--- title: "Pavement classification; flexible layer functions" subject: "Transportation Engineering II" chapter: 2 key: "semester_7/transportation_engineering_ii:pavement-classification-flexible-layer-functions" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/pavement-classification-flexible-layer-functions site: BCT Engineering --- # Pavement classification; flexible layer functions Transportation Engineering II · Chapter 2: Highway Pavement - Asked in: 2066 Bhadra, 6 marks - Video: [Layers of Flexible and Rigid Pavement || Transportation Engineering](https://www.youtube.com/watch?v=yG9_CxP8efg) — 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/pavement-classification-flexible-layer-functions - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-2 ## Question Classify pavement and explain the functions of different layers of flexible pavement. ## Short answer Pavements are flexible, rigid, or semi-rigid. Flexible pavement layers: surface course resists wear and water, binder course spreads load, base course is main load-bearing, sub-base provides drainage and support, subgrade carries all load. ## Answer #### Classification of pavements Pavements are classified by how they transfer load to the subgrade. 1. **Flexible pavement** - bituminous (or granular) surface over granular base and sub-base; the load spreads through grain-to-grain contact, with high stress near the surface and reduced stress on the subgrade. Examples: WBM with surface dressing, bituminous macadam, asphalt concrete (IRC:37). 2. **Rigid pavement** - cement concrete slab (PQC) on a sub-base (DLC/GSB); the slab resists load by flexural strength and spreads it over a wide area (IRC:58). Types: JPCP, JRCP, CRCP, prestressed. 3. **Semi-rigid (composite) pavement** - cement-treated or lean-concrete base with a bituminous surface; or concrete overlay on bituminous pavement. By surface type, pavements are also divided into **earthen, gravel, WBM, bituminous (surface dressing, premix, BM, DBM, BC)** and **cement concrete** roads. Nepal DoR groups roads as paved (bituminous/concrete) and unpaved (gravel/earth). #### Functions of layers of a flexible pavement | Layer | Main functions | |---|---| | **Surface (wearing) course** | Resists tyre wear and abrasion, gives a smooth, skid-resistant and waterproof riding surface, protects layers below from water, takes the high compressive and shear stresses of the wheel | | **Binder course (DBM/BM)** | Spreads load to the base, gives a stiff bituminous layer for fatigue strength, bonds the wearing course to the base | | **Base course (WBM/WMM/CTB)** | Main load-bearing layer, distributes load to sub-base, provides drainage of the pavement and structural strength against shear | | **Sub-base (GSB)** | Improves the support to the base, works as a drainage and filter layer, prevents intrusion of subgrade soil and capillary rise, saves costly base thickness | | **Subgrade (compacted soil)** | The natural or improved soil (top 500 mm) that finally carries all load, so it must be compacted to at least 97 percent of Proctor density | The thickness of each layer is fixed so that the stress reaching the layer below is within its capacity. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How are pavements classified by how they transfer load to the subgrade? A. Earthen, gravel and sealed B. Urban, rural and highway C. Flexible, rigid and semi-rigid (composite) D. Light, medium and heavy Answer: C. Pavements are flexible (grain-to-grain spreading), rigid (concrete slab in flexure) or semi-rigid/composite. (Key point: Classification by load transfer) 2. Which is a function of the sub-base? A. Resists tyre wear and abrasion B. Works as a drainage and filter layer and prevents subgrade soil intrusion and capillary rise C. Bonds the wearing course to the binder D. Provides a skid-resistant surface Answer: B. Sub-base supports the base, drains, filters and stops subgrade intrusion and capillary rise, saving costly base thickness. (Key point: Function of sub-base) 3. Which of these is the role of the wearing (surface) course? A. Takes high compressive and shear stresses of the wheel, giving a smooth, skid-resistant, waterproof surface B. Acts as the main load-bearing layer C. Carries all load to the subgrade D. Is the compacted natural soil Answer: A. The surface course resists wear and wheel stresses and waterproofs the layers below; base and subgrade do the structural job. (Key point: Function of surface course) ## Related in Transportation Engineering II - [Pavement layer functions and rigid pavement joints](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Apavement-layer-functions-rigid-joints) — Transportation Engineering II, chapter 2 - [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× - [Flexible pavement design with 8 CBR values](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-design-eight-cbr-340-cvd) — Transportation Engineering II, chapter 2 - [Flexible pavement life with 140 cvpd traffic](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-design-life-years-140-cvpd) — Transportation Engineering II, chapter 2 - [Flexible pavement failures: causes and remedies](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-pavement-failure-cause-remedy) — Transportation Engineering II, chapter 4 - [Flexible pavement failures; deflection overlay design](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-failures-deflection-overlay) — Transportation Engineering II, chapter 4 ## Related in other subjects - [Materials in pavement layers](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Apavement-layer-materials) — Transportation Engineering I, chapter 6 - [Functions of data link layer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Adll-functions) — Computer Networks and Security, chapter 3, asked 3× - [Functions of physical layer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aphysical-layer-functions) — Computer Networks and Security, chapter 2 - [Functions of network layer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Anetwork-layer-functions) — Computer Networks and Security, chapter 4