--- title: "Double surface treatment materials and procedure" subject: "Transportation Engineering II" chapter: 3 key: "semester_7/transportation_engineering_ii:double-surface-treatment-material-procedure" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/double-surface-treatment-material-procedure site: BCT Engineering --- # Double surface treatment materials and procedure Transportation Engineering II · Chapter 3: Road Construction Technology - Asked in: 2076 Asoj, 8 marks - Video: [Single and Multiple Surface Treatments](https://www.youtube.com/watch?v=ci7y36KkWFI) — PublicResourceOrg - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/double-surface-treatment-material-procedure - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-3 ## Question Write down material selection and construction procedure of double surface treatment pavement. ## Short answer Double surface treatment uses two coats: first about 1.2 kg/m2 bitumen with 13.2 mm chips, second about 1.0 kg/m2 with 11.2 mm chips; aggregate must be clean, AIV below 30%. Procedure: clean and prime base, spray first binder, spread chips, roll, repeat second coat, final roll, open after 24 hours. ## Answer **Double bituminous surface dressing (DBSD)** is a surface treatment of two successive applications of bitumen and stone chips on a prepared WBM or granular base, forming a 20-25 mm waterproof wearing surface (IRC:17 and IRC:23; Nepal DoR "Standard Specifications for Road and Bridge Works"). It is used for low-cost roads. **Materials** - **Binder**: bitumen 80/100 or 60/70, cutback or emulsion; typical rates are about 1.2 kg/m2 for the first coat (with 13.2 mm chips) and about 1.0 kg/m2 for the second coat (with 11.2 mm chips), as fixed by the specification. - **Aggregate**: crushed stone or gravel, AIV below 30 percent, flakiness below 25 percent, water absorption below 1 percent, stripping value below 5 percent; first coat 13.2 mm (about 0.15 m3 per 10 m2); second coat 11.2 mm or 6.7 mm (about 0.09 m3 per 10 m2). - **Prime coat** over a WBM base if required: 0.6-1.0 kg/m2 of cutback or emulsion. **Construction procedure** 1. Prepare the base: sweep and clean it, fill all depressions, patch potholes and ensure the correct camber. Apply a prime (or tack) coat and let it cure. 2. Spray the first coat of binder with a pressure distributor at the specified rate and spraying temperature (about 150-170 C for paving bitumen; lower for cutback, and emulsion is sprayed cold or warm), as a uniform film, one lane width at a time. 3. Immediately spread the first-coat chippings (13.2 mm) by chip spreader or manually, covering 100 percent of the binder without piling. 4. Roll with an 8-10 t roller, moving from the edge to the centre; brush off surplus chips. 5. Apply the second coat of binder and the smaller chips (11.2 mm) in the same way, then roll. 6. Do the final rolling with a pneumatic roller and sweep off loose chips; open to traffic after 24 hours at low speed (20 km/h) for a few days. 7. Quality control: bitumen temperature and rate of spread (tray test), chip spread rate, grading, cleanness and surface regularity. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is DBSD? A. Two successive applications of bitumen and chips on a prepared base forming a 20-25 mm wearing surface B. A 100 mm hot mix layer C. A single coat of cement slurry D. Penetration macadam with grouting Answer: A. Double surface treatment applies binder and chips twice to give a thin waterproof surface. (Key point: Definition of DBSD) 2. Which aggregate requirements apply to DBSD? A. AIV below 30 percent, flakiness below 25 percent, stripping value below 5 percent B. AIV above 50 percent, flakiness above 40 percent C. Any gravel with clay coating D. Only sand below 2 mm Answer: A. Chips must be hard, cubical and resistant to stripping: AIV below 30, flakiness below 25, absorption below 1, stripping below 5 percent. (Key point: Aggregate quality limits) 3. What are the typical binder rates for the two coats? A. About 1.0 kg/m2 first, 1.2 kg/m2 second B. About 1.2 kg/m2 first and 1.0 kg/m2 second C. About 5 kg/m2 each D. About 0.2 kg/m2 each Answer: B. The first coat takes about 1.2 kg/m2 with 13.2 mm chips, the second about 1.0 kg/m2 with 11.2 mm chips. (Key point: Binder rates) 4. At what temperature is the binder sprayed by pressure distributor? A. 50-70 C B. 90-100 C C. 150-170 C D. 220-250 C Answer: C. The binder is sprayed at 150-170 C in a uniform sheet within one lane width at a time. (Key point: Binder spraying) ## Related in Transportation Engineering II - [WBM: material, equipment, procedure, quality control](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Awbm-materials-equipment-quality-control) — Transportation Engineering II, chapter 3 - [Road construction equipment and DBSD procedure](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aequipment-plants-activities-dbsd) — 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 - [Surface dressing and DBSD construction](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asurface-dressing-dbsd-procedure) — Transportation Engineering II, chapter 3 - [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 - [Rigid pavement thickness by IRC procedure](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Arigid-thickness-irc-procedure) — Transportation Engineering II, chapter 2 ## Related in other subjects - [Anti-termite treatment procedure](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Aantitermite-procedure) — Civil Engineering Materials, chapter 9, asked 3× - [Post construction anti-termite treatment](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Apost-construction-antitermite) — Civil Engineering Materials, chapter 9 - [Materials in pavement layers](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Apavement-layer-materials) — Transportation Engineering I, chapter 6 - [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×