ADMIXTURES

CHEMICAL ADMIXTURES

DEFINATION -CHEMICAL ADMIXTURES MAY BE DEFINED

AS THE SUBSTANCES OTHER THAN CEMENT, WATER, COARSE AGGREGATES, FINE AGGREGATES WHICH ARE ADDED IN THE FRESHLY PREPARED TO MODIFY ITS PROPERTIES LIKE STRENGTH, DUARABILITY, etc.

NEED OF ADMIXTURES-NEED COULD BE DUE TO ANY OF

FOLLOWING-TECHNICAL Strength Requirement, Workability ,etc.ECONOMICAL Costly things used may be replaced ENVIROMENTAL Some Materials used they may not get

disposed off properly which could lead to problems like pollution, etc.

IMPORTANT FACTS-THESE ARE AVALIABLE IN LIQUID FORM.DOSAGE TO BE GIVEN IS VERY SMALL

(<2% by weight of cement) SO SPECIAL CARE IS TAKEN.

IT IS BATCHED BY VOLUME.CONCENTRATED ADMIXTURE IS NOT

ADDED DIRECTLY BUT THESE ARE DILUTED FIRST AND THEN ADDED SO THAT THESE MIX THROUGH OUT THE CONCRETE PROPERLY AND UNIFORMLY.

HOW TO USE ADMIXTURES-

This could be explained with the help of an example- Let us say we want to add a dosage of 1% of

admixture in the concrete mix containing a cement of 500kg.

Therefore I will have to add admixture of 5kg.To add this it is to be diluted using water. Let us

assume I add this in 10 liters of water . So these 10 liters are compensated for the total amount of water to be added that is 180 liters of total water is to be added, I need to add only 170 liters of water and dilute solution of 10 liters of admixtures.

FUNCTIONS-To accelerate the initial set of concrete that is to gain

strength at early stages.To retard the initial set that is to keep concrete

workable for a longer time for placement.To enhance the workability.To improve penetration and reduce segregation in

concrete mixtures.To increase strength by reducing w/c ratio.To increase the durability (to enhance resistance).To reduce the heat of hydration.To inhibit corrosion and improve resistance against

chemical attack.

TYPES BASED ON PURPOSE-Accelerating Admixtures-• These are used where early strength is required• These may also use in cold regions where we want to

reduce the setting time of concrete.Retarding Admixtures-• These are admixtures used where we need to increase

the setting time for the concrete to settle.• These may also be used in hot weather where concrete

sets very early due to high temperatures.Slump loss may be used for analyzing the acceleration

and retardation in concrete when admixtures are used.

SLUMP ANALYSIS-

WATER REDUCING ADMIXTURES-These are the admixtures which enable us to

reduce the amount of water content that is required to be added to the concrete mix by keeping the slump same which indirectly helps up in maintaining the same strength and durability.

WHY BEST?These help in making the project more economical.These help in reducing the heat of hydration.These are highly effective.

Effectiveness is decided on the basis of amount of water reduction.

If a water reducer , A on dosage of 1% reduces the water by 5-10% of the total amount of water to be added & if a water reducer B, on the same dosage reduces the water by 15-20% of the total amount of water to be added then B is more effective than A to achieve the same slump.

TYPES BASED ON EFFECTIVENESSHIGH RANGE WATER

REDUCERS/PLASTICIZERS-These are water reducing admixtures which

reduce the amount of water by 5-10% of the total amount of water to be added.

VERY HIGH RANGE WATER REDUCERS/SUPER-PLASTICIZERS-

These are water reducing admixtures which reduce the amount of water by 15-20% of the total amount of water to be added

HOW TO USE WATER REDUCERS-S. NO.

WATER(Kg/m3

CEMENT(Kg/m3)

W/C(%)

CA SLUMP(cm)

STRENGTH (M pa)

COMMENT

•1. 180 360 0.5 0 8 32 BASE•2. 160 360 0.4

41 8 >32 HIGHER

STRENGTH•3. 160 320 0.5 1 8 32 CEMENT

SAVING•4. 180 360 0.5 1 >8 32 PASTICIZIN

G ACTION

AIR ENTRAINERS-These are used to intentionally add/entrain the air in the

concrete mix.It is used to improve/uniform the pore structure of the

concrete. Air enters the concrete in form of bubbles and form the ball

bearings and hence the workability of concrete mix is improved.It is recommended for use in environments with cyclic, freezing

and thawing to increase the durability.

Environments with cyclic, freezing and thawing means the regions where water may freeze or melt due to change in temperature.

OTHERS-Corrosion Inhibitors such as nitrites(presence of these

ions help in improving the resistance against forces).Grouting Admixtures are used to prevent the rapid

loss of water to the surroundings.Air-detraining Admixtures are used to dissipate excess

gases and to remove a part of entrained gases.Shrinkage Reducing Admixtures (also called

expansion producing admixtures) either expand themselves or by reacting with cement to expand the concrete.

Concrete Coloring Admixtures are added to produce colored concrete surfaces and cements.

QUESTIONS???