Reinforced Concrete Structures: Condition Surveying, Rehabilitation and Establishment of Corrosion Protection Measures
MATCO has extensive experience as corrosion consultants for reinforced concrete structures. When approaching the problem of a deteriorating reinforced concrete structure, it is necessary to visually observe and make measurements of the corrosion activity, geometry, concrete and steel materials, associated construction materials, etc., in addition to the state of corrosion which the structure has already suffered. After such observations and measurements, assessment of potential rehabilitation techniques and, as required, corrosion analysis, MATCO can recommend measures and materials to consider which will help to mitigate further corrosion deterioration of the structure for its expected life using cathodic protection and/or coatings. The methodology employed is described below.
On-Site Condition Evaluation Survey:
The on-site condition evaluation survey 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. Several analysis techniques are implemented during this on-site evaluation survey, including but not limited to the following.
- Visual examination - to identify surface defects.
- Petrography - to determine concrete condition.
- Hammer/chain- to detect delaminations.
- Phenolphthalein - to determine carbonation depth.
- Chloride content - to identify chloride corrosion.
- Half cell potential mapping - to determine corrosion risk (map corrosion hot areas).
- Linear polarization - to determine corrosion rate.
- Continuity - to determine continuity/connectedness of rebar.
- Stray current identification - to determine stray current corrosion risk.
- Resistivity - to determine concrete resistivity and corrosion risk.
Concrete core samples are marked and retrieved for petrographic analysis. At least one will be from an area of rusting of the rebar reinforcement or concrete. At least one will be from an undamaged and uncorroded area of the concrete structure.
Laboratory Petrographic and Corrosion Analysis:
Laboratory analysis of petrographic and corrosion product samples are conducted by experienced petrographic and corrosion specialists. Petrographic evaluation will determine aggregate type and size, depth of carbonation, air void content and mode of deterioration if present. These will determine integrity of concrete and the best means of rehabilitation and corrosion protection.
Determination of Extent of Damage and Remaining Service Life:
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?
Materials Selection and Coatings Application:
Consideration is 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.
Assessment of Repair and Cathodic Protection Systems:
Assessment is undertaken of suitable repair systems, and of suitable cathodic protection systems for the reinforced concrete structure. Cathodic protection (CP) is a method wherein a sufficient amount of electric or impressed current (DC) is continuously supplied to a submerged or buried metallic structure to mitigate, slow down or stop altogether the natural corrosion processes from occurring. This technique is routinely used in service of submerged units or structures in brine and seawater environments.
The galvanic anode cathodic protection system generates DC as a result of the natural electrical potential difference (electrochemical reaction) between the metal to be protected (cathode) and another metal to be sacrificed (anode). The sacrificing metals such as zinc (Zn) or aluminum (Al) all have a lower more negative electrical potential. The current output of this system is affected by factors such as the driving voltage difference between the anode and the cathode, the resistivity of the electrolyte (concrete), pH, and salinity.