Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Corrosion of Reinforcement

[Subject Prev][Subject Next][Thread Prev][Thread Next]
INDIAN ASSOCIATION OF STRUCTURAL ENGINEERS
Gujarat State Centre
Web : www.iaseguj.org     e-mail : secy(--nospam--at)iaseguj.org
******************************************************
Dear All,

Sub : Corrosion of reinforcement

The meeting was arranged at Gujarat State Centre for discussions on usage of
different types of steel in view of the corrosion.
Following shows the report based on presentation made by Shri H. J. Shah.

The report also may be downloaded (Power Point Presentation)
http://www.iaseguj.org/forum/Files/viewthread.php?tid=123&page=1#pid178
 
Kindly go through the report. We are going to arrange very shortly one day
seminar for discussions on these issues. Your views / suggestions /
questions are invited  at : Iaseforum(--nospam--at)iaseguj.org . You may put the same on
the website by going to :

http://www.iaseguj.org/forum/Files/post.php?action="">


Regards,

Bhavin Shah
Hon. Secretary
Indian Association of Structural Engineers, Gujarat State Centre



______________________________________________________________________

REINFORCEMENT
(DIFFERENT TYPES & SELECTION CRITERIA )
( Report based on presentation made by Shri H.J. Shah ( Director, VMS EDS,
Ahmedabad) during meeting of IAStructE, Gujarat State Centre of 30-12-2004)
________________________________________________________________________

Qualities that we look for when we select the type of reinforcement -


§  Strength & other mechanical  properties
§  Serviceability -Corrosion resistance
§  Ductility
§  Bond with concrete
§  Bending capabilities


These requirements vary from project to project basis - depending upon

§          Type of exposure Condition
§          Economy
§          Strength requirements
§          Desired Service life



Types of reinforcements available

********************************************************
 Depending upon strength , chemistry and manufacturing process -
*********************************************************

§ Mild steel - out dated, not in much use
§  HYSD            - in use for most of the RCC works
                        -  problems of corrosion
                         -  higher carbon content means problems of
ductility and weldability

§TMT            - becoming popular
                      - Different process of manufacturing
                      - better ductility/ weldability  ( lower    carbon
content)
                      - corrosion resistnace ( absence of cold twisting
stresses)

§ TMT with additional corrosion resistance
                   -additional elements in chemistry to make it more
corrosion  resistant


 ********************************************
Depending upon protective Coating  -
**********************************************

Galvanised bars

Ø       HZL has made arrangements to make these bars   available in
different parts of the Country  for quantities as small as              50
t. also.
Ø       Indian standard is available for the same - IS  : 2594

Fusion bonded epoxy coated bars

Ø        several reservations regarding its usage because of reduction in
bond strength.
Ø       damage to coating during handling


 Depending upon the project requirements - options are to be weighed
   Type of reinforcement to be selected accordingly.

***********************************************
Issues related to Corrosion Resistance  of   Reinforcement
***********************************************

Ø       Corrosion of reinforcement and its effect on durability of
Structures has of late attracted the attention of Structural
designers.

Ø       This has lead to a trend of specifying reinforcements having special
corrosion resistance.

Ø       However, in most of such cases, the Designer neglects the role
played by good quality concrete in resisting corrosion.

Ø       Specifying special reinforcement leads to a false complacency  -
that provision of such special reinforcement will
compensate for known and avoidable deficiencies of good quality concrete !!

 ***************************************
 Factors affecting Corrosion
****************************************

o        Quality of concrete - porosity - affects the     alkaline
conditions within the  concrete

o        Exposure conditions - marine   environment, chemical attacks,
humidity / moisture

o        Quality of steel -  No steel having carbon is corrosion proof -
depending upon different  characteristics, one steel may             have
more / less corrosion.
o       Detailing of reinforcement - cover, location  of  laps, etc.


As can be seen from above, type/ quality of steel is only a part of the
corrosion problem - and NOT THE ONLY factor affecting corrosion !!!


Ø       A holistic view of the problems related to corrosion in Concrete is
required from a Civil Engineer/ Structural Designer             rather than
his abilities to study and give his opinion about the metallurgy of
Reinforcement !!

Ø       Claims of so called special / corrosion resistant reinforcements are
doubtful - to say the least - and require detailed                 and
unbiased analysis.

Ø       Corrosion resistant properties of CRS bars are found to be less
effective in embedded condition than in 'open to
atmosphere' condition.
Ø       Fusion bonded epoxy coated (FBEC) bars also have problems of bond
strength with concrete.

Ø      Considering the practices followed at construction sites in India, it
is difficult to handle FBEC  at site without damage to         the coating.

*********************************************************
Actual process of corrosion in RCC can be described in two stages -
*********************************************************

            -  Onset of corrosion

            -  Actual corrosion

Ø       It is the first stage i.e onset of corrosion that decides the Life
of a structure

Ø      Ironically, Onset of corrosion in concrete is more dependent on
exposure conditions , quality of concrete and detailing         of
reinforcement - rather than the type of reinforcement !!

Ø      Quality / type of steel comes into picture only in the second stage.

Ø       A structure having good quality concrete is not expected to move in
to the second stage during its design life

Ø       Effectiveness of cover concrete's resistance to penetration is much
more in increasing the life of a Structure - than use             of any
special steel, which comes into action only after the onset of corrosion !!!

 *******************
IMPORTANT :
********************

As per the data available, Improvement factor obtained by use of special
steels is 1.5 to 1.6 in comparison to the use of normal steel.

On the other hand, use of pozzolanic material in right proportion or
increase in concrete cover - can have improvement factor of  8 to 12 as per
the researchers'  data !