POZZOLANIC ACTIVITY OF NATURAL ZEOLITES: MINERALOGICAL, CHEMICAL AND PHYSICAL CHARACTERIZATION AND EXAMINATION OF HYDRATION PRODUCTS A THESIS SUBMITTED TO THE GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES OF MIDDLE EAST TECHNICAL UNIVERSITY BY SEVGİ ÖZEN IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGICAL ENGINEERING JUNE 2013