Diffusivity in the context of cement and concrete refers to the ability of substances such as gases, liquids, or ions to diffuse through the material. This property is critical because it influences the durability and longevity of concrete structures, particularly under severe environmental conditions. High diffusivity can lead to faster ingress of harmful substances like chlorides, sulfates, and water, which can accelerate degradation processes such as corrosion of reinforcement, sulfate attack, and freeze-thaw damage. Understanding and controlling diffusivity is therefore crucial for enhancing the performance and service life of concrete structures.