Lecture 12 Admixture: Use of admixtures in concrete technology

Admixtures

1. Department of Civil Engineering
Concrete Technology
Admixture
Prof. Vinod Shikhare
Department of Civil Engineering,
ICEEM, Aurangabad
www.iceemabad.com
E-mail : [email protected]

2. Admixture
Prof. Vinod Shikhare
Thetermadmixtureas“amaterialotherthan
water,aggregates,hydrauliccement,andfiber
reinforcement,usedasaningredientofa
cementitiousmixturetomodifyitsfreshlymixed,
setting,orhardenedpropertiesandthatisadded
tothebatchbeforeorduringitsmixing.

3. Functions of Admixture
Prof. Vinod Shikhare
1.Increaseworkability
2.Retardoracceleratetimeofinitialsetting;
3.Reduceorpreventshrinkageorcreateslightexpansion
4.Modifytherateorcapacityforbleeding;
5.Reducesegregation;
6.Improvepumpability;
7.Retardorreduceheatevolutionduringearlyhardening;
8.Acceleratetherateofstrengthdevelopmentatearlyages;
9.Increasestrength(compressive,tensile,orflexural);
10.Increasedurabilityorresistancetosevereconditionsofexposure,including
applicationofdeicingsaltsandchemicals;other
11.Decreasepermeabilityofconcrete
12.Increasebondofconcretetosteelreinforcement;
13.Improveimpactandabrasionresistance;
14.Controlexpansioncausedbythereactionofalkalieswithpotentiallyreactive
aggregateconstituents;

4. Modern Concrete Admixture
Prof. Vinod Shikhare
Plasticizers
Superplasticizers
Retarders & Retarding Admixtures
Accelerator & Accelerating Admixtures
Air Entraining Admixtures
Pozzolanic or Mineral Admixtures
Damp Proofing & Water proofing Admixtures
Gas Forming Admixtures
Air detraining Admixtures
Alkali aggregate expansion inhibiting Admixtures
Workability Admixtures
Grouting Admixtures
Corrosion inhibiting Admixtures
Bonding Admixtures
Fungicidal, Germicidal & Insecticidal Admixtures
Colouring Admixtures

5. Construction Chemical
Prof. Vinod Shikhare
ConcreteCuringCompounds
PolymerBondingAgents
PolymermodifiedMortorforrepair&maintance
MouldReleasingAgents
Protective&DecorativeCoatings
InstallationAids
FloorHardener&DustProofer
SurfaceRetarders
Bondaidforplastering
Readytouseplaster
Constructionchemicalsforwaterproofing

6. Plasticizers
Prof. Vinod Shikhare
Amaterial,whicheitherincreasesworkabilityoffreshlymixed
concretewithoutincreasingwatercementratioormaintains
workabilitywithareducedamountofwater,istermedas
Plasticizersorwaterreducingadmixture
Astheirnameimplies,thefunctionofwaterreducingadmixtureis
toreducethewatercontentofthemix,usuallyby5to10%,
sometimes(inconcreteofveryhighworkability)up-to15%.
Thus,thepurposeofusingawaterreducingadmixtureinaconcrete
mixistoallowareductioninthewatercementratiowhileretaining
thedesiredworkabilityor,alternatively,toimproveitsworkability
atagivenwatercementratio.

7. Plasticizers
Prof. Vinod Shikhare

8. Super Plasticizers
Prof. Vinod Shikhare
Theadmixturescapableofreducingwatercontentby
about30%areknownassuperplasticizers.
Atagivenwater/cementratioandwatercontentinthe
mix,thedispersingactionofsuperplasticizeincreases
theworkabilityofconcrete,typicallybyraisingthe
slumpfrom75mmto200mm,themixremaining
cohesive.
Theresultingconcretecanbeplacedwithlittleorno
compactionandisnotsubjecttoexcessivebleedingor
segregation.

9. Super Plasticizers
Prof. Vinod Shikhare

10. Retarders
Prof. Vinod Shikhare
Thistypeofchemicaladmixturesdecreasestheinitialrateof
reactionbetweencementandwaterandtherebyretardsthesetting
ofconcrete.
ItfunctionsbycoatingthesurfaceofC3S(Tricalciumsilicate)
components,thus,delayingthisreactionwiththewater.
Reactionproductsareslowtoformassuchthesettingand
hardeningofconcretearedelayedreducingearlycompressive
strengths.
Retardationinsettingtimeupto8-10hoursispossiblebysuitable
useofretarders.

11. Retarders
Prof. Vinod Shikhare
The main ingredients of retarders are as follows:
Ligno-sulphonicacids and their salts. e.g. Na, Ca or NH4,
Hydro-carboxylic acids and their salts.
Carbohydrates including sugar.
Inorganic salts based on flourates, phosphates, oxides, borax and
magnesium salts.

12. Accelerators
Prof. Vinod Shikhare
Theseadmixtureswhenaddedtoconcrete,mortaror
groutincreasestherateofhydrationofhydraulic
cement,shortensthetimeofset,acceleratesthe
hardeningordevelopmentofstrengthofconcrete/
mortar.
TheseadmixturesfunctionbyinteractionwithC3S
(Tri-calciumsilicate)componentofthecementthus
increasingthereactionbetweencementandwater

13. Air Entraining Agents
Prof. Vinod Shikhare
Airisintentionallyincorporatedinformofminutespherical
bubblesof5micronto80microndistributedevenlyinentiremass
ofconcrete.
Variousadmixturesusedasairentertainer:
Naturalwoodresins.
Animalandvegetablefats.
Oliveoilandfattyacid.
Wettingagentssuchassulphonatedorganiccompounds.
Watersolublesoaps.

14. Water Proofing Materials
Prof. Vinod Shikhare
Concreteisaporousmaterialpronetocracking.That’swhynearly
allcommercialandresidentialconcreteprojectsspecifysometype
ofwaterproofingsystem.Usually,aspray-appliedcoatingora
peel-and-sticksheetmembraneisusedtokeepmoistureout.
However,anincreasingnumberofprojectsareusingintegral
waterproofingadmixtures,whichplugthenaturalporesand
capillariesfromwithintheconcreteandmakestheconcreteitself
impervioustomoisture.Someformsofintegralwaterproofingwill
evenself-healminorcracking.