Inspection of deteriorating asbestos cement force mains with georadar technique

Abstract

Several breaks on asbestos cement force mains indicated a problem with these kind of force mains. An inspection technique that could give a good idea about the state of asbestos cement pipes was searched for. A georadar technique already existed to inspect drinking water mains and gravity sewers. The technique measures the wall thickness of cement containing materials and it can differentiate between ‘healthy’ and deteriorated material. The technique was applied on four wastewater force mains in Flanders. The results indicated a rapid deterioration of the asbestos cement. A deterioration mechanism called ‘calcium leaching’ was known from asbestos cement drinking water mains. Further it was known that H2S is produced in force mains and that it can attack concrete containing materials by mains of biogenic sulphuric acid attack. This research checked if both deterioration mechanisms cause the measured rapid deterioration of the asbestos cement force mains. Finally deterioration speeds and minimum required wall thickness were calculated. With the results the residual lifetimes of the force mains were calculated and these could be applied in an asset management program.