Evaluation on effect of carbonation on chloride binding capacity and stability of cement hydration products with multiple testing methods

Carbonation leads to decrease in chloride (Cl-) binding capacity of hardened cement paste, and subsequently endangers safety of reinforced concrete structures. During the research process, the results obtained by different standards and methods used to quantify the deterioration differ greatly and are unsuitable for comparison. To solve this issue, multiple standards, appointed with various conditioning regimes, for testing acid- and water-soluble Cl- contents in hardened cement paste were followed to evaluate binding capacity and stability of monosulfoaluminate (AFm) and tricalcium aluminate (C3AH6) on premixed Cl- exposed to external CO2. Results show that the methods used in three standards can completely dissolve the acid-soluble Cl-; the different conditioning temperatures lead to different water-soluble Cl- content measured, resulting in significance difference in the AFm chloride binding results, while the difference can be slight and negligible in the C3AH6. Cl- binding products of AFm was relatively stable within room temperature to 70 °C, and the stability decreased once higher than 70 °C; the products of C3AH6 showed relatively good stability between 20 and 100 °C. The Cl- binding capacity and stability of both AFm and C3AH6 were greatly reduced after a carbonation of 3 d. Detailed results for evaluating changes in the binding capacity of AFm before and after carbonation were related to the standards selected, while that for the C3AH6 was quite close.