As CSC Services undertake a scheme of work protecting steel rebar at Hartlepool Power Station, Mick Flounders, Contracts Director looks at the importance of waterproofing concrete to protect rebar.
Concrete has many advantages, including high compressive strength, formability and durability. Steel reinforcement is usually added to provide solid tensile strength that concrete normally lacks, and to resist the tension a load could cause for a structure.
Corrosion
The high-alkalinity of concrete will normally protect steel rebar by forming an iron oxide protective film around the steel, providing protection against corrosion. However, while hardening, concrete develops minute pores which become a potential source for the ingress of corrosive agents into the concrete. This can break down iron oxide film enabling corrosion to take place.
When the steel begins to rust and produce pits or holes in its surface, a reduced strength capacity is seen, which negatively affects the structure’s viability. By the time the signs of damage become visible on the outside of the concrete structure, the extent of the corrosion of reinforcement steel will have reached an advanced stage. A full programme of refurbishment will be required which will include the breaking out of concrete, use of steel reinforcement protector ahead of the repair being reinstated and protective coatings installed.
The importance of Waterproofing
Steel, water, and oxygen must all be present for corrosion to occur to the steel rebar. Eliminating any one of these will prevent the oncoming chemical reaction and is the reason why there is no corrosion in dry concrete and also why concrete fully submerged in water has limited corrosion, except in instances where the water can entrain air.
The first line of defence against corrosion in reinforced concrete is to prevent the penetration of water through concrete pores, cracks, and micro-cracks.
There a range of cementitious coatings specified for both existing and new structures to waterproof concrete, reinstate concrete cover and provide an effective barrier to chloride ingress, amongst many other challenges typically encountered on buildings, infrastructure and structures in sectors such as the nuclear power industry and the water / waste water industry.
Epoxy coatings, Polyurethanes and Polyurea can also be used for waterproofing purposes.
CSC Services were onsite at Hartlepool Power Station to refurbish crane support columns suffering from steel rebar corrosion. Waterproofing concrete with cementitious coatings will increase durability, improve lifespan, and lower maintenance costs over the structure’s service life. For advice on protecting reinforced concrete structures please contact 0191 410 3444.
