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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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PostPosted: Thu Mar 08, 2012 9:08 am    Post subject: HVFAC, Reply with quote

Some comments in response to questions raised by Alpa and Vijay shah.
  • The main hinderance in use of HVFAC and Fly ash as an additive mineral admixture in general has been Ignorance on part of the engineers involved in design & construction.
  • Fly ash is still seen as a "cheap replacement" of cement by many ignorant structural engineers. It is their belief that anything cheap replacing the most expensive component of concrete must result in an inferior product.
  • Too many of us think that use of Fly ash or HVFAC is justifiable only if it reduces the cost of concrete.They'll be surprised to know that a dam project in Egypt imported Fly ash from India for their concrete at a cost of 3 times the cost of cement available in their country. Same is true for the 1000 yr. Temple on the island of Quai ( hawaii) by Dr. p.K. Mehta. Fly ash was brought in from 5000 km away at a cost much higher than the Cement it replaced. 'Knowledgeable people' are willing to pay a higher price because they know the value it adds to conventional concrete.
  • Fortunately ( or unfortunately) in most Indian situations, HVFAC costs lesser than conventional concrete.  
  • I fear that our engineers will start thinking favourably of Flyash only after it becomes a rare commodity & it's price goes up. I know of a smart company owned by white skinned people who have been selling our own Fly ash ( Nashik) to us in fancy packaging at Rs. 80 -100 / bag as a beneficial additive to concrete. And our people happily pay for it.
  • Most of our engineers (instead of getting carried away by cynical rumors about use of Fly ash in concrete) should test for themselves and get convinced of the facts like
    • reduced porosity ( by RCPT test)& hence durability ,
    • improved strength gain with time ( More than 50% increase in strength after 6 -9 months compared to 28 day strength) ,  
    • reduction in heat of Hydration (and therefore microcracking),  
    • Higher young's modulus etc.
    • Improved workability
    • Increased resistance to sulphate attack
    • Increased resistance to Alkali Silica Reaction
    • Improved surface finish
    • lesser tendency to segregate
    • major relief to the environment due to reduced emissions as well as reduced pressure on scarce natural resources.
  • HVFAC is no longer in research stage. It has already been used successfully since the Hoover dam ( 40% ash) and in a bigger way since 1985 when Dr. V. M. Malhotra gave it a new life. It has been sucessfully used in several projects in north america and canada - details of which are easily available. It has also been used happily in several demo projects in India. ( hvfac project india). Unfortunately the website on hvfacprojectindia which was being supported by HCC has been offloaded only recently. Interested people can request CII - Centre for excellence in Sustainability for published material on HVFAC. I can also provide casehistories of the demo projects to those interested.
  • Attributes of concrete incorporating FA like -  
    • slightly delayed setting ( so what ! ),  
    • need for longer and more immediate curing  
    • lower early strength ( need not be ! it can easily be designed for)

can easily be addressed appropriately, given the vast benefits in performance reaped.  
  • Users should understand that addition of Flyash restricts bleeding which in conventional concrete partly compensates the evaporation losses. Therefore there is an increased risk of plastic shrinkage cracking( that happens within a few hrs. of placement). This however should not discourage the use of HVFAC given the many advantages . It only needs to be addressed accordingly - i.e preventing evaporation loss by :
    • either covering the concrete by plastic membrane asap after placement
    • sprayiing evaporation retarders
    • simply spraying a water mist ( an agricultural backpack sprayer is fine) for a few critical hours.
  • Defects like scaling / dusting / weak top layer are often due to wrong finishing procedure rather than holding Fly ash as the culprit.  

  • Do not use HVFAC because it is "cheaper". Instead, use it because it gives us a far superior Concrete.
  • HVFAC is (in Dr. P.K.Mehta's language ) THE sustainable concrete for this century !
  • Knowledge dissemination regarding SCMs ( and field practices for GOOD CONCRETE ) at all levels starting from college, is an important need of the hour.  


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PostPosted: Fri Mar 09, 2012 6:27 am    Post subject: PFA Use Reply with quote

Dear Eng TPS,

  1. I appreciate your views.
  2. Fly Ash, GGBS & MS are very commonly used all over Middle east & Gulf.
  3. All major concrete elements are designed based on such SCMs.
  4. In fact, nowhere OPC is being used excepting pre cast factories.
  5. UAE use GGBS everywhere.
  6. Qatar use PFA.
  7. Combination of PFE/GGBS & MS are used on many projects.
  8. Use of GGBS provide a better control on thermal gradient.
  9. Morever, design engineers should specify its use & its methods to control that involves effect on formwork as well as on curing.
  10. To achieve effective controls, designers should write clear directions to site team.
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