Which are the methods for concrete repair used in marine structures?
Reinforcement and steel repair and protection
– Rebar corrosion protection, passivation during repair
Treatment of reinforcements with proper materials and agents is one of the defensive layers against corrosion attacks in aggressive environments.
There are many reinforcement treatment methods for instance anticorrosive treatment like epoxy coating and rust converting coatings or cement-based grouts.
Mortars based on polymers in water dispersion, cement binders and corrosion inhibitors, also are available to be applied on reinforcing rods to prevent rust formation.
However, it must be noted that, by using epoxy coatings, if the rebar is not properly cleaned, corrosion can still occur between steel and coating, resulting in new delamination of the concrete protection.
The basic principle of these treatment methods is to prevent the reaction between aggressive substances like chloride ions and steel reinforcement.
Hence, the time needed for reaching such harmful materials to steel bars increases and consequently the durability of the structure is increased substantially.
-Cathodic protection
The cathodic protection method is also commonly used as a repair method. C
-Corrosion inhibitors
The use of corrosion inhibitors is also commonly used as a repair method.
-Concrete repair methods
-Sectional reconstruction
After the removal of the deteriorated concrete, the preparation of the surface of the element, and the treatment and repair of the reinforcement, the concrete section must be rebuilt with concrete or mortar.
To prepare the steel surface for receiving concrete patch material, corrosion and marine growth should be removed, as well as any other action that might be required in each case.
The materials commonly used for sectional reconstruction are listed below:
- Concrete
- Fibre-reinforced concrete using FRP Fluid structural mortar
- Thixotropic structural mortar (this type of mortar could contain corrosion inhibitors and is available on the market in Europe)
- Epoxy resins for underwater application
The following table outlines the main recommendations for the application of the different materials used in the reconstruction of the section.
It must be noted that an economical and common (short-term) approach to the treatment of reinforcement corrosion is to strictly replace the concrete only where cracks or delaminations have occurred.
In general, this approach is not the most appropriate as it fails to address the presence of chlorides and active corrosion of the reinforcement within the concrete surrounding the repaired area, which encourages the continuation of corrosion immediately after the repair.
When performing patch repairs, the introduction of new concrete restores the high pH environment on the reinforcement only in the area of the patch.
Without additional treatment, this can lead to what is called the anodic, ring anode, or halo effect.
The ring anode effect results in accelerated corrosion of the reinforcement surrounding a patch repair due to a greater difference in potential between the steel within the patch and that surrounding the patch, which is in contact with old, lower pH concrete.
The application of SACIs during the repair process, and/or the addition of migrating corrosion inhibitors into the repair mortar can both minimize the ring anode effect by minimizing the difference in the corrosion potentials between patched and unpatched areas.
A sufficient volume of concrete around the reinforcement must be cleaned, checking that the level of chlorides is below the minimum corrosion threshold or, if not, applying a product to protect the reinforcement.
The condition of the reinforcement in areas without apparent damage should also be assessed to check the level of chlorides and the risk of corrosion. Such partial repairs may even aggravate the corrosion in the area adjacent to them by an anodic effect.
-Treatment of cracks
The treatment of cracks in reinforced concrete normally has two objectives:
a. Protection: to prevent the penetration of aggressive agents for concrete or reinforcement.
b. Structural restoration: to restore the initial structural monolithism.
Apart from knowing the objective pursued, the origin of the cracking must be known, as cracks in concrete can have very different causes that must be studied to be able to carry out the appropriate treatment:
- Concrete shrinkage during the plastic phase or hardening
- Overstressing of the structure by load, movement, or impact
- Discontinuities in the material: concreting joints, lack of consolidation/vibration
- Expansion of the reinforcement by oxidation
- Expansion of concrete due to a physicochemical reaction
In some cases, they can be tackled just by protection or injection works, while when the cracks are due to Physico-chemical phenomena, that must be stopped by much more complex repair and waterproofing works against aggressive agents.
In the case of active cracks that are progressing, measures must be taken to stop or control the causes before treating them so that they can be considered passive or dead.
Anyway, as stated above treatments in these cases can be of two types:
When the treatment selected is a surface protection treatment the following criteria can be used to select the most adequate system:
- The overall function of the concrete element or structure
- Mechanical loading of the concrete structure surface
- Possible action of special aggressive media, e.g. sanding salts
- Water vapour permeability or impermeability requirements according to the operation, environment, and other structures
- High diffusion resistance to the penetration of co2 and so2 and other acid-forming gases
- Water tightness requirement
- Requirements for bridging stable or moving cracks
Among the surface treatments, it is worth noting the cracking bandages.
This banding serves to cover stabilized cracks. This technology should be used only when the crack has only an aesthetic meaning and does not reduce the static design function.
The method prevents the intrusion of aggressive media into the structure.
The bandage fabric is glued over the crack so that the crack passes through the fabric strip. After glueing and the fabric is dried, the bandage is provided with a surface treatment or paint.
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