joints in cement concrete pavement

1. JOINTS IN CC PAVEMENTS
• Concrete slabs are subjected to volumetric
changes due to temperature variations,
shrinkage during setting and moisture changes
• If a long slab is built without any joints, cracks
may develop due this volumetric changes
• A concrete pavement reasonably free from
cracks can only be built if it is divided into slabs
by interposing joints

2. • Joints are provided in cc pavements at optimal
regular intervals to allow volumetric changes
– Shrinkage
– Contraction
– Expansion
– Warping in upward and downward directions

3. Types of Joints
• Based on function and purpose of joints

5. Transverse Joints
• Joints provided in transverse direction are
called transverse joints
– Expansion joints
– Contraction joints
– Construction joints

6. Expansion Joints
• Expansion joints are intended to provide space
for expansion of slabs due to rise in temperature
of slab above the construction temperature
• Expansion joints also relieve stresses caused by
contraction and warping

7. • The main features of an expansion joint
– A space for expansion
– A joint filling compressible material interposed in the
above space
– A joint sealing arrangement
– Dowel bars for load transfer
– A thin coating of bitumen in the expanding portion of
dowel bar to break bond with concrete and permit
expansion
– A card board or metal cap at the expanding end of
dowel bar filled with cotton waste

8. Contraction Joints
• When temperature of slab falls below the laying
temperature, slab contracts
• If long length of slab is laid, contraction induces
tensile stresses and slab cracks
• If contraction joints are provided at suitable
intervals transversely, cracks at places other
than the joints can be avoided
• Contraction joints also relieve warping stresses
to some extend
• These joints are placed closer than expansion
joints

9. • A groove joint, also called a dummy joint is a
popular form of contraction joint

10. • The main features of contraction joint are
– A surface groove formed by driving a flat metal plate
when concrete is green. It is not less than 6 mm wide
and has a depth equal to 1/3 rd to ¼ th the depth of
pavement
– A sealing compound to prevent ingress of external
material
– A dowel bar arrangement to adequately transfer load
across joint. This is dispensed with if aggregate
interlock is able to transfer the load

11. Construction Joint
• A construction joint is necessary when work has
to be stopped at a point where there would be
otherwise no other joint
• A groove in the joint with a sealing compond is
desirable
• Reinforcement should be provided across the
joint
• It is advisable to plan a day’s work such that the
works stops at a contarction or expansion joint
such that separate construction joints can be
avoided

12. Longitudinal Joints
• When pavement width is more than 4.5 m, it is
necessary to provide longitudinal joint
• However as the lane width of pavements are
generally 3.5 m to 3.75 m, longitudinal joints are
provided between each traffic lane
• These joints mainly responsible for relieving
warping stresses
• To aid load transfer, tie bars are often used
across longitudinal joints. Tie bars are thinner
than dowels, and use deformed reinforcing bars
rather than smooth dowel bars.

13. Spacing of Joints
• Spacing of joints is governed by number of
factors such as
– Temperature variation
– Thickness of slab
– Amount of reinforcement provided

14. Spacing of expansion joints
• Spacing of expansion joint is decided based on
– maximum temperature variation expected and
– width of the joint
• Width/gap in expansion joint depends on the
length of slab
– Greater the length of slab, greater the width of gap
required for expansion
– Use of wide expansion joint gap should be avoided as
it is difficult to keep them properly filled in
– It is recommended a maximum gap width of 2.5 cm

15. • Spacing of expansion joint is given by,
Where, Le- spacing of expansion joint in m
δ’- half the width of gap in cm
e- coefficient of thermal expansion of
concrete
T2-T1- rise in temperature
• IRC recommends a maximum spacing 140 m
between expansion joints

16. Spacing of Contraction Joints
• Slab contracts due to fall in temperature below
construction temperature
• Contraction also happens due to shrinkage
during initial curing period
• Contraction is resisted by the friction developed
at the interface
• Spacing of contraction joints depends on
– Coefficient of friction
– Allowable stress in in tension in cc
– Unit weight of concrete

17. • Spacing of contraction joint is given by,
• Where Lc-spacing of contraction joint in m
f – coefficient of friction
Sc- allowable stress in tension in
concrete
W – unit weight of concrete kg/m3

18. • Spacing of contraction joint, when reinforcement
is provided
– It is assumed that the reinforcement takes the entire
tensile force in the slab caused by frictional resistance
of interface
– Then spacing of contraction joint is given by,
– Where, Ss-allowable tensile strength of steel reinforcement
b- width of slab in m
h- thickness of slab in cm
As-total area of steel reinforcement across the slab
width in cm2