Abstract
Durability and service life of concrete structures can be endangered by chloride ions. Two phenomena help to keep control of chloride effects. On one hand cements are able to bind chloride ions by their aluminate clinker phases or by the clinker substituting materials. On the other hand resistivity of concrete against chloride penetration can be improved by careful selection of concrete constituents and production. Detailed results of two series of extensive experimental studies are presented herein. Chloride ion binding capacity of tested cements in decreasing sequence was the following: (1) CEM III/B 32,5 N-S; (2) CEM III/A 32,5 N; (3) CEM II/B 32,5 R; (4) CEM II/B-M (V-L) 32,5 R; (5) CEM I 42,5 N. Test results indicated that the increasing substitution of clinkers by GGBS improves the chloride resistivity in concrete made with the same water to cement ratio. The application of air entraining agent increases considerably the values of Dnssm. Based on the migration coefficients (Dnssm) the following sequence of efficiency was found (from the best): CEM III/B 32,5 N > CEM V/A (S-V) 32,5 N > CEM III/A 32,5 N > CEM II/B-S 42,5 R > CEM II/A-S 42,5 N > CEM I 42,5 N.
Highlights
One of the most important objectives of durability design is to control the penetration of chloride ions up to the level of steel reinforcement
Test results indicated that the increasing substitution of clinkers by GGBS improves the chloride resistivity in concrete made with the same water to cement ratio
The reaction of sulphate ions and the aluminate-ferrite mono- (AFm-) phases lead to the secondary ettringite formation observed here
Summary
One of the most important objectives of durability design is to control the penetration of chloride ions up to the level of steel reinforcement. The increase of concrete cover seems to be a possible solution This should not be the optimal solution since the dead load of the structure increases by the increase of concrete cover in addition to the increased probability of spalling of concrete cover for high thicknesses. Another solution is the application of high performance concrete with low permeability and improved resistivity against chloride diffusion. When chlorides penetrate through the concrete cover and reach the steel reinforcement, the corrosion will initiate when a certain chloride concentration (the threshold value) is reached [2,3,4,5]. It is well-established that both C3A and C4AF are able to bind chloride ions by the formation of Friedel’s salt (C3A⋅CaCl2⋅H10), or its iron analogue (C3F⋅CaCl2⋅H10), if chlorides originated from CaCl2 are dissolved in the mixing water [10]
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