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De-icing salts when dissolved in a solution allow chlorides to migrate through concrete structures resulting in ultimate rapid rusting of steel reinforcement. A parallel situation exists in a marine environment with sea water/spray on exposed areas of reinforced concrete.
PREVENTS INGRESS
Application of Xypex Crystalline Waterproofing to concrete prevents ingress of water, salt solutions and many aggressive chemicals. As well as a preventative measure, Xypex also provides remedial treatment by halting further corrosion of steel already attacked. It permits the concrete to 'breathe’ out existing moisture vapour whilst the entry of further solutions is excluded.
PERMANENT
Xypex forms crystals within the pores and capillary tracts of concrete preventing the passage of water. This crystalline waterproofing is permanent for the life of the structure. It is resistant to strong hydrostatic pressure and has the same freeze/thaw characteristics as the concrete. The surface of the structure is protected against spalling, efflorescence and popouts.
SALT ATTACK
The use of salt on concrete is known to form solutions capable of penetrating the structure and causing reinforcement steel to rust. This can occur on the immediate site of salt spread such as on a bridge deck, or indirectly, from traffic spray on to adjacent concrete structures.
Sodium chloride (common salt) in a dry state is stable and remains inactive. It is the presence of water which produces the solution resulting in electrolytic corrosion of the steel. The greater volumes formed by oxidised steel reinforcement weaken the concrete structure and eventually, cracks may be visible as they break through to the exterior surface.
THE IONIC LATTICE
Ions are electrically charged atoms. A crystal of sodium chloride consists of equal numbers of positive sodium ions and negative chloride ions. These ions are retained in a stable ionic lattice when the salt is in its normal dry condition.
Energy is needed to break the lattice and it is readily provided by molecules of water which are attracted to ions. The process of dissolving salt in water produces a clear solution and significantly, removes ions from the lattice. In fact, salt is soluble when water attracts the ions more than if the ions attract each other.
ELECTROLYTIC CORROSION OF STEEL
The chloride ions (negative) in salt solutions easily migrate through concrete to form an electrolyte and which in contact with steel create an electrical cell. Reinforcement bar rusts when it becomes the anode (positive) of a cell in which steel oxides.
This process relates to a reduction of oxygen at the cathode (provided from the chloride ions) to produce hydroxyl ions so that the initial corrosion product of the oxidised steel is represented by ferrous hydroxide.
Differential concentration cells formed by chloride ions and varying levels of oxygen provide a condition of inequality which rapidly develops anodic areas of steel reinforcement.
REDUCTION IN ALKALINE PROTECTION
The usually high alkaline environment of concrete structures gives a measure of protection to steel reinforcement. This immunity is reduced by the action of chloride ions from a salt solution which lower the high pH value. Even in highly alkaline conditions, sufficient concentrations of chloride ions can still induce corrosion.
Once such a condition exists, local ionic reduction tends to accelerate migration of salt solutions to that area. Therefore, electrical conductivity of concrete is enhanced, permitting an increase in corrosion currents and consequently a faster rate of rusting is experienced.
SUMMARY
Applied to concrete, Xypex products cause a catalytic reaction which in contact with moisture, forms crystals of dendritic fibres in the natural voids and capillary tracts of the structure. This non-soluble crystalline structure is so small as to ensure that water cannot pass through.
The ability of chloride ions to migrate through concrete is dependent on salt solutions penetrating into the structure. The integral waterproofing achieved by Xypex crysallisation prevents the ingress of such solutions. Once treated with Xypex, concrete structures are protected from penetration.
LITERATURE
Explanatory brochures, technical manuals, testimonials and lists of complete Xypex projects are available together with laboratory reports on permeability and chemical resistance.
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