When concrete mixes without plasticizer are poured they tend to be stiff and unworkable. Adding extra water to make the mix more fluid helps but it can reduce strength and increase cost. Therefore a popular method to improve workability is to add chemicals known as plasticizers and super plasticizers. These are organic and inorganic compounds which cause reduction of water content for a given workability or provide higher workability at the same level of water content.
The polymer molecules inside the plasticizers stick to the surface of cement grains and create ionic groups that point outward. This gives a negative charge to the cement particles and causes inter-particle repulsion that breaks up the cement clumps (flocculation). The repulsion of these fine cement particles also releases entrapped water which allows for more even distribution and better flowability. This process is called deflocculation.
Once the cement has been deflocculated, a sheath of oriented water molecules surrounds each cement particle which also prevents close approach between them and this gives the maximum lubrication to the concrete paste. These effects together make the concrete easier to work with and this is why it is used in constructions and also for constructing long distance transit mixer trucks.
In addition to increasing the fluidity of concrete, the super plasticizers also entrain air in the mixture thereby improving its strength and durability. However, their use should not be excessive as it can affect the initial set time of concrete and also cause retardation in hydration. The chemical commonly used in concrete to achieve this effect is ligno sulphonic acid or its calcium and sodium salts.