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Alternatives to early strength cements for controlling Cr
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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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lkjain.ngp
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PostPosted: Tue Mar 06, 2012 9:51 pm    Post subject: Alternatives to early strength cements for controlling Crack Reply with quote

Fellow engineers,
 
1.  In my opinion, Prof Mehta's view are valid. This information is known since 80's, when we had a seminar in Nagpur on durability of concrete.
2.  Our engineers resist even 20% flyash addition. I feel this is due lack of understanding of the subject. But the pretext is the imaginary quality problems, without going in to any details, testing & trials.
3.  HVFA (high volume flyash concrete) has become a distant dream due to ignorance of 95% of the professionals, who are holding down the other 5%. However HVFA is not a solution for all cases. 
4. We should not be comparing self compacting concrete with high volume flyash concrete. We can develop / deign a self compacting concrete which also has flyash in large proportion. 
5.  Self compacting concrete does not mean a less durable concrete. Modern approach should be to design a self compacting concrete, which has the desired level of parameters for durability. It should be an engineered concrete rather pick one of the available design mix.

L. K. JAIN

On 2 March 2012 19:28, alpa_sheth <forum@sefindia.org (forum@sefindia.org)> wrote:
Quote:
  Dear All:

In one of Prof P K Mehta’s papers, http://icjonline.com/views/2001_01_Mehta.pdf, he has mentioned that in earlier times (pre-1930s) when there was coarser ground portland cements with lesser C3S, deterioration in concrete was due to factors other than cracking (leaching etc.). In recent times due to demand of early strength cements, the cements have gotten finer. This has lead to increased cracking and while the relationship between cracking and deterioration in concrete is not mathematically established, it is indisputable that cracking causes deterioration. He further laments the undue importance given to the strength – durability relationship which in his opinion sidetracks the issue.

Dr. Mehta panacea to the durability pains is use of lesser water content, use of coarser Portland cements and use of HVFA. I am aware Prof Dr Mehta has expanded much on this since


a) I would like the opinion of cement experts on the validity of this stand, 10 years after the paper was published. Are all conc. technologists on the same page with Prof Mehta or there are other equally valid theories?
b) If there is concensus, why has HVFA concrete not taken on as it should have?
c) What is better for durability, self compacting concrete or HVFA concrete?
d) Is there any chance that expensive self-compacting concrete/viscosity-controlling admixtures will become more affordable and thus more prevalent as a more durable alternative?




Best regards,
Alpa








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JVCSNL
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PostPosted: Wed Mar 07, 2012 5:00 am    Post subject: Alternatives to early strength cements for controlling Cr Reply with quote

Dear Members,

Mr. Deepak Bhattacharya has raised a valid point about knowledge of Ash composition, while using the same for structural concrete.  

I tried to gather some input for the same for domestic as well as overseas coal.

I would like to mention that the ash content in overseas coal is quite low (4 to 6%) whereas the same for domestic coal is as high as 35 to 42%. In most of the overseas power plants we don't see ash storage area, whereas in Indian power plants, one of the major portion of plant is ash storage area.  

Table below shows the ash constituent comparison.

Fly Ash Constituents  

ItemUnit
Indian
Overseas
SiO2%
56~64
46
Al2O3%
27~32
19
Fe2O3%
2~67
17
CaO%
1.~1.5
5
MgO%
0.3~1
4
Na2O%
1.8
K2O%
1
TiO2%
1 ~1.5
1
P2O5%
0.2~0.75
0.2
SO3%
5
Alkalies
0.65~1.6
Not Reported
  

I seek advice from concrete experts the considerations to be given to this type of data when considering mixing of ash in concrete at field, both in terms of % usage of ash and durability considerations. Also, it would be great if significance of each of this constituent on durability of concrete can be explained by expert. If some proactive or maintenance measures also needs to be highlighted, the same shall be advised.  

I am seeking this information especially with regard to consideration of fly ash usage in concrete mix design specifications. The concrete volume in some plants is as high as 2,00,000 cu.m. in various applications, lightly loaded, water conveying, highly loaded, hot environment, machine foundations etc.  

Regards,

Jignesh V Chokshi

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PostPosted: Wed Mar 07, 2012 5:59 am    Post subject: Reply with quote

Dear Members,

Further to my previous post, I would also like to seek opinion on the fly ash quality of the two representative ash analysis reports.  

Which one is better fly ash to be used in structural concrete?

What would be role of other constituents on concrete durability?

I would like to inform that the analysis given will change based on coal source.  Only two representative cases for comparison and discussion purpose were given in my earlier posts.

Regards,

Jignesh V Chokshi
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Dr. N. Subramanian
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PostPosted: Wed Mar 07, 2012 5:59 am    Post subject: Re: Alternatives to early strength cements for controlling C Reply with quote

Dear Er Jignesh V Chokshi,

Not all fly ash produced by power plants are useful for concrete applications. The ash content of  Coals in some parts of India (I think South India) are more than in other parts of India.

Flyash  produced are classified into two categories , according to the type of coal used. Anthracite and bituminous coal produces flyash classified as Class F. Class C flyash is produced by burning lignite or subbituminous coal. Class C flyash is preferable for the applications presented in the Green Building Guide and is used by ready-mix suppliers.

Flyash for use in portland cement concrete shall conform to the requirements of ASTM C 618, Standard Specification for Flyash and Raw or Calcined Natural Pozzolan Class C Flyash for use as a Mineral Admixture in Portland Cement.(A similar stad. should be there in India too). Specifically, it shall conform to all requirements of Table 1 and Table 2 as outlined therein. Not all fly ashes meet ASTM C618 requirements.Class C fly ash generally contains more than 20% lime (CaO). Unlike Class F. Alkali and sulfate (SO4) contents are generally higher in Class C fly ashes. Read the paper by my friend Karthik Obla for more info. The link is:http://www.nrmca.org/research/cif%20spring%2008%20fly%20ash.pdf

I also have a doubt: Are people mixing fly ash at site? It is difficult to mix it at site as it is much finer than cement. I think it is better to use PPC manufactured by cement companies.

Regards,
NS
JVCSNL wrote:
Dear Members,

Mr. Deepak Bhattacharya has raised a valid point about knowledge of Ash composition, while using the same for structural concrete.  

I tried to gather some input for the same for domestic as well as overseas coal.

I would like to mention that the ash content in overseas coal is quite low (4 to 6%) whereas the same for domestic coal is as high as 35 to 42%. In most of the overseas power plants we don't see ash storage area, whereas in Indian power plants, one of the major portion of plant is ash storage area.  

Table below shows the ash constituent comparison.

Fly Ash Constituents  

ItemUnit
Indian
Overseas
SiO2%
56~64
46
Al2O3%
27~32
19
Fe2O3%
2~67
17
CaO%
1.~1.5
5
MgO%
0.3~1
4
Na2O%
1.8
K2O%
1
TiO2%
1 ~1.5
1
P2O5%
0.2~0.75
0.2
SO3%
5
Alkalies
0.65~1.6
Not Reported
  

I seek advice from concrete experts the considerations to be given to this type of data when considering mixing of ash in concrete at field, both in terms of % usage of ash and durability considerations. Also, it would be great if significance of each of this constituent on durability of concrete can be explained by expert. If some proactive or maintenance measures also needs to be highlighted, the same shall be advised.  

I am seeking this information especially with regard to consideration of fly ash usage in concrete mix design specifications. The concrete volume in some plants is as high as 2,00,000 cu.m. in various applications, lightly loaded, water conveying, highly loaded, hot environment, machine foundations etc.  

Regards,

Jignesh V Chokshi

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PostPosted: Wed Mar 07, 2012 6:16 am    Post subject: Reply with quote

Dear Dr. NS,

I agree that all fly ash can not be used.  I guess, most of the cement plants take FA from power plants.  Probably, they may be testing the same for use in making PPC.

With regard to mixing of FA at site, it is generally done in my knowledge.  

Some specifications indicate that the FA can be added in OPC-43 using batching plant.  The FA shall conform to IS 3812 and they limit of the fly ash replcement in range of 20-25%.  Higher grade cement like OPC-53 with FA is also permitted.  The trial mix design is based on various percentage of FA and OPC combination.  

I really have to verify how FA is tested to meet Indian code requirement.  But as we know, testing and practice differ.  

My point was that if we have prior knowledge of FA properties, how it can be read by structural engineer to ensure durability.

Thanks for your valuable inputs and references.

Regards,

Jignesh V Chokshi
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PostPosted: Wed Mar 07, 2012 8:48 am    Post subject: Producing Durable Concrete at Site Reply with quote

Dear All,

Producing durable concrete at site successfully is like winning a 3 legged race (or multi-legged !). It depends on all of parties involved taking responsibility for the finished product and executing their role in the most responsible manner.  

Durable concrete is a team work of Engineer, Contractor, Sub-Contractors, Producers, Consultants & above all Owner. If anyone in this chain of teams fails to perform their role, the durability may be lost.  

Best Wishes

Alok Bhowmick  

Structural Engineering Forum of India  

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mkalgal
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PostPosted: Thu Mar 08, 2012 8:00 pm    Post subject: Reply with quote

Dear Sefians,
I thank Ms. Alpa raising this very important topic of cement constituents and fineness. I thank Er. Kulkarni and Dr. Subramanian for excellent treatment of the subject.
As a Structural Engineer who has migrated to the field of Cement and other building materials, I have been surprised (and pained) at this madness for speed. Speed at what cost? We are not ready to give a reasonable time for concrete to gain strength along with sufficient durability. We want one slab every 3 days while we want the concrete to last more than 50years. We are told that the average age of a concrete building worl over is around 35 years and in India it is 27 years(give and take a few years)
Today project managers are asking for 16MPa in 12 hours! But they don't mind if it takes a few months for finishing items since the more beautiful they finish, the more money it fetches in real estate market.
Cement companies would be happy to give lesser fineness. It saves on grinding energy and cost. Even the increase in C3S has been towards achieving this high early strength at the cost of lower later day strength.
Regarding SCMs, it is very important to understand the quality parameter of these materials when blending or intergrinding with clinker as has been emphasized. Characterisation of the mineral admixtures is extremely important in fixing the optimal doses and the cement manufacturers have better facilities compared to a site where indiscriminate addition of SCMs could lead to unhappy results.
In India significant Concrete consumption is in unorganised sector where there is no control on batching, mixing, transportation, compaction and curing. How do we address the right of an Individual
House Builder to have a durable abode? Today concrete is more abused than used (except in large constructions).
This brings us to the need to disseminate knowledge on good construction practices and training of workmen at site. A mammoth task indeed!
Cheers
Dr. M. R. Kalgal
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Dr. N. Subramanian
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PostPosted: Fri Mar 09, 2012 6:04 am    Post subject: Reply with quote

Dear Dr Kalgal,

Thank you for the kind words. I totally agree with you. As you have rightly pointed out we need to educate the work force about the developments that are talking place in concrete technology-even Engineers are not aware of the problems of using high early strength cements and the imp. of proper curing-Only then we can dream off durable structures. With dwindling natural resources- already India is witnessing shortage of fine aggregates and Er Kulkarni has informed about shortage of lime stones- it is important to build structures which should last at least 100 years. We should also make Cement companies to re-introduce  Grade 33 cement.

Regards,

Subramanian
mkalgal wrote:
Dear Sefians,
I thank Ms. Alpa raising this very important topic of cement constituents and fineness. I thank Er. Kulkarni and Dr. Subramanian for excellent treatment of the subject.
As a Structural Engineer who has migrated to the field of Cement and other building materials, I have been surprised (and pained) at this madness for speed. Speed at what cost? We are not ready to give a reasonable time for concrete to gain strength along with sufficient durability. We want one slab every 3 days while we want the concrete to last more than 50years. We are told that the average age of a concrete building worl over is around 35 years and in India it is 27 years(give and take a few years)
Today project managers are asking for 16MPa in 12 hours! But they don't mind if it takes a few months for finishing items since the more beautiful they finish, the more money it fetches in real estate market.
Cement companies would be happy to give lesser fineness. It saves on grinding energy and cost. Even the increase in C3S has been towards achieving this high early strength at the cost of lower later day strength.
Regarding SCMs, it is very important to understand the quality parameter of these materials when blending or intergrinding with clinker as has been emphasized. Characterisation of the mineral admixtures is extremely important in fixing the optimal doses and the cement manufacturers have better facilities compared to a site where indiscriminate addition of SCMs could lead to unhappy results.
In India significant Concrete consumption is in unorganised sector where there is no control on batching, mixing, transportation, compaction and curing. How do we address the right of an Individual
House Builder to have a durable abode? Today concrete is more abused than used (except in large constructions).
This brings us to the need to disseminate knowledge on good construction practices and training of workmen at site. A mammoth task indeed!
Cheers
Dr. M. R. Kalgal
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tsriharivaishu
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PostPosted: Fri Mar 09, 2012 7:10 pm    Post subject: Alternatives to early strength cements for controlling Cr Reply with quote

Dear sir,when it is conforming to 33 grade cement,then there should not be any problem even if we use for mass concrete...Sent from BlackBerry® on Airtel
From: "abhio" <forum@sefindia.org>
Date: Sat, 03 Mar 2012 11:40:36 +0530
To: <econf@sefindia.org>
ReplyTo: econf@sefindia.org
Subject: [ECONF] Re: Alternatives to early strength cements for controlling Cr

     Please correct me if I am mistaken, but as far as I know, IS: 269, IS: 8112 and IS: 12269 specify only the MINIMUM fineness of cement. This allows cement manufacturers to pack the same cement as 33, 43 or 53 grade as per their discretion and demand. This is particularly unfortunate for projects where large concrete pours are required for massive structures where we would like to have slow setting times with gradual evolution of heat of hydration.
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tsriharivaishu
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PostPosted: Fri Mar 09, 2012 7:14 pm    Post subject: Alternatives to early strength cements for controlling Cr Reply with quote

Dear all,please explain the reasons for using 43 grade cement for concrete with slip form...Sent from BlackBerry® on Airtel
From: tsrihari11@gmail.com
Date: Fri, 9 Mar 2012 19:12:12 +0000
To: <econf@sefindia.org>
ReplyTo: tsrihari11@gmail.com
Subject: Re: [ECONF] Re: Alternatives to early strength cements for controlling Cr

Dear sir,when it is conforming to 33 grade cement,then there should not be any problem even if we use for mass concrete...Sent from BlackBerry® on Airtel
From: "abhio" <forum@sefindia.org>
Date: Sat, 03 Mar 2012 11:40:36 +0530
To: <econf@sefindia.org>
ReplyTo: econf@sefindia.org
Subject: [ECONF] Re: Alternatives to early strength cements for controlling Cr

     Please correct me if I am mistaken, but as far as I know, IS: 269, IS: 8112 and IS: 12269 specify only the MINIMUM fineness of cement. This allows cement manufacturers to pack the same cement as 33, 43 or 53 grade as per their discretion and demand. This is particularly unfortunate for projects where large concrete pours are required for massive structures where we would like to have slow setting times with gradual evolution of heat of hydration.
        --

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