A composite fan casing for a gas turbine engine includes, in an exemplary embodiment, a core having a plurality of core layers of reinforcing fiber bonded together with a thermosetting polymeric resin. The disclosed paste comprises an activated carbon additive having a mesopore volume of greater than about 0. A supporting mechanism for supporting the connection portion of the first electrode is provided in a groove. In an end view, four cutting points on the four major cutting edges define the transitions between the first and second pairs of opposing side surfaces, and a minimum first length dimension between the second pair of opposing side surfaces is less than six-tenths of a minimum second length dimension between two of the four cutting points.