Water Reducing admixture/ Plasticizers
The requirement of right workability is the essence of good concrete. The easy method generally followed for obtaining high workability is to use extra water. This tendency ultimately affects the strength and durability of concrete badly. Use of plasticizer in the concrete mix is one of the suitable ways to overcome this problem.
The organic substance or combination of organic & inorganic substances capable of reducing water requirements for the given workability or give higher workability at the same water content is termed as water reducer or plasticizer.
The plasticizer is used @ 0.1% to 0.4% by weight of cement which reduces the water requirement by 5% to 15% at constant workability
Action of plasticizer
The action of plasticizer is mainly to fluidity the mix & improves the workability of concrete the mechanisms involved a) Dispersion b) Retarding effect
When water is added to a mortar or concrete mixture, the cement & other fine particles flocculate together which entraps certain amount of water used in the mix thereby reduces the amount of water available to the fluidity of the mix.
When the plasticizer is added, the cement particles are deflocculated & the water trapped inside the flocks gets released & becomes available fluidity the mix.
b) Retarding Effect
The plasticizer gets absorbed on the surface of cement particles prohibit the surface hydration of cement as long as sufficient plasticizer molecules are available.