Good concrete in the fresh state requires appropriate workability for placing the concrete at the required location.Concrete requires different degree of workability in different situation. A high degree of workability is required in placing concrete in deep beams , thin walls of water retaining structures with percentage of steel reinforcement , at column and beam junctions, in pumping concrete in hot weather concreting and also in ready made concrete industries.
Plasticisers are water reduces that is they fluidise the mortar or concrete at low water cement ratio.The increase in workability that can be expected by using plasticizers at the same water cement ratio may vary from 30 mm to 150 mm slump depending on the dosage,initial slump of concrete, cement content and type.
The basic product constituting plasticizers are,
- An iconic surfactants such as lignisulphonates and salts of sulphonates hydro-carbons.Calcium,sodium and ammonium lignosulphonates are most commonly used in dosage of 0.1 % to 0.4 % by weight of cement.At this dosage at constant workability the reduction in mixing water is expected to be the order of 5% to 15 % .This naturally increase the strength.
- Non-iconic surfactance such as polyglycol,esters,acid of hydroxilated carbosilic acid.
- Other products such as carbohydrates.
Superplasticisers are high range water reducers as described in literature.They are a new class of water reducing admixtures,chemically different from normal water reducers,i.e plasticisers,capable of reducing water contain as much as 25% to 30% in contrast to the possible reduction up to 15% in case of plasticisers.
The use of superplasticisers is practice for production of flowing,self levelling, self compacting and for the production of high strength and high performance concrete.
Superplasticisers are grouped in four categories,
A. Sulphonated Melamine Formaldehyde.
B. Sulphonated Napthelene Formaldehyde.
C. Modified Lignosulphonate
D. Polyhydroxilatedpolymer or mixture of acid-amids and polsaccharides
There are many new generation superplasticisers used in other countries such as,
Accrylic polymer base
Poly carboxylate ester