Use and importance of Plasticizers and Super-plasticizers in concrete

In the situation such as in concrete pumping, ready-made concrete industry, tremie concreting, concreting in deep beams etc, high degree of workability in grading or use of high percentage can be increased by the improvement in grading or use of high percentage of fine aggregates or increasing cement content or others but it is very difficult to apply in the field. Extra water can be used to increase workability but it causes harm to the strength and durability of concrete. Hence, nowadays, it is very popular to use admixtures named plasticizers and super-plasticizers (available in various brand names) to reduce water requirement and to make concrete strong and workable.

Plasticizers are the organic or combination of organic and inorganic substances which reduces water content for certain degree of workability, when added in mix. The basic products consisting plasticizers are anionic surfactants (such as lignosulphonates, salts of sulphonates hydrocarbon) nonionic surfactants (such as polyglycol esters, hydroxylated carboxylic acid products) and others such as carbohydrates, etc. among them calcium, sodium and ammonium lignosulphonates are commonly used. Plasticizers are mixed from 0.1% to 0.4% by weight of cement used and it reduces 5% to 15% of water with the increment of workability from 3 to 8cm slump. In the mix, the cement grains absorbs the plasticizers molecules and results change in the surface charge of the same sign which causes repulsive forces and makes the dispersion which increases plasticity and workability. Some Plasticizer also entrails the air but a good plasticizer is that which entrains air less than 2% only. The plasticizers are available in market in various brands with specifications for composition, dosages etc.

However, the super-plasticizers are the improvement of plasticizers. It increases workability at same water cement ratio (w/c) and decreases w/c ratio at the same workability level. The fluidizing property remains longer due to the retarding property on cement hydration. Hence it is possible to obtain so called “flowing concrete” or “self leveling concrete”, which is pumpable or requires very little effort in the compaction. In the concrete with super-plasticizer segregation and bleeding are nearly absent. In other words, use of super-plasticizers reduces much more segregations and bleedings than any normal plasticizers. Hence, super-plasticizers are most effective mix ingredient for concrete. The super-plasticizers are normally grouped as sulphonated melamine, Naphthalene sulphonate, modified sulphonates and others. The super-plasticizers are also available in market in various brands with specifications for composition, dosages etc.

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