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2- Improve drainage.
3- Minimize frost action damage.
4- Provide a working platform for construction.
The subbase consists of
OECO, 2008
: 1-
Consists of solid thick gravel or remnants of quarries and the bonding materials to fill in the voids.
2- Materials should be conspecific, clean and free of any impurities.
3- Must not exceed the maximum size of half the thickness of the layer not more
than 3 inches with the exclusion of larger sizes. 4-
Should not increase percentage passing the No. 4 sieve is than 70. 5-
the properties of material passing the No. 10 sieve as follows:
No. sieve No 10
No 40 No 200
Percent passing `100
25-70 0-35
The liquid limit not more than 25 and plastic limit must be between 0-10. CBR value must be more than 25 .
c. Base Course
The base course is immediately beneath the surface course. It provides additional load distribution and contributes to drainage and frost resistance.
Base courses are usually constructed out of: Required Materials
OECO, 2008
:
No. of sieve o.375in
0.75in 1.5in
2in 4 in
10 in 40 in
200 in Percent passing
40-70 50-80
70-100 100
30-60 20-50
10-25 5-10
1- The liquid limit of material passing the No. 40 sieve should be not more than
25 and plastic limit ranges from 0 to 6.
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2- CBR ratio for a sample submerged and compressed to the maximum density
should be not less than 80. 3-
Would rather be a regular gradient-General should also not exceed the pass- through the No. 200 sieve 0.5 from passing No. 40 sieve.
The thickness of base course is 25 cm
d. Prime coat
It is a MC asphalt mixture by the kerosene is sprayed over the base layer before placing the asphalt.
e. Tack Coat
Consists of adding gasoline to the bituminous is sprayed on the first layer of asphalt for preparation to serve second layer, for paste layers.
f. Surface Course
the surface course of a flexible structure consists of a mixture of mineral aggregates and bituminous materials placed as the upper course and usually
constructed on a base course .In addition to its major function as a structural portion of the pavement, it must also be designed to resist the abrasive forces of
traffic, to reduce the amount of surface water penetrating the pavement, to provide a skid resistance surface, and to provide a smooth and uniform riding surface.
Thickness of This top structural layer of material is 11 cm subdivided into 6 cm
layer the first layer is called Binder Course and 5 cm and a second layer called
wearing Course.
