Admixtures Presentation1

8/10/2019 Admixtures Presentation1

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ContentAdmixtures

Definition

Types Of Admixtures

Purpose of Admixture

Chemical Admixture

Mineral Admixtures


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DMIXTURES

A material which , except in special cases, is added toconcrete mix in quantity not more

than 5% by mass of cement during mixing or anadditional mixing operation prior to the

placing of concrete for the purpose of achieving specific

modifications .

Admixtures maybe used in solid or liquid form . Liquids

are more used due to the fact thatliquid can be dispersed rapidly in uniform manner during

the mixing of concrete.


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Types of Admixtures

Mineral

Admixture

Mineral admixtures (fly ash, silica fume

[SF], and slug) are usually added to

concrete in larger amounts to enhance

the workability of fresh concrete; to

improve resistance of concrete tothermal cracking, alkali-aggregate

expansion, and sulfate attack; and to

enable a reduction in cement content.

Chemical

Admixture

Chemical admixtures are added to

concrete in very small amounts mainly

for the entrainment of air, reduction

of water or cement content,

plasticization of fresh concretemixtures, or control of setting time.


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Purposes of AdmixtureS

To accelerate the initial setting of concrete.

To retard the initial setting .

To improve the strength of concrete .

To reduce the heat of evolution.

To improve the workability.To inhibit the corrosion of concrete.

To increase the durability of concrete.

To increase the bond of concrete to the steelreinforcement.

To increase the resistance to chemical attack.


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ChemicalAdmixtures

AirEntrained

Accelerating PlasticizersSuper

PlasticizersRetarding


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Air Entrainment Admixture

They are traditionally based on Abeitic acidsalts(Vinsol resin) and fatty acids.

Now a days synthetic surfactants based on olefinsulphonates, Alkyl sulphates,

Diethanaol amines, Alcohol ethoxylates betainsare used.

Lowers the surface tension of the water and facilitatein bubble formation.

Decreases bleeding and segregation thus the provideresistance against freezing and thawing.

It improves workability but for every 1% ofadmixture strength decreases by 5%.


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Accelerating Admixture

The most commonly used accelerator is CaCl2but it causes corrosion in reinforcement.other accelerators are Ca(NO3)2, NaNO3,NaCl and sea water.

It reduces initial setting time and curing time.

It is used in cold weather concreting.

Accelerators are used in large projects and fasttrack construction.

The amount should not exceed by 2%.


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Retarding Admixtures

This admixture delay initial setting time from 1 hour to3 hours.

Organic: refined calcium, sodium, NH4, salts oflignosulfonic acids, hydrocarboxylic acids and

carbohydrates Inorganic: oxides of leads and zinc, phosphate,

magnesium salts, flourates and borates.

It is used when temperature is higher than 85oF (30o c)

It increase workability, prevent the formation of coldjoints and increase ultimate strength.


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Plasticizers

They are usually based on lignosulphnates.Hydroxylated polymers are also widely used as

plasticizers.

It reduces water cement ratio thus increase

strength without reducing workability. It is used in hot weather concreting.

They are added from 130 to 390 ml per 100 kg.

It improves durability, provide easier placement,control the setting time and reduce

segregation.


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Super Plasticizers

There are 4 main families of super pasticizers:1. Sulfonated melamine formaldehyde

condensates (SMF)

2. Sulfonated napthalene formaldehyde

condensates (SNF)3. Modified lignosulfonates (MLS)

4. Polycarbxylate derivatives.

Super Plasticizers are used in hot weather forlarge projects.

It reduce water requirement from 12% to 25 %.


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Super Plasticizers..

It produce high strength cement .

Water cement ratio ranges from o.3 to 0.4 and

compressive strength is upto 14ooo psi (96.5

MPa)

It produce flowing cement with very high

slump in range of 7-9 inches (175 to 225 mm)


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MineralAdmixtures

Cementitious Pozzolanic


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Cementitious

These have cementing properties themselves.

For example: Ground granulated blast furnace slag (GGBFS)


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Pozzolanic

A pozzolan is a material which, when combinedwith calcium hydroxide (lime), exhibitscementitious properties. Pozzolans are commonlyused as an addition (the technical term is

"cement extender") to Portland cement concretemixtures to increase the long-term strength andother material properties of Portland cementconcrete and in some cases reduce the material

cost of concrete.Examples are

Fly ashy Silica Fume


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Bibliography

http://www.admixtures.org.ukhttp://www.basf-admixtures.com

http://www.nrmca.org/aboutconcrete/cips/15p.

pdfhttp://www.fhwa.dot.gov/infrastructure/materi

alsgrp/admixture.html

http://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtures

http://www.concrete.org/general/fE4-03.pdf
http://www.admixtures.org.uk/http://www.basf-admixtures.com/http://www.nrmca.org/aboutconcrete/cips/15p.pdfhttp://www.nrmca.org/aboutconcrete/cips/15p.pdfhttp://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.htmlhttp://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.htmlhttp://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtureshttp://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtureshttp://www.concrete.org/general/fE4-03.pdfhttp://www.concrete.org/general/fE4-03.pdfhttp://www.concrete.org/general/fE4-03.pdfhttp://www.concrete.org/general/fE4-03.pdfhttp://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtureshttp://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtureshttp://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtureshttp://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtureshttp://www.toolbase.org/Technology-Inventory/Foundations/concrete-admixtureshttp://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.htmlhttp://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.htmlhttp://www.nrmca.org/aboutconcrete/cips/15p.pdfhttp://www.nrmca.org/aboutconcrete/cips/15p.pdfhttp://www.basf-admixtures.com/http://www.basf-admixtures.com/http://www.basf-admixtures.com/http://www.admixtures.org.uk/

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Admixtures Presentation1