--- title: "Bituminous premix carpet construction" subject: "Transportation Engineering II" chapter: 3 key: "semester_7/transportation_engineering_ii:premix-carpet-construction" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/premix-carpet-construction site: BCT Engineering --- # Bituminous premix carpet construction Transportation Engineering II · Chapter 3: Road Construction Technology - Asked in: 2080 Baisakh, 8 marks; 2070 Chaitra (old course), 6 marks; 2066 Bhadra, 2 marks (asked 3 times) - Video: [construction procedure of Premix bituminous carpet](https://www.youtube.com/watch?v=FfCaMWbT9g0) — Harshada Nilesh Wagh - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/premix-carpet-construction - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-3 ## Question Describe the construction procedure of bituminous premix carpet including the requirements on materials, equipment and the tests for quality control. ## Short answer Bituminous premix carpet (20–25 mm) is constructed by spreading pre-coated 13.2 mm and 11.2 mm chippings with 80/100 or 60/70 bitumen over a tack coat at 100–120°C, compacting with an 8–10 t roller, and applying a seal coat. Quality control tests aggregate/bitumen, mix temperature, thickness (±5 mm), and evenness (≤8 mm under 3 m straight edge). ## Answer **Bituminous premix carpet (PMC)** is a 20-25 mm thick open-graded wearing course in which pre-coated chippings are laid and compacted over a tack-coated base (IRC:14, MoRTH Section 508; used on rural and low-volume roads in Nepal under DoR/DoLIDAR specifications). **Materials** - **Aggregate**: 13.2 mm and 11.2 mm nominal size crushed stone/gravel; AIV below 30 percent, LAA below 35 percent, flakiness below 25 percent, water absorption below 1 percent, stripping value below 5 percent. - **Binder**: bitumen 80/100 or 60/70 grade, or cutback / emulsion; quantities of binder and chippings per 10 m2 are taken from the IRC:14 table for the 20 mm carpet (per 10 m2: 0.18 m3 of 13.2 mm and 0.09 m3 of 11.2 mm chippings, with 9.5 kg and 5.1 kg of bitumen respectively, 14.6 kg in all). - **Tack coat**: 0.25-0.30 kg/m2 of bitumen emulsion. **Equipment**: bitumen boiler with sprayer, mixer (drum mixer or mixing platform), 8-10 t smooth wheel roller, tipper, brooms, hand tools, thermometers. **Construction procedure** 1. Prepare the base: clean, repair, apply tack coat (0.25-0.30 kg/m2) and allow to break. 2. Heat aggregates to 130-165 C and bitumen to 120-165 C, mix in a mixer so that each chipping is uniformly coated (a mixing platform for small jobs). 3. Spread the premix at 100-120 C immediately by paver or by hand rake, to uniform camber and thickness. 4. Roll with an 8-10 t roller from edges towards the centre, starting at about 100 C, until the chippings are firmly keyed and the surface is true. 5. Apply the seal coat (a bitumen film with 6.7 mm chips or sand) after the carpet has set; this closes the open texture and makes it waterproof. 6. Open to traffic after the surface cools. **Quality control**: aggregate and bitumen tests; temperature checks of mix at laying; rate of spread of materials by measuring the area covered; thickness (+- 5 mm) and cross-section; surface evenness with a 3 m straight edge (max 8 mm); bitumen content by extraction on random samples. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is bituminous premix carpet? A. A 100 mm dense base course of graded stone B. A 20-25 mm open-graded wearing course of pre-coated chippings over a tack-coated base C. A concrete slab with premixed joints D. A cold gravel layer with no binder Answer: B. PMC uses pre-coated 13.2/11.2 mm chippings laid thin as an open-graded surface. (Key point: Nature of PMC) 2. Why is a seal coat applied on the carpet after it sets? A. To close the open texture and make the surface waterproof B. To make the surface more open for drainage C. To replace the tack coat D. To raise the stability above 9 kN Answer: A. Premix carpet is open-textured; the seal coat of bitumen with 6.6 mm chips or sand seals it. (Key point: Seal coat purpose) 3. At what condition is the premix laid and rolled? A. Spread cold and rolled with a vibratory roller from centre to edges B. Spread at 200 C and left unrolled C. Spread at about 100-120 C and rolled from edges to centre starting about 100 C with an 8-10 t roller D. Rolled only after it cools below 60 C Answer: C. The premix must be spread hot and rolled before it cools so chippings key properly. (Key point: Laying and rolling) 4. Which checks control quality of the premix carpet? A. Only the CBR of the carpet B. Only a visual check at opening day C. Slump and cube strength D. Mix temperature at laying, rate of spread of materials, thickness, and evenness with a 3 m straight edge Answer: D. Temperature, spread rate by area covered, thickness and straight-edge evenness are the field checks. 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