Concrete Admixtures

Admixtures Admixtures

SyllabusSyllabusAdmixturesAdmixtures

•Plasticizers, Retarders, Accelerators and Plasticizers, Retarders, Accelerators and other admixtures, Tests on admixtures, other admixtures, Tests on admixtures, chemistry and compatibility with Concretechemistry and compatibility with Concrete

What are chemical admixtures?What are chemical admixtures?

• The definition of RILEM (International Union of Testing and The definition of RILEM (International Union of Testing and Research Laboratories for Materials and Structures) is:Research Laboratories for Materials and Structures) is:

• • • Admixtures for concrete, mortar or paste are inorganic or Admixtures for concrete, mortar or paste are inorganic or organic materials these are added to the normal components of organic materials these are added to the normal components of a mix not normally exceeding 5% by mass of cement or a mix not normally exceeding 5% by mass of cement or cementations materialscementations materials

• • • Admixtures interact with hydrating cement by physical, Admixtures interact with hydrating cement by physical, chemical or physicochemical actions.chemical or physicochemical actions.

What are chemical admixtures?What are chemical admixtures?

what are chemical admixtures?what are chemical admixtures?

• • • They modify one or more properties of concrete, mortar or They modify one or more properties of concrete, mortar or paste either in fresh or hardened state.paste either in fresh or hardened state.

• • • Admixtures are usually very complex compounds chemically Admixtures are usually very complex compounds chemically excepting a few.excepting a few.

• • • They are unlikely to be pure compounds but associated with They are unlikely to be pure compounds but associated with some other minor chemical compounds or they may be mixed some other minor chemical compounds or they may be mixed formulations.formulations.

• • • It is rather difficult for a civil engineer to understand them It is rather difficult for a civil engineer to understand them through their chemical nature.through their chemical nature.

Thus, Admixtures are those Thus, Admixtures are those ingredients in concrete other than ingredients in concrete other than Portland cement, water, and Portland cement, water, and aggregates that are added to the aggregates that are added to the mixture immediately before or mixture immediately before or during mixing . Admixtures can be during mixing . Admixtures can be classified by function as follows: classified by function as follows:

1. Air-entraining admixtures1. Air-entraining admixtures2. Water-reducing admixtures 2. Water-reducing admixtures 3. Plasticizers3. Plasticizers4. Accelerating admixtures4. Accelerating admixtures5. Retarding admixtures5. Retarding admixtures6. Hydration-control admixtures6. Hydration-control admixtures

7. Corrosion inhibitors7. Corrosion inhibitors8. Shrinkage reducers8. Shrinkage reducers9. Alkali-silica reactivity inhibitors9. Alkali-silica reactivity inhibitors10. Colouring admixtures10. Colouring admixtures11. Miscellaneous admixtures such workability, 11. Miscellaneous admixtures such workability,

bonding, damp proofing, permeability bonding, damp proofing, permeability reducing, grouting, gas-forming, and pumping reducing, grouting, gas-forming, and pumping admixturesadmixtures

AdmixturesAdmixtures

• For our country, the most common chemical For our country, the most common chemical admixtures are plasticizers and Super-plasticizers. admixtures are plasticizers and Super-plasticizers. These are also known as water reducers and high-These are also known as water reducers and high-range water reducers, respectively.range water reducers, respectively.

• • • Retarders are likely to be needed, especially for hot Retarders are likely to be needed, especially for hot weather concreting, ready mixed concrete or for weather concreting, ready mixed concrete or for special continuous poursspecial continuous pours



• Other types of admixtures are:Other types of admixtures are:• • • AcceleratorsAccelerators• • • Air-entraining agentsAir-entraining agents• • • Pumping aidsPumping aids• • • Shot Crete/ Guniting aidsShot Crete/ Guniting aids• • • Corrosion inhibitors, and some others.Corrosion inhibitors, and some others.

How do they act?How do they act?

• • • The chemical, physical or physico-chemical actions of admixtures in The chemical, physical or physico-chemical actions of admixtures in cement concrete are quite complex.cement concrete are quite complex.

• • • In fact, cement itself is an extremely complex compound with major In fact, cement itself is an extremely complex compound with major compounds such as calcium silicates, calcium aluminates, gypsum.compounds such as calcium silicates, calcium aluminates, gypsum.

• • • Besides it contains many alkali and other calcium salts.Besides it contains many alkali and other calcium salts.• • • The action of admixtures can, however, be simplified for the sake ofThe action of admixtures can, however, be simplified for the sake of• Understanding, as:Understanding, as:• (i) adsorption(i) adsorption• (ii) De-flocculation or dispersion(ii) De-flocculation or dispersion• (iii)Chemical absorption or interaction(iii)Chemical absorption or interaction

The major reasons for using The major reasons for using admixtures are:admixtures are:

1. To reduce the cost of concrete construction1. To reduce the cost of concrete construction

2. To achieve certain properties in concrete 2. To achieve certain properties in concrete more effectively than by other meansmore effectively than by other means

3. To maintain the quality of concrete during 3. To maintain the quality of concrete during the the stages of mixing, transporting, stages of mixing, transporting, placing, and placing, and curing in adverse weather curing in adverse weather conditionsconditions

4. To overcome certain emergencies during 4. To overcome certain emergencies during concreting operationsconcreting operations

Air-Entraining AdmixturesAir-Entraining Admixtures

• used to purposely introduce and stabilize used to purposely introduce and stabilize microscopic air bubbles in concrete. Air-microscopic air bubbles in concrete. Air-entrainment will dramatically improve the entrainment will dramatically improve the durability of concrete exposed to cycles of durability of concrete exposed to cycles of freezing and thawing. Entrained air greatly freezing and thawing. Entrained air greatly improves concrete's resistance to surface improves concrete's resistance to surface scaling caused by chemical de-icers scaling caused by chemical de-icers

Air-Entraining AdmixturesAir-Entraining Admixtures

Frost damage at joints of a Frost damage at joints of a pavementpavement

Frost induced cracking near jointsFrost induced cracking near joints

Scaled concrete Scaled concrete surface resulting surface resulting from lack of air from lack of air entrainment, use of entrainment, use of deicers, and poor deicers, and poor finishing and curing finishing and curing practicespractices

• The primary ingredients used in air-The primary ingredients used in air-entraining admixtures are salts of wood entraining admixtures are salts of wood resin (Vinsol resin), synthetic detergents, resin (Vinsol resin), synthetic detergents, salts of petroleum acids, etc.salts of petroleum acids, etc.

Water-Reducing AdmixturesWater-Reducing Admixtures

• used to reduce the quantity of mixing water used to reduce the quantity of mixing water required to produce concrete of a certain required to produce concrete of a certain slump, reduce water-cementing materials ratio, slump, reduce water-cementing materials ratio, reduce cement content, or increase slump. reduce cement content, or increase slump.

• Typical water reducers reduce the water Typical water reducers reduce the water content by approximately 5% to 10%. content by approximately 5% to 10%.



• Materials: Materials: – Lignosulfonates.Lignosulfonates.– Carbohydrates.Carbohydrates.– Hydroxylated carboxylic acids.Hydroxylated carboxylic acids.


• The effectiveness of water reducers on The effectiveness of water reducers on concrete is a function of their chemical concrete is a function of their chemical composition, concrete temperature, cement composition, concrete temperature, cement composition and fineness, cement content, and composition and fineness, cement content, and the presence of other admixtures. the presence of other admixtures.

Superplasticizers (High-Range Superplasticizers (High-Range Water Reducers)Water Reducers)

• These admixtures are added to concrete These admixtures are added to concrete with a low-to-normal slump and water-with a low-to-normal slump and water-cementing materials ratio to make high-cementing materials ratio to make high-slump flowing concrete.slump flowing concrete.

• Flowing concrete is a highly fluid but Flowing concrete is a highly fluid but workable concrete that can be placed workable concrete that can be placed with little or no vibration or compaction with little or no vibration or compaction while still remaining essentially free of while still remaining essentially free of excessive bleeding or segregation. excessive bleeding or segregation.

Super-plasticizers Super-plasticizers (High-Range Water Reducers)(High-Range Water Reducers)


• Applications where flowing concrete is used:Applications where flowing concrete is used:1.1. thin-section placements, thin-section placements, 2.2. areas of closely spaced and congested reinforcing areas of closely spaced and congested reinforcing

steel,steel,3.3. pumped concrete to reduce pump pressure, pumped concrete to reduce pump pressure,

thereby increasing lift and distance capacity, thereby increasing lift and distance capacity, 4.4. areas where conventional consolidation methods areas where conventional consolidation methods

are impractical or can not be used, and are impractical or can not be used, and 5.5. for reducing handling costs. for reducing handling costs.

Flowable concrete with high slumpFlowable concrete with high slump

Is easily placedIs easily placed

Even in areas of heavy reinforcing Even in areas of heavy reinforcing steel congestionsteel congestion

• Low water to cement Low water to cement ratio concrete with low ratio concrete with low chloride permeability--- chloride permeability--- easily made with high-easily made with high-range water reducers- is range water reducers- is ideal for bridge decksideal for bridge decks

• Plasticized, flowing Plasticized, flowing concrete is easily placed concrete is easily placed in thin sections in thin sections


• Typical superplasticizers include:Typical superplasticizers include:– Sulfonated melamine formaldehyde Sulfonated melamine formaldehyde

condensates.condensates.– Sulfonated naphthalene formaldehyde Sulfonated naphthalene formaldehyde

condensate.condensate.– Lignosulfonates.Lignosulfonates.– Polycarboxylates.Polycarboxylates.


• bleed significantly less than control concretes of bleed significantly less than control concretes of equally high slump and higher water content.equally high slump and higher water content.

• High-slump, low-water-content, plasticized concrete High-slump, low-water-content, plasticized concrete has less drying shrinkage than a high-slump, high-has less drying shrinkage than a high-slump, high-water-content conventional concretewater-content conventional concrete..

• has similar or higher drying shrinkage than has similar or higher drying shrinkage than conventional low-slump, low-water-content conventional low-slump, low-water-content concrete.concrete.

• The effectiveness of the plasticizer is increased with The effectiveness of the plasticizer is increased with an increasing amount of cement and fines in the an increasing amount of cement and fines in the concrete. concrete.

Super-plasticizers Super-plasticizers (High-Range Water Reducers)(High-Range Water Reducers)

Retarding AdmixturesRetarding Admixtures • used to retard the rate of setting of concrete at high used to retard the rate of setting of concrete at high

temperatures of fresh concrete (30°C or more).temperatures of fresh concrete (30°C or more).• One of the most practical methods of counteracting One of the most practical methods of counteracting

this effect is to reduce the temperature of the concrete this effect is to reduce the temperature of the concrete by cooling the mixing water or the aggregates. by cooling the mixing water or the aggregates.

• Retarders do not decrease the initial temperature of Retarders do not decrease the initial temperature of concrete. concrete.

• The bleeding rate and capacity of plastic concrete is The bleeding rate and capacity of plastic concrete is increased with retarders. increased with retarders.

Retarding AdmixturesRetarding Admixtures

• The typical materials used as retarders are:The typical materials used as retarders are:– Lignin, Lignin, – Borax, Borax, – Sugars, Sugars, – Tartaric acid and salts.Tartaric acid and salts.

Retarding AdmixturesRetarding Admixtures

• Retarders are used to: Retarders are used to: 1.1. offset the accelerating effect of hot weather on the offset the accelerating effect of hot weather on the

setting of concrete, setting of concrete, 2.2. delay the initial set of concrete when difficult or delay the initial set of concrete when difficult or

unusual conditions of placement occur, unusual conditions of placement occur, 3.3. delay the set for special finishing processes such delay the set for special finishing processes such

as an exposed aggregate surface.as an exposed aggregate surface.

Retarding AdmixturesRetarding Admixtures • some reduction in strength at early ages (one to some reduction in strength at early ages (one to

three days) accompanies the use of retarders. three days) accompanies the use of retarders. • The effects of these materials on the other properties The effects of these materials on the other properties

of concrete, such as shrinkage, may not be of concrete, such as shrinkage, may not be predictable. predictable.

Therefore, acceptance tests of retarders should be Therefore, acceptance tests of retarders should be made with actual job materials under made with actual job materials under anticipated job conditions. anticipated job conditions.

Accelerating AdmixturesAccelerating Admixtures

• used to accelerate strength development of used to accelerate strength development of concrete at an early age. concrete at an early age.

• Typical Materials are:Typical Materials are:– Calcium chloride: most commonly used for plain Calcium chloride: most commonly used for plain

concrete.concrete.– Triethanolamine.Triethanolamine.– Calcium formate.Calcium formate.– Calcium nitrate.Calcium nitrate.– Calcium nitrite.Calcium nitrite.

Accelerating AdmixturesAccelerating Admixtures

Corrosion InhibitorsCorrosion Inhibitors



• The chlorides can cause corrosion of steel The chlorides can cause corrosion of steel reinforcement in concrete. reinforcement in concrete.

• Ferrous oxide and ferric oxide form on the Ferrous oxide and ferric oxide form on the surface of reinforcing steel in concrete. surface of reinforcing steel in concrete.

• Ferrous oxide reacts with chlorides to form Ferrous oxide reacts with chlorides to form complexes that move away from the steel to complexes that move away from the steel to form form rustrust. The chloride ions continue to attack . The chloride ions continue to attack the steel until the oxide layer is destroyed. the steel until the oxide layer is destroyed.


• Corrosion-inhibiting admixtures chemically arrest the Corrosion-inhibiting admixtures chemically arrest the corrosion reaction.corrosion reaction.

• Commercially available corrosion inhibitors include: Commercially available corrosion inhibitors include: – calcium nitrite, calcium nitrite, – sodium nitrite, sodium nitrite, – dimethyl ethanolamine, dimethyl ethanolamine, – amines, amines, – phosphates, phosphates, – ester amines. ester amines.

Shrinkage-Reducing AdmixturesShrinkage-Reducing Admixtures

• Shrinkage cracks, such Shrinkage cracks, such as shown on this bridge as shown on this bridge deck, can be reduced deck, can be reduced with the use of good with the use of good concreting practices and concreting practices and shrinkage reducing shrinkage reducing admixtures.admixtures.

Chemical Admixtures to reduce Alkali-Chemical Admixtures to reduce Alkali-aggregate Reactivity aggregate Reactivity

(ASR Inhibitors(ASR Inhibitors))

• Expansion of specimens made with lithium carbonate admixture

Coloring admixtures (Pigments)Coloring admixtures (Pigments)

• Red and blue pigments Red and blue pigments were used to color this were used to color this floorfloor

Coloring admixtures (Pigments)Coloring admixtures (Pigments)• Natural and synthetic materials are used to color concrete for Natural and synthetic materials are used to color concrete for

aesthetic and safety. Red concrete is used around buried aesthetic and safety. Red concrete is used around buried electrical or gas lines as a warning to anyone near these electrical or gas lines as a warning to anyone near these facilities. Yellow concrete safety curbs are used in paving facilities. Yellow concrete safety curbs are used in paving applications. Generally, the amount of pigments used in applications. Generally, the amount of pigments used in concrete should not exceed 10% by eight of the cement. concrete should not exceed 10% by eight of the cement. Pigments used in amounts less than 6% generally do not Pigments used in amounts less than 6% generally do not affect concrete properties Before a coloring admixture is used affect concrete properties Before a coloring admixture is used on a project, it should be tested for color fastness in sunlight on a project, it should be tested for color fastness in sunlight and autoclaving, chemical stability in cement, and effects on and autoclaving, chemical stability in cement, and effects on concrete properties.concrete properties.

Damp-proofing AdmixturesDamp-proofing Admixtures

• The passage of water through concrete can usually The passage of water through concrete can usually be traced to the existence of cracks or areas of be traced to the existence of cracks or areas of incomplete consolidation. Sound, dense concrete incomplete consolidation. Sound, dense concrete made with a water cement ratio of less than 0.50 by made with a water cement ratio of less than 0.50 by mass will be watertight if it is properly placed and mass will be watertight if it is properly placed and cured. Admixtures known as damp proofing agents cured. Admixtures known as damp proofing agents include certain soaps, stearates, and petroleum include certain soaps, stearates, and petroleum products. products.

Damp-proofing AdmixturesDamp-proofing Admixtures

Fungicidal, Germicidal, AndFungicidal, Germicidal, AndInsecticidal AdmixturesInsecticidal Admixtures

• Bacteria and fungal growth on or in hardened Bacteria and fungal growth on or in hardened concrete may be partially controlled through the use concrete may be partially controlled through the use of fungicidal, germicidal, and insecticidal of fungicidal, germicidal, and insecticidal admixtures. The most effective materials are admixtures. The most effective materials are polyhalogenated phenols, dieldrin emulsions, and polyhalogenated phenols, dieldrin emulsions, and copper compounds. The effectiveness of these copper compounds. The effectiveness of these materials is generally temporary, and in high materials is generally temporary, and in high dosages they may reduce the compressive strength dosages they may reduce the compressive strength of concrete.of concrete.

Storing And DispensingStoring And DispensingChemical AdmixturesChemical Admixtures

• Liquid admixtures can be stored in barrels or bulk tankers.Liquid admixtures can be stored in barrels or bulk tankers.• Powdered admixtures can be placed in special storage bins and Powdered admixtures can be placed in special storage bins and

some are available in premeasured plastic bags.some are available in premeasured plastic bags.• Admixtures added to a truck mixer at the jobsite are often in Admixtures added to a truck mixer at the jobsite are often in

plastic jugs or bags. Powdered admixtures, such as certainplastic jugs or bags. Powdered admixtures, such as certain• plasticizers, or a barrel of admixture may be stored at the project plasticizers, or a barrel of admixture may be stored at the project

site.site.• Dispenser tanks at concrete plants should be properly labeled for Dispenser tanks at concrete plants should be properly labeled for

specific admixtures to avoid contamination and avoid dosing the specific admixtures to avoid contamination and avoid dosing the wrong admixture. Most liquid chemical admixtures should not be wrong admixture. Most liquid chemical admixtures should not be allowed to freeze; therefore, they should be stored in heated allowed to freeze; therefore, they should be stored in heated environments.environments.

• Consult the admixture manufacturer for proper storage Consult the admixture manufacturer for proper storage temperaturestemperatures

Storing And DispensingStoring And DispensingChemical AdmixturesChemical Admixtures

ReferencesReferences

• Concrete Technology by: R.P. RethaliyaConcrete Technology by: R.P. Rethaliya• Concrete Technology by . M.S. ShettyConcrete Technology by . M.S. Shetty

• Internet websitesInternet websites• http://www.foundationsakc.org/http://www.foundationsakc.org/

http://www.foundationsakc.org/

Engineering

Concrete Admixtures