CONCRETE ADMIXTURES

SUBMITTED BY-

VIDHI SINGH

B.TECH 4th yr

CIVIL ENGG.

CONTENTS INTRODUCTION

CONCRETE ADMIXTURES

WHY CHEMICAL ADMIXTURES?

IMPORTANT CHEMICAL ADMIXTURES

AIR ENTRAINING ADMIXTURES

PLASTICIZERS (WATER REDUCERS)

SUPERPLASTICIZERS (HIGH RANGE WATER REDUCERS)

RETARDERS

ACCELERATORS

COLORING ADMIXTURES

CONCLUSON

INTRODUCTIONAdmixtures are the material, other than

Cement

Water

Aggregates

Which are used as an ingredient of concrete and is

added to batch immediately before or during mixing.

Admixtures are normally provided as water based

solutions and can be added to the concrete at upto

5% on cement weight.

CONCRETE ADMIXTURES

A chemical added to the concrete at the time of

mixing to impart desirable behaviour.

WHY CHEMICAL ADMIXTURES?

Produce desire effect.

To make a poor concrete better.

When properties cannot be made by varying the

composition of basic material.

To overcome certain emerencies during concretin

operation.

IMPORTANT CHEMICAL ADMIXTURES

Air entraining admixtures

Plasticizers

Super plasticizers

Retarders and Retarding Plasticizers

Accelerators and Accelerating Plasticizers

Coloring admixtures

Damp-proofing and Waterproofing Admixtures

Fungicidal, Germicidal, Insecticidal Admixtures

AIR ENTRAINING ADMIXTURES

It introduce and stabilize microscopic air bubbles in

concrete.

Scaling due to lack of air.

AIR ENTRAINING ADMIXTURES

The following types of air entraining agents are used

for making air entrained concrete.

Natural wood resins

Animal and vegetable fats and oils, such as tallow,

olive oil and their fatty acids such as stearic and

oleic acids.

Various wetting agents such as alkali salts or

sulphated and sulphonated organic compounds.

PLASTICIZERS (WATER REDUCERS)

The organic substances or combinations of

organic and inorganic substances, which

allow a reduction in water content for the

given workability, or give a higher workability

at the same water content, are termed as

plasticizing admixtures.

USED AT-

PLASTICIZERS (WATER REDUCERS)

SUPERPLASTICIZERS (HIGH RANGE WATER REDUCERS)

Superplasticizers constitute a relatively new

category and improved version of

plasticizer, the use of which was developed

in Japan and Germany during 1960 and

1970 respectively. They are chemically

different from normal plasticisers.

CLASSIFICATION OF SUPERPLASTICIZERS

1. Sulphonated malanie-formaldeyde condensates

(SMF)

2. Sulphonated napthalene-formaldehyde

condensates (SNF)

3. Modified lignosulphonates (MLS)

SUPERPLASTICIZERS (HIGH RANGE WATER REDUCERS)

Superplasticizers is practised for -

Production of flowing, self levelling, self compacting

concrete

Production of high strength and high performance

concrete.

RETARDERS

A retarder is an admixture that slows down the

chemical process of hydration so that concrete

remains plastic and workable for a longer time than

concrete without the retarder.

Retarders are used to overcome the accelerating

effect of high temperature on setting properties of

concrete in hot weather concreting.

RETARDERS

USED AT-

Casting and consolidating large

number of pours without the

formation of cold joints.

Grouting oil wells, where temperature

is about 200 °C, at a depth of 6000

meters.

ACCELERATORS

Accelerating admixtures are added to concrete to

increase the rate of early strength development.

Why accelerators? Permit earlier removal of formwork

Reduce the required period of curing

Advance the time that a structure can be placed in

service

In the emergency repair work.

ACCELERATORS

Commonly used materials as an

accelerator:

Calcium chloride (Not used now)

Some of the soluble carbonates

Silicates fluosilicates (Expensive)

Some of the organic compounds such as

triethenolamine (Expensive)

COLORING ADMIXTURES

Natural and synthetic materials are used to color

concrete for aesthetic and safety reason.

CONCLUSION

Overviews of the conclusion by using admixtures in concrete are-

Increase workability without increasing water content or decrease the water content at same workability.

Retard or accelerate time of initial setting.

Reduce or prevent shrinkage.

Modify the rate or capacity for bleeding.

Reduce segregation.

Reduce rate of slump loss.

Increase bond of concrete to steel reinforcement.

Decrease permeability of concrete.

QUERIES???