Different Types of Admixtures in Concrete Structure - A Review PDF
Different Types of Admixtures in Concrete Structure - A Review PDF
Different Types of Admixtures in Concrete Structure - A Review PDF
Keywords: Accelerators, Water-reducing agents, Super plasticizers, Fly-ash, Slag, Silica fume
and Rice husk Ash
I. INTRODUCTION
Concrete consists of cement, sand, aggregate and water. Anything other than these if added in concrete either
before or during mixing to alter the properties to our desired requirement are termed as admixtures. The use of
admixtures offers certain beneficial effects to concrete like improved workability, acceleration or retardation of
setting time, reduce water cement ratio, and so on
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Admixtures are the special ingredients added during concrete mixing to enhance the properties and performance
of fresh concrete. Various types of admixtures are available in the market which is used in construction work.
Concrete admixtures are used to enhance the properties of concrete for applications in concrete works with
special requirements. Concrete admixtures are used to modify the properties of concrete to achieve desired
workability in case of low water cement ratio, and to enhance setting time of concrete for long distance
transportation of concrete.
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6. To decrease the permeability.
7. To achieve other desired properties.
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The common Air-Entraining agents are natural wood resins, neutralized vinsol resins, polyethelene oxide
polymers and sulphonated compounds.
Mechanism of Air Entraining Concrete Admixtures
These are anionic, because the hydrocarbon structures contain negatively charged hydrophilic groups, such as
COO, SO3 and OSO so that large anions are released in water. Conversely, if the hydrocarbon ion is positively
charged, the compound is cation active or cationic.
In other words, anionic surface active agents produce bubbles that are negatively charged, cationic charged
cause bubbles to be positively charged, surface active agents of all classes can cause air
Strength development in freshly cast concrete.
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Effect on shrinkage
Admixture of this type when used as workability aids on water reducers do not adversely affect the shrinkage.
Effect on creep
Materials of this type of admixture have no deleterious effect on the creep of concrete.
Detrimental effect
a) While using water reducing agent. Care must be taken in controlling the air content in the mix. Most water-
reducing agent entrain air due to their surfactant properties.
b) At high dosages of lignosulphonate material, retardation of the mix occurs.
Applications of Water Reducing Concrete Admixtures
The application of the type of admixtures are as follows —
a) When concrete pours are restricted due to either congested reinforcement or this sections.
b) When harsh mixes are experienced such as those produced with aggregates (crushed). Then considerable
improvement in the plastic properties of concrete can be obtained.
c) When required strengths are difficult to obtain within specified maximum cement content and where early
lifting strengths are required.
d) By addition of this admixture in concrete cement economics of about 10% can be obtained.
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b) Materials of this class (lignosulphonate containing sugar and derivatives of hydroxyl carboxylic acid) in some
cases have a much higher dispersing effect and hence water reducing capacity.
c) Durability increases.
Detrimental effect
a) When lignosulphonate based material used, then the air content might be 0.2 to 0.3% higher unless materials
of the tributyle phosphate type are added.
b) As the water content increases, so there is a tendency for drying shrinkage.
Applications of Retarding Concrete Admixture
Retarding admixtures are used
a) Where long transportation of ready mixed concrete is required then premature setting can be usefully avoided
by this type admixture.
b) When concrete is being placed or transported under conditions of high ambient temperature.
c) In case of large concrete pours
d) Concrete construction involving sliding formwork
Advantages of Super Plasticizer Admixtures
a) The concrete using this admixture can be placed with little or no compaction and is not subject to excessive
bleeding or segregation.
b) They can be used as high dosages became they do not markedly change the surface tension of water.
c) It does not significantly affect the setting of concrete except that when used the cements having a very low
C3A content.
d) They do not influence shrinkage, creep modulus of elasticity or resistance to freeing to thawing.
Disadvantage
The only real disadvantage of superplasticizer is their relatively high cost.
Applications of Super Plasticizer Admixtures
a) In very heavily reinforced sections, in inaccessible areas in floor or road slabs.
b) Where very rapid placing is desired.
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mineral admixtures which can be of the order of 50 – 60% by weight of total cementitious material, represents
considerable energy savings.
b) The ability of cement and concrete industries to consume mithions of tons of industrial byproducts containing
toxic metal would qualify these industries to be classified as environmentally friendly.
c) Since natural Pozzolana and industrial by products are generally available substantially lower costs than
Portland cement, the exploitation of the Pozzolanic and cementitious properties of mineral admixtures are used
as a partial replacement of cement can lead to a considerable economic benefit.
d) Possible technological benefits from the use of mineral admixtures in concrete include entrancement of
impermeability and chemical durability, improved resistance to thermal cracking and increase in ultimate
strength.
Classification of Mineral Admixture
Mineral admixtures may be classified as follows —
a) Pozzolanic — Siliceon or siliceons and admixtures material which itself possesses little or no cementitious
value but is the presence of moisture chemically react with CalOH 2 at ordinary temperature to form compounds
possessing cementitious properties.
b) Pozzolanic & Cementitious — The materials which have some cementitious properties in itself.
ASIM specification C618 recognizes the following three classes of mineral admixtures.
a) Class N — Raw or calcined natural pozzolanic such as diatomaceous earths, clay and shales, tuffs and
volcanic ashes.
b) Class F — Fly ash produced from burning anthracite or bituminous coal.
c) Class C — Ash normally produced from lignite or sub-bituminous coal which may contain analytical CaO
higher than 10%.
Silica Fume as Concrete Admixture
Although the use of silica fume (SF) in concrete has increased significantly in the past few years, its beneficial
properties were not well realized until comprehensive research was undertaken in the late 70’s and early 80’s at
the Norwegian Ins. of technology to study the influence of SF on concrete properties.
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according to specification and method of application to avoid adverse effect on concrete properties at fresh and
hardened state.
Concrete admixtures should be accepted with test certificate, manufacturing date and its chemical composition,
should comply specifications given by the authorities.
It can be seen that proper use of admixtures offers certain beneficial effects to concrete including improved
quality, acceleration or retardation of setting time, enhanced frost & sulphate resistance improves workability.
REFERENCES
[1.] Tagnit-Hamou, Arezki, and Aítcin, Pierre-Claude, ―Cement and Superplasticizer Compatibility,‖ World
Cement, Palladian Publications Limited, Farnham, Surrey, England, August 2009.
[2.] Tang, Fulvio J., and Bhattacharja, Sankar, Development of an Early Stiffening Test, RP346, Portland
Cement Association, 2008
[3.] Thomas, Michael D. A., and Stokes, David B., ―Use of a Lithium-Bearing Admixture to Suppress
Expansion in Concrete Due to Alkali-Silica Reaction,‖ Transportation Research Record No. 1668,
Transportation Research Board, Washington, D.C. 2007
[4.] Kosmatka, Steven H., ―Discoloration of Concrete—Causes and Remedies,‖ Concrete Technology Today,
PL861, Portland Cement Association, 2007
[5.] Lackey, Homer B., ―Factors Affecting Use of Calcium Chloride in Concrete,‖ Cement, Concrete, and
Aggregates, American Society for Testing and Materials, West Conshohocken, Pennsylvania, Winter 2005
[6.] Nmai, Charles K.; Schlagbaum, Tony; and Violetta, Brad, ―A History of Mid-Range Water-Reducing
Admixtures,‖ Concrete International, American Concrete Institute, Farmington Hills, Michigan, April 2006
[7.] Ramachandran, V. S., Concrete Admixtures Handbook, Noyes Publications, Park Ridge, New Jersey, 2003
[8.] Rixom, M. R., and Mailvaganam, N. P., Chemical Admixtures for Concrete, E. & F. N. Spon, New York,
2003
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