The document discusses various topics related to concrete structures including: - Concrete is the second most used construction material after water due to its durability and ability to be molded into different shapes. Reinforcement is added to concrete to improve tensile strength. - Types of cement used in concrete structures including Type K and Type M cement. - Reinforced concrete uses steel reinforcement bars to improve tensile strength. Prestressed concrete applies stress before external loads to increase load capacity. - Advantages of concrete structures include availability/cost of materials and ability to take compressive/bending forces. Disadvantages include cracking from shrinkage and weakness in tension. - Concrete creep is a permanent deformation over time under load. Cre

1. ADAM MUSLIM HUSSAINI(阿达姆）
PRESENTATION
• Concrete Structure
• Concrete is the second most used
material for construction after
water in the world. Concrete
structure can take compressive
stresses very effectively but it
cannot take tensile stresses. So
the reinforcement is given to
concrete where the structure is
under the tension load. Concrete
is widely used in today
construction industry today
because of its durability and
compatibility. Moreover concrete
can be mould in any shape which
make it a very useful.

2. • Type K cement:
• It is also referred to as
Klein cement. It
comprises of C4A3S
(C=CaO, A=Al2O3, and
S=SO3), calcium
sulphate (CaSO4) and
lime CaO.
• Type M cement:
• It is constituted by

3. Plain Cement Concrete
• Plain cement concrete has
very low tensile strength. To
improve the tensile strength of
concrete some sort of
requirement is needed which
can take up the tensile
stresses developed in the
structure. The most common
type of reinforcement is in the
form of steel bars which are
quite strong in tension. The
reinforced concrete has
innumerable uses in
construction. For eg: in
building, flyovers, water tanks,
etc.

4. Prestress concrete
• In ordinary reinforced cement concrete,
compressive stresses are taken up by concrete and
tensile stresses by steel alone. The concrete below
the neutral axis is ignored since it is weak in
tension. Although steel takes up the tensile
stresses, the concrete in the tensile zone develops
minute cracks. The load carrying capacity of such
concrete sections can be increased if steel and
concrete both are stressed before the application of
external loads. This is the concept of prestress
concrete.
• The prestressed concrete is uses
in the structures where tension
develops or the structure is
subjected to vibrations, impact
and shock like girders, bridges,
railway sleepers, electric poles,
gravity dam, etc.

5. Advantages of concrete
structure
• Ingredients used in concrete such as, cement, aggregates and
water are readily available and cheap.
• Concrete assumes the shape of its mould and it can be poured and
cast into any shape.
• Concrete when used along with reinforcement, is capable of taking
bending and tension forces.
• The compressive strength of concrete is very high making it
reliable to be used for structures and components under
compressive loads.
• The break through in prestressed concrete applications enables
reduced section sizes and reduction in self-weight.
• Due to massive nature, high unit weight and water tightness,
concrete can be used for water retaining structures like Dams.

6. Disadvantages of concrete
structure
• Due to drying shrinkage and moisture
expansion concrete may crack. Therefore
construction joints are provided to avoid these
types of cracks.
• Concrete is weak in tension.
• High Self weight of concrete is not always
favorable for seismic prone structures.
• Sustained loads develop creep in structures.
• If salts are present in the concrete then it will
results in the efflorescence in concrete structure

7. Concrete Creep Definition, Creep
deformation Stages & Design Strategies
• When load is applied on a
concrete specimen, shows an
instantaneous deformation
followed by slow increase of
deformation is called concrete
creep. Creep is a time-
dependent permanent (plastic)
deformation under a certain
applied load. Generally, creep
occurs at high temperature
(thermal creep) but can also
happen at room temperature
depending on the material
(e.g. lead or glass), although
this happens at a much slower
rate.

8. • As a result, the material
undergoes a time-
dependent increase in
length, which could
become quite dangerous
while in use. The rate of
deformation is called the
creep rate. It is the slope
of the line in a creep
strain vs. time curve (see
below).

9. stages of creep deformation
• Creep deformation has three
stages; Primary creep starts
rapidly and slows down with
time. Secondary creep
progresses at a relatively
uniform rate. Tertiary creep
has an accelerated rate of
deformation which terminates
when the material fails (breaks
or ruptures). It is associated
with both necking and the
formation of grain boundary
voids. There are several
design strategies that can be
adopted to avoid creeping in
materials:
• Reduce the effect of grain
boundaries (use single crystal
material with large grains).
• Add solid solutions to fill
the voids in the material.
• Use materials with high
melting temperatures.
• Consult creep test data
during materials selection.

10. Creep In Detail
• When a load is applied on a concrete
specimen. the specimen first shows an
instantaneous deformation which is
then followed by slow further increase
of deformation. This slow increase of
deformation, discovered in 1907 by
Hatt, is called creep. There is always
strain associated with applied stresses
to any material. ASTM E 6-03 defines
creep as “the time-dependent increase
in strain in a solid resulting from force.”
To define creep one must consider two
identical specimens subjected to
exactly the same environmental
histories, one specimen being loaded
and the other load-free (companion
specimen). The difference of the
deformation of these two specimens
defines the instantaneous deformation
plus creep.

11. Reinforcements in a Reinforced
Concrete Beam
• In RCC beams, elements are designed to
resist the loads that cause bending moment,
shear forces and sometimes in some cases,
it also causes torsion along their length. It’s
a known fact that concrete is strong in
compression and very weak in tension. The
steel reinforcement present in the concrete,
is used to take up tensile stresses in
reinforced concrete beams.
• Mild steel bars of round
section were utilized in
RCC work. But when
deformed and twisted
bars were introduced, the
usage of mild steel bars
declined. Ribs are
indented on the surface
of the deformed or HYSD
bars which results in
increasing the bond
strength by atleast 40%
when compared to that of
mild steel bar.

12. Beam and Slab Floor System
• This system consists of beams framing into
columns and supporting slabs spanning
between the beams. It is a very traditional
system. The relatively deep beams provide
a stiff floor capable of long spans, and able
to resist lateral loads. However, the
complications of beam formwork, co-
ordination of services, and overall depth of
floor have led to a decrease in the popularity
of this type of floor.
• The traditional reinforced
concrete beam-and-slab floor
has an economical span ‘L’ of
D x 15 for a single span and D
x 20 for a multi-span, where D
is the depth of the slab plus
beam. The depth of slab
between the beams can be
initially sized using the span-
to-depth ratios for a flat plate.
Prestressing is not normally
used with this system.

13. • Advantages:
• Traditional effective
solution
• Long spans.
• Disadvantages:
• Penetrations through beams for
large ducts difficult to handle
• Depth of floor
• Greater floor-to-floor height.

14. Formwork for Beams and Slabs
• Forms are molds to receive
concrete in its’ plastic form.
• Formwork is temporary
structure, as such, it is not
normally shown on the
drawings.
• Formwork Materials
• Wood
• Either all-wood or some wood components
• Plywood
• Aluminum
• Steel
• Plastics
• Lumber
• Designated by Cross Sections, Nominal Dimensions (prior to
finishing)
• After cut length wise, finishing operations reduces actual dimensions
• 2 x 4 Plank 1 1/2 x 3 1/2 ® 2” by 4” in S4S
• Lengths are multiples of 2 ft (8, 10, 12, 14, 16,…)
• Specified by type and grade
• Type: pine, oak, fir
• Grade: Selected (A, B, C, D) and Common (1, 2, 3, 4)
• Selected (A best, D poor quality)
• Cost ® Kind, grade, size, length, milling, quantity, freight

15. Shrinkage Cracking in Concrete
Structures | Long Term Effects
• Internal or external restraints in a concrete
structural element may resist free shrinkage
of concrete, over time this leads to
Shrinkage Cracking. In concrete structures,
the volumetric reduction that happen due to
the loss of moisture by evaporation is known
as the shrinkage of concrete. This
deformation is time dependent and it
reduces the volume without any impact of
external forces. When cement paste is pure
(cement+water), it may shrink upto 1%.
Further, the aggregates added to it resists
the deformation which reduces the
magnitude of this volume decrease to
0.06%. Deydration of cement is one of the
reasons for shrinkage in concrete. This
dehydration is the loss of water due to
evaporation. Thus, concrete
continues to shrink during
its life span at a reduced
rate.

16. What is Shrinkage Compensating
Concrete?
• Shrinkage compensating concrete is the
most efficient and extensively used material
in the recent years used to eradicate or
minimize cracking which is caused due to
drying shrinkage in RCC structures. Drying
shrinkage is basically decrease in volume
caused by moisture loss in the process of
hardening of concrete, which ultimately
results in crack formation.
• Shrinkage Compensating Concrete can be
defined as an expansive concrete or a
concrete consisting of an expansive cement
or expansive admixture, which induces
expansion whilst hardening and
consequently offsets the contraction during
drying shrinkage. When the expansive
concrete is restrained accurately with
appropriate reinforcement, it will expand to a
value equal or slightly higher than the
foreseen amount of drying shrinkage.

17. Mechanism of Shrinkage
compensating concrete
• Shrinkage compensating concrete is designed to
work co-jointly with internal restraints,
reinforcements. Compressive stresses will be
induced in the concrete as well as tension in the
steel restraints during time of expansion of the
concrete. This results in off-setting of tensile
stresses and negative strains induced in the
concrete by drying shrinkage. Further, a residual
compression will always remain in the concrete,
eradicating the risk of shrinkage cracking.
• Expansion is achieved by huge amount of
ettringite formed, as soon as the type K
cement hydrates. Ettringite is nothing but a
mineral crystal that forms rapidly when
Portland cement and water is mixed. The
crystal nature of ettringite takes up a
significantly huge amount of volume in
concrete. This property of ettringite results in
the primary expansion of concrete after
setting.

18. Types of Expansive Materials
• Expansive component is the key
ingredient of shrinkage compensating
mechanism. These are added to a
dosage of 5.0 to upto 15% by cement
weight. The mix proportioning is
adjusted accordingly when these
additive are used. Various types of
expansive materials are as follows:
• Type K cement:
• It is also referred to as Klein cement. It comprises of C4A3S
(C=CaO, A=Al2O3, and S=SO3), calcium sulphate (CaSO4)
and lime CaO.
• Type M cement:
• It is constituted by blending mixes of Portland cement,
calcium-aluminate cement (CA and C12A7), and calcium
sulphate proportioned in accordance with the requirement.
• Type S cement:
• It is primarily Portland cement
consisting of large amount of
Tricalcium aluminate (C3A)
and gypsum (Calcium
Sulphate (CS)).
• Admixtures
• Expansive admixtures are
made of clinker, alumstone,
anhydrous gypsum.

19. Methods to repair Shrinkage Cracks
• If shrinkage cracks have already
occurred in the structure, following
repair methods can be adopted.
These repair methods will prevent
further deterioration of the
structure or reinforcement due to
environmental effects.
• Epoxy injection
• Routing and sealing depending on width of
crack
• Drilling and plugging can be adopted where
cracks run in straight lines and are
accessible at one end
• Gravity filling
• Dry packing
• Polymer impregnation