Concrete - Diffuse materials
Diffuse materials like concrete are characterized by their high roughness. Typical diffuse materials like walls, paper, and concrete have a roughness close to 100%. A value of 100% represents a fully diffuse material (also called Lambertian), which is a theoretic perfect material so it's better to avoid it to keep the material realistic. This is the simplest type of material.
Set your material’s roughness to 100% to create a completely diffuse surface. Use an image of concrete for the Refl 0º. The Refl 90º color is not important here because we are using a high roughness value.
Use a bump map to add bumps to the surface. Check the Normal map icon if you prefer to use a Normal map.
The basic structure of a plain diffuse material like concrete. You can download this material example here.