A common method of corrosion control of buried pipeline is that of cathodic protection involving the use of sacrificial anodes. To ensure maximum effectiveness of an anode, a suitable backfill material of Gypsum/Bentonite is required to maintain the necessary current flow. This material is generally inert and moisture retentive. In the River Project of Libya,the bentonite used was collected from two different clay member formations.The destructive inspection of zinc anodes revealed that the backfill material used from one formation (No. 1) has dried quickly and shrunk away from the anode and the other backfill used from formation No. 2 was still moisture retentive and working properly. Therefore a laboratory tests were carried out to determine the causes of the shrinkage of formation 1 and also to identify the characteristics of Bentonite used and its suitability for use in the backfill, and how to delay the moisture content loss with minimum shrinkage.