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Fly ash based concrete subjected to high temperature
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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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narayan_nayak
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PostPosted: Mon Mar 05, 2012 6:43 am    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Dear Ms. Alpa Sheth,

I refer to your query to “ALL” and your response to Mr. Moruf.

Now it is beyond doubt that addition of mineral admixtures like Fly ash, GGBS, Metakaoline, Micro Silica, improves the durability of the concrete. Reduction in water binder ratio also improves the durability.

I have no hesitation in recommending Fly Ash upto 50% replacement for foundations and sub-structures. I may restrict to lesser extent say 30 to 35% in super structures.

By adding Fly ash early strength gain will get little slow which can be overcome by addition of “Alcofine” (a ultra-fine gained GGBS) or Chemical Admixture, etc.

The attached Table -1 [from Nayak NV (2012)] gives broadly summary of effectiveness of secondary cementing material on concrete.

The Self Compacting Concrete (SCC) is used where structures are heavily reinforced and chances of honey combing are high inspite of vibration. SCC also contains secondary cementing materials like Fly ash. Presently cost difference between SCC and Normal Concrete is not very substantial if you take the advantage of reduction in cost of not providing vibration in SCC.

From sustainability and durability consideration, one should encourage use of Fly ash, GGBS, etc. in our practices.

Thanks and Regards,

NV Nayak



From: alpa_sheth [mailto:forum@sefindia.org] ([mailto:forum@sefindia.org])
Sent: Friday, March 02, 2012 7:30 PM
To: econf@sefindia.org (econf@sefindia.org)
Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature



Dear Mr. Moruf:

This is a very interesting thread. I had posted a mail an hour ago requesting alternative opinions re. the efficacy of HVFA concrete for improving durability.
You seem to providing a response here. Can you expand on the comparision of others SCMS with Fly ash? Which do you think would be more effective from durability point of view?

Regards,

Alpa


From: Moruf [mailto:forum@sefindia.org] ([mailto:forum@sefindia.org])
Sent: 29 February 2012 11:01
To: econf@sefindia.org (econf@sefindia.org)
Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature




Thanks for this initiative. Concrete durability is something really important to reduce the cost of retrofitting and extension of structural service life. However, the recent research output has proved the following regarding fly-ash usage towards improving concrete durability. These are among the conclusions made by R.W Burrows (member ACI committee 222 which I also belong) :
1. Fly-ash does not help the concrete due to damage from drying because microcracks caused by drying shrinkage open up rather than heal autogenously if fly ash is present
2.It decreases resistance to freezing and thawing
3. low permeability to chloride ingress is achievable due to long curing but disappears when if the concrete is weathered by cycle of wetting and drying.
4. If chloride comes in contact with steel, the fly-ash aggravates corrosion rate.
5.Performance due to creep, thermal contraction, alkali-silica reaction among others are not really satisfactory compare to other Supplementary Cementitious materials (SCM)

-

Moruf O. Yusuf, CCE,PMP,MNSE
Project Department
King Fahd University of Petroleum and Minerals
P.O.Box 5019
+96638604703






Think Green & Live green.
This e-mail is confidential and it is intended only for the addressees. Any review, dissemination, distribution, or copying of this message by persons or entities other than the intended recipient is prohibited. If you have received this e-mail in error, kindly notify us immediately by telephone or e-mail and delete the message from your system. The sender does not accept liability for any errors or omissions in the contents of this message which may arise as a result of the e-mail transmission.""

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PostPosted: Mon Mar 05, 2012 8:11 am    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Dear Mr Nayak,

Thanks for your valuable inputs. I would like to know your views on :

<![if !supportLists]>a) <![endif]>whether you recommend 50% replacement for Fly Ash with blending at site or at plant (or both !).
<![if !supportLists]>b) <![endif]>Do you consider our present technical specifications / standards / codes sufficient to allow for increase in fly ash content of the mix
<![if !supportLists]>c) <![endif]>Any additional precautions required to be taken at site in this case ?

Best Wishes

Alok Bhowmick  
From: narayan_nayak [mailto:forum@sefindia.org]
Sent: Monday, March 05, 2012 1:09 PM
To: econf@sefindia.org
Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature



Dear Ms. Alpa Sheth,

I refer to your query to “ALL” and your response to Mr. Moruf.

Now it is beyond doubt that addition of mineral admixtures like Fly ash, GGBS, Metakaoline, Micro Silica, improves the durability of the concrete. Reduction in water binder ratio also improves the durability.

I have no hesitation in recommending Fly Ash upto 50% replacement for foundations and sub-structures. I may restrict to lesser extent say 30 to 35% in super structures.

By adding Fly ash early strength gain will get little slow which can be overcome by addition of “Alcofine” (a ultra-fine gained GGBS) or Chemical Admixture, etc.

The attached Table -1 [from Nayak NV (2012)] gives broadly summary of effectiveness of secondary cementing material on concrete.

The Self Compacting Concrete (SCC) is used where structures are heavily reinforced and chances of honey combing are high inspite of vibration. SCC also contains secondary cementing materials like Fly ash. Presently cost difference between SCC and Normal Concrete is not very substantial if you take the advantage of reduction in cost of not providing vibration in SCC.

From sustainability and durability consideration, one should encourage use of Fly ash, GGBS, etc. in our practices.

Thanks and Regards,

NV Nayak



From: alpa_sheth [mailto:forum@sefindia.org]
Sent: Friday, March 02, 2012 7:30 PM
To: econf@sefindia.org (econf@sefindia.org)
Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature



Dear Mr. Moruf:

This is a very interesting thread. I had posted a mail an hour ago requesting alternative opinions re. the efficacy of HVFA concrete for improving durability.
You seem to providing a response here. Can you expand on the comparision of others SCMS with Fly ash? Which do you think would be more effective from durability point of view?

Regards,

Alpa


From: Moruf [mailto:forum@sefindia.org] ([mailto:forum@sefindia.org])
Sent: 29 February 2012 11:01
To: econf@sefindia.org (econf@sefindia.org) (econf@sefindia.org (econf@sefindia.org))
Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature




Thanks for this initiative. Concrete durability is something really important to reduce the cost of retrofitting and extension of structural service life. However, the recent research output has proved the following regarding fly-ash usage towards improving concrete durability. These are among the conclusions made by R.W Burrows (member ACI committee 222 which I also belong) :
1. Fly-ash does not help the concrete due to damage from drying because microcracks caused by drying shrinkage open up rather than heal autogenously if fly ash is present
2.It decreases resistance to freezing and thawing
3. low permeability to chloride ingress is achievable due to long curing but disappears when if the concrete is weathered by cycle of wetting and drying.
4. If chloride comes in contact with steel, the fly-ash aggravates corrosion rate.
5.Performance due to creep, thermal contraction, alkali-silica reaction among others are not really satisfactory compare to other Supplementary Cementitious materials (SCM)

-

Moruf O. Yusuf, CCE,PMP,MNSE
Project Department
King Fahd University of Petroleum and Minerals
P.O.Box 5019
+96638604703






Think Green & Live green.
This e-mail is confidential and it is intended only for the addressees. Any review, dissemination, distribution, or copying of this message by persons or entities other than the intended recipient is prohibited. If you have received this e-mail in error, kindly notify us immediately by telephone or e-mail and delete the message from your system. The sender does not accept liability for any errors or omissions in the contents of this message which may arise as a result of the e-mail transmission.""  





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alpa_sheth
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PostPosted: Mon Mar 05, 2012 8:45 am    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Jignesh, 

I had a cursory glance at the report you mentioned in trailing mail. 
If you look at the compressive strength results of concrete without  fly ash and varying % of fly ash (Fig 4.5) , irrespective of the % of fly ash, the compressive test results at room temperature are significantly lower at 56 days than they are at 28 days. Seems incredulous, no? 


I think we should stick to reports in reputed journals as I am afraid there is not adequate review of Thesis reports. It is indeed an unhappy comment to make. 


regards,


Alpa 



On Sat, Mar 3, 2012 at 10:01 AM, JVCSNL <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           Dear All,

Some experimental work done in India on this topic is available http://dspace.thapar.edu:8080/dspace/bitstream/123456789/144/1/8042306.pdf.

The results show that there is reduction in Compressive and Tensile capacity and Modulus of elasticity at Higher temperatures.

Regards,

Jignesh V Chokshi
     



     



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narayan_nayak
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Joined: 02 Mar 2012
Posts: 9

PostPosted: Mon Mar 05, 2012 10:28 am    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Dear Mr. Alok Bhowmick,

My views on questions raised by you are as follows :-

a. I prefer 50% replacement for fly ash for blending at site. I have no objection if blending is done in the cement plant but it is observed that financial benefit / reduced cost obtained by adding fly ash (if fly ash is available nearby) is taken by the cement manufactuers. Further at present our indian code restricts the fly ash content to 35% and manufacturer will not produce PPC with 50% fly ash. Even now they restrict to less than 35%.

b. Our present technical knowledge is adequate. In fact Nuclear Power Corporation Limited are using fly ash with permissible 50% replacement even in some Nuclear Power Projects. As noted earlier our codes need to be revised to allow increase percentage of fly ash. The BS code permits use upto 55% fly ash.

c. I would recommend that mixing should be done using batching plant with pan mixture. Deshuttering time may need to be slightly increased. This can be verified based on the strength achieved at the deshuttering time. Further we have to ensure that quality of fly ash meets our codal requirement viz. IS 3812.

Trust this clarifies the points raised by you.

Thanks & regards,


N.V. Nayak

[quote]--Original Message-- From: bsec <forum@sefindia.org> To: <econf@sefindia.org> Date: Mon, 5 Mar 2012 14:06:49 +0530 Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature  Dear Mr Nayak,   Thanks for your valuable inputs. I would like to know your views on :   a) whether you recommend 50% replacement for Fly Ash with blending at site or at plant (or both !).  b) Do you consider our present technical specifications / standards / codes sufficient to allow for increase in fly ash content of the mix  c) Any additional precautions required to be taken at site in this case ?   Best Wishes   Alok Bhowmick  From: narayan_nayak [mailto:forum@sefindia.org]  Sent: Monday, March 05, 2012 1:09 PM To: econf@sefindia.org (econf@sefindia.org) Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature     Dear Ms. Alpa Sheth,  I refer to your query to &ldquo;ALL&rdquo; and your response to Mr. Moruf.  Now it is beyond doubt that addition of mineral admixtures like Fly ash, GGBS, Metakaoline, Micro Silica, improves the durability of the concrete. Reduction in water binder ratio also improves the durability.  I have no hesitation in recommending Fly Ash upto 50% replacement for foundations and sub-structures. I may restrict to lesser extent say 30 to 35% in super structures.  By adding Fly ash early strength gain will get little slow which can be overcome by addition of &ldquo;Alcofine&rdquo; (a ultra-fine gained GGBS) or Chemical Admixture, etc.  The attached Table -1 [from Nayak NV (2012)] gives broadly summary of effectiveness of secondary cementing material on concrete.  The Self Compacting Concrete (SCC) is used where structures are heavily reinforced and chances of honey combing are high inspite of vibration. SCC also contains secondary cementing materials like Fly ash. Presently cost difference between SCC and Normal Concrete is not very substantial if you take the advantage of reduction in cost of not providing vibration in SCC.  From sustainability and durability consideration, one should encourage use of Fly ash, GGBS, etc. in our practices.  Thanks and Regards,  NV Nayak    From: alpa_sheth [mailto:forum@sefindia.org]  Sent: Friday, March 02, 2012 7:30 PM To: econf@sefindia.org (econf@sefindia.org) (econf@sefindia.org (econf@sefindia.org)) Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature    Dear Mr. Moruf:   This is a very interesting thread. I had posted a mail an hour ago requesting alternative opinions re. the efficacy of HVFA concrete for improving durability.  You seem to providing a response here. Can you expand on the comparision of others SCMS with Fly ash? Which do you think would be more effective from durability point of view?   Regards,   Alpa    From: Moruf [mailto:forum@sefindia.org] ([mailto:forum@sefindia.org])  Sent: 29 February 2012 11:01 To: econf@sefindia.org (econf@sefindia.org) (econf@sefindia.org (econf@sefindia.org)) (econf@sefindia.org (econf@sefindia.org (econf@sefindia.org))) Subject: [ECONF] Re: Fly ash based concrete subjected to high temperature      Thanks for this initiative. Concrete durability is something really important to reduce the cost of retrofitting and extension of structural service life. However, the recent research output has proved the following regarding fly-ash usage towards improving concrete durability. These are among the conclusions made by R.W Burrows (member ACI committee 222 which I also belong) : 1. Fly-ash does not help the concrete due to damage from drying because microcracks caused by drying shrinkage open up rather than heal autogenously if fly ash is present 2.It decreases resistance to freezing and thawing 3. low permeability to chloride ingress is achievable due to long curing but disappears when if the concrete is weathered by cycle of wetting and drying. 4. If chloride comes in contact with steel, the fly-ash aggravates corrosion rate. 5.Performance due to creep, thermal contraction, alkali-silica reaction among others are not really satisfactory compare to other Supplementary Cementitious materials (SCM)  -   Moruf O. Yusuf, CCE,PMP,MNSE Project Department King Fahd University of Petroleum and Minerals P.O.Box 5019 +96638604703       Think Green & Live green. This e-mail is confidential and it is intended only for the addressees. Any review, dissemination, distribution, or copying of this message by persons or entities other than the intended recipient is prohibited. If you have received this e-mail in error, kindly notify us immediately by telephone or e-mail and delete the message from your system. The sender does not accept liability for any errors or omissions in the contents of this message which may arise as a result of the e-mail transmission.""       Download Attachments: Table_A.docx      --

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PostPosted: Mon Mar 05, 2012 2:47 pm    Post subject: Reply with quote

Dear Members,

Regarding use of FA in concrete, Two documents have been uploaded by highly respected experts of the field.

The conclusions appears to be contradicting.  

One literature demonstrates the use of fly ash with cautions, other recommends its use extensively.  

From these, can we conclude that use of FA shall be judiciously considered and Pozzolanic based cements shall not be universally granted.  The mix designer has to consider all these aspects of application and advise mix designs to ensure better durability of the concrete.  

Fly ash based concrete can be certainly used in moist environment like water conveying/retaining structures and in foundations (where moisture is likely).  For dry areas the same shall be used with great cautions.

I find this discussion extremely useful and informative.  

Regards,

Jignesh V Chokshi
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