MohammadHosein Tadayon - Construction Material Institute, University of Tehran, Tehran, Iran,
Mohammad Shekarchi - Road, Housing & Urban Development Research Center (BHRC), Tehran, Iran
Mohsen Tadayon - Iranian Concrete Institute, Tehran, Iran

In general, the use of pozzolans such as silica fume, metakaolin and natural zeolite enhance concrete permeability and durability [6]. This is because of improving the distribution of pore size and structure of concrete matrix, improving interfacial transition zone of the interface between aggregates and the matrix, reducing chloride ingress, and increasing chloride binding [3,4,7-9]. Silica fume and metakaolin are commonly used pozzolans in construction projects. These two pozzolans can sharply increase the compressive strength of concrete and decrease its permeability [3, 6 and 10]. However, recent tendency to use natural pozzolans because of lower cost and accessibility have been led to use natural zeolite, one of the most common natural pozzolanic material [11]. Natural zeolite as cement replacement of 5 to 30% canlead to concrete with a lower permeability and higher compressive strength. However, natural zeolite is not as effective as silica fume in decreasing chloride iondiffusivity or increasing compressive strength [11,12]. Exposure condition of concrete affects greatly on chloride diffusion coefficient. Studies showed that tidalzone and splash zone are the most severe conditions in the case of chloride ingress and steel corrosion in concrete, in compare to atmosphere and immerged zone [3,13].In the case of durability, long-term measurements can be more valuable and provide better estimations from longterm performance of concrete structures.In this research, long-time in situ studies are presented to investigate the effect of different w/b ratios and pozzolan replacement on chloride penetration under laboratory and tidal exposure in the field conditions in the Persian Gulf.