Concrete Mix Design

Many naive Engineers, assume Mix Design of Concrete to be a very difficult task, but on the contrary I feel it is nothing more than a combination of Basics of Maths that we have learnt in our Schools, Knowledge of effect of material properties to some extent, Lot of imagination and playfulness. the most basic and important thing is to recognise the fact that 1 cubic metre of concrete will be equal to sum of individual volumes of its ingredients. The reason that Engineers like to design mix of concrete for a specific volume is because it gives 2 advantages 1) It gives you idea on economics of your concrete (2 concretes of same grade but different costs per cubic metre of concrete, will easily denote the better option). 2) The proportions remain undistorted, plus in addition you also can detect exact correlation between concrete property and content of a particular ingredient. if you just had to design concrete on the basis of inter proportions, as was done earlier, it would have been very difficult to economise the mixes, or to improve the properties of concrete. for example let us say you made a concrete with 10 kg cement, 20 kg fine aggregate, 40 kg coarse aggregate and you got less strength. you decide to increase the cement (thus indirectly reduce w/c ratio) and the new mix proportion you think is 12 kg cement, 20 kg fine aggregate and 40 kg coarse aggregate. if you had to see the economics you would say that the cost of concrete has increased by an equivalent rate of 2 kg of cement. But if you really had to check the economics, the new cost of your concrete would be higher by 2 kg of cement and lesser by 1.7 kg of total aggregates. the Formula 980= C/Sc + W + Fa/Sfa * 1/p is nothing but an equation which says that 1 cubic metre of concrete is equal to volume of cement per cubic metre of concrete plus volume of water per cubic metre of concrete plus volume of total aggregates per cubic metre of concrete.
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