Comparing a natural pozzolan, zeolite, to metakaolin and silica fume in terms of their effect on the durability characteristics of concrete: A laboratory study

► Optimal replacement level is 7.5–10% for silica fume, 10–15% for metakaolin and approximately 10% for zeolite. ► Utilizing pozzolans is more effective in enhancing the durability of concrete than lowering w/c ratio. ► Because zeolite is environmentally friendly, it could be a good substitute for silica fume and metakaolin. The durability of concrete structures and, consequently, their service life, have improved significantly due to the introduction of pozzolans to the industry; thus, using newly developed pozzolans has become a necessity for the construction of concrete structures, especially in aggressive environments. In the laboratory study presented here, the effects of substituting cement with 10%, 20% and 30% natural zeolite on concrete durability were compared to the effects of substituting 5%, 10% and 15% metakaolin and 5%, 7.5% and 10% silica fume, along with water-to-cement ratios of 0.35, 0.40, 0.45 and 0.50. The comparison is made according to the test results of compressive strength, water absorption, sorptivity, volume of voids, electrical resistance, gas permeability and chloride diffusion, and their inter-relationships also were investigated. Results show that, in general, the zeolite is not as active as silica fume or metakaolin, although it could be used as a substitute for pozzolans because it has better durability characteristics and is economical and environmentally friendly as well.