---
title: "Materials in pavement layers"
subject: "Transportation Engineering I"
chapter: 6
key: "semester_6/transportation_engineering_i:pavement-layer-materials"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/pavement-layer-materials
site: BCT Engineering
---

# Materials in pavement layers

Transportation Engineering I · Chapter 6: Highway Materials

- Asked in: 2071 Bhadra
- Video: [Flexible Pavement (Bitumen Road) में कौन-कौन सी Layer होती हैं? | Types of Layer in Bitumen Road](https://www.youtube.com/watch?v=smPaOcM1Xc8) — REINFORCE
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/pavement-layer-materials
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-6

## Question

Explain the materials used in different layers of the road pavement.

## Short answer

Subgrade uses compacted soil (CBR ≥5%); sub-base, granular material like GSB; base, WBM, WMM or bituminous macadam; binder course, DBM; surface, bituminous concrete or SDBC. Rigid pavements have a concrete slab over DLC. Stronger, costlier materials are placed in upper layers.

## Answer

A flexible pavement consists of layers, each made of materials suited to the stress at that level. Materials are specified in NRS 2070 / DoR Standard Specifications and IRC.

| Layer | Function | Materials |
|---|---|---|
| **Subgrade** (top 500 mm of soil) | Foundation, supports pavement | Natural/compacted soil with CBR at least 5%; improved with lime/cement or granular material |
| **Sub-base** | Distributes load, drainage, frost protection | Natural gravel, moorum, crushed stone, granular sub-base (GSB), stabilised soil |
| **Base course** | Main load-bearing and distribution | Water-bound macadam (WBM), wet-mix macadam (WMM), crushed aggregate, bituminous macadam/DBM, cement/lime stabilised |
| **Binder course** | Links base and surface, gives strength | DBM, bituminous macadam |
| **Surface / wearing course** | Takes traffic, waterproof, skid-resistant | Bituminous concrete (BC), SDBC, premix carpet, surface dressing, mastic asphalt, cement concrete |

#### Rigid pavement layers
- **Subgrade**, **granular sub-base**, **dry lean concrete (DLC) base** and **pavement quality concrete (PQC)** slab of M30-M40 concrete, with dowel and tie bars and joint sealants.

#### Binders and other materials
- Bitumen (VG-30, 60/70), cutback, emulsion for tack coat and prime coat; cement, lime, fly ash for stabilisation; geotextiles and geogrids; steel in reinforcement.

The materials get stronger and costlier upwards, so cheaper local materials are used in lower layers.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is required of the subgrade soil?
   A. Bituminous concrete only
   B. Dry lean concrete
   C. Natural or compacted soil with CBR at least 5%
   D. Mastic asphalt
   Answer: C. Subgrade is the foundation soil, improved if needed. (Key point: Subgrade)

2. Which materials suit the surface or wearing course?
   A. Natural gravel and moorum
   B. Granular sub-base
   C. Geogrids only
   D. Bituminous concrete, SDBC, premix carpet, surface dressing
   Answer: D. Surface course takes traffic, is waterproof and skid-resistant. (Key point: Surface course)

3. Which layers form a rigid pavement?
   A. Subgrade, granular sub-base, DLC base and PQC slab
   B. Subgrade, WBM and BC
   C. Only a PQC slab on bare soil
   D. Subgrade and premix carpet
   Answer: A. Rigid pavements have DLC base and PQC slab with dowel and tie bars. (Key point: Rigid pavement)

## Related in Transportation Engineering I

- [Desirable properties of road aggregates](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Aaggregate-desirable-properties) — Transportation Engineering I, chapter 6, asked 5×
- [Types of bitumen and bituminous materials](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Abitumen-types) — Transportation Engineering I, chapter 6, asked 6×

## Related in other subjects

- [Why pozzolanic materials are used](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Awhy-pozzolanic-materials-used) — Civil Engineering Materials, chapter 4, asked 2×
- [Why composite materials are used](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acomposite-materials-why-used) — Civil Engineering Materials, chapter 10, asked 2×
- [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
- [Rolled vs normal concrete; CC pavement construction](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Arolled-concrete-cc-pavement-construction) — Transportation Engineering II, chapter 3