Concrete Mix design is complete science and it is based on a lot of research. Popular Mix Design method is highlighted in ACI 2011 committee report. It is a systematic approach in which user starts with defined slump and strength and some other parameters. End result gives quantities of different constituents.
Performance-based methods are alsoavailable in which engineer based on his experience selects initial proportions and modifies as needed. Both systematic and performance-based methods have certainadvantages and disadvantages which will be covered in later posts.
Though mix design is a comprehensive process still it is very useful for engineers to know certain mix design concrete thumb rules which will make his life easier. Here is the list,
By adding 1 litre of water in 1 cubic meter of concrete mix
Increase slump of about 25 mm is expected.It will decrease compressive strength of about 1.5 to 2.0 N/mm2Increase shrinkage potential of about 10%Waste as much as ¼ bag of cement
Effect of increasing concrete mix temperature by 1 celsius
About 4 liters of water per cubic metermaintains equal slumpAir content decreases about 1%Compressive strength decreases about 1.0 to 1.5 N/mm2
Effect of air content on concrete mix
If air content increases 1%, it will result incompressive strength decrease of about 5%If air content decreases 1%, then it will cause yield to decrease about 0.03 cubic meter per 1 cubic meter of concrete mix.If air content decreases 1%, then slump willdecrease about 12.5 mmIf air content decreases 1%, it will result in durability decreases of about 10%.
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