Civil Engineering/rebar corrosion

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Expert: - 6/8/2011


Question
Sir my question is that when a steel is placed in open atmosphere, it gets corrosion,when it reacts with air in the presence of water,but when R.C.C is used , then y the steel is not getting corrosion in spite of water,is present in Concrete and it is quite porous so it can absorb air, it must gets corrosion ? But in actually practice it does not happen??y?

Answer
Hi Umair,

Yes, the rebar is protected from rusting due to the alkaline present in the concrete. You are right that concrete is porous, which is why it is so important to have dense concrete and provide sufficient amount of cover. Over a period of time (many years, depending on quality of concrete, cover and environment/exposure), the concrete cover does get subjected to carbonation, and when this carbonation reaches the rebar, the latter starts to corrode.

Read about it here:

http://www.theconstructioncivil.com/2010/02/concrete-carbonation.html

http://en.wikipedia.org/wiki/Reinforced_concrete  

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Arshad Khan

Expertise

I can answer any questions to do with civil and structural engineering consultancy and construction industry in East Africa and the Middle East, and specifically with the analysis and design of reinforced concrete structures. My particular expertise is in the aseismic design and optimisation of tall buildings.

Experience

Employment history: 36 years in Construction and consultancy in the UK, Kenya, Tanzania, Uganda, Ethiopia, Eritrea, South Africa, Somalia, Zambia, Austria, Bahrain, Kuwait, Doha and the U.A.E.

Organizations
.Fellow of Institution of Structural Engineers (UK) .Fellow of Institution of Civil Engineers(UK) .Member of the Institution of Engineers, Kenya .Registered Engineer, ERB, Kenya .Member of the Architectural Association of Kenya (Engineers Chapter) .Chartered Engineer (UK)

Publications
•1984: International Conference on the Art and Practice of Structural Design, London •1994: 3rd Int. Kerensky Conference in Structural Engineering, Singapore •2008: International Conference on High-Rise Towers, Abu Dhabi

Education/Credentials
BSc, 1st Class Hons, in Building Engineering, University of Bath, UK MSc in Concrete Structures and Technology, University of London. Diploma of Imperial College, UK.

Awards and Honors
•Science Congress Special Award (for 2-seater Hovercraft - 1968) •Institution of Civil Engineers Award for outstanding performance at Bath University (1975) •Concrete Society Postgraduate study Bursary Award (1976) •Consular Representative for British High Commission, Nairobi. (1995 to 1998) •Examiner for Institution of Civil Engineers Professional Interviews, Nairobi. (1997 to 1998) •Branch Representative in Vienna for PI assessment for Inst. of Struct. Engrs. (1999 to date)

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