What does a PG 64-28 designation indicate about binder modification?

• A. It is always modified
• B. It may or may not be modified
• C. It is guaranteed to be unmodified
• D. It indicates low performance

Answer: (B)

The PG 64-28 designation refers to a performance grade of asphalt binder, specifically indicating the expected high and low temperature performance characteristics. The 'PG' stands for Performance Grade, while '64' signifies that the binder can withstand high temperatures up to 64 degrees Celsius without experiencing significant deformation. The '-28' indicates the lowest temperature at which the binder will perform adequately, which is down to -28 degrees Celsius.

The designation does not specify whether the binder is modified or unmodified; it only defines its performance criteria. This means that a binder with a PG 64-28 designation may or may not be modified. Modifications are often made to enhance performance characteristics, but it is possible for an unmodified binder to meet this specific grade as well. Hence, the correct understanding is that the binder's designation allows for both modified and unmodified options, making it accurate to say it may or may not be modified.