Super plasticizer work in concrete
Super
plasticiszers are high range water reducers and they reduce water requirement
of concrete up-to an extent of 30 percent.
They are used to produce self levelling, self compacting and
high strength concrete
Dosage may be limited to 0.5 to 3% by weight of cement.
Action of superplasticizers :
1)Dispersion :
Portland cement being in the state of division, have a tendency
to flocculate in wet concrete. It entraps certain amount of water used in mix
and thereby water is not available to fluidy the mix.
When superplasticizers are added the get absorbed on the cement
particle. Adsorption of charged polymer on particles of cement create and
particle to particle repulsive force which overcome the attractive forces.
This repulsive force is called as ZETA Potential.
Overall result is that the cement particles are deflocculated
and dispersed hence the water trapped inside flocc get a released and is now
available to fludify the mix.
2) Retarding effect :
superplasticizers gets absorbed to cement particles forming a film
like sheet thus this prevents or delays the process of surface hydration of
cement.
*Advantages:-
It does not imparts air inside concrete unlike plasticizers.
It is responsible for both strength gain and improvement in work
ability.
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