concrete will not acquire its full intended
strength.
 Moreover, shrinkage cracks will develop.
 Curing brings improvement in durability,
impermeability, wear and weather resistant

Curing Methods
1. Methods which supply additional water to the
surface of concrete during early hardening
stages.
PONDİNG
SPRİNKLİNG
WET COVERS

Curing Methods
2. Methods that prevent loss of moisture from
concrete by sealing the surface.
 Water proof plastics
 Forms left in place

Curing Methods
3. Methods that accelerate strength gain by
supplying heat & moisture to the concrete.
 By using live steam (steam curing)
 Heating coils.

Internal Curing (IC)
 Internal curing was originally defined by the
American Concrete Institute (ACI) as
“supplying water throughout a freshly placed
cementitious mixture using reservoirs, via pre-
wetted lightweight aggregates, that readily
release water as needed for hydration or to
replace moisture lost through evaporation or
self-desiccation

Removal of forms
Type of Form Removal Time Period
Walls, columns and vertical sides of
beams
24 to 48 hours as may be decided by
the engineer-in-charge.
Slabs (props left under) 3 days
Beam soffits (props left under) 7 days
Removal of props to slabs
(Spanning upto 4.5 m)
7 days
Removal of props to slabs
(Spanning over 4.5 m)
14 days
Removal of props to beams and
arches (Spanning upto 6 m)
14 days
Removal of props to beams and
arches (Spanning over 6 m)
21 days

1. STRENGTH:
 Concrete is strong in compression but relatively
weak in tension and bending. It takes a great
deal of force to crush concrete, but very little
force to pull it apart or cause bending cracks.
 Tensile strength usually ranges from 7 or 8
% of compressive strength in high-strength
mixes to 11 or 12% in low-strength mixes.
Properties of fresh and Hardened
concrete

2. DURABILITY:
 Durability might be defined as the ability to
maintain satisfactory performance over an
extended service life. Satisfactory performance
is related to intended use.
 Just as concrete mix designs can be
adjusted to produce a variety of strengths,
appropriate concrete ingredients, mix
proportions, and finishes can and should
be adjusted on the basis of required
durability
concrete

3. VOLUME STABILITY:
 All materials expand and contract with changes
in temperature, and porous materials like
concrete also expand and contract with
changes in moisture content. Cement-based
products such as concrete, concrete masonry,
and stucco experience initial shrinkage as the
cement hydrates and excess mixing water
evaporates.
 The higher the cement content, the greater
the tendency for shrinkage cracks to form
concrete

4. WORKABILITY:
 Workability is the relative ease with which a
fresh concrete mix can be handled, placed,
compacted, and finished without segregation
or separation of the ingredients.
 Good workability is required to produce
concrete that is both economical and high
in quality.
concrete

5. CONSISTENCY:
 Consistency is the aspect of workability related
to the flow characteristics of fresh concrete.
 A high-slump concrete is one that is very
fluid, and a low-slump concrete is drier and
more stiff.
concrete

6. COHESIVENESS:
 Cohesiveness is the element of workability
which indicates whether a mix is harsh, sticky,
or plastic.
 Plasticity is a desirable property in
concrete, indicating that a mix can be
moulded and hold a shape when formed.
concrete

Effect Of Temperature On
Shrinkage
Thermal Cracks | Shrinkage Surface Expansion Due To Temperature
Change
Shrinkage of Concrete
Concrete is subjected to changes in volume either
autogenous or induced. Volume change is one of the most
detrimental properties of concrete, which affects the long-
term strength and durability. It causes unsightly cracks in
concrete and called concrete shrinkage.

Creep of Concrete
Creep is indicated when strain in a
solid increases with time while the
stress producing the strain is kept
constant. In more practical terms,
creep is the increased strain or
deformation of a structural element
under a constant load. Depending on
the construction material, structural
design, and service conditions, creep
can result in significant displacements
in a structure. Severe creep strains
can result in serviceability problems,
stress redistribution, prestress loss,
and even failure of structural

Mix design concrete of ordinary
grade concrete
 Mix design is the process of selecting suitable
ingredients of concrete & determining their relative
quantities with the objective of producing as
economically as possible concrete of certain
minimum properties such as workability, strength &
durability.
 Factors to be considered:
1. Water–cement ratio or cement content
2. Cement–aggregate ratio
3. Gradation of aggregate
4. Consistency

Mix design concrete of ordinary
grade concrete

Reinforced Cement Concrete
(RCC)
 Reinforced concrete (RC), also called reinforced
cement concrete (RCC), is a composite
material in which concrete's relatively low tensile
strength and ductility are compensated for by the
inclusion of reinforcement having higher tensile
strength or ductility.
 The reinforcement is usually, though not
necessarily, steel bars (rebar) and is usually
embedded passively in the concrete before the
concrete sets. Worldwide, in volume terms it is an
absolutely key engineering material

Corrosion problem of reinforced
concrete
Corrosion can reduce the
effective cross sectional
area of transverse
reinforcement in beams
and columns, and reducing
the shear capacity of the
section. In concrete slabs,
this can reduce the shear
strength of the slab close of
the columns, and increasing
the chance of punching shear

Cover for Steel Reinforcement
 Covering is provided to arrest the attack of corrosion.
Reinforcement is prone to corrosion and fire for
atmospheric conditions. If the proper cover isn’t
implemented then there is more chance of corrosion
and cracks in hardened RCC.

Controlled Permeability
Formwork (CPF) Systems
 Controlled Permeability Formwork (CPF) can
be used to improve the strength, durability
and appearance of concrete. This is achieved
by allowing excess water and gas to escape
at the surface adjacent to the formwork.
 CPF (controlled permeability formwork) is a
method that has been proven to improve the
durability of surface concrete during the
casting process.

Vacuum dewatering of
concrete
Is a cement concrete for which entered air and
excess water removed by vacuum pump, after
placing it in position
The removal air and excess water after placing
concrete helps in increasing the strength of
concrete by 15 to 29 percent.

Durability of concrete
 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:
1. External: Environmental
2. Internal: Permeability, Characteristics of
ingredients, Air-Void System.

Concrete Defects
CRACKING CRAZING
BLISTERING
DELAMINATION

Concrete Defects
DUSTING CURLING
EFFLORESCENCE
SCALING
SPALLING
AND

Formwork
 It is a temporary construction to contain wet
concrete in the required shape while it is cast
the setting
 It is the term given to either temporary or
permanent molds into which concrete or
similar materials are poured.

Concreteee-and-Reinforced-Concreteee.ppt

Concreteee-and-Reinforced-Concreteee.ppt

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