---
title: "Soil stabilization by admixture"
subject: "Foundation Engineering"
chapter: 10
key: "semester_5/foundation_engineering:admixture-stabilization"
source: https://www.bctengineer.com/q/semester_5/foundation_engineering/admixture-stabilization
site: BCT Engineering
---

# Soil stabilization by admixture

Foundation Engineering · Chapter 10: Foundation Soil Improvements

- Asked in: 2081 Bhadra, 2 marks; 2076 Asoj, 3 marks (asked 2 times)
- Video: [Stabilization of soil by Adding Admixtures](https://www.youtube.com/watch?v=84JsJp5P93E) — Bhupendra Deshmukh
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/foundation_engineering/admixture-stabilization
- Whole chapter: https://www.bctengineer.com/md/semester_5/foundation_engineering/chapter-10

## Question

Briefly explain soil stabilization by use of admixture.

## Short answer

Admixture stabilization mixes cement, lime, fly ash, or bitumen with soil to enhance strength and durability. Cement binds particles through hydration; lime reduces plasticity and gains pozzolanic strength. The soil is pulverized, mixed at optimum moisture, compacted, and cured.

## Answer

**Admixture stabilization** is the improvement of soil strength, durability and volume stability by mixing a suitable additive (admixture) into the soil and compacting the mixture. The additive changes the soil properties by chemical reaction, cementing action or by filling voids.

Common admixtures and their action:

- **Cement:** hydration forms a cementing gel that binds particles. Best for sands, gravels and low-plasticity silts (soil-cement, 5-12% cement by weight).
- **Lime:** cation exchange and flocculation reduce plasticity; pozzolanic reaction gives long-term strength. Best for clays (usually 3-8% lime).
- **Fly ash:** a pozzolana, used with lime or cement to give extra strength.
- **Bitumen:** waterproofs and binds granular or fine-grained soils.
- **Chemicals (calcium chloride, sodium silicate):** reduce water loss or bind particles.

Procedure: pulverise the soil, spread the admixture, mix with water to optimum moisture content (OMC), compact to maximum dry density, and cure.

Results: higher strength and CBR, lower plasticity, swelling and compressibility, and better resistance to water. It is widely used in subgrades, road bases and under light foundations.

## Check yourself

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

1. Which admixture is best for clays and why?
   A. Sodium chloride, since it dries clay
   B. Cement, since it only fills voids
   C. Bitumen, since it makes clay granular
   D. Lime, since cation exchange reduces plasticity and pozzolanic reaction gives strength
   Answer: D. Lime (about 3-8%) flocculates clay, reduces plasticity and gives long-term pozzolanic strength. (Key point: Admixture for clay)

2. For which soils is soil-cement most suitable?
   A. Sands, gravels and low-plasticity silts
   B. Highly plastic clays only
   C. Peat
   D. Organic soils only
   Answer: A. Cement hydration forms a gel binding particles, most effective in granular and low-plasticity soils. (Key point: Cement admixture)

3. What is the correct sequence of the stabilization procedure?
   A. Spread admixture, compact dry, then add water
   B. Saturate soil, then add admixture
   C. Pulverise soil, spread admixture, mix with water to OMC, compact to MDD, cure
   D. Compact soil, then spray admixture on top
   Answer: C. The mix is brought to optimum moisture content, compacted to maximum dry density and cured. (Key point: Procedure)

## Related in Foundation Engineering

- [Methods of soil stabilization](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asoil-stabilization-methods) — Foundation Engineering, chapter 10, asked 2×
- [Bituminous stabilization](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Abituminous-stabilization) — Foundation Engineering, chapter 10
- [Stabilization by injection of grouts](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Agrouting-stabilization) — Foundation Engineering, chapter 10

## Related in other subjects

- [Soil stabilization methods and lime stabilized road](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-methods-lime-road) — Transportation Engineering II, chapter 3
- [Soil stabilization, equipment, mass haul characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-definition-equipment-mass-haul) — Transportation Engineering II, chapter 3
- [Soil stabilization methods; soil cement construction](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-methods-soil-cement-road) — Transportation Engineering II, chapter 3
- [Soil stabilization factors; mechanical; cement-soil base](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Asoil-stabilization-factors-mechanical-cement-soil) — Transportation Engineering II, chapter 3