Influence of carbonation on the chloride concentration in the pore solution of concrete

Author(s): X. Wan, T. Zhao, F.H. Wittmann
Paper category: Conference
Book title: Concrete Repair, Rehabilitation and Retrofitting III (ICCRRR)
Editor(s): M.G. Alexander, H.-D. Beushausen, F. Dehn, P. Moyo
Print ISBN: 978-0-415-89952-9
Publisher: Taylor & Francis Group
Pages: 138 – 139
Total Pages: 2
Language: English

Abstract: 
Chloride content and pH value of the pore solution in the neighborhood of steel reinforcement are decisive parameters for initiation and rate of corrosion. The pore solution of cement mortar and hardened cement paste has been expressed from the pore space by high pressure. The influence of water-cement ratio, age, and the addition of chloride to the fresh mix on chloride content of the pore solution has been determined by ion chromatography. At the same time the pH value of the pore solution has been determined. It was found that the content of free chloride decreases with increasing water-cement ratio and it increases with the amount of chloride added to the fresh mix. The amount of chemically bound chloride increases with time, but it decreases with decreasing content of dissolved chloride in the pore solution. A significant influence of carbonation on the chloride content of the pore solution has been observed. After complete carbonation of cement mortar and of hardened cement paste with different water-cement ratios (W/C = 0.5 and 0.7) and with different amounts of chloride added to the fresh mix (0%, 0.5% and 1%) the dissolved chloride content increases by a factor between 2 and 12. In
parallel the chemically bound chloride decreases significantly due to carbonation. As has been expected the pH value decreases from values around 13.2 to values as low as 8.0. It can be concluded that carbonation not only lowers the pH value but at the same time it liberates chemically bound chloride. This is one obvious reason why combined action of chloride penetration and carbonation accelerates steel corrosion and shortens service life of reinforced concrete structures.

Online publication: 2014
Publication Type: abstract_only
Public price (Euros): 0.00