ABSTRACT
Corrosion of steel in concrete is considered to be the most common cause of concrete deterioration affecting the lifetime of transportation structures. It is mainly a result of chloride ingress from de-icing salts or marine environments but carbonation of the concrete cover zone can also initiate corrosion.
The remediation of corrosion affected structures can be carried out using conventional and electrochemical concrete repair techniques. Electrochemical techniques, in particular cathodic protection (CP), are established and sustainable solutions which can be used to control on-going corrosion. Cathodic prevention is achieved by using an essentially optimised CP system which prevents the onset of corrosion in reinforced concrete elements. The main benefit of electrochemical techniques is that chloride contaminated or carbonate concrete can remain in place and ongoing chloride penetration can be tolerated whereas conventional concrete repair techniques require the removal of contaminated concrete. The electrochemical side effects of cathodic protection systems allow to further optimize such systems to reduce the water content (electro-osmosis), extract chlorides (chloride extraction) and to realkalise the carbonated concrete.
Electrochemical repair techniques have advantages and disadvantages and the suitability of each method should be assessed for each individual structure under consideration of being repaired. The repair methods should be selected based on the following parameters:
– The intended service life extension;
– Access restrictions;
– Maintenance/monitoring requirements and their budget;
– Structural restrictions – dead load and headroom;
– Robustness and vulnerability to theft and damage;
– Noise, dust and environmental impact;
– Time and budget restrictions.
Structures may also be repaired using a combination of several methods. In the first instance conventional repairs are usually carried out to prevent health and safety risks to the public by removing all delaminated/spalled concrete. This first intervention allows the maintainer to initiate root cause inspections and then specify the required design life extensions which may be achieved by the following methods:
– Patch repairs: quick repair strategy but short term solution of ˂5 years.
– Inhibitors: Simple application but limitations with regards to the maximum allowable chloride content ˂1.0% Cl− by mass of cement; short to medium term solution ˂10 years.
– Galvanic cathodic protection: Flexible systems without power source and minimal maintenance requirements but only provide a medium term solution of up to 15 years.
– Impressed current cathodic protection (ICCP): systems may comprise mesh and overlay, discrete anodes, cassettes and conductive coatings. The design life is generally in excess of 25 years and therefore provides a long term solution. ICCP however require a power source and therefore annual monitoring and maintenance.
– Electro-osmosis: is rarely used.
– Realkalisation and chloride extraction: application time is difficult to define and therefore the cost estimation.
There are a variety of electrochemical repair solutions which can be implemented to significantly extend the service life of transport structures. The options discussed in this paper are all appropriate for specific requirements but every structure and each individual element need to be assessed taking all restrictions which may be imposed by the structure into account.
