CONSTRUCTION OF CONCRETE ROAD:
CONSTRUCTION OF
CONCRETE ROAD: -The construction of concrete roads involves the
following constructional stages:
[1] Preparing the sub grade: - The
sub grade is properly compacted by rolling, if necessary, and is brought to the
required camber and gradient. All elevations or depressions should be brought
to true profile.
[2] Preparing the Base Course: - Over
the sub grade, a base or foundation course is sometimes provided. The function
of base course is to be provided leveled and smooth surface for the slab and
hence to provide uniformity support to the slab.
[3] Placing of Form Work: - After
the base course is completed, form work for the concrete slab is laid. The
forms, which are set on the edges, can be of steel or timber. The depth of the
form work should be equal to the thickness of the slab. Channels are sometimes
used for steel form works.
[4] Watering: - After the form work has been laid,
the surface of the base or sub grade, as the case may be, is wetted with as
much water as it can readily absorb. Water should not be allowed to stand on
the surface. The surface should be kept wet for about 12 hours before
concreting.
[5] Mixing and Placing of Concrete: - The
ingredients of concrete are mixed in proper proportion in a dry state. Generally
1:2:4 mix is adopted. Mixing should be preferably be done in mechanical mixers.
Measured quantity of water should be added to have designed water cement ratio.
The concrete is placed in the form works by manual labour, and it should be
laid in layers of thickness not more than 5 to 8cm or two or three times the
size of aggregates. The concrete should
be laid in entire width of the form work and proceed lengthwise.
[6] Compaction and Floating: - The
compaction and consolidation of concrete is done by manual labour or by means
of hand tampers. Consolidation may also be done by mechanical vibrators. The
purpose of floating is to produce a uniform and even surface of concrete, free
for transverse waves or corrugations.
Floats are made of wooden boards 20cm wide and 5cm thick provided with
suitable handles.
[7] Belting: - The purpose of belting is to
finish the surface of the concrete. The belt is 15 to 30cm wide strip of canvas
or rubber, fitted with handles at both ends. The belt is moved longitudinally
by two persons.
[8] Curing: - Thefinished surface, after 12 hours, is covered with
gunny bags which are kept wet for about 24 hours. After 24 hours the gunny bags
are removed and the surface is covered with a layer of sand which is kept wet
for about 14 days. Sometimes the whole surface is divided into small bays by
forming earthen banks or ridges 5cm high. The bays are now filled with water to
a depth of nearly 4cm for 14days.
[9] Edging: - Before the road is opened to traffic, brick edging is
constructed to protect the slab. Earth is then spread on the berms up to the
top of the brick edging.
[10] Joints in Concrete Roads: - The
main difficulty in concrete pavements is, that due to temperature variations,
cracks are developed in the slab. If sufficient care is not taken at the time
of construction, these cracks will make the road unserviceable. To overcome
this difficulty joints are provided. If the joints are properly spaced, cracks
are reduced and if at all, only minor cracks are develop.