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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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JVCSNL
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Joined: 26 Jan 2003
Posts: 159

PostPosted: Fri Mar 02, 2012 8:57 am    Post subject: Reply with quote

Dear Members,

If any deteriorating agent is in direct contact with concrete surface, then we will definitely protect it by applying protective coating.  

The protection may be given in inside face or outside face based on severity.

My point of raising this topic was that since chemical reactions will always be continuing in concrete, though a slow process as time goes, the presence of moisture, temperature etc. will have some role in effects of this chemical process.  

Chemical reaction in case of higher temperature (that to sustained) induced due to surrounding atmosphere (because of any reason, I explained in other posts) will have some effects.  

Following are few more questions for which definite answers are not given.

Does Pozzolonic material react the same way as other SCMs?  

How ASR will be affected in case of higher temperature?  Shall we specify all the aggregates and cementitious material in case concrete will be exposed to higher temperatures?

Do we need to monitor concrete for safety in such situations?  

What is the maximum temperature allowed in contact with concrete that will not effect the mechanical properties of the concrete?  

While searching answers for few of the above questions, I found contradictory answers.  Some research says that there is no/minor effect on concrete properties.  However, some other say that there is going to be some effect and the same shall be considered by engineer.

If concrete looses the properties slowly there would be cascaded increase in deterioration.  

Regards,

Jignesh V Chokshi
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alpa_sheth
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PostPosted: Fri Mar 02, 2012 11:35 am    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

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]
Sent: 29 February 2012 11:01
To: 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

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nwalavalkar
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Joined: 18 Nov 2010
Posts: 63

PostPosted: Fri Mar 02, 2012 2:35 pm    Post subject: Reply with quote

Dear Mr Moruf

I would like to seek your opinion on use of Microsilica (Silica Fume) as Supplementary Cementitious materials (SCM).

Regards

Narendra
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JVCSNL
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PostPosted: Fri Mar 02, 2012 5:39 pm    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Dear Members,  

I am appending a note from some literature regarding effects of high temperature and pressure on concrete.


"A physico-chemical transformation of the paste took place with the rise in temperature. At high temperatures, chemical transformation of the gel weakened the matrix bonding, which brought about a loss of strength and elasticity of f ly ash and silica fume concrete."


Very interesting to note this.


Up to certain percentage of fly ash will have not much effect. But larger FA will have detrimental effects.


The effect will be very crucial to note for machine foundations, which are very sensitive and are many times subjected to high temperature and pressures. Hence, use of FA based concrete is avoided.


Regards,


Jignesh V Chokshi

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JVCSNL
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Joined: 26 Jan 2003
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PostPosted: Fri Mar 02, 2012 5:57 pm    Post subject: Reply with quote

Dear Members,

I am appending a note from some literature regarding effects of high temperature and pressure on concrete.

"A physico-chemical transformation of the paste took place with the rise in temperature. At high temperatures, chemical transformation of the gel weakened the matrix bonding, which brought about a loss of strength and elasticity of f ly ash and silica fume concrete."

Very interesting to note this.  

Up to certain percentage of fly ash will have not much effect.  But larger FA will have detrimental effects.

The effect will be very crucial to note for machine foundations, which are very sensitive and are many times subjected to high temperature and pressures.  Hence, use of FA based concrete is avoided.

Regards,

Jignesh V Chokshi
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bsec
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Joined: 26 Jan 2003
Posts: 202

PostPosted: Sat Mar 03, 2012 2:04 am    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Dear Mr Moruf,

I would like to get the thread to the original paper by R W Burrows on the subject matter.


I am sure there will be many experts in this forum, who would not like to be in the same page with you on this issue. I am looking forward to opinions from Mr Rajmane and Mr Kulkarni on the subject.


Best Wishes


Alok Bhowmick

On Fri, Mar 2, 2012 at 7:29 PM, alpa_sheth <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
           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 (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
     




     



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JVCSNL
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PostPosted: Sat Mar 03, 2012 4:06 am    Post subject: Fly ash based concrete subjected to high temperature Reply with 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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JVCSNL
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PostPosted: Sat Mar 03, 2012 4:29 am    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Dear Members,

Another interesting investigation on HSC subjected to elevated temperatures.

http://ibe.sagepub.com/content/19/6/612.refs

Regards,

Jignesh V Chokshi

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narayan_nayak
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Joined: 02 Mar 2012
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PostPosted: Sat Mar 03, 2012 11:06 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]
Sent: Friday, March 02, 2012 7:30 PM
To: 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






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Moruf
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PostPosted: Sun Mar 04, 2012 5:25 pm    Post subject: Fly ash based concrete subjected to high temperature Reply with quote

Sorry for the belated response, the attached is the requested paper by R.W Burrows

On Sat, Mar 3, 2012 at 7:31 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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