Source : Webster's Revised Unabridged Dictionary (1913)

Constructiveness \Con*struct"ive*ness\, n.
   1. Tendency or ability to form or construct.

   2. (Phren.) The faculty which enables one to construct, as in
      mechanical, artistic, or literary matters.

Source : WordNet®

constructiveness
     n : the quality of serving to build or improve [ant: {destructiveness}]