This presentation is prepared specially for the Otta seal work to be executed in SNRTP project in Nepal

1. Otta Seal
(Design &Construction Procedures)
Sujit Dhital
Quality Management and Monitoring Specialist
SNRTP (PMU West )

2. SURFACING OPTION
Non Structural
Sand Seal
Otta Seal
DBSD
Structural
Asphalt Concrete

3. FACTORS AFFECTING CHOICES
Traffic Volume
Riding Quality Required
Operational Factor
Safety
Environmental Considerations
Construction and Maintenance
 Properties of Available Aggregate
Construction Cost
Required Service Life

4. OTTA SEAL
An Otta seal is a thin bituminous seal
comprising Natural or crushed
aggregate of all sizes and either a cut-
back or soft penetration grade bitumen
with or without sand cover seal

5. MECHANISM
Graded aggregate is placed on a relatively
thick film of comparatively soft binder
which on rolling and trafficking, works its
way upwards through the aggregate
interstices. The graded aggregate relies both
on mechanical interlocking and bitumen
binding for its strength

6. GENERAL
Similar to Conventional Chip Seal
(DBSD)
Binder Spray – Aggregate
Spreading – Rolling
Prime Normally Not Required
Like All Other Surface Treatments, An
Otta Seal Will Not Contribute Directly
To The Structural Strength Of The
Pavement
Pavement Must Be Properly Designed
To Withstand The Traffic Loading
Throughout Its Designed Life

7. OTTA SEAL CHOICES

8. LIMITATIONS
Lack of information regarding the Otta
Seal, properties, design, construction
and performance
 Reluctance to adopt new technology
Extra contractual Obligation

9. Otta seal Guiding Document

10. RECOMMENDED TYPE OF OTTA SEAL
IN RELATION TO TRAFFIC

11. PREFERRED AGGREGATE GRADING

12. DESIGN OF OTTA SEAL
GRADING GUIDELINES
Sieve
Sizes
(mm)
Open Grading Medium Grading Dense Grading
(% passing) (% passing) (% passing)
16.0 100 100 100
13.2 52 - 82 68 - 94 84 - 100
9.5 36 - 58 44 - 73 70 - 98
6.7 20 - 40 29 - 54 54 - 80
4.75 10 - 30 19 - 42 44 - 70
2.0 0 - 8 3 - 18 20 - 48
1.18 0 - 5 1 - 14 15 - 38
.425 0 - 2 0 - 6 7 - 25
.075 0 - 1 0 - 2 3 - 10

13. DESIGN OF OTTA SEAL
STRENGTH REQUIREMENT
Los Angeles
Abrasion value
IS: 2386 40 percent (Max)
Aggregate
Impact value
IS: 2386 30 percent (Max)
FI
IS: 2386 35 percent (Max)
Stripping Value
5 percent (Max)

14. DESIGN OF OTTA SEAL
Type of
Seal
Aggregate Spread Rates (m3/m2)
Open
Grading
Medium
Grading
Dense
Grading
Otta Seals 0.013-0.016 0.013-0.016 0.016-0.020
Sand Seals 0.010-0.012
Aggregate Application Rates

15. DESIGN OF OTTA SEAL
Binder Spray Rates Depends on:
Traffic (AADT)
Aggregate Grading
(Open/Medium/Dense)
Absorbency of Aggregate Particles
Priming of Base Course

16. DESIGN OF OTTA SEAL
Choice of Binder
 MC 3000, in warm weather
 MC 800, in cold weather when night temperature <10°
C.
 Blending of 80/ 100(VG10) with kerosene done at site
to produce required consistency

17. WEATHER LIMITATIONS
The minimum surface temperatures for
spraying of the different types and grades of
binder shall be :
 80/100 penetration grade bitumen: 50
o
C
 MC-3000 cutback bitumen: 22
o
C
 MC-800 cutback bitumen: 15
o
C
 MC-30 cutback bitumen: 10
o
C
 Emulsions: 5
o
C

18. DESIGN OF OTTA SEAL
Choice of Binder
AADT at
Construction
Type of Bitumen for Different Aggregate grading
Open Medium Dense
>1000 NA 150/200 pen MC 3000
MC 800 in cold
100 – 1000 150/200 pen 150/200 pen in
cold
MC 3000
MC 800 in cold
<100 150/200 pen MC 3000 MC 800

19. DESIGN OF OTTA SEAL
Binder Spray Rates (in litres/m2)
Type of Otta Seal Grading
Open Medium Dense
Double 1st Layer 1.6 1.7 1.8
2nd Layer 1.5 1.6 2.0
Single with
a Sand
Cover Seal
Fine Sand 0.7 0.7 0.6
Coarse sand 0.9 0.8 0.7
1st Layer 1.6 1.7 2.0
Single 1.7 1.8 2.0
Maintenance Reseal 1.5 1.6 1.8

20. DESIGN OF OTTA SEAL
Blending Guidelines
Required
Product
Cutter (kerosene) in percent of total
80/100 base Bitumen
150/200 Base
Bitumen
150/200
3-5% (flux oil is used
instead of Cutter)
-
MC 3000 8-10% 5-8%
MC 800 18-20% 15-18%
*

22. PRIME
Normally Not Required
Required only when calcareous base
Required because of High
Amount of Bitumen
Absorption

23. CONSTRUCTION PROCESS
Sub-grade preparation
Preparation of Sub Base
Preparation of CRM
Binder application
Aggregate spreading
Rolling
Sand sealing after about 8
weeks

24. OTTA SEAL CONSTRUCTION
EQUIPMENT USED:
 Bitumen boiler 1 No.
 Bitumen distributor 1 No.
 Pneumatic rollers 2 Nos.
 Steel roller 1 No.
 Chips spreader 1 No.
 Air compressor 1 No.

25.  speed of the distributor can be calculated from
equation
Speed of distributor = S/(R*W)
Where S is the rate of delivery (mass) from
the spray bar in kg/s
R is the design spray rate (mass) in kg/m
W is the sprayed width in metres
The required speed will then be in m/s.
DISTRIBUTOR CALIBRATION

26. PREPARATION OF BASE COURSE
Good Bond Between Base Course and
Surfacing Necessary
Brooming Dust and Foreign Matter
Light Watering to Suppress Dust and to
Facilitate Penetration of Binder

27. SEALING OPERATION
Spraying of Binder
Spreading of Aggregate
Initial Rolling
(On the Day of Construction)
Rolling Afterwards(Back Rolling )

28. ROLLING
Extensive Rolling with PTR is
Essential to Achieve a Good Result
One Pass with a Steel Roller will
Improve the Embedment of the
Larger Aggregate

29. TREATMENT
 Commercial Traffic Allowed After Initial
Rolling With PTR
 A Speed Limit (?) Should be Enforced for
2-3 Weeks
 Road may be reopen to traffic after
minimum of three passes with restricted
speed.

30.  On the Day of Construction :15 Passes
with PTR + 1 Pass with Steel Roller
 For Each of Next 2 Days :15 Passes with
PTR
 During First 2- 3 Weeks: Brooming Back
Aggregate
 2-3 Weeks After Construction :Sweep Off
Excess Aggregate and speed restriction
lifted.
ROLLING REQUIREMENTS

31. POST CONSTRUCTION
 Minimum of 8 - 12 Weeks Between First and
Second Layers
 Bleeding in Localised Areas and Wheel Path
is Normal in Otta Seals
 Any Available Fine Aggregate Can be Used for
Blinding Off
 In Case of Extensive Bleeding, Coarse
Aggregate May be Used

32. ADDITIONAL CONSIDERATIONS
Curing of 1st Seal for 8 – 12
Weeks
Enough Cover Aggregate to be
Applied for Sand Cover Seal and
Broomed Back Regularly until fully
Embedded. Normally 4 Weeks.

38. COMPLETED SECTION
 Single Otta
Seal +
Sand Seal

39. COMPLETED SECTION
 Single Otta
Seal without
Sand Seal

40. THANK YOU