25-06-2012, 01:37 PM
MIX-DESIGN
MIXDESIGN.ppt.......01.ppt (Size: 2.73 MB / Downloads: 152)
DATA FOR MIX DESIGN
The following basic data required for mix design for a concrete mix
Characteristic compressive strength of concrete at 28 days(fck).
Degree of workability desired.
Limitation on the water-cement ratio and the minimum cement content to ensure the adequate durability.
Type and max size of aggregate to be used
Standard deviation(s) of compressive strength of concrete.
Target Strength for mixed design
In order that not more than the specified proportion of test results are likely to fall below the Characteristic strength, the concrete mix has to be designed for a some what higher target average compressive strength (fck ).
The margin over the characterirtic strength depends upon the quality control (expressed by the standard deviation ) and the accepted proportion of results of strength tests below the characteristic strength (fck ), given by the relation:
Calculation of Cement Content
The cement content per unit volume of concrete may be calculated from the free water-cement ratio
and the quantity of water per unit volume of concrete.
The cement content so calculated shall be checked against the
minimum cement content for the requirements of durability and the greater of the two values adopted .