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concrete mix design

 
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mohan30 at mantrafreen...
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PostPosted: Sat Apr 05, 2003 4:46 pm    Post subject: concrete mix design Reply with quote

dear all,

let me attract the attention of structural engineers towards the concrete mix design using higher grade cements.

has anyone some idea how to fix up water content per m3 for mix design.

If IS procedure for mix design is followed (wherein water content is 186 kg/m3 followed by some adjustments in this value), the resulting mix in much uneconimical.

Many designers arbitarily keep this mixing water well below 186 k/m3 to get an economical mix.


-----------------------------------------------------------
Mohan Gupta
Reader
Department of Civil Engineering
Bhilai Institute of Technology
DURG  491001, C. G., INDIA

Phone: 91-788-2323997, 2321163 (Off.)
91-788-2391674, 5032338 (Res.)

e-mail: mohan30@mantrafreenet.com
URL:    http://www.mohangupta.com
-----------------------------------------------------------

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spsvasan at eth.net
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PostPosted: Sun Apr 06, 2003 9:24 am    Post subject: Concrete mix design Reply with quote

Dear Mohan Gupta

The water requirement given in IS:10262 is reasonable. This much of water
is required for reasonable workability of mix. British Standards requires
approximately 180 litres per cum for a slump of 10 to 30mm. ACI standards
requires approximately 185 litres per cum for a slump of 30 to 50mm.

Problem with IS:10262 is that it is too conservative in the water-cement
ratio. As per IS:10262, a w/c ratio of 0.5 will result in a cube
compressive strength of 25 N/sqmm (with Grade 43 cement), as against 45
N/sqmm by British Standards and 42 N/sqmm by ACI standards (after
converting cylinder strength to cube strength).

If IS:10262 is followed strictly and if the maximum cement content of
IS:456 is also followed, it will not be possible to design high strength
concrete mix at all! Since our higher grade cements are likely to satisfy
the BS requirements for cement, we can adopt the British method of mix
design which will result in a reduction of cement consumption.

Regarding the practice of reducing the water content in the mix, I feel it
can be done only by adding plasticising admixtures. A plasticiser can
reduce water demand (and hence cement requirement) by approximately 10%. A
superplasticiser may reduce water demand by about 20%.

Regards
Srinivasan,S.P.
17, West Masi Street, Madurai 625001, Ph/Fax: 0452-2347075

At Sat Apr 5 22:16:17 2003, you wrote:
Quote:
dear all,

let me attract the attention of structural engineers towards the concrete
mix design using higher grade cements.

has anyone some idea how to fix up water content per m3 for mix design.

If IS procedure for mix design is followed (wherein water content is 186
kg/m3 followed by some adjustments in this value), the resulting mix in
much uneconimical.

Many designers arbitarily keep this mixing water well below 186 k/m3 to
get an economical mix.
-----------------------------------------------------------
Mohan Gupta, Reader, Department of Civil Engineering, Bhilai Institute of
Technology, DURG  491001, C. G., INDIA


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