Nagarjuna college of engineering and technology Devanahalli, bangalore-562110 Presentation on Mix design of concrete By: Ms. Preethi a v, Asst professor Dept. of civil engg. Ncet, bangalore 8/24/2019

Methods of Concrete Mix Design are as follows: :introduction: Mix Design is the science of determining the relative proportions of the ingredients of concrete to achieve the desired properties in the most economical way. Methods of Concrete Mix Design are as follows: Indian standard recommended method IS:10262-2009 American Concrete Institute Method of Mix Design BS Method 8/24/2019

:principles of mix design: The environment exposure condition for the structure The grade of concrete, their characteristic strength and standard deviations Type of Cement Type and sizes of aggregates and their sources of supply Nominal maximum sizes of aggregates maximum and minimum cement content water cement ratio Degree of workability of concrete on placing conditions Air content inclusive of entrained air Maximum/minimum density of concrete Maximum/minimum temperature of fresh concrete Type of water available for mixing and curing Source of water and the impurities present in it 8/24/2019

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Indian standard recommended method IS:10262-2009 Design Mix for M20 Grade of Concrete Design stipulations Characteristic compressive strength at 28days = 20N/mm2 Maximum size of aggregates = 20mm Type of aggregates = Crushed Rock Workability = 25mm to 50mm Degree of quality control = Good Type of exposure = Severe Type of cement = OPC 53 Grade Minimum cement content = 250 kg/m3 Maximum cement content = 450 kg/m3 Maximum water cement ratio = 0.50 Method of concrete placing = Manual 8/24/2019

Data obtained from tests on ingredients in the laboratory Cement = Ordinary Portland Cement (53 grade) Specific gravity of cement = 3.09 Aggregates Specific gravity of : Coarse aggregates = 2.676 Fine aggregates = 2.57 Water absorption Coarse aggregates = NIL Fine aggregates = NIL Free moisture Fine aggregates = NIL Sieve analysis (as per IS:383-1970)   Fine aggregates = Zone III 8/24/2019

Target Strength for mix Proportioning F'ck= fck + 1.65S =20 + 1.65*4 =26.60N/mm2 Where F'ck = Target average compressive strength at 28 days. fck = Characteristic compressive strength at 28 days S = Standard deviation (Table-1 of IS: 10262-2009) Selection of w/c From table 5 of IS:456-2000, maximum water content = 0.50 Based on trial and error W/c = 0.50 Selection of water content From table 2 of IS:10262-2009, maximum water content for 20mm aggregate =186litres Estimated water content f or 25-50mm slump=1861itres 8/24/2019

Calculation of cement content W/c = 0.50 Cement content = 186/0.50 ` =372 kg/m3 From Table 5 of IS 456, minimum cement = 250kg/m3 Therefore 372kg/m3 > 250kg/m3, Hence O.K. Proportion of volume of Coarse Aggregate and Fine Aggregate content: From Table 3. volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone III) for water-cement ratio of 0.50 = 0.64. Volume of coarse aggregate = 0.64m3 Volume of fine aggregate =1-0.64 = 0.36 m3 8/24/2019

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:american concrete institute method of mix design: Data to be collected: i) Fineness modulus of selected Fine Aggregates ii) Unit weight of dry rodded coarse aggregate iii) Specific gravity of Coarse and Fine aggregates iv) Absorption characteristics of both Coarse and Fine aggregates v) Specific gravity of Cement From the minimum strength specified, estimate the average deisgn strength by using standard deviation. Find the water/cement ratio from the strength and durability points of view. Adopt the lower value. Maximum size of the aggregate to be decided. 8/24/2019

Workability in terms of slump need to be decided. The total water in kg/m3 of concrete is determined, corresponding to the selected slump and selected maximum size of aggregate. Cement content if computed by dividing the total water content by the water/cement ratio. Select the bulk volume of dry rodded coarse aggregate per unit volume of concrete, for the particular maximum size of coarse aggregate and fineness modulus of fine aggregates. Weight of C.A per cubic meter of concrete is calculated by multiplying the bulk volume with bulk density. 8/24/2019

Solid volume of C.A in one cubic meter of concrete is calculated by knowing the specific gravity of C.A. Similarly the solid volume of cement, water and volume of air is calculated in one cubic meter of concrete. The solid volume of F.A is computed by subtracting from the total volume of concrete the solid volume of cement, CA, water and entrapped air. Weight of FA is calculated by multiplying the solid volume of FA by specific gravity of FA 8/24/2019

:american concrete institute method - design example: 8/24/2019

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Thank you 8/24/2019