Superplasticizers (SPs), also known as high range water reducers, are additives used for making high-strength concrete or to place self-compacting concrete. Plasticizers are chemical compounds enabling the production of concrete with approximately 15% less water content. Superplasticizers allow reduction in water content by 30% or more. These additives are employed at the level of a few weight percent. Plasticizers and superplasticizers also retard the setting and hardening of concrete.
According to their dispersing functionality and action mode, one distinguishes two classes of superplasticizers: 
# Ionic interactions (electrostatic repulsion): lignosulfonates (first generation of ancient water reducers), sulfonated synthetic polymers (naphthalene, or melamine, formaldehyde condensates) (second generation), and;
# Steric effects: Polycarboxylates-ether (PCE) synthetic polymers bearing lateral chains (third generation).
Superplasticizers are used when well-dispersed cement particle suspensions are required to improve the flow characteristics (rheology) of concrete. Their addition allows to decrease the water-to-cement ratio of concrete or mortar without negatively affecting the workability of the mixture. It enables the production of self-consolidating concrete and high-performance concrete. The water–cement ratio is the main factor determining the concrete strength and its durability. Superplasticizers greatly improve the fluidity and the rheology of fresh concrete. The concrete strength increases when the water-to-cement ratio decreases because avoiding to add water in excess only for maintaining a better workability of fresh concrete results in a lower porosity of the hardened concrete, and so to a better resistance to compression.
The addition of SP in the truck during transit is a fairly modern development within the industry. Admixtures added in transit through automated slump management system, allow to maintain fresh concrete slump until discharge without reducing concrete quality.