--- title: "Asphalt concrete construction and quality control" subject: "Transportation Engineering II" chapter: 3 key: "semester_7/transportation_engineering_ii:asphalt-concrete-construction" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/asphalt-concrete-construction site: BCT Engineering --- # Asphalt concrete construction and quality control Transportation Engineering II · Chapter 3: Road Construction Technology - Asked in: 2079 Bhadra, 8 marks; 2078 Bhadra, 8 marks; 2076 Chaitra, 8 marks; 2070 Chaitra, 8 marks; 2066 Bhadra, 2 marks (asked 5 times) - Video: [Asphalt Quality Control](https://www.youtube.com/watch?v=T374R-0UfLw) — Plantmix Asphalt Industry of Kentucky - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/asphalt-concrete-construction - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-3 ## Question Describe the construction procedure of Asphalt Concrete including the requirements on material, construction steps, plants and equipments and the tests for quality control. ## Short answer Use dense-graded aggregate, filler, and bitumen; mix at hot-mix plant, transport, lay with paver, compact with steel and pneumatic rollers. Apply tack or prime coat, control temperatures, open traffic below 60 C. QC includes Marshall stability, density, binder content, gradation, thickness and surface regularity. ## Answer **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, flakiness index below 30 percent combined, stripping value below 5 percent, water absorption below 2 percent), graded to the 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, repair defects, and apply a **tack coat** (0.20-0.25 kg/m2 of emulsion) to the old 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 by paver with proper level sensors and uniform speed; hand-lay only at small patches. 5. Initial (breakdown) rolling by 8-10 t steel roller at 110-135 C, intermediate rolling with pneumatic tyre roller, final rolling with tandem roller at 70 C or more to remove marks. Roll longitudinally from edge towards centre, overlapping. 6. Joints: cut transverse joints vertical and apply tack coat; stagger longitudinal joints. 7. Traffic opens when the surface cools below 60 C. **Quality control**: tests on aggregates, bitumen (penetration, softening point, ductility), mix design by Marshall method; at site: temperature of mix, binder content (extraction), gradation, Marshall stability and flow, density by core cutter (above 98 percent of laboratory Marshall density), thickness (+-5 mm) and surface regularity with 3 m straight edge (max 5 mm) and bump integrator. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Before laying asphalt concrete, which coat is applied where? A. Tack coat on an old bituminous surface, prime coat on a granular base B. Prime coat on an old bituminous surface, tack coat on a granular base C. Tack coat on both, prime coat is never used D. Seal coat on the base before laying Answer: A. Tack coat bonds to existing bituminous surfaces; prime coat treats and binds a granular base. (Key point: Tack vs prime coat) 2. How is the binder content (5 to 6 percent) of asphalt concrete fixed? A. By the CBR test B. By the contractor's visual judgment on site C. By Marshall mix design (stability, flow, air voids, VMA) D. By the Los Angeles abrasion value Answer: C. The Marshall method sets the job-mix binder content against stability, flow, air voids and VMA limits. (Key point: Mix design) 3. What is the correct rolling sequence? A. Breakdown with 8-10 t steel roller at 110-135 C, intermediate with pneumatic tyre roller, finish with tandem roller at 70 C or more B. Pneumatic roller first, then steel roller after the mix cools below 60 C C. Only a single finishing pass once the mix is cold D. Roll from centre to edge once, with no overlap Answer: A. Hot breakdown rolling gives compaction, then kneading and finishing to remove marks; rolling is edge to centre with overlap. (Key point: Rolling sequence) 4. What compaction is required at the site? A. Core density above 80 percent of Marshall density B. Core density above 98 percent of the laboratory Marshall density C. Density is not checked, only thickness D. Exactly 100 percent of maximum dry Proctor density Answer: B. Density by core cutter must exceed 98 percent of laboratory Marshall density. 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