Cement Growth Failure Mechanism in Porcelain Suspension Insulators

The paper describes a study undertaken to elucidate the mechanisms of cement grout expansion which leads to radial cracks in the shells of porcelain suspension insulators. The delayed hydration of periclase (MgO) is isolated as the dominant mechanism responsible for cement growth failure although sulphate related expansion may be a secondary influence. The expansion required to cause failure is quantified through extensive long term water expansion tests on cement pastes and autoclave tests on insulators assembled with both industrial and laboratory produced cements. From this study, a maximum ASTM C 151 autoclave expansion limit of about 0.12 percent is recommended for suspension insulator grout.