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Tuesday, March 18, 2008 - 8:30 AM
Convention Center, Second Level, R03 (Ernest N. Morial Convention Center)
08051
Evaluation of Sacrificial Anode Backfill Material
Galvanic sacrificial zinc anodes are used to protect the steel in the Great Manmade River Project pipeline.The zinc anodes are placed in a backfill mixture of 75% gypsum, 25% Bentonite and emplaced at a Bentonite mix to water ratio of 1.75:1.0, which provides a bulk density of 1.48 to 1.60 Mg/m3In some places, most notably in the desert interior of anodes from the ground has shown that the Bentonite backfill has shrunk away from the zinc anodes reducing the efficiency of the anode.
This has urged GMRA to carryout further laboratory testing to determine the causes of this shrinkage 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.The tests revealed that the Bentonite which was in use was in commercial terms relatively low grade. Engineering testing suggests that if the ground conditions cause the backfill to dry, shrinkage may lead to a loss of anode function. Such shrinkage would be reduced if the backfill was emplaced at lower moisture content and higher density, and the Bentonite should be calcium base not sodium base.
This has urged GMRA to carryout further laboratory testing to determine the causes of this shrinkage 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.The tests revealed that the Bentonite which was in use was in commercial terms relatively low grade. Engineering testing suggests that if the ground conditions cause the backfill to dry, shrinkage may lead to a loss of anode function. Such shrinkage would be reduced if the backfill was emplaced at lower moisture content and higher density, and the Bentonite should be calcium base not sodium base.
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