Study on the Mechanical Properties and Binding Behavior of Chloride in Cement Paste Under Premixed High Concentration of Chloride Ions

Chloride erodes steel bars through concrete pores, seriously affecting the durability of reinforced concrete structures. Improving the binding ability to chloride is an important measure. We explored the effects of W/C, curing age, and premixed Cl− concentration on the compressive strength and Cl− binding capacity in cement pastes. The results indicate that a premixed 5% concentration of Cl− can improve the compressive strength, whereas an excessive Cl− negatively impacts the mechanical properties. The total Cl− content in cement pastes is a crucial factor that influences the binding ability of Cl−. When the total Cl− content is within 2% (i.e., the premixed Cl− concentration is 5%), the cement paste has a strong binding ability of Cl−. W/C and curing age indirectly affect the binding ability by affecting the total Cl− content. Furthermore, with the increase in content of Cl−, the adsorption content of Cl− by C-S-H increased, while the proportion of Cl− bound by Fs to the total bound Cl− initially declines and then tends to stabilize. It is worth noting that a premixed concentration of 5% is a “safety limit” for cement paste, but for reinforced concrete, the presence of free Cl− above normative thresholds should not be underestimated.