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mohan30 at mantrafreen... Guest
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Posted: Sat Apr 05, 2003 4:46 pm Post subject: concrete mix design |
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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 Guest
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Posted: Sun Apr 06, 2003 9:24 am Post subject: Concrete mix design |
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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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