Joints in concrete

JOINTS IN
CONCRETE
STRUCTURES
PRESENTED
BY
AGLAIA

Introduction
 Joints in concrete construction are construction,
expansion, contraction and isolation joints. These
joints are placed in concrete slabs and pavements
at regular intervals to prevent development of
cracks in concrete.
Types of joints in concrete constructions are:
 Construction Joints
 Expansion Joints
 Contraction Joints
 Isolation Joints

Construction Joints
 They are placed in a concrete slab to define the extent
of the individual placements, generally in conformity
with a pre determined joint layout.
 They must be designed in order to allow displacements
between both sides of the slab.
 They have to transfer flexural stresses produced in the
slab by external loads.
 They must allow horizontal displacement right-angled
to the joint surface that is normally caused by thermal
and shrinkage movement.
 At the same time they must not allow vertical or
rotational displacements.

Types of Construction
Joints in Concrete
Structures

Expansion joints
 They are placed in concrete to prevent expansive
cracks formed due to temperature change.
 Concrete undergoes expansion due to high
temperature when in a confined boundary which
leads to cracks.
 Expansion joints are provided in slabs, pavements,
buildings, bridges, sidewalks, railway tracks, piping
systems, ships, and other structures.
 This article emphases on need of expansion joint in
concrete, characteristics of expansion joints, types of
expansion joint and installation of expansion joints.

Cracks developed due to expansion of
concrete.

Need of Expansion Joint in
Concrete
 Concrete moves during expansion and shrinkage, due to
which the structural elements shift slightly.
 To prevent harmful effects due to concrete movement,
several expansion joints are incorporated in concrete
construction, including foundations, walls, roof
expansion joints, and paving slabs.
 These joints need to be carefully designed, located, and
installed.
 If a slab is positioned continuously on surfaces
exceeding one face, an expansion joint will be necessary
to reduce stresses.
 Concrete sealer may be used for the filling of gaps
produced by cracks.

Characteristics of Expansion
Joints
 They permits thermal contraction and expansion
without inducing stresses into the elements.
 It is designed to absorb safely the expansion and
contraction of several construction materials, absorb
vibrations, and permit soil movements due to
earthquakes or ground settlement.
 They are normally located between sections of
bridges, paving slabs, railway tracks, and piping
systems.
 They are incorporated to endure the stresses.
 It is simply a disconnection between segments of the
same materials.
 In the concrete block construction, they are expressed
as control joints.

Types of Expansion Joint
 Bridge Expansion Joint
 Masonry Expansion Joint
 Railway Expansion Joint
 Pipe Expansion Joints

Bridge Expansion Joint
 They are designed to allow for continuous traffic
between structures while accommodating
movement, shrinkage, and temperature variations on
reinforced and prestressed concrete, composite, and
steel structures.
Expansion joint in bridges

Masonry Expansion Joint
 Clay bricks expand as they absorb heat and
moisture. This places compression stress on the
bricks and mortar, encouraging bulging or flaking.
 A joint replacing mortar with elastomeric sealant will
absorb the compressive forces without damage.

Railway Expansion Joints
 if the track is laid on a bridge having expansion
joint, providing a expansion joint in the track
becomes mandatory to mitigate the expansion in
base concrete structure.
Fig 3: Expansion joint in
railway tracks.

Pipe Expansion Joints
 Pipe expansion joints are necessary in
systems that convey high temperature
substances such as steam or exhaust gases,
or to absorb movement and vibration.

 Based on the type of material used in making of
joint, expansion joints are further classified into
following types,
1. Rubber expansion joint
2. Fabric expansion joint
3. Metal expansion joint
4. Toroidal expansion joint
5. Gimbal expansion joint
6. Universal expansion joint
7. In-line expansion joint
8. Refractory lined expansion joint

Use of filler material in expansion joint

Installation of Expansion Joints
 The depth of an expansion joint is usually one
fourth of the slab thickness, or more if necessary.
 The expansion joint gap depends on the type of
slab, like floating slab floor, vehicle pavement,
sidewalk, or monolithic slab foundation.
 It is also influenced by the slab dimensions, type
of concrete, and the reinforcing materials being
used.
 Cracks in concrete may occur at the expansion
joints due to improper concrete mix or curing.
 These conditions cause shrinkage between the
expansion joints and cracks can be formed.

Pre-Concrete Installation
 When the site is prepared for the concrete pouring
and the provisioning of the expansion joints in
slabs are made prior to the placing of concrete.
 An individual expansion joint is created by the
insertion of a flexible material that runs along the
joint length.
After Concrete Installation
 Once the concrete is set, suitable tools are used
for making grooves in the poured concrete for
placing of the joint materials.

Contraction Joints
 Contraction joints in concrete are provided at
regular interval to from a weak plane, so that
cracks are formed at the joints but not in
undesired places.
 Contraction joints are provided in concrete
pavements, slabs, walls, floors, dams, canal
linings, bridge, retaining walls etc.
 When concrete is placed, due to shrinkage,
creep and thermal movement concrete tends to
reduce in size due to which small cracks are
formed in the concrete at weak zone.

Cracks formed due to shrinkage of concrete.

Need of Contraction joint in
Concrete
 Concrete tends to shrink or reduce in size when it
starts hardening. This shrinkage of concrete
creates tensile stresses in the concrete which
develops the minute cracks at the weak plane.
 These cracks are restricted and prevent the
formation of large cracks due to the presence of
reinforcement in the concrete. But if its unreinforced
concrete, the small cracks tends to develop into a
large cracks at irregular interval
 To prevent such cracks, contraction joints must be
installed at appropriate intervals. It is also
recommended to install these joints in reinforced

Fig 2 : Forming of
vertical contraction
joint
Fig 3: Sawed contraction joint.

Fig 4: Finishing of contraction joint.

Isolation Joints
 The joints provided to accommodate the expansion of
adjacent parts in a building are known as expansion
joints.
 They allow movement to occur between a concrete
slab and adjoining columns and walls of a building.
 They are provided to separate new concrete from
existing or adjacent construction, which might expand
and contract differently or experience different soil
settlement or other movement.
 If the fresh concrete were not separated from these
elements by an isolation joint, a crack could form
where the two meet.
 The should be 1/4 in. to 1/2 in. wide, and filled with a
molded fiber, cork, or rubber strip that is set 1/4 in.

Thank you
For more…. Mail to
aglaiaconnect2018@gmail.com

Joints in concrete

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