--- title: "Seal, prime, tack coat and bituminous concrete" subject: "Transportation Engineering II" chapter: 3 key: "semester_7/transportation_engineering_ii:seal-prime-tack-coat-bituminous-concrete" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/seal-prime-tack-coat-bituminous-concrete site: BCT Engineering --- # Seal, prime, tack coat and bituminous concrete Transportation Engineering II · Chapter 3: Road Construction Technology - Asked in: 2082 Baisakh, 8 marks - Video: [What is Prime coat, Tack coat and Seal coat in Pavement](https://www.youtube.com/watch?v=6Xqgga3-mkc) — Civil Engineering - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/seal-prime-tack-coat-bituminous-concrete - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-3 ## Question Define seal coat, prime coat and tack coat. Write down the material, equipment, construction procedure and quality control for Bituminous Concrete pavement. ## Short answer Prime coat is low-viscosity cutback on granular base, tack coat is thin emulsion on old surface, seal coat is bitumen with chips to seal voids. Bituminous concrete uses dense hot mix of aggregate, filler and VG-30, laid by paver and compacted by rollers. QC includes Marshall stability, density above 98%, thickness and regularity. ## Answer #### Prime coat, tack coat and seal coat - **Prime coat**: low-viscosity cutback bitumen (MC-30 / MC-70) or emulsion sprayed on an unbound granular (WBM/WMM) surface before bituminous layers are laid (rate 0.6-1.0 kg/m2). It binds loose dust, plugs the surface voids, hardens the top, and provides adhesion between the base and the bituminous layer (IRC:16). - **Tack coat**: a thin film of bitumen emulsion (RS-1 / SS-1) or cutback (rate 0.20-0.30 kg/m2) sprayed on an existing bituminous or cement concrete surface before overlaying. It bonds the old and new layers, preventing slippage and delamination. - **Seal coat**: a thin surface treatment of bitumen (about 0.7-1.0 kg/m2) with 6.7 mm chips or sand, laid on a newly laid open-textured surface (such as premix carpet) or on an old surface (IRC:14 / MoRTH Section 513). It seals the voids, makes the surface waterproof, protects it against weathering and improves skid resistance. #### Bituminous concrete pavement **Asphalt concrete (bituminous concrete, BC)** is a dense-graded hot mix of aggregates, filler and bitumen (VG-30/60-70 penetration grade) laid as a wearing or binder course (IRC:29 / MoRTH Section 509, Nepal DoR specifications). **Materials** - Aggregate: crushed, clean, hard and cubical (LAA below 30 percent, AIV below 24 percent, combined flakiness and elongation index below 30 percent, stripping value below 5 percent, water absorption below 2 percent), graded to BC Grading 1 or 2. - Filler: stone dust, cement or hydrated lime passing 75 micron. - Binder: bitumen 60/70 or VG-30; 5 to 6 percent by weight of mix as fixed by Marshall design (stability above 9 kN, flow 2-4 mm, air voids 3-5 percent, VMA 12-14 percent). **Plant and equipment**: hot-mix plant (batch or drum mix) with dryer, mixing unit and temperature control, tippers with tarpaulin, bitumen distributor, paver finisher with screed, steel-wheel roller (8-10 t), pneumatic tyre roller (15-20 t), small plate compactor, thermometers. **Construction steps** 1. Prepare the base: clean it, repair defects, and apply a **tack coat** (0.20-0.25 kg/m2 of emulsion) to an old bituminous surface or a **prime coat** to a granular base. 2. Produce the mix at the plant: aggregate heated to about 160-175 C and bitumen to 150-165 C; the mixed material leaves the plant at not more than 170 C. 3. Transport in covered, insulated tippers; the mix must arrive hot enough to be laid at about 120-165 C, depending on the binder grade. 4. Lay with a paver at uniform speed, using level sensors; hand-lay only small patches. 5. Initial (breakdown) rolling with an 8-10 t steel roller at 110-135 C, intermediate rolling with a pneumatic tyre roller, and final rolling with a tandem roller at 70 C or more to remove roller marks. Roll longitudinally from the edge towards the centre, with overlapping passes. 6. Joints: cut transverse joints vertical and apply tack coat; stagger longitudinal joints. 7. Open to traffic when the surface cools below 60 C. **Quality control**: tests on aggregates and bitumen (penetration, softening point, ductility); mix design by the Marshall method; at site: temperature of mix, binder content (extraction), gradation, Marshall stability and flow, density from cores (above 98 percent of laboratory Marshall density), thickness (+-5 mm), and surface regularity with a 3 m straight edge (max 3 mm undulation) and bump integrator. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a prime coat? A. Low-viscosity cutback or emulsion on an unbound granular surface to bind dust and give adhesion to the bituminous layer B. A bitumen film with chips over an old surface C. A thin emulsion film on bituminous concrete before an overlay D. A concrete curing compound Answer: A. Prime coat treats granular bases (WBM/WMM); it plugs voids and hardens the top. (Key point: Prime coat) 2. What is a tack coat used for? A. Waterproofing a granular base B. Bonding a new layer to an existing bituminous or concrete surface to prevent slippage and delamination C. Providing skid resistance with chips D. Heating the aggregate Answer: B. Tack coat is a thin 0.20-0.30 kg/m2 film that glues the new layer to the old. (Key point: Tack coat) 3. What does a seal coat do? A. Bonds a granular base to bitumen B. Increases base strength C. Seals voids, waterproofs and protects the surface with bitumen and 6.6 mm chips or sand D. Replaces the wearing course completely Answer: C. Seal coat is a thin surface treatment against water and weathering. (Key point: Seal coat) 4. Which is a field quality control check for bituminous concrete? A. Slump of the mix B. UCS of the cube at 7 days C. Lime content test D. Core density above 98 percent of laboratory density and 3 m straight edge regularity Answer: D. Compaction, thickness and surface regularity are checked in the field after laying. (Key point: BC field control) ## Related in Transportation Engineering II - [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 - [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 - [Prime vs tack coat; surface dressing method](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aprime-vs-tack-coat-surface-dressing) — 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 - [Bituminous pavement types and quality control](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Atypes-bituminous-pavement-quality-control) — Transportation Engineering II, chapter 3 - [Asphalt concrete construction and quality control](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aasphalt-concrete-construction) — Transportation Engineering II, chapter 3, asked 5× ## 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× - [Quality control of concrete at site](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aquality-control-at-site) — Concrete Technology and Masonry Structure, chapter 5, asked 11×