Definitions
1. Corrosion
Process of degradation of the concrete reinforcement, when the natural passive oxide protecting layer, provided by the concrete cover, gradually fails to protect it, either due to carbonation or due to chloride ions ( Cl-) infiltration.
2. Crack
A complete or incomplete separation of concrete into two or more parts, produced by breaking or fracturing.
3. Carbonation
Process of degradation that occurs due to the conversion of calcium ions in hardened cementitious materials to calcium carbonate by reaction with atmospheric carbon dioxide.
4. Chloride ions
Anions of the commonly used de-icing salts and the accelerating admixtures calcium chloride and sodium chloride.
The chloride content is the total amount of chloride ions present in concrete or mortar, and it can be measured with a rapid chloride test – a method for on-site determinations of d-soluble and water-soluble chloride ion contents of concrete powder samples with proprietary chloride extraction liquids and calibrated instrument probes.
Furthermore, the chloride threshold – usually assumed to be 0.6 to 0.8 kg/m3 or approximately 0.4% in reinforced concrete and 0.2% in prestressed concrete by weight percent of cement – is the amount of chloride required to initiate steel corrosion in reinforced concrete under a given set of exposure conditions; commonly expressed in the percent of chloride ion by mass of cement.
5. Degradation
A detrimental change in the physical and/or chemical properties of a material.
6. Diagnosis
The technical study aimed to verify that the stability and mechanical resistance of the construction meets the safety requirements established in the project – by the current regulations or those established with the client.
If not, such a diagnosis should indicate the structural failures or degradation mechanisms that are causing the structure to fail and should include – if technically possible and/ or financially achievable – the needed improvement to comply with these, before carrying out any work.
7. Inspection (visual inspection)
An evaluation procedure that involves the observation, classification, and documentation of concrete deterioration on exposed surfaces; is usually the first step in evaluating concrete structures.
8. Individual methods of detection of reinforcement corrosion
- Non-destructive methods (NDT): ultrasound, radiography, thermography.
- Analytical chemical methods: pH measurement, dissolved gas concentration measurement (O2, CO2, H2S), metal ion concentration (Fe2 +, Fe3 +).
- Electrochemical methods: corrosion potential, resistivity and corrosion rate.
- Electrochemistry of liquid solutions: potential method – potentiodynamic, potentiostatic, impedance method.
- Corrosion measurement: weight-loss – corrosion coupons, electrical resistance, linear polarization, galvanic current, half-cell method.
9. Maintenance
Taking periodic actions that will delay damage or deterioration or both.
10. Monitoring
Measures aimed to check the behaviour of a structure over a period in an up-to-date manner, against a given original or actual set of principles or standards.
11. Pathology
The study of structure defects, structure decay and structure performance failure to assist in the formulation of suitable remedial and management solutions.
The discipline looks at the interrelationships between the physical structure, its use, and the environment to gain valuable insights into why structures fail.
12. pH
A measure of the acidity or alkalinity of a solution, with neutrality represented by a value of 7, with increasing acidity represented by increasingly smaller values, and with increasing alkalinity represented by increasingly larger values.
13. Preservation
The process of maintaining a structure in its present condition and arresting further deterioration.
14. Protection
The process of maintaining a concrete structure in its present or restored condition by minimizing the potential for deterioration or damage in the future.
15. Rehabilitation
The process of repairing or modifying a structure to a desired useful condition.
16. Reinforcement
On one hand, bars, wires, strands, fibres, or other slender members are embedded in concrete primarily to improve tensile strength.
On the other hand, fibres, fillers, and NSM – near-surface mounted composites (FRP, Fibrereinforced polymers) or steel strips or rods – for additional flexural strengthening.
17. Repair
To replace or correct deteriorated, damaged, or faulty materials, components, or elements of a structure.
18. In situ testing
The contractor and the controlling body will test the concrete to be repaired to determine if the characteristics given at the beginning are identical to those expected after it has been repaired, not only on stability and mechanical resistance but also on the durability of the repair and of the surrounding areas.
19. Internal controlling plan
An important document that should be prepared in advance of the start of the repair and that mentions all elements of the controlling actions that the contractor should perform, regarding the employed technicians onsite, their competencies, the chosen and employed repair products with the batch numbers, the weather situation during the repair period, the in-situ testing program, the chosen pause or standstill point and at the end.
At the end of the document, after carrying out all steps stated, there should be a report stating that either the repair was done by the given specifications, or that the known non-conformities were corrected, with the approval reasoning why, as well as adding instructions for additional surveys and maintenance.
20. Pause or standstill point
Moments during the repair when the contractor formally acts that the work has been accomplished on a section of the site (cleaning and preparing before the application of the mortar, or when the repair mortar is fully applied), and will perform a series of in situ tests on that section, which the owner or his representative can assist.
The repair work in that section can only be pursued if the test results are within specifications.
21. Repair contracting – Certification level
Similar to Belgian certification, in Europe, a certification program with an ongoing inspection by a neutral body should be implemented for companies involved in concrete repair, with minimum competencies and equipment, on the contractor as an organization, his middle management, and the applicators, responsible for these repairs.
Depending on how detailed a diagnostic report is done and the complexity of the chosen repair system, less or more freedom may be given by the owner to the contractor to fill in his understanding, on this, depending on his competencies, therefore we do propose the following split:
- Level A Contractor – Executes a repair job, based on a complete diagnostic, excluding all not involved pathologies with a full description of the repair job, the used system, and materials.
- Level B Contractor – Executes a repair job, based on a more limited diagnostic, given more liberty to choose the best-adapted repair system/products to fulfil the expectations of the owner.
22. Quality control repaired products (EN1504/3 – Z.A.2.1.)
Since EN1504/3 only requires an initial product identification and certification 2+ by an approved body, no assessment of production is done; this conflicts with the requirement of the local authorities, who do require an assessment of each product on site.
A more severe system should be implemented, including production.
23. Repair applicators
To establish the competency of the applicator, a theoretical and practical evaluation should be performed, formalized by an attestation according to the following sections:
A. Manual repair of carbonated concrete
B. Mechanical repair of carbonated concrete
C. Manual repair of chloride-infected concrete
D. Electro-mechanical repair of chloride infected concrete
E. Reinforcement – NSM- surface mounted composites)
24. Repair systems
The materials and techniques used for repair.
25. Restoration
The process of re-establishing the materials, form, and appearance of a structure to those of a particular era of the structure.
26. Test
A chemical or physical evaluation of material, structural element, or structure by experiment, observation, or inspection.
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