CORROSION RISK ASSESSMENT OF HIGH RISE BUILDINGS
Routine corrosion risk assessments performed by NACE certified corrosion experts are an invaluable asset to owners of aging concrete structures. Not only do they identify corrosion risk, but they can also quantify the severity of corrosion and offer remaining life estimates and corrosion mitigation strategies to prolong the life of these structures at much lower cost than total replacement.
Recommendations for Building Inspection and Condition Assessment
Corrosion mapping should be performed for condominium tower certifications in order to look at the thickness of the concrete around the rebars and load bearing members.
The on-site inspection and condition assessment includes a detailed investigation of all areas of the reinforced concrete structure and may require several hours to several days, depending upon the size of the structure. The inspection and condition assessment of the aging structures in ISO 12944-2: 2017 C5 coastal marine environments such as found in this area should include the following:
- Visual inspection.
- Petrographic analysis – to determine concrete condition.
- Sound test to detect delamination.
- Phenolphthalein – to determine pH and carbonation.
- Chloride content – to identify chloride corrosion risk.
- Linear polarization corrosion rate – to determine direct exposure corrosion rate.
- Continuity Test – to determine continuity of rebars.
- Stray current survey – to determine stray current corrosion risks.
- Resistivity – to determine resistivity and corrosion risk of concrete.
- Corrosion mapping by electrochemical and non-destructive testing (NDT).
Concrete core samples should be retrieved from corroded areas (identified in corrosion mapping) for petrographic analysis to determine if the concrete is structurally sound or requires repair or replacement.
Based upon on-site surveying and laboratory analysis result, and employing sound materials and structural engineering principles, determination of extent of damage and remaining service life are undertaken. Critical questions to be answered here are the following.
- Is the reinforced concrete structurally sound?
- Does the reinforced concrete require repair or replacement?
Consideration should be given to materials selection for repair and/or replacement of the components of the reinforced concrete structure. In addition to concrete repair materials, this will include alternative materials to non-concrete auxiliary materials and maintenance coatings which may be applied to mitigate corrosion.
Specifically, it is imperative that future regulations require that both corrosion engineering experts, in addition to structural engineers, take part in building inspections to provide detailed reporting and an exact quantification of corrosion risk in their condition assessments. Condominium associations are also now on notice that they need to take immediate action with respect to corrosion assessment.
Identifying corrosion is only the beginning
determining the severity of corrosion and immediately responding can prevent disasters and save hundreds, or even thousands of lives
Engineering Solution: Coatings and Cathodic Protection
If accelerated corrosion is captured early on coating application and cathodic protection can mitigate the accelerated corrosion with low costs
Consideration should be given to coatings for repair prior to replacement of the components of the reinforced concrete structure. In addition to concrete repair materials, this will include alternative materials to non-concrete auxiliary materials and maintenance coatings which may be applied to mitigate corrosion.
Cathodic protection is a method wherein a sufficient amount of electric DC current is continuously supplied to a submerged or buried metallic structure to mitigate, slow down or temporarily stop the natural corrosion processes from occurring. The DC current corrodes a sacrificial anode when it is connected to a structure to be protected. There are two methods for supplying DC to cathodically protect a structure. They are the following:
- Galvanic or sacrificial anode cathodic protection system (SACP).
- Impressed current cathodic protection system (ICCP).