Concrete admixtures are substances added to concrete during mixing to enhance its properties. These additives can improve workability, reduce water content, accelerate or retard setting time, and increase durability. Common types include plasticizers, which make the mixture easier to work with, and superplasticizers, which significantly improve flow without adding extra water. Using admixtures can lead to better performance in various conditions, such as extreme temperatures or high-stress environments. They help achieve specific requirements for construction projects, ensuring that the concrete meets the necessary standards for strength and longevity.