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 also available in which engineer based on his experience selects initial proportions and modifies as needed. Both systematic and performance-based methods have certain advantages 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/mm2
- Increase 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 meter maintains equal slump
- Air 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 in compressive 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 will decrease about 12.5 mm
- If air content decreases 1%, it will result in durability decreases of about 10%.