MIXED SEAL SURFACING

                                                                 MIXED SEAL SURFACING

SCOPE:-

This work shall consist of the preparation, laying and compaction of a close-graded premix surfacing material of 20 mm thickness composed of graded aggregates premixed with a bituminous binder on a previously prepared surface, in accordance with the requirements of these Specifications, to serve as a wearing course.

Close graded premix surfacing shall be of Type A or Type B.

F Materials:-

·        Binder

·         Coarse aggregates :

Fine aggregates :- The fine aggregates shall consist of crushed rock quarry sands, natural gravel / sand or a mixture of both. These shall be clean, hard, durable, un-coated, mineral particles, dry and free from injurious, soft or flaky particles and organic or deleterious substances.

Aggregate gradation:- The coarse and fine aggregates shall be so graded or combined as to conform to one or the other gradings shown in Table.

AGGREGATE GRADATION

IS Sieve Designation (mm)	Cumulative per cent by weight of total aggregate passing
	Type A	Type B
13.2 mm	-	100
11.2 mm	100	88 - 100
5.6 mm	52 - 88	31 - 52
2.8 mm	14 - 38	5 - 25
0.090 mm	0 - 5	0 - 5

Proportioning of materials:- The total quantity of aggregates used for Type A or B close-graded premix surfacing shall be 0.27 cubic metre per 10 square metre area. The quantity of binder used for premixing in terms of straight-run bitumen shall be 22.0 kg and 19.0 kg per 10 square metre area for Type A and Type B surfacing respectively.

Construction Operations:-

         

F Opening to Traffic

              Traffic may be allowed after completion of the final rolling when the mix has cooled      down to the surrounding temperature. Excessive traffic speeds should not be permitted.

F Surface Finish and Quality Control of Work

 For control on the quality of materials supplied and the works carried out, the relevant provisions of Section 900 shall apply,

F Measurements for Payment

Close-graded premix surfacing. Type A or B shall be measured as finished work, for the area specified to be covered, in square metres at a specified thickness. The area will be the net area covered, and all allowances for wastage and cutting of joints shall be deemed to be included in the rate.

SEAL COAT

F Scope:-

This work shall consist of the application of a seal coat for sealing the voids in a bituminous surface laid to the specified levels, grade and cross fall (camber).

Seal coat shall be of either of the two types specified below:

A)         Liquid seal coat comprising of an application of a layer of bituminous binder followed by a cover of stone chips.

          B)      Premixed seal coat comprising of a thin application of fine aggregate premixed with bituminous binder.

                                               

PRIME COAT

The work shall consist of application of a single coat of low viscosity liquid bituminous material on Wet Mix Macadam (WMM) surface before laying bituminous layer on Wet Mix.

Ø MATERIALS:-

       Since WMM is considered to be material of low porosity, it is proposed to use Slow Setting Emulsion for Prime Coat.  The Slow Setting Emulsion shall comply with IS: 8887 and shall be procured from reputed manufacturer.

Ø PLANT & EQUIPMENT:-

a)   Bitumen pressure distribution                           

b)   Tractor mounted mechanical broom                 

c)    Air compressor (when necessary)                      

d)   Hand sprayer                                               

e)   Water tanker

Ø WEATHER AND SEASONAL LIMITATION:-

           Prime coating shall not be applied to a Wet Surface or 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.

Surface to receive emulsion primer should be damp, but no free or standing water shall be present.

Ø STORAGE OF MATERIALS:-

        The material shall be stored at plant area in Emulsion Storage Tank and shall be transferred to Bitumen/Emulsion distributor as and when material is required for consumption.

Ø RATE OF SPRAY:-

VISCOSITY REQUIREMENT AND QUANTITY OF BITUMINOUS PRIMER

Type of surface	Kinematic Viscosity of Primer at 60°C (Centistokes)	Quantity per 10 sq. m(kg)
Low porosity	30 – 60	6 to 9
Medium porosity	70 – 140	9 to 12
High porosity	250 – 500	12 to 15

Ø CONSTRUCTION OPERATIONS:-

·        ROAD SURFACE:-

       The road surface to be primed shall be prepared by cleaning surface with mechanical broom and air compressor. Prior to applying primer, the surface shall be carefully swept clean of dust and loose particles, care being taken not to disturb the interlocked aggregate. To achieve this, the WMM surface layer, if required, shall be lightly sprayed with water and surface allowed to dry to a stage where the surface is slightly moist at the time of priming.

APPLICATION OF BITUMINOUS PRIMER:-

      The bituminous primer shall be sprayed uniformly with Bitumen Pressure Sprayer at specified speed. The speed of Bitumen Sprayer shall be so regulated so as to achieve the required rate of spray within tolerance limits.  The spray test shall be conducted to check the bitumen spray rate per unit area.

                                                 

VIEW OF APPLICATION OF PRIME COAT

Ø SAFETY AND TRAFFIC MANAGEMENT:-

a)   Minimum of 2 flagmen with reflective vests and holding a red flag each shall be deployed to control the traffic, which may be affected due to the construction operations.

b)   All locations adjacent to existing road where construction of pavement works is in progress shall be barricaded and provided with visible safety and road signs.

c)    No machines or equipment shall be permitted to remain on the existing road or shoulder unattended at all times unless it is properly protected and secured in a safe manner.

d)   The Safety Officer shall make frequent patrols along the highway to ensure that the safety equipment and signs are operational at all times.

TACK COAT

Tack coat shall consist of the application of a single coat of low viscosity liquid bituminous material to an existing bituminous road surface and also over the prime coat before laying each layer of DBM.

Ø Materials Quality

This tack coat used shall be of rapid setting bituminous emulsion and applied at a rate of between 0.25 to 0.3 kg per sq. meters.

Ø Weather and Seasonal Limitation

Tack coating shall not be applied to a Wet Surface or 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.

Surface to receive emulsion should be dry/ slightly damp, but no free or standing water shall be present.

Ø Plants & Equipments

1) Bitumen pressure distributor                              1 unit

2) Tractor mounted mechanical broom                   1 unit

3) Air compressor (when necessary)                        1 unit

4) Hand sprayer                                                          1 unit

5) Water tanker (Where necessary)                         1 unit

Applying Procedure

·        Before applying the tack coat the surface shall be swept by tractor mounted mechanical broom/air compressor to clean the dust and loose particles.

·        Prior to tack coating the material to be used must be approved by Supervision consultant. The tack coat material shall be sprayed on to the bituminous using bitumen pressure distributor and at a rate which is stipulated in the specification as per clause 503.4.3, & Table 500-2. The spray rate is measured using the tray method or sponge method. Hand spraying of small areas, inaccessible to the distributor, or in a narrow stripe, shall be sprayed with a pressure hand sprayer.

·        After application of the tack coat same shall be left to cure until all the volatiles have evaporated (from brown to black) before any subsequent construction is started. No plant or vehicles shall be allowed on the tack coat other than those essential for the construction.  

                                    

USE OF AIR COMPRSSOR BEFORE TACK COAT

                                         VIEW OF APPLICATION OF TACK COAT