vikram.jeet General Sponsor
![General Sponsor General Sponsor](//www.buonovino.com/forum/images/sefi_general.gif)
Joined: 26 Jan 2003 Posts: 3698
|
Posted: Sat Mar 10, 2012 5:56 pmPost subject: Summary #7 of E-Conf -Days 11 & 12 |
![Reply with quote Reply with quote](//www.buonovino.com/forum/templates/subSilver/images/lang_english/icon_quote.gif) |
|
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 也有助于规范等框架和过程dures 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 - - - - - - -
嗯阿洛克Bhowmick觉得耐久混凝土是一个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 M/ sand.
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 开裂,可以通过覆盖c照顾onc 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 durability /sustainability.
I also express my regret for typo mistake of name of our esteemed and respected 半岛软件下载sefi成员Er B.V Harsoda霁,同时总结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
vikramjeet Conf- raconteur
Posted via Email |
|