What material is used to surround anodes in their bed?

The correct choice is that chemical backfill is used to surround anodes in their bed because it plays a crucial role in enhancing the efficiency and lifespan of the anodes employed in cathodic protection systems. Chemical backfill can improve electrical conductivity, creating an optimal environment for the anodes to operate effectively. This is vital in facilitating the intended electrochemical reactions that help to protect metal structures from corrosion.

Granular fill, sand, and concrete are materials often associated with construction and may provide some level of support or stability for anodes, but they do not offer the same level of electrical performance enhancement that chemical backfill does. In cathodic protection systems, especially in soil or corrosive environments, the specific composition and characteristics of the chemical backfill can be tailored to optimize the anodes' sacrificial performance, ensuring that they provide adequate protection over time.