Scope :
The work shall consist of the application of a single coat of low viscosity liquid bituminous
material to existing bituminous, cement concrete or primed granular surface preparatory to
the superimposition of a bituminous mix, when specified in the Contract or as instructed by
the Engineer.
Materials :
The binder used for tack coat shall be either Cationic bitumen emulsion (RS 1) complying
with IS:8887 or suitable low viscosity paving bitumen of VG 10 grade conforming to IS:73.
The use of cutback bitumen RC:70 as per IS:217 shall be restricted only for sites at sub-zero
temperatures or for emergency applications as directed by the Engineer. The type and grade
of binder for tack coat shall be as specified in the Contract or as directed by the Enginee .
503.3 W eather and Seasonal L imitations
Bituminous material shall not be applied during a dust storm or when the weather is foggy,
rainy or windy or when the temperature in the shade is less than 10°C. Where the tack coat
Bases and Surface Courses (Bituminous) Section 500
169
consists of emulsion, the surface shall be slightly damp, but not wet. Where the tack coat is
of cutback bitumen, the surface shall be dry.
Construction Equipment :
The tack coat shall be applied by a self-propelled or towed bitumen pressure sprayer, equipped
for spraying the material uniformly at a specified rate. Hand spraying shall not be permitted
except in small areas, inaccessible to the distributor, or narrow strips, shall be sprayed with
a pressure hand sprayer, or as directed by the Engineer.
Preparation of Base
The surface on which the tack coat is to be applied shall be clean and free from dust, dirt, and
any extraneous material, and be otherwise prepared in accordance with the requirements
of Clauses 501.8. The granular or stabilized surfaces shall be primed as per Clause 502.
Immediately before the application of the tack coat, the surface shall be swept clean with
a mechanical broom, and high pressure air jet, or by other means as directed by the
Engineer.
Application of Tack Coat :
The application of tack coat shall be at the rate specified in Table 500-5, and it shall be applied
uniformly. If rate of application of Tack Coat is not specified in the contract, then it shall be the
rate specified in Table 500-5. No dilution or heating at site of RS1 bitumen emulsion shall be
permitted. Paving bitumen if used for tack coat shall be heated to appropriate temperature
in bitumen boilers to achieve viscosity less than 2 poise. The normal range of spraying
temperature for a bituminous emulsion shall be 20ºC to 70ºC and for cutback, 50ºC to 80ºC.
The method of application of tack coat will depend on the type of equipment to be used, size
of nozzles, pressure at the spray bar, and speed or forward movement. The Contractor shall
demonstrate at a spraying trial, that the equipment and method to be used is capable of
producing a uniform spray, within the tolerances specified
|
Type of Surface
|
Rate of Spray of Binder in Kg per sq. m
|
| Bituminous surfaces
|
0.20 - 0.30
|
| Granular surfaces treated with primer
|
0.25 - 0.30
|
| Cement concrete pavement
|
0.30 - 0.35
|
Curing of Tack Coat :
The tack coat shall be left to cure until all the volatiles have evaporated before any subsequent
construction is started. No plant or vehicles shall be allowed on the tack coat other than those
essential for the construction.
Quality Control of Work
For control of the quality of materials and the works carried out, the relevant provisions of
Section 900 shall apply.
Arrangements for Traffic :
During the period of construction, arrangements for traffic shall be made in accordance with
the provisions of Clause 112.
Measurement for Payment
Tack coat shall be measured in terms of surface area of application in square metres.
Rate :
The contract unit rate for tack coat shall be payment in full for carrying out the required
operations including for all components listed in Clause 401.8 (i) to (v) and as applicable to
the work specified in these Specifications. The rate shall cover the provision of tack coat, at
0.2 kg per square metre or at the rate specifie in the Contract, with the provision that the
variation between this quantity and actual quantity of bitumen used will be assessed and the
payment adjusted accordingly.