4.2 Chloride Corrosion Flashcards
What are the three main sources of chlorides?
De-icing salts
Marine environment
Intrusive chlorides
Two types of intrusive chlorides
Calcium chloride admixture (accelerator)
Contaminated constituents eg marine aggregates
Three mechanisms for chloride induced corrosion
Absorption (dry)
Diffusion - conc gradient Ficks Law
Permeability
Three types of chloride that enter through permeation
Free
Physically absorbed
Chemically absorbed
How do free chlorides enter concrete?
Diffuse through pore fluids
breakdown oxide layer
How do physically absorbed chlorides enter concrete?
Through weakly bound cement hydrate walls
How do chemically absorbed chlorides enter concrete?
Bound within cement hydrates - cannot penetrate deep
What factors influence chloride induced corrosion?
Surface absorption
Tortuosity and penetration
Chemical binding
Chloride concentration
Temp
Physical ways to reduce chloride induced corrosion
Reduce pore size
Distribution and interconnectivity
CPF liner
Chemical ways to reduce chloride induced corrosion (5)
Improve chloride binding capacity of cement
Increase PFA, GGBS, silica fume
High alumina content
Dispersal of fine particles
Increase of tortuosity
How does high alumina content help reduce chloride induced corrosion?
High chlorine binding capacity
How does dispersal of fine particles help reduce chloride induced corrosion?
Physically absorbs chloride ions
How does increasing tortuosity help reduce chloride induced corrosion?
Reduces pore size and interconnectivity
