CHLORIDE PENETRATION IN NON-SATURATED CONCRETE Ayman Ababneh , Farid Benboudjema , and Yunping Xi * ** * *University of Colorado at Boulder, USA **ENS, Cachan, France ABSTRACT The two governing equations, which describe the diffusion of chloride ions into non- saturated concrete, are established. Material models for the four material parameters involved in the governing equations are developed, including chloride binding capacity, chloride diffusion coefficient, moisture capacity and moisture diffusion coefficient. The attempt is to establish the material models based on analytical results first, and if not possible, empirical models are developed based on dominant physical or chemical mechanism(s) at different scale levels, and calibrate the individual model by related test data. The Alternating-Direction Implicit (ADI) finite difference method was employed for solving coupled two-dimensional moisture diffusion and chloride penetration equations. The numerical solutions are compared with the experimental results obtained by the 90-day ponding test (AASHTO T259-80). The numerical prediction agrees very well with the test data. Free chloride concentration profiles at different depths and different ages of concrete slab are presented. Two limiting cases for different initial relative humidity levels are analyzed in detail to study the dependence of the chloride diffusion on the moisture diffusion in non-saturated concrete. INTRODUCTION Chloride penetration is one of the major problems that affect the durability of reinforced concrete structures. The chloride ions in concrete do not cause direct damage to the concrete, but attribute to the corrosion of embedded steel bars in the structure. The formation of rust in the