This document provides an introduction to reinforced concrete, including its components and advantages/disadvantages as a structural material. It discusses how concrete and steel work together compatibly in reinforced concrete. The key structural elements and design considerations like fitness for purpose, safety, economy and maintainability are outlined. Common types of Portland cement and admixtures like air-entraining, water-reducing, retarding and accelerating admixtures are described. Design codes and the historical background of reinforced concrete are also mentioned.

1. INTRODUCTION TO REINFORCED CONCRETE
CE 535 /D

2. CONCRETE AND REINFORCED CONCRETE
CONCRETE
 Rocklike Material
 Ingredients
 Portland Cement
 Course Aggregate
 Fine Aggregate
 Water
 Admixtures (optional)
REINFORCED CONCRETE
 It is a combination of concrete and steel wherein the steel
reinforcement provides the tensile strength lacking in the
concrete.

3. ADVANTAGES OF REINFORCED CONCRETE AS A
STRUCTURAL MATERIAL
1. High compressive strength
2. Great resistance to the actions of fire and water.
3. Very rigid.
4. Low-maintenance material
5. Very long service life
6. Only economical material available for footings, floor
slabs, basement walls, piers, and similar applications.
7. Formed into different shapes.
8. Inexpensive local materials.
9. Lower grade of skilled labor is required for erection

4. DISADVANTAGES OF REINFORCED CONCRETE AS A
STRUCTURAL MATERIAL
1. Very low tensile strength
2. Formwork is very expensive.
3. The low strength per unit of weight of concrete
leads to heavy members.
4. The properties of concrete vary widely because of
variations in its proportioning and mixing.

5. HISTORICAL BACKGROUND

6. COMPATIBILITY OF CONCRETE AND STEEL
 Concrete: high
compressive strength, low
tensile strength
 Steel: high tensile strength,
low compressive strength
Concrete + Steel:
• Economical structural material, strong in compression
& tension
• Concrete provides corrosion protection and fire
resistance

7. STRUCTURAL DESIGN
Process of
determining, selection
of and determination
of for the structure to
be built
Aim: ensure that the
structure will perform
satisfactorily during its
design life

8. STRUCTURAL DESIGN PURPOSES
Fitness for purpose Safety and reliability
Economy Maintability

9. FITNESS FOR PURPOSE
Arrangement of spaces, spans, ceiling height, access and traffic flow must
complement the intended use.
The structure should fit its environment and be aesthetically pleasing

10. SAFETY AND RELIABILITY
Structure must be strong to safely support all anticipated loadings
Structure must not deflect, overturn, tilt, vibrate or crack in a manner
that impairs its usefulness

13. ECONOMY
Overall cost of structure
should not exceed the client’s
budget
Designer should take into
account: cost of materials,
buildability, construction time,
cost of temporary structures
and maintenance costs

14. MAINTAINABILITY
STRUCTURE SHOULD BE
DESIGNEDTO REQUIRE A
MINIMUM MAINTENANCE,
CAN BE MAINTAINED IN A SIMPLE
FASHION

15. STRUCTURAL ELEMENTS
Beams: horizontal
members carrying lateral
loads
Slabs: horizontal plate
elements carrying lateral
loads
Columns: vertical members
carrying primarily axial
loads but generally
subjected to axial load and
moment
Walls: vertical plate
elements resisting vertical,
lateral or in-plane loads
Foundations: pads or strips
supported directly on the
ground that spread loads
from columns or walls to
the ground
Stairs: plate elements
consists of a flight of steps,
usually with one or more
landings provided between
the floor levels

17. DESIGN CODES

18. TYPES OF PORTLAND CEMENT
Type 1
Standard Portland
cement - Used for
general purposes;
air entrained
Type II
Modified Portland
cement - Used
when sulphate
resistance and/or
generation of
moderate heat of
hydration are
required; air
entrained
Type III
High early strength
Portland cement -
Used for early
strength and cold
weather
operations; air
entrained
Type IV
Low heat Portland
cement - Used
where low heat of
hydration is
required; air
entrained
TypeV
High sulphate-
resistant concrete -
Used where
sulphate
concentration is
very high; also used
for marine and
sewer structures;
air entrained

19. ADMIXTURES
ADMIXTURES ARE THOSE INGREDIENTS IN
CONCRETE OTHER THAN PORTLAND
CEMENT,WATER,AND AGGREGATES THAT
ARE ADDED TO THE MIXTURE
IMMEDIATELY BEFORE OR DURING MIXING
(FIG. 6-1).ADMIXTURES CAN BE CLASSIFIED
BY FUNCTION AS FOLLOWS:

20. MOST USED
ADMIXTURES
Air-entraining admixtures
Water-reducing admixtures
Plasticizers
Accelerating admixtures
Retarding admixtures
Hydration-control admixtures

21. MOST USED
ADMIXTURES
Corrosion inhibitors
Shrinkage reducers
Alkali-silica reactivity inhibitors
Colouring admixtures
Miscellaneous admixtures such workability, bonding, damp proofing,
permeability reducing, grouting, gas-forming, and pumping admixtures

23. THE MAJOR REASONS FOR USING ADMIXTURES ARE:
To reduce the cost of concrete
construction
To achieve certain properties in
concrete more effectively
than by other means
To maintain the quality of concrete
during the stages of mixing,
transporting, placing, and curing in
adverse weather conditions
To overcome certain emergencies
during concreting operations

24. AIR-ENTRAINING
ADMIXTURES
 used to purposely introduce
and stabilize microscopic air
bubbles in concrete.Air-
entrainment will dramatically
improve the durability of
concrete exposed to cycles of
freezing and thawing (Fig. 6-2).
Entrained air greatly improves
concrete's resistance to surface
scaling caused by chemical
 de-icers

25. AIR-ENTRAINING
ADMIXTURES
 The primary ingredients used
in air-entraining admixtures are
salts of wood resin (Vinsol
resin), synthetic detergents,
salts of petroleum acids, etc.

26. WATER-REDUCING ADMIXTURES
used to reduce the quantity of
mixing water required to produce
concrete of a certain slump, reduce
water-cementing materials ratio,
reduce cement content, or increase
slump.
Typical water reducers reduce the
water content by approximately 5%
to 10%.

27. WATER-
REDUCING
ADMIXTURES
MATERIALS:
LIGNOSULFONATES.
CARBOHYDRATES.
HYDROXYLATED
CARBOXYLIC ACIDS.
The effectiveness of water reducers on concrete is a function of
their chemical composition, concrete temperature, cement
composition and fineness, cement content, and the presence of
other admixtures.

29. SUPERPLASTICIZERS
(HIGH-RANGE
WATER REDUCERS)
These admixtures are added to
concrete with a low-to-normal
slump and water-cementing
materials ratio to make high-
slump flowing concrete.
Flowing concrete is a highly
fluid but workable concrete
that can be placed with little or
no vibration or compaction
while still remaining essentially
free of excessive bleeding or
segregation.

30. APPLICATIONS WHERE FLOWING CONCRETE IS USED:
thin-section
placements,
areas of closely spaced
and congested
reinforcing steel,
pumped concrete to
reduce pump pressure,
thereby increasing lift
and distance capacity,
areas where
conventional
consolidation methods
are impractical or can
not be used, and
for reducing handling
costs.

31. FLOWABLE CONCRETE WITH HIGH SLUMP

32. IS EASILY PLACED

33. EVEN IN AREAS OF HEAVY REINFORCING STEEL
CONGESTION

34.  Low water to cement
ratio concrete with low
chloride permeability---
easily made with high-
range water reducers- is
ideal for bridge decks

35.  Plasticized, flowing concrete is
easily placed in thin sections

36. SUPERPLASTICIZERS (HIGH-RANGE WATER REDUCERS)
 Typical superplasticizers include:
 Sulfonated melamine formaldehyde condensates.
 Sulfonated naphthalene formaldehyde condensate.
 Lignosulfonates.
 Polycarboxylates.

37. SUPERPLASTICIZERS (HIGH-RANGE WATER
REDUCERS)
 bleed significantly less than control concretes of equally high slump and
higher water content.
 High-slump, low-water-content, plasticized concrete has less drying
shrinkage than a high-slump, high-water-content conventional concrete.
 has similar or higher drying shrinkage than conventional low-slump,
low-water-content concrete.
 The effectiveness of the plasticizer is increased with an increasing
amount of cement and fines in the concrete.

38. RETARDING ADMIXTURES
 used to retard the rate of setting of concrete at high temperatures of
fresh concrete (30°C or more).
 One of the most practical methods of counteracting this effect is to
reduce the temperature of the concrete by cooling the mixing water or
the aggregates.
 Retarders do not decrease the initial temperature of concrete.
 The bleeding rate and capacity of plastic concrete is increased with
retarders.

39. RETARDING ADMIXTURES
 The typical materials used as retarders are:
 Lignin,
 Borax,
 Sugars,
 Tartaric acid and salts.

41. RETARDING ADMIXTURES
 Retarders are used to:
1. offset the accelerating effect of hot weather on the setting of concrete,
2. delay the initial set of concrete when difficult or unusual conditions of
placement occur,
3. delay the set for special finishing processes such as an exposed aggregate
surface.

42. RETARDING
ADMIXTURES
some reduction in strength at early ages (one to three
days) accompanies the use of retarders.
The effects of these materials on the other properties of
concrete, such as shrinkage, may not be predictable.
Therefore, acceptance tests of retarders should be
made with actual job materials under anticipated
job conditions.

43. ACCELERATING
ADMIXTURES
used to accelerate strength development
of concrete at an early age.
Typical Materials are:
• Calcium chloride: most commonly used for plain
concrete.
• Triethanolamine.
• Calcium formate.
• Calcium nitrate.
• Calcium nitrite.

44. CORROSION INHIBITORS

45. CORROSION
INHIBITORS
The chlorides can cause corrosion of steel reinforcement
in concrete.
Ferrous oxide and ferric oxide form on the surface of
reinforcing steel in concrete.
Ferrous oxide reacts with chlorides to form complexes
that move away from the steel to form rust.The chloride
ions continue to attack the steel until the passivating oxide
layer is destroyed.

46. CORROSION
INHIBITORS
Corrosion-inhibiting admixtures chemically
arrest the corrosion reaction.
Commercially available corrosion
inhibitors include:
• calcium nitrite,
• sodium nitrite,
• dimethyl ethanolamine,
• amines,
• phosphates,
• ester amines.

47. SHRINKAGE-
REDUCING
ADMIXTURES
 Shrinkage cracks, such as
shown on this bridge deck, can
be reduced with the use of
good concreting practices and
shrinkage reducing admixtures.

48. CHEMICAL ADMIXTURESTO REDUCE ALKALI-AGGREGATE REACTIVITY
(ASR INHIBITORS)
 Expansion of specimens made with lithium
carbonate admixture

49. COLORING
ADMIXTURES
(PIGMENTS)
 Red and blue pigments were
used to color this floor