Which term refers to materials that modify properties of concrete?

The term that refers to materials that modify the properties of concrete is "admixtures." Admixtures are chemical or mineral ingredients added to the concrete mix to enhance its performance or properties. They can improve workability, accelerate or retard setting time, reduce water content, improve bonding, increase strength, and provide other beneficial effects that might be required for specific applications.

Additives, while they may sound similar to admixtures, generally refer to substances that are added to improve the properties of existing materials rather than specifically designed for modifying concrete's characteristics. Composites refer to materials made from two or more constituent materials with significantly different physical or chemical properties, and aggregates are inert materials like sand, gravel, or crushed stone that are mixed with cement and water to create concrete, rather than materials that modify its properties.