Pick up the correct statement applicable to cased columns.

• Single I-beam or channels back with or without flange plates may be used
• The overall dimensions of the steel section do not exceed 750 x 450 mm over plate if used
• The column is unpainted and is solidly encased in ordinary dense concrete with 10 mm aggregates having a minimum of cube strength 160 kg/cm2 at 28 days
• The surface and edges of the steel column should be provided a concrete cover not less than 50 mm
• All the above.