What is BIS ??
BIS Procedure of Mix Design - Step by Step Procedure of BIS Concrete MiX Design
The Bureau of Indian Standards (BIS), the National Standards Body of India responsible for formulating Indian Standards was established under The Bureau of Indian Standards Act, 1986. To protect the interest of consumers, BIS operates a Product Certification Scheme. Under the scheme, BIS grants licenses to such manufacturers who are capable of producing goods on continuous basis as per relevant Indian Standards.
The Laboratory Recognition Scheme is governed by the provisions under Section 10 (1) h of The BIS Act 1986 and the BIS Rules, 1987 [10(2) (a) & (b)]. These statutory provisions confer upon BIS, powers to recognize any laboratory in India or in any other country for carrying out testing of samples in relation to use of the Standard Mark and such other functions as may be necessary.
BIS Method Procedure For Concrete Mix Design
The BIS method of mix design can be applied for the design of both medium and high strength concrete.
Step 1: Data Collection
Step 2: Target Mean Strength for the Mix Design ( ft )
The mean target strength is determined from the specified characteristic compressive strength at the 28th day fck and at the level of quality control.
ft = fck + 1.65 S
where S is the standard deviation. fck is the compressive strength at 28 days
Step 3: Selection of Water Cement Ratio
The free water cement ration corresponding to the target mean strength may be determined from the SP- 23. ( In page 119 - Fig : 47 of SP-23 Concrete Mix Design Handbook ) The figure is shown below.
|Fig.1: Generalised relation between free water cement ratio and Characteristic compressive strength of the concrete|
The lower of the two values must be taken
Step 4: Estimation of the Entrapped Air
The amount of entrapped air for the maximum nominal size of the aggregate is obtained from the Table 41 of SP-23 of Concrete Mix Design Handbook (Page 113). The Table from the code is given below.
Table-1 : The Table 41 from SP-23
Step 5: Selection of Water Content
The water is selected for the required workability and maximum size of aggregates,sands that conform to the grades zones based on the Table 42 and 43 of SP 23 for Concrete Mix Design.