The effect of metakaolin on chloride penetration into concrete

Extensive research and practical experience have shown that partial replacement of cement by metakaolin improves concrete durability as a result of the refinement of the pore structure. While literature confirms much research on the performance of concrete with metakaolin, it is scarce concerning the performance with regards to chloride penetration. For the study, reference mixes where made with CEM I 42,5R cement. Two contents levels where defined: 330 kg/m³ and 440 kg/m³ based on mix designs currently used in the ready-mix industry for C20/25 and C30/37 concretes. Cement was partially replaced with metakaolin with levels varying from 10-20%. All mixes where tested for compressive strength, electrical resistivity and chloride diffusion characteristics (migration and immersion testing). The results demonstrate the improved resistance to chloride penetration of concretes with metakaolin additions. In addition, a beneficial effect on strength and durability properties of metakaolin also observed. Service life design calculations of reinforced concrete structures in marine environment based on the result obtained show a significant increase in the time to fulfill the serviceability limit state of corrosion initiation.