---
title: "Liquid bitumen explained"
subject: "Transportation Engineering I"
chapter: 6
key: "semester_6/transportation_engineering_i:liquid-bitumen"
source: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/liquid-bitumen
site: BCT Engineering
---

# Liquid bitumen explained

Transportation Engineering I · Chapter 6: Highway Materials

- Asked in: 2071 Magh
- Video: [Bitumen | Types of bitumen | bitumen road construction | Highway Engineering](https://www.youtube.com/watch?v=_bcL6iq4L2A) — Engineer's Coach
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/transportation_engineering_i/liquid-bitumen
- Whole chapter: https://www.bctengineer.com/md/semester_6/transportation_engineering_i/chapter-6

## Question

Explain briefly liquid bitumen.

## Short answer

Liquid bitumen is bitumen fluid at ambient temperature, made as cutback (bitumen + solvent, curing by evaporation) or emulsion (bitumen droplets in water). It is used for prime coat, tack coat, cold mixes, and repairs, allowing work without heavy heating.

## Answer

**Liquid bitumen** is bitumen that is made fluid at ordinary temperature, so that it can be sprayed or mixed with aggregate without heavy heating. It is produced in two ways: by *cutting back* the bitumen with a solvent (cutback bitumen) or by *emulsifying* it in water (bitumen emulsion).

#### Cutback bitumen
Bitumen dissolved in a volatile petroleum solvent. After laying, the solvent evaporates (cures) and leaves the bitumen binder.

| Type | Solvent | Curing | Use |
|---|---|---|---|
| Rapid curing (RC) | Gasoline/naphtha | Fast | Tack coat, surface dressing, patching in cold |
| Medium curing (MC) | Kerosene | Medium | Prime coat, premix, stockpile patching |
| Slow curing (SC) | Diesel/gas oil | Slow | Prime coat on dense base, dust laying |

Grade numbers (0 to 3, for example MC-0, MC-3) show the viscosity: the higher the number, the thicker.

#### Bitumen emulsion
Tiny globules of bitumen (about 60% by weight) suspended in water with an emulsifier. Types: *rapid setting (RS)*, *medium setting (MS)* and *slow setting (SS)*; *cationic* (suited to most aggregates and wet conditions) and *anionic*.

#### Importance
- Used for **prime coat**, **tack coat**, surface dressing, patch repairs and cold mixes.
- Allows work in cold weather and where heating facilities are not available, such as remote hill roads.
- Emulsions are safe, save fuel and can be applied on damp surfaces.
- Disadvantages of cutbacks: solvent cost, fire risk and loss of solvent to the air.

## Check yourself

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

1. How is liquid bitumen produced?
   A. By cutting back with solvent or by emulsifying in water
   B. By heating to 300 degrees C
   C. By mixing with cement
   D. By distilling coal
   Answer: A. Cutback and emulsion are the two forms. (Key point: Definition)

2. Which cutback uses gasoline or naphtha and cures fast?
   A. Slow curing (SC)
   B. Rapid curing (RC)
   C. Medium curing (MC)
   D. Rapid setting (RS)
   Answer: B. RC uses gasoline; MC kerosene; SC diesel. (Key point: Cutback types)

3. An advantage of emulsion over cutback is
   A. It needs heavy heating
   B. It has fire risk from solvent
   C. It is safe, saves fuel and can be applied on damp surfaces
   D. It cannot be used in cold weather
   Answer: C. Cutbacks have solvent cost and fire risk. (Key point: Advantages of emulsion)