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Use of pozzolana cement

 
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dkmishra
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Joined: 26 Jan 2003
Posts: 1

PostPosted: Wed Oct 20, 2004 7:26 pm    Post subject: Use of pozzolana cement Reply with quote

Dear All;

With respect to use of pozzolana cement and/or use of fly ash as a mineral
admixture to concrete, we may do better to focus on the mechanism and/or
basic rationale behind the fact that it is better than Ordinary Portland
Cement Concrete, provided proper mix design, quality control, curing etc. is
followed more rigorously than is normally practiced in our construction
industry. During my years of working for an Australian pre-cast
manufacturer, the thumb rule was that no concrete should have more than 15%
binder and no binder should have less than 30% fly ash when Ordinary
Portland Cement was used. With these rules, it was possible to produce
concrete of compressive strength ranging from 50 MPa (cast concrete with
steam curing) to 90 MPa (roller suspension method of pipe concrete - steam
cured).

The advantages of using fly ash as cement replacement in concrete or as part
of the cement as in case of PPC concrete stems from two primary sources -

1. Filling up of mico-pores resulting in a denser better packed
micro-structure which results in long-term durability benefits. The particle
size distribution of the fly ash is important parameter in this respect.
2. Long-term strength development from the reaction of fly ash with Calcium
Hydroxide generated from cement hydration, which results in Calcium Silicate
Hydrate gel.

In addition, the round particles of fly ash helps in workability of fresh
concrete and it's delayed reaction in the system helps in reduction in heat
of hydration resulting in reduced plastic shrinkage cracks etc.

Above all, the cost of fly ash being much lower than cement (any where
between one-fifth to one-tenth), the resultant concrete most often is more
economical.

Although the above clearly goes in favour of using fly ash almost in all
concrete in all applications, the following factors must be paid attention
to especially in the Indian context,

1. To be most effective, fly ash concrete needs to be designed properly for
particular fly ash. Use of nominal mix is at best not advantageous and at
worst quite dangerous.
2. Attention must be paid to proper micro-mixing of the concrete which can
not be achieved in our commonly used drum mixers. Suitable pan type mixers
with planetary motion type paddles commonly employed in Ready Mixed Concrete
plants must be employed wherever possible.
3. A minimum of 14 days of proper curing would be essential for Flyash
concrete to gain strength close to it's potential.

A wealth of information is available at
http://www.hvfacprojectindia.com/hvfac_techdocuments.htm as indeed at many
other sites on the internet on the subject.

Regards,
Dhanada Mishra
Kalinga Institute of Industrial Technology (KIIT)
Deemed University
Bhubaneswar, Orissa 751003
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p_kadam
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Joined: 26 Jan 2003
Posts: 165

PostPosted: Thu Oct 21, 2004 10:39 am    Post subject: Use of pozzolana cement Reply with quote

Dear all,

Mr Mishra's mail encouraging.Could we share more experience with pozzolana cement manufactured in factories where strict quality control is achievable?

regards,

P Kadam

Message From  dkmishra@kiit.org

Date: Thursday, October 21, 2004 3:43 am

Subject: RE: Use of pozzolana cement



Dear All;

With respect to use of pozzolana cement and/or use of fly ash as a
mineraladmixture to concrete, we may do better to focus on the
mechanism and/or
basic rationale behind the fact that it is better than Ordinary
PortlandCement Concrete, provided proper mix design, quality
control, curing etc. is
followed more rigorously than is normally practiced in our
constructionindustry. During my years of working for an Australian
pre-cast
manufacturer, the thumb rule was that no concrete should have more
than 15%
binder and no binder should have less than 30% fly ash when Ordinary
Portland Cement was used. With these rules, it was possible to produce
concrete of compressive strength ranging from 50 MPa (cast
concrete with
steam curing) to 90 MPa (roller suspension method of pipe concrete
- steam
cured).

The advantages of using fly ash as cement replacement in concrete
or as part
of the cement as in case of PPC concrete stems from two primary
sources -

1. Filling up of mico-pores resulting in a denser better packed
micro-structure which results in long-term durability benefits.
The particle
size distribution of the fly ash is important parameter in this
respect.2. Long-term strength development from the reaction of fly
ash with Calcium
Hydroxide generated from cement hydration, which results in
Calcium Silicate
Hydrate gel.

In addition, the round particles of fly ash helps in workability
of fresh
concrete and it's delayed reaction in the system helps in
reduction in heat
of hydration resulting in reduced plastic shrinkage cracks etc.

Above all, the cost of fly ash being much lower than cement (any where
between one-fifth to one-tenth), the resultant concrete most often
is more
economical.

Although the above clearly goes in favour of using fly ash almost
in all
concrete in all applications, the following factors must be paid
attentionto especially in the Indian context,

1. To be most effective, fly ash concrete needs to be designed
properly for
particular fly ash. Use of nominal mix is at best not advantageous
and at
worst quite dangerous.
2. Attention must be paid to proper micro-mixing of the concrete
which can
not be achieved in our commonly used drum mixers. Suitable pan
type mixers
with planetary motion type paddles commonly employed in Ready
Mixed Concrete
plants must be employed wherever possible.
3. A minimum of 14 days of proper curing would be essential for Flyash
concrete to gain strength close to it's potential.

A wealth of information is available at
http://www.hvfacprojectindia.com/hvfac_techdocuments.htm as indeed
at many
other sites on the internet on the subject.

Regards,
Dhanada Mishra
Kalinga Institute of Industrial Technology (KIIT)
Deemed University
Bhubaneswar, Orissa 751003
---
Outgoing mail is certified Virus Free.
Checked by AVG anti-virus system (http://www.grisoft.com).
Version: 6.0.766 / Virus Database: 513 - Release Date: 17/09/2004




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PostPosted: Thu Oct 21, 2004 12:39 pm    Post subject: Use of pozzolana cement Reply with quote

21 Oct 2004

Dear All
We may note the following with reference to the points raised by Shri Dhanada Mishra of Kalinga Institute of Industrial Technology (KIIT), Deemed University, Bhubaneswar, Orissa 751003

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