Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers



Last updated: April 8, 2018

What Does Backfill Mean?

Backfill refers to products or materials used to fill excavations. The most common form is composed of a mixture of gypsum and calcium bentonite.

Apart from filling holes, one of the primary purposes is to mantle sacrificial anodes under the ground. This enhances the ability of the anode to lessen electrical resistance, thus reducing corrosion as well.


Corrosionpedia Explains Backfill

The kind of backfill to be utilized in ground beds is determined according to the type of cathodic protection: impressed or sacrificial. In general, there are two types:

  • Chemical – These are commonly utilized through galvanic anodes, creating an atmosphere that is conducive for the dissolution of the anode. The usual mixture is 75% gypsum powder and 25% bentonite. This kind of backfill mixture is perfect for soils with high levels of resistivity. With this backfill, the water is expanded and absorbed, leading to suitable contact between the soil and the anode through reducing resistance in the ground bed.
  • Carbonaceous – These are intended for impressed anodes. The common elements include natural graphite and coke breeze. The chief purposes of this backfill are the following: lower ground bed resistance, create an adequate surface where oxidation may take place. It also helps in prolonging the lifespan of the anode.

To ensure effectiveness, the correct type of backfill must be chosen along with the appropriate particle shape and size.


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