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Crucial issues in respect of durability of Concrete
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This forum is locked: you cannot post, reply to, or edit topics.This topic is locked: you cannot edit posts or make replies. Thank Post    www.sefindia.org Forum Index -> E-conference on Durability of Concrete - Feb 27 to March 11 - 2012
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Dr. N. Subramanian
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Joined: 21 Feb 2008
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Location: Gaithersburg, MD, U.S.A.

PostPosted: Thu Mar 01, 2012 5:37 pm    Post subject: Re: Implementation of quality standards and practices must. Reply with quote

Dear Dr Ashwath,

Thank you for your posting and for your concerns reg. the quality of concrete used in India. As you say in concrete construction Quality should be given priority. As pointed by you the Govt. should take the initiative to train Masons and others.

Yes. Our Er Kulkarni's efforts in bringing quality to RMC plants should be appreciated- especially after learning the exp. of Er Alpa and others in this forum.

The link you have given for Part 1 of the QC Manual is not working. It may be got from http://www.rmcmaindia.org/quality_policy.html#rmcma

Regards
NS
aswathmu wrote:
Recently Association of Consulting Civil Engineers (India) Bangalore Centre conducted a three day National Seminar and Exhibition on Recent Developments in Repair, Rehabilitation and Retrofitting.  Eminent consultants shared their experiences with the civil engineering community. It was very clear that due to fast track construction, new materials, design deficiencies, negligence, unskilled manpower, lack of will power to implement quality construction practices and standards, many of the structures have durability issues. The problems connected with durability of structures are increasing as we claim that we are progressing. In this context the efforts by SEFI, having an e-conference on ‘Crucial issues in respect of durability of Concrete’ moderated by  Dr N Subramanian and Mr. Vijay Kulkarni will be very useful in understanding the behaviour of concrete and to handle concrete in a better way.

Civil construction works are visible process and looks simple. We see concrete making materials viz., cement, sand, aggregates and water everywhere unlike IC’s, Chips, Software codes. Everyone, the designers, architects, constructors, contractors, the field workers etc. including the clients feel and think that they know everything about these materials and concrete. Many a times we fail to give importance for the selection of right ingredient materials and preparation of concrete. Concrete Technology is one of the major subjects for all civil engineering students in all the engineering colleges but the way the subject is thought needs focus on the quality issues of concrete and it is very important to understand the behaviour of concrete during its service life.

We keep hearing about training of the work force for good construction including the engineers in various occasions. We do have bodies like Construction Industry Development Council (CIDC) to provide the impetus and the organizational infrastructure to raise quality levels across the industry. One of the focus areas is training manpower at skilled worker level and construction management level but the concerted efforts in this direction are missing. However the efforts of such organizations including BMTPC, ICI, ACCE (I), INSTRUCT etc should be appreciated.

The way concrete is prepared has changed from hand mix to Ready Mixed Concrete. Many projects have their own batching plants. In the last few years I have interacted with many civil and structural engineering consultants, visited many RMC plants and interacted with the RMC plant workforce only to get surprises. Be it, Concrete ingredient material selection, testing of materials, preparation of concrete, transportation, handling the delays, use of admixtures and placing of concrete, all are taken very casually. In my view this casual attitude is the main cause for quality and durability issues of concrete.

I would like to stress here on quality of Ready Mixed Concrete since use of RMC has increased many folds. The number of RMC plants (other than site based batching/mixing plants) are increasing and the kind of infrastructure, trained human resource and quality systems in many of these plants are not up to the mark and there is no regulatory body to check all this. Many of these plants are surviving on the ignorance and the casual attitudes of the stake holders towards concrete.

I must congratulate the efforts made by associations like Ready-Mixed Concrete Manufacturers Association (RMCMA) who have taken enormous efforts in evolving a quality scheme* for RMC. The scheme follows the best practices from advanced countries, with Indian character and is based on the different provisions contained in the relevant specifications of BIS. The efforts of Mr. Kulkarni in this direction will go a long way in improving the quality and durability of concrete.
*( Download the Quality Manuals from :
QC Manual Part I: http://www.rmcmaindia.org/CHECK%20LIST.pdf  
QC Manual Part II: http://www.rmcmaindia.org/Guidelines%20Final.pdf

Some state governments also have task forces for quality in construction but struggling to implement the quality standards.  I fail to understand why such task forces and authorities like PWD are not making it mandatory to follow the standards and quality principles. If we are serious to have durable structures, implementation of the quality standards at all levels must be made mandatory. There are no shortcuts.



Dr.Aswath M.U.
Immediate Past Secretary General
Association of Consulting Civil Engineers (I)
Editor-in -Chief: ACCE (I) Bulletin
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Professor and Head, PG and Research studies-Civil Engineering
Training & Placement Officer
Bangalore Institute of Technology
K.R.Road, V.V.Puram, Bangalore-560 004
Ph: 080-22422741(direct), 080-26613237(O)
Fax: 080-26526796, 080-22422741
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aswathmu
SEFI Member
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Joined: 01 Sep 2009
Posts: 2

PostPosted: Fri Mar 02, 2012 3:30 am    Post subject: Re: Implementation of quality standards and practices must. Reply with quote

Dear Dr. N.S. Sir,

I am trying to enforce the quality standards through the Govt. Departments in the State of Karnataka. Looking support from all the Consultants and civil engineering community.

The link for Quality manual Part-I is corrected.

Dr N. Subramanian wrote:
Dear Dr Ashwath,

Thank you for your posting and for your concerns reg. the quality of concrete used in India. As you say in concrete construction Quality should be given priority. As pointed by you the Govt. should take the initiative to train Masons and others.

Yes. Our Er Kulkarni's efforts in bringing quality to RMC plants should be appreciated- especially after learning the exp. of Er Alpa and others in this forum.

The link you have given for Part 1 of the QC Manual is not working. It may be got from http://www.rmcmaindia.org/quality_policy.html#rmcma

Regards
NS
aswathmu wrote:
Recently Association of Consulting Civil Engineers (India) Bangalore Centre conducted a three day National Seminar and Exhibition on Recent Developments in Repair, Rehabilitation and Retrofitting.  Eminent consultants shared their experiences with the civil engineering community. It was very clear that due to fast track construction, new materials, design deficiencies, negligence, unskilled manpower, lack of will power to implement quality construction practices and standards, many of the structures have durability issues. The problems connected with durability of structures are increasing as we claim that we are progressing. In this context the efforts by SEFI, having an e-conference on ‘Crucial issues in respect of durability of Concrete’ moderated by  Dr N Subramanian and Mr. Vijay Kulkarni will be very useful in understanding the behaviour of concrete and to handle concrete in a better way.

Civil construction works are visible process and looks simple. We see concrete making materials viz., cement, sand, aggregates and water everywhere unlike IC’s, Chips, Software codes. Everyone, the designers, architects, constructors, contractors, the field workers etc. including the clients feel and think that they know everything about these materials and concrete. Many a times we fail to give importance for the selection of right ingredient materials and preparation of concrete. Concrete Technology is one of the major subjects for all civil engineering students in all the engineering colleges but the way the subject is thought needs focus on the quality issues of concrete and it is very important to understand the behaviour of concrete during its service life.

We keep hearing about training of the work force for good construction including the engineers in various occasions. We do have bodies like Construction Industry Development Council (CIDC) to provide the impetus and the organizational infrastructure to raise quality levels across the industry. One of the focus areas is training manpower at skilled worker level and construction management level but the concerted efforts in this direction are missing. However the efforts of such organizations including BMTPC, ICI, ACCE (I), INSTRUCT etc should be appreciated.

The way concrete is prepared has changed from hand mix to Ready Mixed Concrete. Many projects have their own batching plants. In the last few years I have interacted with many civil and structural engineering consultants, visited many RMC plants and interacted with the RMC plant workforce only to get surprises. Be it, Concrete ingredient material selection, testing of materials, preparation of concrete, transportation, handling the delays, use of admixtures and placing of concrete, all are taken very casually. In my view this casual attitude is the main cause for quality and durability issues of concrete.

I would like to stress here on quality of Ready Mixed Concrete since use of RMC has increased many folds. The number of RMC plants (other than site based batching/mixing plants) are increasing and the kind of infrastructure, trained human resource and quality systems in many of these plants are not up to the mark and there is no regulatory body to check all this. Many of these plants are surviving on the ignorance and the casual attitudes of the stake holders towards concrete.

I must congratulate the efforts made by associations like Ready-Mixed Concrete Manufacturers Association (RMCMA) who have taken enormous efforts in evolving a quality scheme* for RMC. The scheme follows the best practices from advanced countries, with Indian character and is based on the different provisions contained in the relevant specifications of BIS. The efforts of Mr. Kulkarni in this direction will go a long way in improving the quality and durability of concrete.
*( Download the Quality Manuals from :
QC Manual Part I: http://www.rmcmaindia.org/CHECK%20LIST.pdf  
QC Manual Part II: http://www.rmcmaindia.org/Guidelines%20Final.pdf

Some state governments also have task forces for quality in construction but struggling to implement the quality standards.  I fail to understand why such task forces and authorities like PWD are not making it mandatory to follow the standards and quality principles. If we are serious to have durable structures, implementation of the quality standards at all levels must be made mandatory. There are no shortcuts.



Dr.Aswath M.U.
Immediate Past Secretary General
Association of Consulting Civil Engineers (I)
Editor-in -Chief: ACCE (I) Bulletin
--------------------------------------------------------------------------
Professor and Head, PG and Research studies-Civil Engineering
Training & Placement Officer
Bangalore Institute of Technology
K.R.Road, V.V.Puram, Bangalore-560 004
Ph: 080-22422741(direct), 080-26613237(O)
Fax: 080-26526796, 080-22422741
Mobile: 98452-62955
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N. Prabhakar
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Joined: 25 Apr 2009
Posts: 445

PostPosted: Fri Mar 02, 2012 2:29 pm    Post subject: E-Conference on Durability of Concrete Reply with quote

Dear Sefians,

I would like to congratulate organisers SEFI in bringing out this conference on a very important topic concerning durability of concrete structures.  The excellent introductory notes by Mr. V.R. Kulkarni and Dr. N. Subramanian have set the proper tone for the deliberations of this conference.  I have few comments and suggestions to make on the topic which are written hereunder:
1.  Corrosion of reinforcement

a)  It is one of the main reasons to cause cracking and spalling of concrete which affects durability of concrete very much in the long run.  A good quality and dense concrete is the pre-requisite against reinforcement corrosion,  but the quality of steel rebars itself has a significant influence on it. It is well established that mild steel (MS) bars are more corrosion resistant as compared to cold-twisted deformed (CTD) bars or TMT bars, as the level of induced stresses in CTD and TMT bars are much higher than those in MS bars which enhances the potential of initiating corrosion.  Besides, CTD and TMT bars have inherent deficiency in its manufacturing process to slow down initiation of corrosion in bars. In CTD bars, a part of the residual strain is withheld which initiates the corrosion faster.
b)  Many have mentioned in this forum about how the older structures have stood test of time without having any durability problem.  Prior to the introduction of  high strength CTD bars in India in 1968, only mild stars were used as reinforcement. The concrete mix used then were usually 1:2:4 (equivalent to M20) for most structures, and 1:1½:3 (≈ M25) for more important or special structures.  The difference between then and now is the use of CTD and TMT bars replacing MS bars, and more aggressive environment we are living in now. Although higher concrete grades are being used now for important structures, the durability problem is still there in some of them because of the poor quality construction practices combined with the use of CTD and TMT bars.
c)  In the case of liquid-retaining structures where durability is of utmost importance, the design practice by working stress method considers lower permissible stress in reinforcement combined with limitation on permissible tensile stress in concrete as an uncracked section.  The limit-state method for design of these structures has stringent requirement on permissible crack width under service load condition.
d)  Considering the above phenomena, in severe environmental exposure conditions and/or in situations where the quality of concrete is not guaranteed due to lack of quality construction and supervision, it would be prudent to use only MS bars instead of CTD and TMT bars. Although this may not be an economical proposition initially, but in the long run it would pay off.  For any structural engineer to adopt this proposition in practice, there should be necessary support by way of codal provisions.  
e)  Similarly, for stirrups in beams and links in columns which form the outermost reinforcement and closer to the outer face of concrete, only MS bars are to be used to safeguard against early corrosion.  If the design demands, closer spacing of stirrups and links can be provided.

2.Cover

a)  There is a tendency to specify too much cover to reinforcement in the name of durability.  Any cover more than 75mm requires extra nominal reinforcement by way of mesh reinforcement with about 50mm cover near the surface.  These are required, particularly in structural elements having large surface area such as floor and ground slabs, retaining and shear walls, to avoid surface cracks due to initial thermal and shrinkage effects.  Such provisions are there in some of the international codes, and our codes should also incorporate such provisions.
b)  The concrete grade of concrete blocks used to provide the necessary cover should be of the same grade as that of the main concrete of the structural member.  If the concrete blocks are of poor quality, they would become weak spots for early deterioration.  A better proposition is to use PVC cover blocks which do not rust thus eliminating blemishes on the concrete surface.

3.Slip form construction

a)  Slip-form method of construction is very much used for the construction shafts like structures, like tall chimneys, shafts of over-head tanks, bridge piers, cable-stayed bridge pylons, shear walls for multi-storied buildings etc., as it has the advantage of speedy construction.  The use of ready-mixed concrete (RMC) is also in vogue these days for this type of construction.  The speed of slip-form construction varies in the range of 2.5m to 5m height per day.  When the concrete is mixed at site, retarders are usually added as admixtures to concrete to slow down the setting time of concrete, after doing initial trials to suit the volume of concrete and height at which it is to be placed.  While using RMC for such constructions, extra care is required as there have been cases of construction failures due to formation of cold separation joints in the shaft leading to transfer of whole load on the reinforcement alone and eventual failure.
I trust you will find the above observations useful.
With best wishes,
Yours truly,
N. Prabhakar
Chartered Structural Engineer
Vasai (E)
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