STRENGTH DURABILITY INDEX (SDI) FOR IMPROVED CONCRETE STRENGTH AND DURABILITY ASSESSMENT by HECTOR GARCIA-MONZON, B.S.C.E., M.S.C.E. A DISSERTATION IN CIVIL ENGINEERING Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of DOCTOR OF PHILOSOPHY Approved Sanjaya Senadheera Chairperson of the Committee Priyantha W. Jayawickrama Charles Newhouse Accepted John Borrelli Dean of the Graduate School August, 2006