Please enable JavaScript.
Coggle requires JavaScript to display documents.
TOPIC 3 CONSTRUCTION OF ROAD LAYERS (Roadbase (crushed rock, crushed…
TOPIC 3
CONSTRUCTION OF ROAD LAYERS
Introduction
Carried out after all the survey and alignment works, site clearing, earthwork and temporary drains have been constructed
Drainage layer (if required)
Laid on a prepared and accepted subgrade
Consists of coarse aggregate or fine aggregate
Laid and compacted at MC +1 to -2% of OMC
Subbase
natural or artificial mixture of gravel, sand and free from organic matter
Laid in 100 - 200 mm compacted thickness,
compacted at MC +1 to -2% of OMC
Compaction to produce density minimum of 95% Maximum Dry Density(MDD)
Roadbase
crushed rock, crushed gravel or mixture of both
laid in 100 - 200 mm compacted
Spread using motor grader or at
OMC ± 1%
Compaction to produce density minimum of 95% MDD
conform to the physical and mechanical quality requirement in asphaltic concrete section
Coating
Prime coat
sprayed onto clean roadbase at
the rate of 0.5 – 1 liter/m2
Material used
Medium Curing Cutback-70
Slow Setting Emulsified Bitumen
Tack coat
Sprayed onto bituminous layer, rate 0.25 – 0.55 liter/m2
Surfacing
Asphaltic Concrete
Binder course will be laid on the broomed, clean
and prime coated roadbase.
carried out in
dry weather
After binder course has been properly compacted,
sprayed with tack coat, wearing course will then
be laid and compacted
Shoulder
furnishing, compacting and shaping earth, gravel,
or paved shoulder
Type of shoulders
Paved
– constructed as normal bituminous layer
Earth
– using suitable material
Gravel
– using approved material for gravel surfacing
Top level of shoulder should be level and flushed with pavement
Compaction of premix
Types of compaction
Final
Smooth wheel
Breakdown
Smooth wheel
Intermediate
Pneumatic
Rollers, heavy vehicles shall not be allowed to stand
on newly laid mix before compaction
Construction joint cut back straight, brushed on with RS-1K 10-15 minutes before laying of next section, no joints along wheelpaths
Compaction requirement – 90% (Road Base), 95% (Binder Coarse), 98% (Wearing Coarse)
Open to traffic > 4 hrs, < 30 km/hr, no sharp turning