The process of mixing of various ingredients of concrete in specified proportions is termed as mixing of concrete.
Methods of mixing
There are two methods of mixing are
- Hand mixing
- Machine mixing
The process of mixing the ingredients of concrete by manual labour is called hand mixing.
Hand mixing is adopted for small and unimportant works and where quantity of concrete used is small. Hand mixing method requires more cement (10%more) than machine mixing for obtaining the small strength of concrete.
Following is Step Wise Procedure for Mixing by Hand
- A platform of bricks, lean concrete or iron sheets is constructed. The size of the platform depends upon the quantity of concrete to be mixed at a time.
- Spread out a measured quantity of sand evenly on the mixing platform.
- Spread the cement uniformly on this sand and mix it till the colour of mixture is uniform.
- Spread this mixture evenly again on platform.
- Spread the measured coarse aggregate evenly on the mixing platform.
- Mix the material dry.
- Make a hollow in the centre of the mixed material. After this 75% of the required quantity of water based on water-cement ratio is added and then start remixing taking care that no water escapes the mixture.
- The remaining water is added with the continuation of mixing process.
- Normally mixing time should not exceed 3 min.
- The platform should be cleaned at the end of day’s work so that it is ready for use on the next day.
The process of mixing the ingredients of concrete by a machine is called machine mixing.
In this case where a large quantity of concrete is to be produced, hand mixing becomes costly even if the labour is cheap. The machine mixing becomes essential. The concrete can thus be produced at a faster rate and at a lesser cost. The quality of concrete by machine mixing is also better.