Influence of Chloride Transport Modes and Hydrated Cement Chemistry on Chloride Profile and Binding Mechanisms in Concrete

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“…The chemical deterioration of concrete can occur due to various factors and the ingress of harmful agents such as sulphate ions (SO 4 2− ), carbon dioxide (CO 2 ), and chloride ions (Cl − ), which are considered the most significant and common deterioration agents of concrete [40,41]. Additionally, there are other factors that can lead to the deterioration of concrete, including calcium leaching, alkali-silica reaction (ASR), freeze-and-thaw cycles, and bacterial attacks [3,5,16,[42][43][44]. The engineering properties of concrete durability are mainly influenced by the permeability and diffusion medium of the concrete [18,[45][46][47].…”

“…The accurate determination of the free chloride concentration is imperative in estimating various concrete service life parameters such as the corrosion initiation period, the remaining service life, etc. [37,43]. Once chloride reacts with steel, it forms Fe(OH) 2 deposits along the steel reinforcement, which leads to an expansion of the concrete, whilst the oxidation which occurs within the cell leads to a significant reduction in the cross-section of the steel rebar [65].…”

“…Furthermore, a fraction of the different aluminate phases present in cement, namely, C 3 A and C 4 AF, react with chloride ions to form Friedel's salt (FS: Ca 4 Al 2 (OH) 12 Cl 2 •4H 2 O), Kuzel's salt (KS: Ca 4 Al 2 (OH) 12 Cl(SO 4 ) 0.5 •5H 2 O) and oxychloride phases [37,43,69,70]. However, only a highly chloride-concentrated environment can give rise to Kuzel's salts and oxychloride phases, whilst the formation of Friedel's salt lies within the critical chloride concentration in concrete [43,69]. Moreover, C 3 A content and exposure temperatures also have a very strong impact on the chloride threshold [58].…”

“…The remaining chloride ions present in the pore solution are free chloride ions, which tend to diffuse through the concrete and depassivate the steel rebar, initiating corrosion [43,69,70]. Hence, one of the strategies to eliminate or prolong chloride-triggered corrosion is to optimize the chloride-binding ability of concrete, which, in return, would lessen the number of free chlorides present in the pore solution.…”

“…The corrosion of steel reinforcements in concrete structures predominantly occurs owing to two primary mechanisms: chloride-induced corrosion and carbonation-induced corrosion. Among these mechanisms, chloride-induced corrosion stands as the most prevalent and frequently observed deterioration process affecting concrete structures, due to the high volume of concrete structures present in coastal areas [43,60]. Chloride ingress into concrete structures causes extensive damage, which may eventually lead to failure, resulting in a reduced service life [2,51,61].…”