Design and construction procedure of otta seal
- 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
- 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
- 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