TG8.1 - Model technical specification for repairs and interventions

Task Group 8.1 is preparing a technical report on the subject of the requirements for a model specification for repairs and interventions with the goal of achieving publication as an fib bulletin. Consideration will be given as to whether this work should later be taken forward as a future Guide to Good Practice.

A first draft report is under development. It has been decided to further develop the approach employed in a Norwegian document containing model technical specifications for a number of rehabilitation methods and align them to the Eurocode convention. In so doing it is envisaged that this report will deliver a model technical specification for a range of rehabilitation methods, each underpinned by their principles. Topics and techniques being considered for inclusion include: Concrete removal, concrete reinstatement, patch repair; surface treatments and coating; cathodic protection; chloride extraction; realkalisation; crack sealing; physical protection / barriers; cladding; inhibitors; electro–osmosis; sacrificial anode (in patch repair); strength; external reinforcement; jacketing; external pre-stressing and replacement and reconstruction of elements. These topics will be preceded by chapters covering the investigation of defective concrete from inspection and testing to monitoring.

Convener
Eduardo Julio

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TG8.4 - Life cycle cost (LCC) - Design life and/or replacement cycle

The work of TG8.4 comprises the preparation of a state-of-the-art report on LCC including the following:

• A flow chart for life cycle cost analyses;
• Examples and/or case studies concerning life cycle cost evaluations of design strategies,including narratives and consequences of the favoured strategy;
• A risk analysis covering costs and benefits;
• Identification of hazard scenarios (weak points);
• Discussion on the value added by the LCC analyses including:
• Design;
• Inspection;
• Testing;
• Monitoring;
• Birth Certificate;
• Inspectability;
• Interventions.
• Reference to relevant fib documents.

Convener
José A. Campos e Matos

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TG8.5 - Durability of post-tensioning systems

Task Group 8.5 (TG8.5) will produce an update of Bulletin 33, “Durability of post-tensioning tendons” (Recommendation published in 2005). This update will include a title change to address the ever changing post-tensioning systems and the advancement of tendon protection systems to include prepackaged grouts and wax systems.

Convener
Brett H. Pielstick

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TG8.7 - Durability design of steel fibre reinforced concrete

Steel fibres are supported in MC2010 but no limitation are placed on their use in regards durability. While it is recognised that Steel Fibre Reinforced Concrete (SFRC) may be highly durable, steel fibres do corrode in some exposures and when corrosion occurs a very small loss of fibre thickness may lead to significant loss of concrete performance. Although structural guidance codes for SFRC exist today, and provide valuable design information and procedures, durable structures may not result in exposure classes XD2, XD2, XS3 and XD3 (DafStb Guideline on Steel fibre reinforced concrete) due to the lack of any durability guidance. At best current codes suggest the need for special provisions for exposure class 3 or higher (RILEM TC 162-TDF) without providing durability design methods.

A literature review of research and use of steel fibres in concrete in regards durability will be the main method of developing and understanding the performance of SFRC under several exposure environments. The group will consider the notion of critical chloride content distributions that support initiation of fibre corrosion, alkalinity reduction due to carbonation and the effect of cracking with regard to fibre corrosion. The aim is to define model equations that also consider reduction of mechanical capacity. This will include a review of loss of concrete performance vs corrosion of fibres considering fibre types, steel types and fibre surface effects due to the manufacturing and installation processess. Also to be reviewed is the effects of mix designs and quality control on corrosion resistance.

Convener
David Gardiner

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TG8.8 - Common approaches

Throughout durability design there are a number of common inputs that should be handled in a consistent approach, e.g. reliability, cracking, exposure risk assessment, verification approaches.

This Task Group will maintain approaches that are consistent across different materials and durability design approaches consistency and provide liaison with other Commissions to ensure consistency across all aspects of Model Code.

The scope:

• This Task Group shall investigate various aspects that have a common impact on modelling of deterioration mechanisms but the TG is not directly involved in the mechanisms or materials.
• Many of these items are fundamental to all aspects of structural design and cannot be
• considered durability issues alone. However, the issues are key to durability design.

Consider “Levels of Approximation” approach in durability design and set out how it is to be incorporated in durability design using the four durability verification approaches, inspection and testing and materials evaluation.

Convener
Steinar Helland

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TG8.9 - Deterioration Mechanisms

TG8.9 will investigate models for the following deterioration processes: Rebar Corrosion Initiation; Rebar Corrosion Propagation; Abrasion, Erosion and Cavitation; Freeze Thaw Attack; Leaching; Water and Water Vapour Migration and Chemical Attack.

In MC2010 and Bulletin 34, some of these mechanisms have only loosely defined models and some have no models. MC2010 also has limited advice for exposure classes, performance tests, deemed to satisfy requirements and avoidance approaches.

None of the deterioration processes have been developed in the fib documents for assessment of existing structures residual life. Design guidance for this phase is a primary objective for TG8.9.

Model Code 2010 notes that a structures robustness (AG10) could be compromised by deterioration but it provides no details of what these failures might be or measures to be taken to avoid them.

Convener
Carmen Andrade

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TG8.10 - Steel reinforcement

The key objective of this task group is to provide clear design procedures for the four durability verification methods in MC2010 for metallic reinforcements in concrete.

Extensive as MC2010 is on durability design, it does not give any guidance on specialty reinforcement noting only, “The following special types of steel that show enhanced corrosion protection properties can be used: galvanized steels, epoxy coated steels and stainless steels”. Use of reinforcement with a high resistance to corrosion has the potential to reduce the impost of reinforcement corrosion by orders of magnitude. With appropriate design procedures, specialty steel can significantly reduce cover requirements leading to increased sustainability. Therefore, it is important to develop clear approaches to durability deign using these materials for MC2020.

Pre-tensioned elements are typically specified to have higher covers and lower crack widths than low carbon steel. It is unclear if the higher covers fully account for the lower critical chloride level, different failure mechanisms and higher reliability requirements based on mode of failure. It is also unclear whether these higher protection requirements are universally required or if they can be relaxed based on the steel specification. This needs to be resolved for MC2020.

Convener
Frank Papworth

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TG8.11 - Testing of new concrete

Durability design of concrete structures may incorporate a number of performance-based requirements depending on the deterioration mechanisms and exposure conditions to consider. While exposure definitions and performance-based requirements are dealt with in other fib TG’s, well documented test procedures for relevant materials properties are needed for support of the durability design and subsequent quality assurance. This includes well-founded probabilistic definitions for those properties.

The objective of Task Group 8.11 is to provide guidance on test methods and corresponding acceptance criteria and testing frequencies concerning quality assurance of concrete production. Furthermore, the objective is to link performance-requirements of concrete as yielded from durability design with the execution. For the latter, all stages of concrete production, i.e. pre-testing in the laboratory, trial testing in laboratory and on-site, and testing of running production are considered.

Convener
Carola Edvardsen

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