 will cause the pavement to rise because of non uniform of ice crystal.

Similarly when
the ice melt the pavement will penetrate into the sub grade when load comes on it. To
overcome this frost protection layer should be provided. Generally good base course
and sub base course themselves act as the frost protection layer.

 GRANULAR SUB BASE OR STABILIZED SUB BASE COURSE:- It is

the third layer from the top and is in contact with sub grade soil and base course. It is
constructed by using low quality aggregate than the base course but they should be
better quality than sub grade. Generally sub base course is not required when the traffic
loading is light. When the loading exceeds 100000 pounds it should be constructed. Its
primary function is to provide support for the top layers and it also serves as frost
action controller and prevents the intrusion of fines from sub grade to top layer. The
drainage facility will also improve when there is a sub base course.

 GRANULAR BASE:- The base course or granular base is the second layer from
the top and constructed using crushed aggregates. The course helps the surface course
to take additional load. It provide stable platform to construct rigid pavement. It is also
useful to provide sub surface drainage system. The frost action can be controlled by the
stabilized base course. It helps to control swelling of sub grade soil. The base course
thickness should be minimum 100mm.

 CONCRETE SLAB:- The concrete slab is the top most layer which direct contract
with vehicular loads. This is also called surface course. It is water resistance and
prevents the water infiltration into base course. It offer friction to the vehicle to
provide skid resistance. The thickness of concrete slab is kept between 150mm to
300mm.

2.4 JOINTS:

Joints are purposefully placed discontinuities in a rigid pavement surface course. The most
common type of pavement joints, defined by their function, are (AASHTO, 1993): contraction,
expansion, isolation and construction.
2.4.1 CONSTRUCTION JOINTS:

A contraction joint is a sawed, formed, or tooled groove in a concrete slab that creates a
weakened vertical plane. It regulates the location of the cracking caused by dimensional changes
in the slab. Unregulated cracks can grow and result in an unacceptabley rough surface as well as
water infiltration into the base, subbase and subgrade, which can enable other types of pavement
distress. Contraction joints are the most common type of joint in concrete pavements, thus the
generic term "joint" generally refers to a contraction joint.

Contraction joints are chiefly defined by their spacing and their method of laod transfer. They are
generally between 1/4 - 1/3 the depth of the slab and typically spaced every 3.1 - 15 m (12 - 50
ft.) with thinner slabs having shorter spacing. Some states use a semi-random joint spacing
pattern to minimize their resonant effect on vehicles. These patterns typically use a repeating.

Pavement showing contraction Joints Missing Contraction Joint

Sequence of joint spacing {for example: 2.7m (9 ft)} then 3.0m (10ft) the 4.3m (14 ft) the 4.0m
(13 ft). Transverse contraction joints can be cut at right angles to the direction of traffic flow or
at an angle (called a "skewed joint"). Skewed joints are cut at obtuse angles to the direction of
traffic flow to help with load transfer. If the joint is properly skewed, the left wheel of each axle
will cross onto the leave slab first and only one wheel will cross the joint at a time, which results
in lower load transfer stresses.
2.4.2 EXPANSION JOINTS:

An expansion joints is placed at a specific location to allow the pavement to expand without
damaging adjacent structures or the pavement itself. Up until the 1950s, it was common practice
in the U.S. to use plain, jointed slabs with both contraction and expansion joints (Sutherland,
1956). However, expansion joint are not typically used today because their progressive closure
tends to cause contraction joints to progressively open (Sutherland, 1956).

Progressive or even large seasonal contraction joint opening cause a loss of load transfer -
particularly so far joint without dowel bars.

2.4.3 ISOLATION JOINTS:

An isolation joint is used to lessen compressive stresses that develop at T- and unsynmmetrical
intersections, ramps, bridges, building foundations, drainage inlets, manholes, and anywhere
different movement between the pavement and a structure (or another existing pavement) may
take place (ACPA, 2001). They are typically filled with a joint filler matterial to prevent water
and dirt infiltration.
2.4.4 CONSTRUCTION JOINTS:

A construction joint is a joint between slabs that results when concrete is placed at different
times. This type of joint can be further broken down into transverse and longitudinal construction
joints. Longitudinal construction joints also allow slab warping without appreciable separation or
cracking of the slabs.

2.5
LOAD TRANSFER:

"Local transfer" is a term used to describe the transfer (or distribution) load across discontinuities
such as joints or cracks (AASHTO, 1993). When a wheel load is applied at a joint or crack, both
the loaded slab and adjacent unloaded slab deflect. The amount the unloaded slab deflects is
directly related to joint performance. If a joint is performing perfectly, both the loaded and
unloaded slabs deflect equally. Load transfer efficiency is defined by the following equation:

Where ∆ 2 = approach slab deflection

∆ 1 = leave slab deflection

This efficiency depends on several factors, including temperature (which affects joint opening),
joint spacing, number and magnitude of load applications, foundation support, aggregate particle
angularity, and the presence of mechanical load transfer devices. Most performance problems
with concrete pavement are a result of poorly performing joints (ACPA, 2001). Poor load
transfer creates high slab stresses, which contribute heavily to distresses such as faulting,
pumping and corner breaks. Thus, adequate load transfer is vital to rigid pavement performance.
Load transfer across transverse joints/cracks is generally accomplished using one of three basic
methods: aggregate interlock, dowel bars, and reinforcing steel.

2.5.1 AGGREGATE INTERLOCK:

Aggregate interlock is the mechanical locking which forms between the fractured surface along
the crack below the joint saw cut. Some low volume and secondary road systems rely entirely on
aggregate interlock to provide load transfer although it is generally not adequate to provide long
term load transfer for high traffic (and especially truck) volumes. Generally aggregate interlock
is ineffective in cracks wider than about 0.9mm (0.035 inches). Often, dowel bars are used to
provide the majority of load transfer.
2.5.2 DOWEL BARS:

Dowel bars are short steel bars that provide a mechanical connection between slabs without
restricting horizontal joint movement. They increase load transfer efficiency by allowing the
leave slab to assume some of the load before the load is actually over it. This reduces joint
deflection and stress in the approach and leave slabs.

Dowel bars are typically 32 to 38mm (1.25 to 1.5 inches) in diameter, 460mm (18inches) long
and spaced 305mm (12 inches) apart. Specific location and numbers vary by state; however a
typical arrangement might look like figure below. In order to prevent corrosion, dowel bars are
either coated with stainless steel as (Figure A) or epoxy as (Figure B). Dowel are usually inserted
at mid slab depth and coated with a bond breaking substance to prevent bonding to the PCC.
Thus, the dowels help transfer load but allow adjacent slabs to expand and contract independent
of one another. Figure B shows typical dowel bar locations at a transverse construction joint.
 Fig. (A) Fig (B)

2.5.3 REINFORCING STEEL:

Reinforcing steel can also be used to provide load transfer. When reinforcing steel is used,
transverse contraction joints are omitted. Therefore, since there are no joints, the PCC cracks on
its own and the reinforcing steel provide load transfer across these cracks. Unlike dowel bars,
reinforcing steel is bonded to the PCC on either side of the crack in order to hold the crack
tightly together.

Typically, rigid pavement reinforcing steel consists of grade 60 (yield stress of 60 ksi (414 MPa)
No. 5 or No. 6 bars (Eres, 2001). The steel constitutes about 0.6 - 0.7 percent of the pavement
cross-sectional area (ACPA, 2001) and is typically placed at slab mid-depth orshallower. At
lease 63mm (2.5 inches) of PCC cover should be maintained over the reinforcing steel to
minimize the potential for steel corrosion by chlorides found in deicing agents (Burke, 1983).

2.5.4 TIE BARS:

Tie bars either deformed steel bars or connectors used to hold the faces of abutting slabs in
contact (AASHTO, 1993). Although they may provide some minimal amount of load transfer,
they are not designed to act load transfer devices and should not be used as such (AASHTO,
1993). Tie bars are typically used at longitudinal joints Figure C or between an edge joint and a
curb or shoulder. Typically tie bars are about 12.5mm (0.5inches) in diameter and betweeen 0.6
and 1.0m (24 and 40 inches long).