--- title: "Pavement layer functions and rigid pavement joints" subject: "Transportation Engineering II" chapter: 2 key: "semester_7/transportation_engineering_ii:pavement-layer-functions-rigid-joints" source: https://www.bctengineer.com/q/semester_7/transportation_engineering_ii/pavement-layer-functions-rigid-joints site: BCT Engineering --- # Pavement layer functions and rigid pavement joints Transportation Engineering II · Chapter 2: Highway Pavement - Asked in: 2082 Bhadra, 4+4 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-layer-functions-rigid-joints - Whole chapter: https://www.bctengineer.com/md/semester_7/transportation_engineering_ii/chapter-2 ## Question Describe the functions of pavement layers. What are the different types of joints used in the rigid pavement? Explain in brief. ## Short answer Pavement layers spread load: surface resists wear and water, binder distributes load, base is main load-bearing layer, sub-base drains and filters, subgrade carries all load. Rigid pavement joints are contraction, expansion, construction, longitudinal, and warping joints, each controlling cracking and slab movement. ## Answer #### Functions of pavement layers A flexible pavement is a layered system; the load spreads downwards so that the stress on each layer reduces with depth. | Layer | Main functions | |---|---| | **Surface (wearing) course** | Resists tyre wear and abrasion, gives a smooth, skid-resistant and waterproof riding surface, protects the 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 the 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 the 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. #### Joints in rigid pavement Joints are provided in a cement concrete slab to control cracking from temperature change, shrinkage and warping, and to allow construction in stages. 1. **Contraction joint (transverse)** - a weakened plane (sawn groove 1/4 to 1/3 of the slab depth) that lets the slab shrink on cooling and creates a controlled crack. Dowels are provided. Spacing is usually 4.5 m (IRC:58), up to 5 m for unreinforced slabs. 2. **Expansion joint** - a full-depth gap (20-25 mm) filled with compressible filler (bitumen-impregnated fibre board or cork) and sealant, provided at bridges, culverts, intersections and wherever the slab meets a structure, so that the slab can expand freely. Smooth dowel bars with a cap on one end carry the load. IRC:58 permits omitting them in long slab runs. 3. **Construction joint** - placed where concreting stops at the end of the day or at a break. It is designed as a butt joint with dowels, preferably at a contraction-joint location. 4. **Longitudinal joint** - between adjacent lanes (about every 3.5 m) to control longitudinal cracking from warping. Tie bars (12 mm deformed bars) hold the slabs together and prevent lane separation. 5. **Warping joint (hinged joint)** - used in older practice in the middle of a slab to relieve warping stress; today the longitudinal joint with tie bars serves this purpose. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is a function of the sub-base course? A. Resisting tyre wear B. Acting as a drainage and filter layer preventing intrusion of subgrade soil C. Bonding the wearing course to the base D. Giving skid resistance Answer: B. The sub-base supports the base, drains water, filters and prevents subgrade intrusion and capillary rise. (Key point: Sub-base function) 2. To what density must the top subgrade be compacted? A. At least 85 percent of Proctor B. At least 97 percent of Proctor density C. 100 percent of CBR D. Not compacted Answer: B. The top 500 mm subgrade is compacted to at least 97 percent of Proctor density. (Key point: Subgrade compaction) 3. A contraction joint is: A. A full-depth gap filled with fibre board B. A weakened plane (sawn groove 1/4 to 1/3 of depth) that controls shrinkage cracking C. A joint at the middle of a lane only D. A joint between slab and bridge Answer: B. It forms a controlled crack as the slab shrinks on cooling; spacing is about 4.5 m. (Key point: Contraction joint) 4. Where is an expansion joint mainly provided? A. At every 4.5 m B. At bridges, culverts, intersections and where slab meets a structure C. Only along the lane centre D. Never in concrete roads Answer: B. A 20-25 mm filled gap lets the slab expand freely at structures and intersections. (Key point: Expansion joint) 5. The purpose of tie bars at a longitudinal joint is to: A. Allow the slabs to separate B. Hold slabs together and prevent lane separation C. Transfer wheel load like dowels D. Permit expansion Answer: B. 12 mm deformed tie bars keep adjacent lanes from separating. 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