Joined: 26 Jan 2003
|Posted: Sat Mar 10, 2012 5:56 pm Post subject: Summary #7 of E-Conf -Days 11 & 12
|Engineers - - - - - - have a Duty towards Durable construction
Conference is approaching towards final days and for last 12 days we all have made
conscious efforts while discussing, expressing, uploading the viewpoints /advice
favoring concrete durability but real test comes on ground and we all ,participating
the conference need to have a sincere and responsible duty towards practical
implementation of ideas, thoughts gathered in the ongoing e- conference.Those
associated with research may develop newer materials , techniques which encourage
durability while Academicians have a potent role in Training . Engineers on execution
side have moral responsibility for not succumbing to the pressures of any kind, rather
impressing upon better ideas gained herein. Engineers of design & planning may
also help in framing such specifications and procedures which can assure concrete
durability through stringent QC checks.
And, as noted a top , All engineers have a moral responsibility towards durable
constructions and shall also arrange training to other technocrats/ manpower
working under them to achieve the objective.
Postings on Days 11 & 12 - - - - - - -
Er Alok Bhowmick feels that Durable concrete is a team work of Engineer, Contractor,
sub-contractor ,Producers , consultants and above all Owners. Any one failing may
lead to loss of durability.
Er Basant Kukreti agrees to Er Jayant Kulkarni in respect of cover stating that
situation at site is pathetic since nobody reads voluminous documents and even rings
are not fabricated in proper way.Tender documents are prepared in hurry.
Er Rajnikant states that corrosion of reinf is major threat to concrete durability. Fusion
bonded epoxy treatment is generally practiced in Mumbai but , Is there any other treatment
for similar exposure conditions world wide. Er SR Karade responded stating that cathodic
prevention/protection can be applied for long life but costly method. Surface coating of
concrete , Use of inhibitors etc are cost -effective but short term measures.
Er Gautam Chattopadhyay states that ASCE members opposed to the use of FBEC
reinforcements since such reinf has shown REDUCED bond.They are rather opined for
using higher strength of conc , more cover and admixtures.
Er Suraj Singh commenting on protection of concrete states that concrete requires protection
to both ,below ground and above ground.Below ground protection can be provided by
bituminous membranes (waterproofing) to protect from chemicals in soils . Above ground
protections are from weather conditions and can be in form of coatings like Foscrock, Sika ,
MBT/Degusaa but surface must be well prepared . Cathodic protection is also applicable
but its scope is limited to major facilities and where it is included ,steel re-bars cannot be
epoxy - coated.
Er S Kalirajan discussed about manufactured sand since river sand is becoming rare
commodity and wants to know long term durability performance of conc using M /sand.
Using it in SCC requires higher mixing time as per his experience. Er BV Harsoda
gave very appropriate reference material for M/sand in form of 'Guide to the
specifications and maintenance of manufactured sand ' by cement conc agrregate
Australia.In another post Er BV Harsoda provided few more information and links
to M/sand . Appreciate his efforts for knowledge sharing .
Dr N Subramanian , conf - Moderator ,responded to posting by Madam Alpa and informed
that IS 456 2000 version was revised mainly by cement industry persons in committee and
durability provisions were added.Cement Industry act on its own in respect of products and
some of products are good and others may not be so . Removal of 33 grade from market
may be good . Also the cracking problems discussed in e conf are mostly due to grade 53
which has high early strength but needs to be cured form very early ( at initial set ). G53
is required for HSC and bags must have precautions for curing painted on bags.
- - - - - - -This is a very sane suggestion from Dr N Subramanian and Industry representatives
may kindly take a note of it .
Er Sriprakash acknowledged Dr N S viewpoint of removal of 33 G cement from market.
while accepting that 53G shall be used in HSC only. Tomorrow Cement manufacturers
may find another grade and stop 43G which is disturbing .. Being Industrial consultants ,
non availability of 33 g cement is problem since in design of large slabs on grade for
industrial Bldgs shrinkage is concern with higher grades.
Er Dipesh Shah wants to know whether Stone dust can be used as sand replacement
in concrete either partially or fully. Er CK Francis responded that in case stone dust is
used , the grading as per sieve analysis must be as per specifications.Deleterious
materials must also be seen. Sand must be washed . Most of dust is supplied as
manufactured sand by Querry owners and hence it shall be confirmed before purchasing
Er Suraj Singh responded on stone dust use for concrete.Stone dust is procured from
crushers and it can be used. In past , river sand (fine sand) was used. Pit sand (coarse sand )
was used for concrete works. For mortar coarse sand and for plaster (coarse +fine) sand
was in use. In gulf dune sand was introduced as partial replacement of cement in conc.but
now it is replaced by SCM, PFA. The PFA provides better workability. Dust 's parent material
is stone/rock and it has strength and it allows grading .Er BV Harsoda advised use
of quarry rock dust for durability while providing link for a related paper.
Posting from email Id accuratetestlab (name of delegate not mentioned ) describes the
mind-set of builders/developers /contractors who feel for good quality , margin of profit
will be reduced.There shall be a law enforcing quality .Also persons actually executing the
job are not knowledgeable. Seminars and Training s must be imparted for proper
quality .Er Suraj Singh feels that ' Quality increases cost ' is not a correct perception.
Deliver of quality requires good level of supervision and control and any cost associated
has to be spent.Engineers must do their job sincerely and should guide architects and
others in matters of durability.Major amount is spent on decorative finishes and not on
needed structural strength.Structures with good quality do not considerably add to cost.
Very Impressive Posting from TPS61 ( here again name of delegate not mentioned ),
responded to Madam Alpa and Er Anand Shah saying that IGNORANCE among engineers
is the main hurdle for use of HVFAC , FA as mineral admixture . FA is still treated as very
cheap replacement to superior binder- Cement and anything cheap becomes cause of
unacceptability. Further many feels that FA is acceptable if cost is reduced , but
knowledgeable persons are willing to pay higher price for value added by it and
citing examples of FA import by some foreign projects. However in India HVFAC costs
less. In case FA become costly , our engineers may start thinking favorably for it. He
listed many advantages of using FA like reduced porosity, increased strength gain with
time, reduction in HOH (thus micro-cracking) , Higher Young's modulus, Improved
workability , higher resistance to sulphate attack , increased resistance to Alkali -silica
reaction, improved surface finish,Lesser tendency to segregate, Eco-friendly due to
reduced emission as also relief for natural depleting resources. The other factors
of conc incorporating FA are slightly delayed setting, need for longer curing, and low
early strength. Further , addition of FA may have increased risk of plastic shrinkage
cracking which can be taken care by covering the conc by plastic asap membrane
after placement, spraying evaporation retarders, simply spraying water mist for few
critical hours. Defects like scaling, dusting , weak top layer are often due to wrong
finishing procedure but FA is held culprit wrongly. Concluding remarks are that
Use HVFAC since gives superior conc rather than using for economy , HVFAC is
sustainable concrete of century , Knowledge dissemination at all levels .
- - - - - -In my opinion the content of the posting is par excellence and thanks are
due to the anonymous(by name) delegate for highly impressive views on concrete
I also express my regret for typo mistake of name of our esteemed and respected
sefi member Er B.V Harsoda ji while summarizing for his posting( in earlier summaries) .
Hope he may ignore the slip from my end due to heavy rush of postings .
Dr M R Kalgal responds to querry by madam Alpa ,first thanking her for raising very
important topic of cement constituents and fineness and also thanking moderators of the
conf. Dr NS and Mr Kulkani for their views. He as a structural Er migrated to cement and
other building materials is disturbed and pained on madness of speed.Concrete
must be given due time to gain strength.
Average age of conc building is 35 yrs world over whereas in india it is 27 yrs.
Construction managers though demand 16Mpa strength in 12 Hrs but take months
for finishing works.Cement companies would be pleased to provide less fineness.
Increase in C3S content by them is to achieve higher early strength at cost of lower
late days strength.Regarding SCM's it is important to see the quality of them.
Characterization of mineral admixtures is prudent. Cement plants have better facilities
compared to site.In India significant construction is also thru un-organized sector
having no control on batching , mixing, transportation , compaction and curing. It is
felt that today concrete is more abused while being used. Training to works men at
site and dissemination of knowledge for good construction practices is the need .
Er Suraj Singh states that it is true that form work removal is at 70% achievement of
strength ,how to ensure at site where actual curing is no way compared to that of
curing of cubes. Removal of forms is also dependent upon span size which is more
significant from deflection and durability. Concrete cover is always increased
when in contact with soil to protect from chemicals.Concrete cover below ground
is higher and designers provide increased section (column pedestal ) to keep
starter bars intact .
Er Manu Santhanam states that it is heartening to see concern for durability conveyed
thru various posting s but bulk of discussions address issues not related directly.
Know-how is available in India. Regarding performance approach, the successful
implementation require clear understanding of Environmental classifications , mechanism
of deterioration ,choice of suitable performance criteria for specific service environment,
and limiting values of parameters that can be specified linking to service life.Some of
issues are provided in papers provided by Mr Kulkarni. Lot of interest is geared by
researchers for evolving scientific approach towards performance specifications.
Service life concept must find way for conc designs ,especially for environments with
carbonation or chlorides. Developments in this direction have taken place in Metro
specifications (durability tests) ,IRC 112 -2011 regarding 100yr service life . Provisions of
IS456-2000 are not updated even after 11 yrs.
Awaiting response from all in remaining couple of days of e-conference and with Thanks & regards
Posted via Email