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The correct answer is super plasticizer. Super plasticizers, also known as high-range water-reducing admixtures, are used in concrete to enhance its flowability without adding more water. This admixture works by altering the surface properties of the cement particles, allowing them to move more freely and reducing the viscosity of the concrete mix.

One of the significant benefits of using super plasticizers is the ability to lower the water-to-cement ratio while maintaining workability, which is crucial for achieving high strength and durability in concrete. By reducing water requirements by up to 30%, super plasticizers help prevent issues such as shrinkage cracking and improve the overall performance of the concrete.

Air-entraining agents, on the other hand, are used to introduce microscopic air bubbles into the concrete mix, which help improve freeze-thaw resistance but do not significantly reduce water requirements. Retarders are additives that slow down the setting time of concrete to allow for longer placement times, and accelerators work to speed up the curing process. Neither of these admixtures specifically targets a reduction in water needs to such an extent as super plasticizers do.