--- title: "Typical pavement structures sketch; otta seal" subject: "Transportation Engineering II" chapter: 3 key: "semester_7/transportation_engineering_ii:pavement-structures-sketch-otta-seal" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/pavement-structures-sketch-otta-seal site: BCT Engineering --- # Typical pavement structures sketch; otta seal Transportation Engineering II · Chapter 3: Road Construction Technology - Asked in: 2071 Chaitra, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/pavement-structures-sketch-otta-seal - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-3 ## Question Draw a neat sketch of typical pavement structures. Explain in detail the construction methodology of Otta Seal. ## Short answer Typical flexible pavement: BC, DBM, WMM, GSB over subgrade; rigid: PQC, DLC, GSB over subgrade; low-volume Otta seal road: Otta seal, base, subbase, subgrade. Otta seal construction: prepare clean base, spray soft binder, spread graded aggregate, roll with pneumatic tyre roller until binder rises, broom and allow traffic. ## Answer #### Typical pavement structures ```text Flexible Rigid (CC) Low volume (highway) (Otta seal) +-----------+ +-----------+ +-----------+ | BC 40-50 | | PQC slab | | Otta seal | +-----------+ | 200-300 | | 16-32 | | DBM 50-170| +-----------+ +-----------+ +-----------+ | DLC 150 | | Base | | WMM 250 | +-----------+ | 150-200 | +-----------+ | GSB 150 | +-----------+ | GSB 200 | +-----------+ | Sub-base | +-----------+ | Subgrade | | 100-200 | | Subgrade | | 500 | +-----------+ | 500 | +-----------+ | Subgrade | +-----------+ +-----------+ ``` Thicknesses in mm (IRC:37, IRC:58, Nepal DoR low volume guidelines); actual values come from the design for the traffic and subgrade CBR. A single Otta seal is about 16 mm thick and a double one about 32 mm. #### Construction methodology of Otta seal **Otta seal** is a low-cost bituminous surfacing made of a single or double layer of graded natural gravel or crushed stone (maximum size 16-19 mm) rolled into a relatively thick film of soft binder (cutback such as MC-3000, or 150/200 penetration bitumen) sprayed on the base. It originated in Norway (Norwegian Public Roads Administration, Note 31) and is used on low-volume roads in Nepal under DoR guidelines. **Materials**: graded aggregate (continuous grading, maximum size 16 or 19 mm; fines below about 10 percent; flakiness below 30 percent) from a crusher or river source; soft binder (150/200 penetration bitumen cut back with kerosene, or emulsion). A prime coat on the base is generally not required, which is one of the advantages of Otta seal. **Construction** 1. Prepare the base (WBM, crushed gravel or stabilised base) to a smooth, tight surface; patch defects and sweep it clean (prime only if the specification asks for it). 2. Spray the binder with a distributor at the specified rate (about 1.4 to 2.0 litres per m2 for the first layer, depending on the grading and the base) at its spraying temperature (about 120-150 C for hot binders). 3. Immediately spread the aggregate (about 13-16 litres per m2, slightly damp) by chip spreader or tipper to cover the binder fully. 4. Roll with a pneumatic tyre roller (at least 12 t) with many passes (about 15 or more); the kneading forces the binder up through the aggregate. 5. Broom loose stones back onto the surface during the first days. For a double Otta seal, apply the second layer (binder and a finer graded aggregate) in the same way after the first layer has bedded in under traffic. 6. Allow traffic at low speed. The seal improves with traffic over the first weeks as the binder works up into the aggregate. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. In the rigid pavement sketch, which layers lie under the PQC slab? A. WMM and GSB B. DLC then GSB then subgrade C. DBM then BC D. Otta seal then base Answer: B. The CC pavement has PQC slab 200-300 mm over DLC 150 mm over GSB 150 mm over subgrade. (Key point: Rigid pavement layers) 2. What binder is used in Otta seal? A. Stiff 30/40 bitumen B. Soft binder: cutback or 150/200 penetration bitumen C. Cement slurry D. Tar only at 20 C Answer: B. A soft binder lets the aggregate be pressed into it. (Key point: Otta seal binder) 3. At what temperature is the Otta seal binder sprayed? A. 20-30 C B. 120-150 C C. 200-250 C D. Not heated Answer: B. Binder is sprayed at 120-150 C at about 1.4-2.0 litre per m2 for the first layer. (Key point: Binder spraying temperature) 4. What is the second layer of a double Otta seal? A. 9.5 mm aggregate, rolled and re-brushed B. 40 mm aggregate C. Hot mix D. Cement concrete Answer: A. After brushing lightly after 24 hours, a smaller 9.5 mm layer is applied. (Key point: Second layer) ## Related in Transportation Engineering II - [Road construction activities; otta seal procedure](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aactivities-otta-seal-construction) — Transportation Engineering II, chapter 3 - [Construction equipment; prime, tack and seal coats](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aequipment-plants-prime-tack-seal-coat) — Transportation Engineering II, chapter 3 - [Typical failures of flexible pavement](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-pavement-failures-causes) — Transportation Engineering II, chapter 4, asked 2× - [Rolled vs normal concrete; CC pavement construction](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Arolled-concrete-cc-pavement-construction) — Transportation Engineering II, chapter 3 - [Construction steps of cement concrete pavement](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Acc-pavement-construction-steps) — Transportation Engineering II, chapter 3 - [Bituminous pavement types; asphalt concrete construction](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Atypes-bituminous-pavement-ac-construction) — Transportation Engineering II, chapter 3 ## Related in other subjects - [Equipment for highway and pavement construction](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Ahighway-pavement-equipment) — Construction Management, chapter 4, asked 3×