---
title: "Types of bituminous mixes"
subject: "Transportation Engineering I"
chapter: 6
key: "semester_6/transportation_engineering_i:bituminous-mix-types"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/bituminous-mix-types
site: BCT Engineering
---

# Types of bituminous mixes

Transportation Engineering I · Chapter 6: Highway Materials

- Asked in: 2078 Baisakh, 4 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/bituminous-mix-types
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-6

## Question

Explain bituminous mixes types.

## Short answer

By aggregate gradation: dense-graded, open-graded, gap-graded, mastic. By mixing temperature: hot, warm, cold. By layer use: surface course, binder/base course. By binder: bitumen, cutback, emulsion, polymer/rubber modified.

## Answer

Bituminous mixes are classified in the following ways.

#### 1. By aggregate gradation
- **Dense-graded mixes** - continuous grading from coarse to fine, with low voids; strong and impermeable. Examples: bituminous concrete (BC), dense bituminous macadam (DBM), semi-dense bituminous concrete (SDBC).
- **Open-graded mixes** - mostly coarse aggregate with few fines, high voids (15-25%), good drainage but lower strength. Examples: bituminous macadam (BM), open-graded premix carpet, porous asphalt.
- **Gap-graded mixes** - some intermediate sizes missing, with a high coarse and filler content and a lot of binder; e.g., stone matrix asphalt (SMA), highly rut-resistant.
- **Sand and mastic mixes** - sand asphalt, mastic asphalt (fine aggregate in rich binder, used for bridge decks).

#### 2. By mixing temperature and method
- **Hot mix asphalt** (prepared at 150-165 degrees C in a hot mix plant).
- **Warm mix** (100-130 degrees C using additives).
- **Cold mix** (with emulsion or cutback at ambient temperature).
- **Plant mix** and **mix-in-place** (road mix).

#### 3. By use in the pavement
- **Surface course** - BC, SDBC, premix carpet, mastic, SMA.
- **Binder/base course** - DBM, BM.

#### 4. By binder
Bitumen, cutback, emulsion, tar and polymer/rubber-modified bitumen (PMB, CRMB) mixes.

## Check yourself

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

1. Dense-graded mixes are characterised by
   A. Mostly coarse with 15-25% voids
   B. Missing intermediate sizes
   C. Continuous grading and low voids; e.g. BC and DBM
   D. Only sand and mastic
   Answer: C. Dense mixes are strong and impermeable. (Key point: Dense-graded)

2. Open-graded mixes have
   A. No voids
   B. Highest strength
   C. Highest binder
   D. Few fines, high voids, good drainage but lower strength
   Answer: D. BM and porous asphalt are open graded. (Key point: Open-graded)

3. Stone matrix asphalt is
   A. A gap-graded mix highly resistant to rutting
   B. An open-graded drainage mix
   C. A cold emulsion mix
   D. A tar-only mix
   Answer: A. Intermediate sizes missing, more filler and binder. (Key point: Gap-graded)

## Related in Transportation Engineering I

- [Desirable properties of bituminous mixes](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Abituminous-mix-desirable-properties) — Transportation Engineering I, chapter 6, asked 3×