Admixtures for Concrete

ByProf. Adel El Kordi

&Dr. Meheddene Machaka

Structural EngineeringDepartment

Faculty of EngineeringBeirut Arab University

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CVLE 321

Admixtures

Air-entraining admixtures Water-reducing admixtures Plasticizers Accelerating admixtures Retarding admixtures Hydration-control

admixtures Corrosion inhibitors Shrinkage reducers ASR inhibitors Coloring admixtures Miscellaneous admixtures

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Types of Admixtures ASTM C 494

STANDARD TYPES

SPECIALITY TYPES

1. Pore Blockers

2. Microsilica

3. Anti-corrosive coating

4. Corrosion Inhibitors

5. Underwater System

6. Shotcrete

7. Water Proofing• Air Entertainers

• Superpalasticisers

• Plasticisers-Type A - Water-Reducing Admixtures

-Type B - Retarding Admixtures

-Type C - Accelerating Admixtures

-Type D - A+B

-Type E – A+C

-Type F

-Type G

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1. As far as the water content of the mix is concerned, the totalvolume of the Liquid admixtures should be counted in.

2. A delay in the setting can be achieved by the addition of retarder.3. Retarders do not alter the composition of hydration products.4. Incorrect quantities of retarder can totally inhibit the hardening

of concrete.5. A small quantity of sugar (0.05%) will act as an acceptable

retarder.6. The increased retardation occurs with cements which have a low

C3A.7. Retarders are frequently used in hot weather.8. The retarding effect is smaller at higher temperature.9. Retarders tend to increase the plastic shrinkage because the

duration of the plastic stage is extended, but drying shrinkage isnot affected.

10. Water-reducing admixtures allow a reduction in W/C ratio whileretaining the workability.

Concrete Admixtures

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11. Retarders improve the workability of concrete at a given w/c ratio.

12. Superplasticizers are adsorbed on the cement particles, giving them a negativecharge which leads to repulsion between the particles.

13. Water-reducing admixtures increase the surface area of water which can undergoinitial hydration and also increase the amount of water available for hydration.

14. The effectiveness of water-reducing admixtures being greatest when used withcements of high C3A content (OPC).

15. The effectiveness of water-reducing admixtures being smallest when used withcements of low C3A content (SRPC).

16. Superplasticizers are water-soluble organic polymers.

17. Superplasticizers are relatively expensive.

18. Superplasticizers have a low content of impurities so that, even at high dosages,they do not exhibit unduly harmful side effects.

19. The majority of plasticizers are in the form of sodium salts.

20. The main action of the long molecules of Superplasticizers is to wrap themselvesaround the cement particles and give them a highly negative charge so that theyrepel each other. This result in flocculation and dispersion of cement particles.

Concrete Admixtures

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21. At a given W/C and water content in the mix, the dispersing action ofSuperplasticizers increases the workability of concrete. Such concrete istermed flowing concrete.

22. The second use of Superplasticizers is in the production of concrete ofnormal workability but with an extremely high strength owing to a veryreduction in the water/cement ratio.

23. Superplasticizers interact with C3A whose hydration is retarded.

24. For increasing workability, the normal dosage of superplasticizers isbetween 5 and 20 liter per cubic meter of concrete.

25. The liquid superplasticizers containing about 5% of solid material.

26. It may be advantageous to add the superplasticizers to the mix in two, oreven three, operations. Such re-dosage, is possible if an agitator truck isused to deliver the concrete to site.

27. The finer the cement the higher the dosage of a superplasticizer.

28. Superplasticizers do not significantly affect the setting time of concreteexcept that, when used with cements having a very low C3A content, theremay be excessive retardation.

Concrete Admixtures

Air-Entraining Admixtures

Improve durability in concrete exposed to Freeze-thaw Deicers Sulfates Alkali-reactive environments

Improve workability

ASTM C 260 or AASHTO M 154

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Frost Damage

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Scaled Concrete Surface

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Water-Reducing Admixtures

Reduce mixing water required toproduce a certain slump

Reduce water-cement ratio Reduce cement content Increase slump

Primarily used to:

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Effects of water reducers

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Water Reducing Admixtures

Type A ― Reduces water content at least 5% Tends to retard ― accelerator often added

Type D ― Reduces water content 5% min. Retards set

Type E ― Reduces water content 5% min. Accelerates set

ASTM C 494

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Water Reducer and Slump Loss

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Retardation (Initial Set)

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Mid-Range Water Reducing Admixtures

Reduce water content 6% to 12% Reduce cement content Reduce water-cement ratio No retardation Improve placeability and

finishability

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Superplasticizers are water-soluble organic polymers.

High-Range Water-ReducingAdmixtures

• Reduce H2O content 12% -30%• Reduced W/C produces conc. with:

• Compressive Strength > 70 MPa• Increased early strength gain• Reduced Cl ion penetration

ASTM C 494

Type F― Water Reducing

Type G ― Water Reducing and Retarding

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Polycarboxylate ether

Cement Hydration

Dispersion effect (A)

Steric effect (B)

High Performance Superplasticiser ( HPSP )

Cement Hydration

The water is partly adsorbed by the cement particleswhich softness the surface. Thin layers of gel aregrowing around the particles. With more hydrationthe gel layers solidify (hydrated cement paste ).

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High Performance Superplasticiser Howit is work ?

Based on Japanese technology blended with propertyenchancing Polymers, High Performance Superplasticiser worksby mean of electrostatic repulsion and steric hindrance .

Water Reduction in ConcreteUsing Different Admixtures

SuperplasticisersNaphthalene and

Melamine

WithoutAdmixturesW / C = 0.5

Normalplasticisers

High PerformanceSuperplasticiser

8%-10% 34 %18%-25%

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Methods of addition of Superplasticizers

It may be advantageous to add thesuperplasticizers to the mix in two, or eventhree, operations. Such re-dosage, is possibleif an agitator truck is used to deliver theconcrete to site.

High-Range Water Reducer and Slump Loss

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Plasticizers for Flowing Concrete

Produce flowing concrete withhigh slump ( 190 mm [7.5 in.])

Reduce bleeding

Extended-slump-life plasticizerreduces slump loss.

ASTM C 1017Superplasticizers

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FlowingConcrete

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Flowing Concrete as Thin Overlay

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Flowing Concretes and Slump Loss

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Retardation of Flowing Concrete (Initial Set)

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Retardation of Flowing Concrete (Final Set)

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Compressive Strength Development in Flowing Concrete

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Retarding Admixtures

Delay setting or hardening rate for:

Hot-weather concreting Difficult placements Special finishing processes

ASTM C 494, Type B

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Slump Loss at Various Temperatures

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Accelerating Admixtures

Accelerate the rate of: Hydration (setting) Early-age strength gain

ASTM C 494, Type C

Calcium chloride accelerators: Increase drying shrinkage,

potential reinforcement corrosion,potential scaling

Darken concrete36

Maximum Chloride-Ion Content

Type of member

Maximum water solublechloride-ion (CI¯) in

concrete, percent by massof cement

Prestressed concrete 0.06Reinforced concrete ex-posed to chloride in service 0.15

Reinforced concrete that willbe dry or protected frommoisture in service

1.00

Other reinforced concreteconstruction 0.30

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Corrosion Inhibitors

Control Corrosion of Steel Reinforcement Dosage dependent on anticipated chloride level

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Corrosion Inhibitors

Condition for Corrosion andDamage exit .

Corrosion are greatly reducedby the effect of Corrosion Inhibitors .

Underwater Concrete

• Cohesive with minimal washout.

• High Workability / flow.

• Low W /C ratio .

• Medium to high compressive strength .

• Melamine Superplasticiser.40

Pore Blocker Swells in Concrete Capillaries

Shrinkage-Reducing Admixtures

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Coloring Admixtures (Pigments)

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Liquid Admixture Dispenser

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Videos 1/2

Air-Entraining Admixture Water Reducer

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Videos 2/2

Retarder/Accelerator Admixture Dispenser

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