What is modified bitumen primarily characterized by?

Modified bitumen is primarily characterized by being a bitumen that has been enhanced with the addition of polymers to improve its properties. The incorporation of these polymers, such as atactic polypropylene (APP) or styrene-butadiene-styrene (SBS), provides the modified bitumen with elastomeric properties, meaning it can expand and contract with temperature fluctuations. This makes modified bitumen suitable for various roofing applications, especially in environments that experience significant temperature changes.

The use of polymers enhances the durability and flexibility of the material, making it more resistant to cracking and splitting when exposed to stress or extreme weather conditions. This adaptability is particularly beneficial for flat roofs, which require roofing materials that can handle ponding water and constant movement due to thermal expansion. In essence, the addition of polymers transforms standard bitumen into a more versatile and effective roofing solution.

Other options do not accurately reflect the defining characteristics of modified bitumen, focusing on different materials and properties unrelated to the specific enhancements made to bitumen through polymerization.