TACK COAT
Materials: Straight-run bitumen of grade VG- 10 conforming to IS 73 specifications.
The rate of application of binder (in the present case is VG-10) at the rate of 0.50 kg/sqm on bitumen
surface.
Preparation of Surface:
All vegetation, loose sealing compound, caked mud, animal dung, dust, dirt and foreign material shall
be removed from the entire surface of the pavement by means of Brooms/sweepers/blowers, as
suitable based on the site condition.
Heating :
Bitumen shall be heated in a boiler to a temperature of 165 deg. C to 175 deg. C and maintained at
that temperature. Temperature shall be checked at regular intervals with the help of a thermometer.
Application of Bitumen :
Hot bitumen shall be applied evenly to the clean, dry surface by suitable means at specified rate as
per the BOQ item (0.5kg per sqm in the present case). Even and uniform distribution of bitumen shall
be ensured. Bitumen shall be applied longitudinally along the length of the pavement and never
across it. Excessive deposits of bitumen for any reason shall be suitably rectified.
No vehicles shall be allowed on the tack coat during this phase. The tack coat shall be followed
immediately by laying Premix Carpet.
PREMIX CARPET
Materials:
Graded stone chipping as per the following sizes and quantities will be used for premix carpet in
addition to the Bitumen grade VG-30
Size of aggregate Quantity, cum/100 Bulk density, Weight of Remarks
sqm (t/cum) aggregates, kg
Stone Chippings of 2.25 As per the
size confirming to calculations
13.2 mm enclosed
Stone Chippings of 1.12
size confirming to
11.2 mm
Bitumen grade VG- 30 conforming to IS 73 specifications brought HPCL refinery at Visakhapatnam is
being used. The rate of application is 180 kg/100 sqm area as specified in the BOQ item.
The above quantities are converted in to the batch mix. The contents in each batch is enclosed
Heating :
Bitumen shall be heated in a boiler to a temperature of 165 deg. C to 175 deg. C and maintained at
that temperature. Overheating shall be avoioded and made ready for pouring. Temperature shall be
checked at regular intervals with the help of a thermometer. The aggregates will be pre heated in
miller before adding the Bitumen
Preparation of Premix
The aggregate shall be dry and suitably heated to temperature in the mixer to facilitate mixing with
the binder. The binder(bitumen confirming to VG-30) shall be poured in to the mixture after
attaining the desired temperatures of Aggregates. The mixing of binder with chippings shall be
continued until the chippings are thoroughly coated with the binder. The process of mixing usually
takes 3 min to 4 min depending upon weather conditions. The mix shall be immediately transported
from the mixer to the point of use in wheel barrows.
Spreading and Rolling
The premixed material shall be spread on the road surface with drag spreader without undue loss of
time to the required thickness. As soon as sufficient length of bituminous material has been laid,
rolling shall commence with smooth wheeled roller. Rolling shall begin at the edges and progress
towards the centre longitudinally. The consolidated thickness shall be checked at regular intervals
and in no case shall be less than 2.5 cm as per the item. When the roller has passed over the whole
area once, any high spots or depressions which become apparent will be corrected by removing or
adding premixed materials. Rolling shall then be continued until the entire surface has been rolled to
compaction and all the roller marks eliminated. The overlapping of the roller passes shall be 1/3
width of the roller.
The temperature of the premix carpet at the time of laying shall not exceed 210 deg. C and shall not
be less than 175 deg. C.
SEAL COAT
Materials:
Straight-run bitumen of grade VG- 10 conforming to IS 73 specifications.
Fine aggregates confirming to the specified size
Heating :
Bitumen shall be heated in a boiler to a temperature of 165 deg. C to 175 deg. C and maintained at
that temperature. Temperature shall be checked at regular intervals with the help of a thermometer.
The aggregates will be pre heated in miller before adding the Bitumen
Preparation of mix for seal coat
The aggregates shall be dry by preheating in the miller drum to evaporate temperature. After
achieving a temperature above 150oC Binder will be poured in to the mix. Mixing will be continued
to achieve uniform mix. The process will take 3 to 4 min inn the mixer to achieve preheating and
mixing binder. The mix shall be immediately transported from the mixer to the point of use in wheel
barrows.
Spreading and Rolling
The seal coat mix shall be spread on the road surface with drag spreader without undue loss of time
to cover the premix surface. As soon as sufficient length of bituminous material has been laid, rolling
shall commence with smooth wheeled roller. Rolling shall begin at the edges and progress towards
the centre longitudinally. When the roller has passed over the whole area once, any high spots or
depressions which become apparent will be corrected by removing or adding premixed materials.
Rolling shall then be continued until the entire surface has been rolled to compaction and all the
roller marks eliminated. The overlapping of the roller passes shall be 1/3 width of the roller. Rolling
shall be continued until the premixed material completely seals the voids in the bituminous course
and a smooth uniform surface is obtained
Further, the prepared finished surface shall be protected from traffic for 24 hours or such period as
may be directed by the Engineer-in-Charge.
