Polymer Modified Bitumen (PMB) is a type of bitumen (also known as asphalt) that has been modified with polymer additives to enhance its properties and performance characteristics. The "-40" you mentioned might refer to a specific grade or specification of Polymer Modified Bitumen, but as of my last knowledge update in September 2021, I'm not aware of a direct association with that specific term.

The "PMB -40" could potentially indicate a certain characteristic or property of the polymer modified bitumen, such as its viscosity or temperature susceptibility. In the realm of bitumen, temperature susceptibility is a significant factor. The "40" could refer to a temperature, possibly indicating that the bitumen remains stable or performs well up to -40 degrees Celsius. However, without more context, it's hard to provide a precise explanation.

If "PMB -40" has emerged as a new standard or term after my last update, I recommend checking with recent sources such as industry publications, standards organizations, or manufacturers to get the most up-to-date and accurate information on its meaning and significance.