Effect of cement composition on chloride binding and corrosion of reinforcing steel in concrete

✍ Scribed by Rasheeduzzafar; S. Ehtesham Hussain; S.S. Al-Saadoun

• Publisher: Elsevier Science
• Year: 1991
• Tongue: English
• Weight: 880 KB
• Volume: 21
• Category: Article
• ISSN: 0008-8846
• DOI: 10.1016/0008-8846(91)90173-f

✦ Synopsis

Pore solution study has been carried out on 2.43 and 14% C3A hardened cement pastes. Data have been analyzed in conjunction with the data developed in two pore solution studies made by Page and Vennesland and Diamond using 7.37 and 9.1% C3A mature cement pastes. The results show that C3A and alkali contents of a cement have significant effect on its chloride-binding capacity.

For similar alkali content, the levels of free chlorides in the pore solutions of 2.43 and 9.1% C3A cement pastes are respectively 4.7 and 2.8 times more than in a 14% C3A cement. The alkali content of a cement appears to have an inhibiting effect on its chloride-binding capacity. However, this effect is overshadowed by a conjoint strong elevation of the OH-ion concentration in the pore solution due to cement alkalies, causing a net lowering of the CI-/OH-ratio which roughly ascertains corrosion risk. Threshold chloride values have been evaluated for different C3A cements. The threshold chloride content for a typical Type I portland cement with C3A upto 8% and Na20 equivalent upto 0.60%, may be taken as 0.4% chlorides by weight of cement. However, for a similar alkali cement with a high C3A content of about 14%, the chloride threshold value is 2.5 times higher and may be taken as 1.0% by weight of cement.