Sterak cage question

Its the +25% AA base damage always active or only when the passive triggers?

If its always active, does it increase to 50% during the passive shield duration?

Was thinking alongside the lines of making a CDR shyvana build for permanent firezone

Cinderhulk/Devourer Titanic Hydra Black Cleaver Ionian Boots Sterak Cage Warmog Armor Or Spirit Visage