The roads having their
wearing surface consisting of cement concrete state (plain or reinforced) are
called cement concrete roads or simply concrete road. These roads fall under
rigid pavement category. These are high cost roads. These are all weather
roads. These roads being having excellent riding surface, pleasing appearance
and long life are much preferred. It has a high initial cost. These are more
popular in advanced countries. These roads are superior to any other roads.
Advantages
Long life
More durable
Better riding surface
Impervious surface
Dustless and sanitary
surface
Do not develop any
corrugation
Can be laid on any
sub-grade
Can be easily
reinforced
Non slippery
Offer less tractive
resistance
Low maintenance
Good visibility during
night
Disadvantages
High initial cost
Requires skill
supervision for construction
Noisy under
iron-wheeled traffic
Liable to crack and warp
due to temperature vibration
Causes glare due to
reflected sun-light
Requires long time for
curing
Less resilient than bituminous
or WBM roads.
Difficult to locate
sewers or water mains.
Structural
components of concrete pavements
Sub-grade
Sub-base
Concrete slab
Materials
required for concrete road slab and their requirements
Cement
Ordinary Portland cement
is mostly used for concrete road side construction. Rapid hardening cement may
also be used in emergency.
Coarse
aggregate
Crushed stone, crushed
gravel (shringle) other suitable stone is used as coarse aggregate for concrete
road slab construction. It must be clean, strong, durable and free from any
other materials.
Fine
aggregate
Natural sand is
commonly used as fine aggregate. When natural sand is not available, crushed
stone sand may be used. It should be sharp and clean.
Water
It is required for
mixing and curing concrete. It should be free from harmful substance. The water
fit for drinking purpose is to be used.
Reinforcement
It consists of mild
steel bars or steel wire fabrics. It is provided when the subgrade is poor and
the road is subjected to heavy traffic. The purpose of providing reinforcement
is to prevent widening of cracks developed in the concrete road slab.
Method
of laying cement concrete road slab
Alternate lay method
Continuous construction
method
Construction of cement
concrete roads: stages
Preparation of
sub-grade
Provision of sub-base
Placing of forms
Batching of materials
and mixing
Transporting and
placing of concrete
Compaction
Floating
Belting
Grooming
Edging
Curing
Filling of joints
Opening to traffic
Joints
in concrete roads
Longitudinal joints
Transverse joints
Objects
of providing longitudinal joints
To control development
of longitudinal cracks
To facilitate
construction of road slab in convenient widths with hand tampers.
To help to maintain the
two slabs together at the same level.
The function of
transverse joints is to allow for expansion, contraction and warping of road
slab and thus to prevent development of cracks in the transverse direction.