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CEMENT AND MIX DESIGN.
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P.K.Mallick
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PostPosted: Thu Jan 29, 2009 2:35 am    Post subject: CEMENT AND MIX DESIGN. Reply with quote

IS:10262-1882 Reaffirmed 2004(Recommended Guidelines for Concrete Mix Design) shows a graph in form of Fig-2 which gives co-relation between water-cement ratio, 28-day concrete strength and 28-day strength of cement tested according to IS:4031-1968.
Now, if a particular brand of 43-Grade cement shows strength of 50N/sqmm,while using the aforesaid graph should we use strength of cement as 50N/sqmm or restrict it to 43N/sqmm as the grade of cement is 43-Grade.
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PostPosted: Thu Jan 29, 2009 10:16 am    Post subject: Reply with quote

Dear Mr.Mallick
The said curve refers to concrete strength and not cement strength.
Cement strength does not depend on cement strength alone!
regards
Dr. M. R. Kalgal
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PostPosted: Thu Jan 29, 2009 10:18 am    Post subject: Reply with quote

Dear Mr. Mallick
I am sorry. I wanted to type "concrete strength does not depend on cement strength alone" and typed it wrongly. Realised it after submitting submit button!!
Dr. M. R. Kalgal
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P.K.Mallick
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PostPosted: Thu Jan 29, 2009 2:48 pm    Post subject: Reply with quote

Respected Dr. M. R. Kalgal
                        I am referring to fig-2 of IS:10262-1982(Reaffirmed 2004),page-8 under the heading "RELATION BETWEEN FREE WATER-CEMENT RATIO AND CONCRETE STRENGTH FOR DIFFERENT CEMENT STRENGTHS.
                                                                                  Regards.
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Dr. N. Subramanian
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PostPosted: Thu Jan 29, 2009 4:18 pm    Post subject: CEMENT AND MIX DESIGN. Reply with quote

Dear Mr. Mallick,

I think you have to determine the cement strength as per IS 4031 : Part 6 : 1988Methods of physical tests for hydraulic cement: Part 6 Determination of compressive strength of hydraulic cement (other than masonry cement). As I do not have a copy of the same here, I am unable to comment. Please look into it for determining the correct cement strength.

In this connection I wish to inform you that my friend Mr. N. P. Rajamane, Head, Concrete Composites Lab., SERC has developed the following equation to represent the Mix design curves of SP 23-1981(see NBM &CW May05, pp.124-127).

fc= 0.39* fcem*[(1/wc)-0.50]

where
fc= 28 day comp. strength of cement concrete, MPa
fcem= 28 day comp. strength of cement as per IS 4031-part6:1988, MPa
wc=Water cement ratio (by weight)

It was found that the above equation differs from BIS curves by a margin of +7.8 % to -2.8% and hence can be used to estimate the initial compressive strength of cement concrete before starting the trial mixes in the Lab.

Best wishes
Subramanian

Dr.N.Subramanian,Ph.D.,F.ASCE, M.ACI,

Consulting Structural Engineer
Maryland, USA

See my books at: www.multi-science.co.uk/subramanian-book.htm
www.oup.co.in/search_detail.php?id=144559





--- On Thu, 1/29/09, P.K.Mallick <forum@sefindia.org> wrote:
Quote:
From: P.K.Mallick <forum@sefindia.org>
Subject: [SEFI] Re: CEMENT AND MIX DESIGN.
To: general@sefindia.org
Date: Thursday, January 29, 2009, 8:18 PM

Respected Dr. M. R. Kalgal
I am referring to fig-2 of IS:10262-1982(Reaffirmed 2004),page-8 under the heading "RELATION BETWEEN FREE WATER-CEMENT RATIO AND CONCRETE STRENGTH FOR DIFFERENT CEMENT STRENGTHS.
Regards.
     



     


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PostPosted: Thu Jan 29, 2009 6:55 pm    Post subject: Re: CEMENT AND MIX DESIGN. Reply with quote

Respected Subramanian Sir,

Can I get a copy that article written by your friend?
My E-mail id: munamallick@yahoo.co.in
OR
mallick.pravatkumar@gmail.com
Warm Regards.
P.K.MALLICK
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PostPosted: Fri Jan 30, 2009 9:30 pm    Post subject: Re: CEMENT AND MIX DESIGN. Reply with quote

Dear Mallick Sir,

The graph in fig-2 is generalized graph of water cement ratio Vs 28th day compressive strength of concrete for a particular grade of cement like A, B, C, D, E, F having compressive strength in respective range like 31.9 - 36.8 N/mm^2, 36.8 - 41.7 N/mm^2 ....... There fore in my opinion, we can use the graph depending upon the test results of cement falling under the range of respective grade.

      I think this graph has been taken from German practice where also 6 Nos of grade of cement was in use. They were Grade 30, 35,40,45,50 & 55 having 28th  day compressive strength 30, 35,40,45,50 & 55 N/ mm^2. Fig -2 of IS: 10262 is also having 6 Nos of curve similar to German Graph namely A, B, C, D, E & F.

Kindly see the attached article of Dr. S.C. Maiti , Mr. Raj K. Agrawal & Mr. Rajeeb Kumar from ICJ.

Regards.

Mithilesh.

  
P.K.Mallick wrote:
IS:10262-1882 Reaffirmed 2004(Recommended Guidelines for Concrete Mix Design) shows a graph in form of Fig-2 which gives co-relation between water-cement ratio, 28-day concrete strength and 28-day strength of cement tested according to IS:4031-1968.
Now, if a particular brand of 43-Grade cement shows strength of 50N/sqmm,while using the aforesaid graph should we use strength of cement as 50N/sqmm or restrict it to 43N/sqmm as the grade of cement is 43-Grade.



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PostPosted: Sat Jan 31, 2009 1:27 pm    Post subject: Re: CEMENT AND MIX DESIGN. Reply with quote

Respected Mithilesh Sir,
                      
                Thanks for your response.Let us look into Indian cement Market. OPC has almost vanished from the market. It is now PSC and PPC. The former is abundant in the Eastern Part of the country.
Now let us look into respective IS Codes for those cement.
IS 1489(Part-1):1991(Reaffirmed 2000) PORTLAND-POZZOLANA CEMENT-SPECIFICATION(FLY ASH BASED)

IS 1489(Part-2):1991(Reaffirmed 2000) PORTLAND-POZZOLANA CEMENT-SPECIFICATION(CALCINED CLAY BASED)

Clause 7.4.1 the average compressive strength at 672+=4h is 33 Mpa,Min
Hence strength wise it is equivalent to Grade-33 OPC.

IS:455:1989(Reaffirmed 2005) PORTLAND SLAG CEMENT-SPECIFICATION

Clause 6.4 the average compressive strength  at 672+=4h is 33 Mpa,Min
Hence strength wise it is also equivalent to Grade-33 OPC.

It is my observation of last six months that particular brand of PPC gives a compressive strength on an average 53 Mpa. Now the question comes while designing concrete mix should we take the observed compressive strength of 53 Mpa or 33 Mpa.
Again it is of my opinion (conservative of course) that while designing mix we should restrict to 33Mpa because fly ash used in PPC is obtained from the exhaust gases of coal fired power station and the quality of fly ash depends on the ash content of the coal used. See the variables associated Fly-ash. So depending upon type of Fly-ash used, the strength of PPC shall vary and we can not question the manufacturer as long as the minimum requirement of 33Mpa is satisfied. Hence is it not risky proposition to depend on undependable observed compressive strength? Of course the consolation is that cement manufactures  usually get the fly ash from one source.

Same can be said about OPC-43 grade which (sometimes) is actually rejected OPC-53 Grade and even sometimes the OPC-53 comes in the bag of OPC-43 because it is not economically viable for a manufacturer to have different manufacturing facilities for different Grade of cement.

Hence let us use the designated compressive strength not the observed compressive strength while using the curves  of Design Mix code.

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PostPosted: Sun Feb 01, 2009 7:00 am    Post subject: CEMENT AND MIX DESIGN. Reply with quote

1/2/2009

My thanks to Mr Mallick for pointing out the realities of the Indian cement scene, especially in the astern part of our country.

Indrajit Barua.

On Sat, 31 Jan 2009 P.K.Mallick wrote :
Quote:
Respected Mithilesh Sir,

Thanks for your response.Let us look
into Indian cement Market. OPC has almost vanished from
the market. It is now PSC and PPC. The former is
abundant in the Eastern Part of the country.
Now let us look into respective IS Codes for those
cement.
IS 1489(Part-1):1991(Reaffirmed 2000)
PORTLAND-POZZOLANA CEMENT-SPECIFICATION(FLY ASH BASED)

IS 1489(Part-2):1991(Reaffirmed 2000)
PORTLAND-POZZOLANA CEMENT-SPECIFICATION(CALCINED CLAY
BASED)

Clause 7.4.1 the average compressive strength at
672+=4h is 33 Mpa,Min
Hence strength wise it is equivalent to Grade-33 OPC.

IS:455:1989(Reaffirmed 2005) PORTLAND SLAG
CEMENT-SPECIFICATION

Clause 6.4 the average compressive strength  at 672+=4h
is 33 Mpa,Min
Hence strength wise it is also equivalent to Grade-33
OPC.

It is my observation of last six months that particular
brand of PPC gives a compressive strength on an average
53 Mpa. Now the question comes while designing concrete
mix should we take the observed compressive strength of
53 Mpa or 33 Mpa.
Again it is of my opinion (conservative of course) that
while designing mix we should restrict to 33Mpa because
fly ash used in PPC is obtained from the exhaust gases
of coal fired power station and the quality of fly ash
depends on the ash content of the coal used. See the
variables associated Fly-ash. So depending upon type of
Fly-ash used, the strength of PPC shall vary and we can
not question the manufacturer as long as the minimum
requirement of 33Mpa is satisfied. Hence is it not
risky proposition to depend on undependable observed
compressive strength? Of course the consolation is that
cement manufactures  usually get the fly ash from one
source.

Same can be said about OPC-43 grade which (sometimes)
is actually rejected OPC-53 Grade and even sometimes
the OPC-53 comes in the bag of OPC-43 because it is not
economically viable for a manufacturer to have
different manufacturing facilities for different Grade
of cement.

Hence let us use the designated compressive strength
not the observed compressive strength while using the
curves  of Design Mix code.

------------------------
P.K.Mallick
munamallick@yahoo.co.in
mallick.pravatkumar@gmail.com








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PostPosted: Sun Feb 01, 2009 8:47 am    Post subject: Re: CEMENT AND MIX DESIGN. Reply with quote

Repected Mallick Sir and Experienced Sifians

Thank u Mallick Sir for your nice elaboration on the issue. I do agree 100%  with your comment that, we shall use the designated compressive strength of the cement in general.

But on the other hand  a lot of improvements has been done  in the quality and strength of Indian cement since 1982 to 2003 (before reaffirmation of IS 10262).  I think Kipping in view of these improvements, the graph in form of  Fig-02  has been included in IS: 10262 1982 (Reaffirmed 2004).  
     It is also the fact that the test results of different samples of cement taken from same batch of cement produced in the same manufacturing unit may varies within some range (minimum to maximum) In my opinion, to generalized the representation of the sample to the bulk quantity and to take the advantage of the improvement of the quality of the cement, the graph of  Fig 2 IS 10262 have 6 nos of curve namely A,B,C,D,E & F having range of 28 Day  strength of cement tested according to IS: 4031- 1968 as 31.9 36.8  Mpa, 36.8 41.7 Mpa, 41.7 -  46.6  Mpa,  46.6 51.5 Mpa, 51.5 56.4 Mpa, 56.4 61.3 Mpa respectively  instead of Grade of cement like 33, 43, 53 Grade of cement.
     
     If interpretation of these curves  is limited to minimum strength of designated grade of cement  then  we have only three grades of cement like 33,43,53 grade as per respective IS code. In this case  the curve B, D and F has no use.

There fore  I am in opinion  to take the proper  advantage  of the strength of cement of  concerned  batch  of supply while doing the Mix design  based on test results as per relevant IS and this result should also be compared with the  manufacturers test certificates for the concerned batch of cement.

comments from Seniors   are highly appreciated

Regards
mithilesh

P.K.Mallick wrote:
Respected Mithilesh Sir,
                      
                Thanks for your response.Let us look into Indian cement Market. OPC has almost vanished from the market. It is now PSC and PPC. The former is abundant in the Eastern Part of the country.
Now let us look into respective IS Codes for those cement.
IS 1489(Part-1):1991(Reaffirmed 2000) PORTLAND-POZZOLANA CEMENT-SPECIFICATION(FLY ASH BASED)

IS 1489(Part-2):1991(Reaffirmed 2000) PORTLAND-POZZOLANA CEMENT-SPECIFICATION(CALCINED CLAY BASED)

Clause 7.4.1 the average compressive strength at 672+=4h is 33 Mpa,Min
Hence strength wise it is equivalent to Grade-33 OPC.

IS:455:1989(Reaffirmed 2005) PORTLAND SLAG CEMENT-SPECIFICATION

Clause 6.4 the average compressive strength  at 672+=4h is 33 Mpa,Min
Hence strength wise it is also equivalent to Grade-33 OPC.

It is my observation of last six months that particular brand of PPC gives a compressive strength on an average 53 Mpa. Now the question comes while designing concrete mix should we take the observed compressive strength of 53 Mpa or 33 Mpa.
Again it is of my opinion (conservative of course) that while designing mix we should restrict to 33Mpa because fly ash used in PPC is obtained from the exhaust gases of coal fired power station and the quality of fly ash depends on the ash content of the coal used. See the variables associated Fly-ash. So depending upon type of Fly-ash used, the strength of PPC shall vary and we can not question the manufacturer as long as the minimum requirement of 33Mpa is satisfied. Hence is it not risky proposition to depend on undependable observed compressive strength? Of course the consolation is that cement manufactures  usually get the fly ash from one source.

Same can be said about OPC-43 grade which (sometimes) is actually rejected OPC-53 Grade and even sometimes the OPC-53 comes in the bag of OPC-43 because it is not economically viable for a manufacturer to have different manufacturing facilities for different Grade of cement.

Hence let us use the designated compressive strength not the observed compressive strength while using the curves  of Design Mix code.
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