Modelling of carbonation of hardened cement pastes with premixed Cl- and resulting Cl- redistribution

Concrete manufactured with desalinated sea sand undergoes carbonation. Consequently, pH decreases and chloride ion (Cl-) is redistributed, interactively impacting the safety of embedded reinforcements. In this study, a physical model considering the processes of cement hydration, pore structure formation, substances transport, and chemical reactions is established. Six key indicators, including the characteristics of carbonation degrees and Cl-distribution, prove the model's high accuracy. Subsequently, durability-related design suggestions, such as avoiding reinforcement corrosion under the combined impact of carbonation and premixed Cl- , are imple-mented. The allowable Cl-in desalinated sea sand must be not more than 1/3 of the present allowable values. To ensure a 50-year service life of a concrete with a 50-mm-thick reinforcement cover, the water-cement ratios under the influence of the coupling interaction and single carbonation must not exceed 0.28 and 0.36, respectively.

Automated summary

A physical model considering various processes involved in concrete carbonation was established in this study and proven to have high accuracy. Based on the model, durability-related design suggestions were proposed, such as limiting the allowable chloride ion content in desalinated sea sand and controlling the water-cement ratios under different carbonation conditions.