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In bituminous primer the distillate is absorbed by the road surface on which it
is spread.
The absorption therefore depends on the porosity of the surface.
Bitumen primers are useful on the stabilised surfaces and water bound macadam
base courses.
Bituminous primers are generally prepared on road sites by mixing penetration
bitumen with petroleum distillate.
Certain additives or blend of additives called
as bitumen modifiers can improve properties of Bitumen and bituminous mixes.
Bitumen treated with these modifiers is known as modified bitumen.
Polymer modified bitumen (PMB)/ crumb rubber modified bitumen (CRMB) should be
used only in wearing course depending upon the requirements of extreme climatic
variations.
The detailed specifications for modified bitumen have been issued by IRC: SP:
53-1999.
It must be noted that the performance of PMB and CRMB is dependent on strict
control on temperature during construction.
The advantages of using modified bitumen are as follows
- Lower susceptibility to daily and seasonal temperature variations
- Higher resistance to deformation at high pavement temperature
- Better age resistance properties
- Higher fatigue life for mixes
- Better adhesion between aggregates and binder
- Prevention of cracking and reflective cracking
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