Coastal
Engineering - RC Structures
 Flexcrete’s
range of purpose designed marine mortars, sprayed mortars
and unique cementitious coatings are based on the Company’s
own highly advanced microsilica, polymer and fibre technology.
This affords optimum application and performance in wet,
chloride-laden environments and offers excellent resistance
to wash-out.
Flexcrete marine products can be installed between tides
to damp substrates and will cure under water to form a resilient,
durable finish that resists abrasion and chloride ion diffusion.
All Flexcrete products are manufactured with sustainable
development in mind and the Company is committed to providing
environmentally aware solutions.
Causes
of Deterioration
Reinforcing steel is protected against corrosion by the
inherent highly alkaline environment of the concrete created
by the release of calcium hydroxide from the cement hydration.
This results in the formation of a passivating layer of
gamma ferric oxide on the surface of the steel, which stifles
the corrosion process. However this is no defence to chlorides
ions, which because of their small size can readily penetrate
the pores and capillaries of even good quality concrete
and readily break down this passivating layer. Where sufficient
oxygen is present, rapid corrosion will occur and the by-products
formed have a greater volume than the original steel, ultimately
leading to the setting up of tensile stresses and spalling
of the concrete.
The highest rates of corrosion occur in the “splash zone”
where the continual wetting and drying exacerbates the penetration
of the chlorides and there is sufficient oxygen to support
the corrosion process. There is also sufficient moisture
present to locally increase the electrical conductivity
of the concrete leading to pitting corrosion. This is a
very aggressive type of corrosion and can cause rapid loss
of steel section and major cracking and spalling of the
concrete, thereby jeopardising structural integrity.
In the tidal zone and below the water line, the concrete
never dries out and the supply of oxygen is limited because
the pores in the structures are continually filled with
water. Nevertheless, in areas where there is low cover to
the reinforcement, corrosion can still occur causing a challenge
for its reinstatement.
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