Impact of Simultaneous Carbonation and Chloride Attack on Chloride Diffusion in Portland Cement Concrete Mixtures Blended with Natural Zeolite and Silica Fume.

There is still a significant problem associated with corrosion of steel bars embedded in concrete structures as a result of simultaneous chloride ingress and carbonation. This results in a decrease in the durability and service life of reinforced concrete structures. An experimental study was conducted to investigate the effect of carbonation on the diffusion of chloride ions in concrete mixtures containing 8% silica fume and 10% natural zeolite. To accomplish this, concrete specimens with water-to-cementitious materials (w/cm) ratios of 0.40 and 0.50 were placed in a system that simulated pure carbonation, tide cycles of the marine environment, and spraying conditions separately. Carbonation results in the release of bound chlorides from concrete pores, which further facilitates chloride ingress into rebar. Additionally, the simultaneous chloride ingress and carbonation can lead to a lower carbonation progress and an increase in the chloride diffusion coefficient. Consequently, rebar corrosion increased and concrete structures were less likely to last for a long period of time. When supplementary cementitious materials (SCMs) are used in concrete mixtures, this problem may become solely important. Based on the results of the present study, it is concluded that adding 8% silica fume or 10% natural zeolite to concrete reduces its carbonation resistance while increasing its carbonation-induced corrosion resistance. Additionally, when carbonation and chloride ingress occur simultaneously, the addition of 10% natural zeolite to concrete improved its diffusion coefficient more than 8% silica fume. [ABSTRACT FROM AUTHOR]