CCS335 _ Neural Networks and Deep Learning Laboratory_Lab Complete Record
13a. Road Construction Methods.pptx
1. Road construction methods
(1) Roman Road Construction
During the roman empire,
roads were constructed in
large scale and earliest
techniques known are those
of Roman Roads.
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2. The main features of the Roman Roads
are:
1) They were built straight regardless of
gradient.
2) They were built after the soft soil was
removed and a hard strata was reached.
3) The total thickness of the construction
was as high as 0.75 to 1.2 m.
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3. Roman Pavement Structure Near Radstock, England
(after Collins and Hart, 1936)
The above construction should have been much
stronger than what was required for the animal
drawn vehicles in those days.
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4. A typical Roman road structure, as seen in the
United Kingdom, consisted of four basic layers
(Collins and Hart, 1936):
(i) Summa Crusta (surfacing). Smooth, polygonal
blocks embedded in the underlying layer.
(ii) Nucleus. A kind of base layer composed of gravel
and sand with lime cement.
(iii) Rudus. The third layer was composed of rubble
masonry and smaller stones also set in lime mortar.
(iv) Statumen. Two or three courses of flat stones set
in lime mortar.
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5. (2) Tresaguet Construction
Pierre Tresaget (1716-1796), developed an improved
method of construction in France.
The main features of his proposal was that the
thickness of construction need be only in the order
of 30 cm.
Due consideration was given by him to sub-grade
moisture condition and drainage of surface water.
The top wearing course was made of smaller stones
and compacted to a thickness of 5 cm at the edge
and gradually increased towards the center with a
cross slope of 1 in 45.
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7. (3) Telford Construction
Thomas Telford began his work in early 19th
century.
He insisted on providing a definite cross slope for
top surface of the pavement by varying the
thickness of foundation stones.
Telford's pavement section was about 350 to 450
mm in depth and generally specified three layers.
The bottom layer was comprised of large stones
100 mm wide and 75 to 180 mm in depth. It is this
specific layer which makes the Telford design
unique.
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8. On top of this were placed two layers of stones of
65 mm maximum size (about 150 to 250 mm total
thickness) followed by a wearing course of gravel
about 40 mm thick.
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9. John McAdam put forward an entirely new method
of road construction in 1815.
McAdam construction introduced the use of
angular aggregates.
Stresses due to wheel load of traffic gets
decreased at the lower layers of the pavement.
Importance of Sub-grade drainage and
compaction.
Sub-grade being the lowest portion be prepared
and kept drained to carry the transmitted load of
the pavement.
(3) McAdam Construction
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11. Angular aggregate (hand-broken with a maximum size
of 75 mm) were placed in two layers for a total depth
of about 200 mm
On top of this, the wearing course was placed (about
50 mm thick with a maximum aggregate size of 25 mm)
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12. The total depth of a typical MacAdam pavement
was about 250 mm.
The term "macadam" is also used to indicate
"broken stone" pavement.
MacAdam realized that the layers of broken stone
would eventually become "bound" together by fines
generated by traffic
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14. Further development of McAdam
Construction.
In Water Bound McAdam construction (WBM),
known after McAdam technique, the broken stones
of the base and surface course are bound by the
stone dust in presence of moisture.
A tar macadam road consists of a basic macadam
road with a tar-bound surface.
Bituminous McAdam Roads
Road mixes, refer to the mechanical mixing of
asphalt and aggregate directly on the road bed to
form a thin 25 - 100 mm wearing course.
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15. Sheet Asphalt Roads
The first pavements made from true hot mix
asphalt (HMA) were called sheet asphalt
pavements.
The HMA layers in this pavement were premixed
and laid hot.
A wearing course 40 to 50 mm thick composed of
asphalt cement and sand.
A binder course about 40 mm thick composed of
broken stone and asphalt cement.
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16. Cement Concrete Roads were designed to take up
the heaviest loads in adverse soil and climatic
conditions and to last for long service life.
They are known to give a good and even riding
surface.
Cement Concrete Roads
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17. Pavement design :
1) Mix design of material
2) Thickness design of structural
layers
Pavement design philosophy:
1) Empirical
2) Mechanistic ( Theoretical , Analytical,
Structural)
3) Mechanistic-Empirical
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18. Design Approaches
Road Note 29 (TRRL, UK 1960, 1970, Empirical)
Road Note 31
The Asphalt Institute Manual Series
AASHTO Guide for Design of Pavement
Structures
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