Low cost roads are meant for low traffic volumes and are constructed using locally available materials at low cost in order to be easily maintained. They are classified into earth roads, kankar roads, gravel roads, water bound macadam roads, and wet mix macadam roads. Earth roads involve compacting layers of suitable soil in stages. Kankar roads involve ramming layers of broken kankar stones. Gravel roads involve compacting layers of a gravel mixture. Water bound macadam roads involve compacting layers of graded aggregates with screenings and binders. Wet mix macadam roads involve spreading and compacting premixed layers of aggregates and water. Standards are provided for alignment, width, and construction methods to allow for future upgrading

1. Low Cost Roads

2. “Roads Constructed at low cost and capable of being
maintained at low cost are termed as low cost roads”
 The low cost roads are meant for low intensity of traffic.
 This road are provided in localities where traffic volume does not
exceed 500 tonnes /day with a maximum of one third bullock carts
or other slow moving vehicles and a truck load of 3 tonnes with a
maximum of 5 tonnes depending upon local conditions.
 The low cost roads are constructed with the maximum use of locally
available road materials.

3. • The standards for low cost roads:
 Route
 Right of way
 Formation level
 Geometrics, i.e. grades, curves, visibility etc.

4. • The standards for carriage way width ,
formation width and nature of crust for low cost
roads should be such that
 No alteration may be required when these roads are upgraded in
future.
 With the increase in traffic, it should be possible to strengthen the
pavement in stages with the maximum utilization of the existing
pavement
 ECAFE(Economic commission for Asia and Far East) suggested
the Desirable and minimum width for Right of way are 30m and
18m respectively for low cost roads.

5. • Classification of low cost roads:
 The low cost roads may be broadly divided in the following five
categories
1. Earth roads
2. Kankar roads
3. Gravel Roads
4. Water bound macadam roads (WBM)
5. Wet mix macadam roads (WMM)

6. • Earth Roads
General :
 Earth road is a type of road whose whole pavement section is
constructed with the locally available earth material preferably.
Borrow pits are located at the nearby sites preferably outside the
land width where, the required earth is available.
 Sub-grade and the surface of the earth roads are given larger
camber of 1in 33 to 1 in 25 because they need faster drainage to
be safe from the moisture. A maximum value of camber of 1 in 25 is
the limit because higher camber will result in the formation of cross
ruts and corrosion of pavement soils

7. • Specifications of Materials:
 The soil survey is carried out and suitable borrow pits are located
within nearer distances.
 The trees ,grass roots and other organic matter are removed before
excavating earth for construction
 The earth material used for the construction of earth roads are
termed as satisfactory if they possess the following properties:
Base Course Wearing Course
 Clay content <5% 10 to 18%
 Silt content 9 to 32% 5 to 15%
 Sand content 60 to 80% 65 to 80%
 Liquid limit <35% <35%
 Plasticity Index <6% 4 to 10%

8. • Location of the centre line:
 The centre line and the road boundaries are marked on the ground
by driving the wooden pegs. To follow the desired vertical profile of
the road, reference pegs are also driven at a certain spacing which
depends upon the estimated length of the road construction per
day.
 Centre line pegs are fixed at 500 m interval.

9. construction procedure of earth road
1. Preparing the subgrade :- The subgrade is prepared and
the surface is brought to the required camber and gradient.
2. Rolling an watering :- The surface is rolle properly and well wetted
with water.
3. Spreading the soil :- After watering, a layer of graded soil, about 10
cm thick is evenly spread.
4. Rolling :- The layer of soil is rolled at optimum moisture content
(OMC ) with a suitable roller and finally finished with a light roller.
The type of roller for compaction is decided based on soil type, desired
amount of compaction and availability of equipment. Atleast 95 per cent
of dry density of its light compaction is considered desirable.

10. Cont…
5. Checking :-The camber of the finished surface is checked an
corrected, if necessary.
6. Curing :- The rolled surface is watered for four or five days for
curing. No traffic should be allowed to pass over the road surface
during this period.
7. Opening to traffic :- After curing, the traffic is allowed to pass but the
surface is sprinkled over with water for a period of 10 to 1 days

11. • Kankar Roads
 Kankar is an impure limestone and it is available as a natural
deposit.
 A good quality kankar will show a bluish surface on being fractured.
 Kankar is found as “Block Kankar” or as “Nodular Kankar”. In the
past block kankar has been used as building material while nodular
kankar is even today used for VR and ODR as a subgrade material
for WBM roads

12. Cont…
 Some times road is built in stages starting from earth formation
which is allowed to settle for two to three monsoons and
subsequently when the surface is to improved, the kankar forms the
subgrade material for such roads
 For road work kankar is broken into sizes varying from 20 to 63
mm.
 The largest size are used for bottom layer and the smallest size is
used for top layer
 Kankar is normally spread at the 15 mm layer

13. Cont…
 The size supplied varies from 12 mm to 80 mm as specified below
1. Passing 80 mm sieve 100%
2. Retrained of 63 mm sieve 20%
3. Passing 25 mm sieve…Not more than 10%
4. Passing 12 mm sieve NIL

14. • The following sequence is followed in the
construction of the kankar roads
 Spreading of kankar over the section
 Ramming over stretch of 3.66 mm road at a time with the help of at
least 16 workers
 Ramming to continue till the surface has been thoroughly
compacted
 Surface to be kept well watered during the process of ramming
 Road to be opened traffic such that the traffic is spread over the
whole road width

15. • Gravel Roads
 A gravel road consists of a carriageway made of a layer of
compacted gravel.
 The gravel used consists of irregular stones mixed with a varying
amount of sand, silt, and clay, which can act as a binder.
 Following consideration govern the construction of gravel roads
(A) The carriageway of the gravel road should be provided with a
camber of 1 in 25 to 1in 30 to achieve good drainage of the road
surface
(B) It should be composed of pebbles which are hard, tough and
durable rock particles to resist abrasion

16. Cont…
(C) For making a good road surface, the pebbles should be held together by some
cementing material such as clay which is the most generally available binder.
 Following procedure is adopted in the construction of a gravel road
1. Material Gravel to be used for the construction is staked along the sides of the
proposed road
2. The pegs are driven to show the limits of excavation, The site is cleared and the
subgrade is then prepared to receive the layer of gravel

17. Cont…
3. The first layer of gravel is spread in the prepared trench. The
compacted depth of gravel road is generally 20 cm and it is
obtained in two layers. The layers is rolled by using smooth
wheeled light rollers starting from the edges and proceeding
towards entre.
4. Some quantity of water is then sprayed and rolling is done again.
5. The final rolling is carried out when the moisture content is at its
optimum so that completed surface which is formed is firm.
6. A few days after the final rolling and drying out, the road is opening
the road traffic.

18. c

19. Water bound macadam roads:
 The water bound macadam road construction technique was
given by the John Macadam. This technique in present day is
used as given below.
 For WBM construction we use three materials:
1. Aggregates
2. Screeners
3. Binders.

20. • Construction of water bound macadam road involves the
following 6 basic steps as given below
1. Preparation of sub-grade
2. Preparation of sub-base
3. Preparation of base
4. Preparation of wearing course
5. Preparation of shoulders
6. Opening to traffic

21. • CONSTRUCTION OF SUB-GRADE
 Sub-grade act as a cushion for other layers i.e. In order to achieve
durable road sub-grade should be strong.
 The sub-grade is thoroughly compacted by rollers weighing 8
tonnes by sprinkling water one night before.
 In rocky regions the sub-grades are not rolled whereas in region of
clay soils, a layer to natural sand, moorum or gravel, is provided
over sub-grade.

22. Sub grade preparation

23. • CONSTRUCTION OF SUB-BASE
 On a well compacted sub-grade, aggregates having size of 90 mm
to 40 mm are preferred for the sub-base material, or over burnt
bricks in layers of 15 cm thickness
 total width of the sub-base to be kept 60 cm wider than pavement
width, projecting 30 cm on each side.
 The sub-base should be compacted by a roller to provide an even
surface.

24. • CONSTRUCTION OF BASE
 The specified materials of the base course is spread and proper
grade, thickness and cross sections maintained as per design
shown on the supplied drawings.
 Aggregates having size of 63 to 40 mm are preferred for the base
material
 For economic considerations IRC has suggested non plastic
materials such as, crushed over burnt bricks, moorum, gravels, etc.
provided the liquid limit of the material is less than 20%, plasticity
index is less than 6.0% and the portion of fines passing 0.075 mm
sieve is less than 10%.

25.  This course may be laid in one or two layers according to the total
designed thickness and the thickness of each layer should not
exceed 10 cm
 Provide either bricks on end edging or earthen kerbs strong enough
to prevent the new road material from spreading outward and also
to retain water used in consolidation of the wearing course
 Spread the road metal evenly over the prepared base to the
specified thickness and hand pack them so that the finished surface
is brought to the required camber.

26. Cont…
 Spread the coarse aggregate over the surface and roll it dry with
a suitable roller till interlocking of the aggregate is achieved with
sufficient void space. The rolling is started from the edges and
gradually shifted towards the centre.
 After dry rolling, spread the screening materials (stones up to 12
mm size) with uniform rate so that voids of coarse aggregates get
filled properly.
 After spreading the screening material, sprinkle sufficient quantity
of water, sweep the surface and roll it with roller again

27. Preparation of wearing course
 Now apply the binding material in two to three thick layers at a slow
and uniform rate. Each layer of binding material is rolled after
adding sufficient water. The slurry is swept in with brooms to fill the
void properly. The moving wheel of the roller should be cleaned
with water.
 After proper compacting allow it to dry over night. Spread a layer of
sand or earth, about 6 mm thick and roll the surface again after
sprinkling water lightly.
 The surface may be allowed for 7 to 10 days of curing.

28. Spreading binder material

29. • CONSTRUCTION OF SHOULDERS
 While curing the pavement surface, prepare the shoulders by filling
earth to the specified cross slope and compact them properly by
rolling or by tamping.
 Width and thickness of the shoulder should be as per specification.

30. • OPENING TO TRAFFIC
 After properly drying, the road pavement may now be opened to
traffic, ensuring that the traffic is distributed uniformly over the full
width of the pavement.

31. Wet mix macadam roads:
 Laying and compacting clean, crushed, graded aggregate and
granular material, premixed with water, to a dense mass on
prepared sub-grade or existing pavement
 Thickness of single compacted Wet Mix Macadam layer shall
not be less than 75 mm
 Coarse aggregate shall be crushed stone
 If crushed gravel is used, not less than 90% by Wt. of gravel
pieces retained on 4.75 mm sieve shall have at least two
fractured faces
 If water absorption value of coarse aggregate is greater than
2%, the soundness test shall be carried out as per
IS:2386(Part-5)

32. Physical Requirement of Coarse
Aggregate for WMM
1. Los Angeles Abrasion IS:2386(Part-4) 40% Value
or
Aggregate Impact Value IS:2386(Part-4) or IS:5640 30%
2. Combined Flakiness and Elongation indices (Total)
IS:2386(Part-1) 30%

33. Grading Requirement for WMM
IS Sieve Destination Percent by Wt. Passing IS Sieve
Destination the IS Sieve
53.00 mm
45.00 mm
26.50 mm
22.40 mm
11.20 mm
4.75 mm
2.36 mm
600 micron
75 micron
100
95-100
-
60-80
40-60
25-40
15-30
8-22
0-8
Materials finer than 425 micron shall have Plasticity Index (PI) not
exceeding 6.

34.  Construction of wet mix macadam road involves the following
basic steps as given below.
1. Weather
2. Preparation of Base
3. Provision of Lateral Confinement of Wet Mix
4. Spreading of Mix and Compaction
5. Setting and Drying
6. Opening to Traffic

35. • weather
 The work of laying of wet mix macadam is not done during rainy
season
• Preparation of Base
The surface of the sub-grade/sub-base/base to receive the WMM
course shall be prepared to the specified lines and cross-fall (camber)
and made free of dust and other extraneous matter. Any ruts or softy
yielding places shall be corrected and rolled until firm surface is
obtained, if necessary by sprinkling water.
• Provision of Lateral Confinement of Wet Mix
 This shall be done by laying materials adjoining shoulders along
with that of wet mix layer. The sequence of operations shall be such
that the construction of the shoulder is done in layers each
matching the thickness of the adjoining pavement layer.

36. Spreading of Mix and compaction
• Preparation of mix
 WMM shall be prepared in an approved mixing plant of suitable capacity
having provision for controlled addition of water
 Optimum moisture for mixing shall be determined in accordance with IS:
2720 (Part-8) after replacing the aggregate fraction retained on 22.4 mm
sieve with material of 4.75 mm to 22.4 mm size
• Spreading of mix
 Immediately after mixing, the aggregate shall spread uniformly and
evenly upon the prepared sub-grade in required quantities by paver or
motor grader

37. • Compaction
After the mix has been laid to the required thickness, grade and
cross fall/camber the same shall be uniformly compacted to the full
depth with suitable roller
• Setting and Drying
 After final compaction of wet-mix macadam course, the road shall be
allowed to dry for 24 hours
• Opening to Traffic
 Preferably no vehicular traffic of any kind should be allowed on the
finished wet-mix macadam surface till it has dried and the wearing course
laid

38. • References
 S.G. RANGWALA “Highway engineering” by Charotar Publication House
 S.P. Chandola “A text book of Transportation engineering” by S.Chand
Publication
 L.R. Kadiyali “principles and practices of Highway Engineering “by Khanna
Publishers
 IRC-19-1977 , IRC-109-1997 Guidelines

39. THANK YOU