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101-0659-01L  Durability and Maintenance of Reinforced Concrete

SemesterAutumn Semester 2016
LecturersB. Elsener, U. Angst
Periodicityyearly recurring course
Language of instructionEnglish

AbstractThe course focuses on durability of RC structures, in particular the corrosion of steel in concrete. The main emphasis lies on understanding the mechanisms, design and execution aspects related to durability of new and existing structures. New methods and materials for preventative measures, condition assessment and repair techniques are treated with lectures and practice related exercises.
ObjectiveUnderstand the mechanism of deterioration of RC structures, in particular reinforcement corrosion.
Know the relevant parameters affecting durability of reinforced concrete, in particular cover depth, concrete quality, moisture, and the ways to control durability
Understand the current approaches for design for durability (exposure classes, prescriptive) and be aware of their limitations
Know the future performance-based models for durability design and the difficulties in defining input parameters (such as critical chloride content).
Know and understand different ways to improve durability of RC structures (e.g. stainless steel reinforcement)
Know the particular problems with post-tensioned structures and ways to overcome them (electrically isolated tendons).
Know and understand the non-destructive methods for inspection and condition assessment (especially half-cell potential mapping) and be aware of the limitations
Know and understand repair methods such as conventional repair, electrochemical methods (in particular cathodic protection)
Be aware of differences in performance of the new blended cements (especially CEM II with limestone) respect to the traditional Portland cement and the possible future problems for durability.
ContentReinforced concrete combines the good compressive strength of concrete with the high tensile strength of steel and has proven to be successful in terms of structural performance and durability. However, there are instances of premature failure of reinforced concrete and prestressed concrete components due to corrosion of the reinforcing steel with very high economic implications of such damage. This course focuses on the chloride and carbonation induced corrosion of steel in concrete, presenting transport mechanisms and electrochemical concepts. The main emphasis lies on design and execution aspects related to durability of new and existing structures. New methods and materials for preventative measures, condition assessment and repair techniques are discussed. The course is a point of reference for engineers and materials scientists involved in research and practice of corrosion protection, rehabilitation and maintenance of reinforced concrete structures and components.

Content of the course in detail:

Lecture 1
Administrative issues, literature, what do students expect to learn? Introduction (economic relevance of durability, transition from building to maintenance). Fundamentals of corrosion and durability / Passivity and pitting corrosion

Lecture 2
Reinforced concrete / Corrosion protection / Degradation mechanism corrosion (chlorides/carbonation) / electrochemical mechanism / controlling parameters / cracks and spalling on surface, danger of localized corrosion

Lecture 3
Other degradation mechanisms: sulphate attack, ASR, frost attack
Various examples, frequency of occurrence of individual deterioration mechanisms

Lecture 4
Service life: initiation stage & propagation stage. Durability design: prescriptive approach, constructive detailing, importance of moisture for almost all degradation mechanisms. Performance based approach, simple diffusion approach for chloride ingress, Critical chloride content (influencing parameters)

Lecture 5
Stainless steel as reinforcing steel for concrete / different types of stainless steels / mechanical properties / corrosion resistance, passivity / coupling with black reinforcing steel / examples of application / life-cycle-costs

Lecture 6
Inspection and condition assessment I: visual inspection / destructive testing (chloride profiles, carbonation depth, thin section analysis, etc.)

Lectures 7
Inspection and condition assessment II: non-destructive testing (potential mapping, cover depth measurement, resistivity measurement). Potential mapping: measurement principle / effect of carbonated cover zone / effect of moisture / examples

Lecture 8
Post-tensioned structures / problem with existing structures: no NDT method / approach for protection (multiple barrier) / new systems with polymer ducts / electrically isolated tendons / fib guidelines / Swiss guideline / Monitoring techniques / Applications

Lecture 9
Repair methods I: conventional repair / coatings / inhibitors / limitations

Lecture 10
Repair methods II: electrochemical repair methods (ECR, ER, CP) / principles / electrochemical chloride removal (theory and examples) / electrochemical realkalization (theory and examples) / when can these methods be applied ? / cost aspects

Lecture 11
Repair methods III: cathodic protection (theory, technical solutions, anode systems, etc and examples). Monitoring of CP.

Lecture 12
New cements, issue of CO2 reduction. Effects of fly ash, slag, limestone on workability, diffusion coefficient, resistivity, pH (including a discussion of the pozzolanic reaction and it's consequences with respect to pH buffering Portlandite reserve). Discuss products on the Swiss market.

Lecture 13
Summary of most important points of this course given by the students. Open discussion about durability design, use of new cements, new materials and repair methods. Expected consequences for practice ? Course evaluation and time for asking questions.
Lecture notesThe course is based on the book
Corrosion of steel in concrete - prevention diagnosis repair (WILEY 2013) by L. Bertolini, B. Elsener, P. Pedeferri and R. Polder)
Slides of the lectures will be distributed in advance
Special hand outs and reprints for particular topics will be distributed
LiteratureA first overview can be found in: B. Elsener, Corrosion of Steel in Concrete, in "Corrosion and Environmental Degradation", ed. M. Schütze, WILEY VCH (2000) Vol.2 pp. 391 - 431

Backbone of the course: Corrosion of Steel in Concrete - Prevention diagnosis repair, L. Bertolini, B. Elsener, P. Pedeferri, R. Polder, WILEY VCH 2nd edition (2013)
Prerequisites / NoticeStudents are encouraged to actively participate during the lectures. Students are expected to work on all the exercises (four). For one exercise a detailed written solution of the exercise has to be delivered (after the discussion).

Students should have passed the exams on Werkstoffe I and II.